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The role of meiofauna in the benthic community of a small oligotrophic lake Hoebel, Michael 1978

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ROLE OF MEIOFAUNA IN THE BENTHIC COMMUNITY OF A SMALL OLIGOTROPHIC LAKE by MICHAEL FRANCIS HOEBEL B.A., Dartmouth College, 1968 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA November, 197 8 ©Michael Francis Hoebel, 1978 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I ag r ee tha t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r ag ree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f ZOOLOGY The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date Dec, 15 , 1978 ABSTRACT Meiofaunal d i s t r i b u t i o n and abundance were studied i n Marion Lake, a small, shallow (8m maximum) oligotrophic lake i n southwestern B r i t i s h Columbia. Experimental techniques were used to investigate the influence of food and predation on meiofaunal populations, and to estimate r e l a t i v e carbon -flow to a l l components (micro-, meio-, and macrofauna) of the zoobenthic community. In two years' sampling of over 50 species of meiofaunal r o t i f e r s , nematodes, copepods, cladocerans and halacarine mites, only a few species were abundant. Three depth zones were sampled (1.0, 2.5, 4.5m) and maximum densities occurred at 2.5m. Population densities of a l l groups were stable over the sampling period, fl u c t u a t i n g less than one order of magnitude annually. In culture studies, representative meiofaunal species had longer generation times and lower reproductive rates than expected. Attempts to use laboratory r e s u l t s to predict f i e l d population dynamics were generally unsuccessful, but led to c l a r i f i c a t i o n of reproductive parameter estimates. Experiments in the laboratory and i n the f i e l d suggested that meiofaunal species are not food-limited. Predation on meiofauna i s not heavy but might be s i g n i f i c a n t for those species whose repro-duction i s suppressed by adverse temperatures. i i i Radiotracer experiments indicated that carbon flow to the zoobenthic community from sediment microflora was partitioned approximately 12% to microfauna ( c i l i a t e s ) , 12% to meiofauna, and 76% to macrofauna, while the contributions to zoobenthic biomass were 1%, 7% and 92% respectively. In related experi-ments, a common harpacticoid copepod species had a high assim-i l a t i o n e f f i c i e n c y but rapidly respired and excreted recently ingested carbon. Meiofaunal organisms are apparently not an important food source for higher trophic levels i n Marion Lake but may play a s i g n i f i c a n t role i n stimulating m i c r o f l o r a l production by t h e i r grazing a c t i v i t y . i v TABLE OF CONTENTS Page Abstract i i L i s t of Tables v i i L i s t of Figures ix Acknowledgement x i i Introduction 1 Chapter I: Meiofaunal D i s t r i b u t i o n and Abundance i n Marion Lake Introduction 6 Description of Marion Lake 7 Methods: Sampling 9 Sample Processing 15 Results 18 Discussion: Species Diversity 42 Dis t r i b u t i o n 4 5 Population Dynamics 4 8 Summary 53 Chapter I I : Laboratory Culture Studies on L i f e History and Population Dynamics Introduction 5 6 Methods: Culture Techniques 56 Data Analysis 59 Results 6 1 V TABLE OF CONTENTS Page Discussion: Meiofaunal L i f e H i s t o r i e s 7 8 Dissotrocha Population Analysis 80 Bryocamptus Population Model 82 Conclusion 84 Chapter I I I : Experimental Studies on Food Supply and Predation Introduction 87 Methods and Results: . Food Supply Experiments 89 Predation Experiments 98 Discussion: Food as a Limiting Factor 105 Predation as a Limiting Factor 109 Conclusion 117 Chapter IV: Experimental Studies on Benthic Carbon Flow Introduction 121 Methods and Results: Community Carbon Flow Experiments 121 Bryocamptus Carbon Budget Experiments 13 9 Discussion: Community Carbon Flow 14 5 Bryocamptus P a r t i t i o n i n g of Carbon 152 v i TABLE OF CONTENTS Page General Discussion and Conclusion 155 References 167 Appendix I: Calculation of r for Micrometazoans 187 Appendix I I : Interpretation of Radiotracer Feeding Experiments 193 i v i i LIST OF TABLES Table Page 1. R e l i a b i l i t y of meiofaunal sampling method: resu l t s of r e p l i c a t e sample sets 14 2. Marion Lake meiofaunal species, with percentage of samples from each station i n which the species were found 21 3. A comparison of the maximum meiofauna population densities recorded for some freshwater and marine habitats 49 4. A comparison of the e f f e c t of temperature on l i f e spans and reproductive parameters for two meio-benthic chydorid cladoceran species 63 5. A comparison of the e f f e c t of temperature on l i f e spans and reproductive parameters for two meio-benthic r o t i f e r species 66 6. The e f f e c t of temperature on s u r v i v a l , l i f e span, and reproductive parameters for the meiobenthic harpacticoid copepod Bryocamptus hiemalis 71 7. L i f e span and reproductive parameters for meiofauna i n culture reported i n the l i t e r a t u r e compared with results for Marion Lake meiofauna 79 8. The e f f e c t of added b a c t e r i a l or a l g a l food on the t o t a l duration of copepodid stages (days from f i r s t copepodid stage to adult) i n Bryocamptus hiemalis .. 99 9. Predation rates on meiofauna i n Marion Lake as percentage of prey population eaten per day, estimated from laboratory studies with radioa c t i v e l y l a b e l l e d meiofauna prey 101 10. The e f f e c t on meiofauna population densities of increasing the number of predators i n undisturbed sediment cores............'............... 104 11. Radioactivity of meiofauna and macrofauna following addition of l a b e l l e d bacteria to undisturbed sediment cores 124 12. Lengths and dry weights of representative meiofaunal animals 130 V l l l LIST OF TABLES Table Page 13. Standing crops of microfauna, meiofauna and macrofauna i n sediment cores 131 14. Turnover rates (per hour) of sediment (T s) and animals (T a) based on results of radiotracer experiments with undisturbed cores 136 15. The e f f e c t of temperature on egestion rates of Bryocamptus hiemalis  140 16. P a r t i t i o n i n g of recently ingested carbon by Bryocamptus hiemalis based on short-term feeding experiments using radioa c t i v e l y l a b e l l e d sediment.. 144 17. A comparison of r e l a t i v e numbers, biomass, and community metabolism rat i o s for microfauna, meio-fauna and macrofauna i n Niva Bay, Denmark, and Marion Lake, B.C 150 i x LIST OF FIGURES Figure Page 1. Diagram of Marion Lake, B.C. showing depth contours and l o c a t i o n of the meiofaunal sampling t r a n s e c t w i t h 1.0m, 2.5m, and 4.5m s t a t i o n s 10 2. Mud-water i n t e r f a c e temperature at three depths i n Marion Lake, 1970-72 19 3. D e n s i t i e s of Marion Lake meiofaunal taxonomic groups at three depths i n r e p r e s e n t a t i v e s p r i n g , summer and f a l l samples (1971) , 23 4. V e r t i c a l d i s t r i b u t i o n of meiofaunal taxonomic groups at 2.5m i n Marion Lake, A p r i l , 1971 24 5. T o t a l meiobenthic r o t i f e r s a t three depths i n Marion Lake, 1969-1972 27 6. T o t a l meiobenthic h a r p a c t i c o i d copepods at three depths i n Marion Lake, 1970-72. 28 7. T o t a l meiobenthic c y c l o p o i d copepods at three depths i n Marion Lake, 1970-72 29 8. T o t a l meiobenthic cladocerans at three depths i n Marion Lake, 1970-72 31 9. T o t a l meiobenthic nematodes at three depths i n Marion Lake, 1970-72 32 10. T o t a l meiobenthic h a l a c a r i n e mites at three depths i n Marion Lake, 1970-72 33 11. A comparison of temperature w i t h p o pulation d e n s i t -. i e s of the common b d e l l o i d r o t i f e r Dissotrocha and t o t a l n o n - b d e l l o i d r o t i f e r s at 2.5m i n 1971-72 34 12. D e n s i t i e s of the two most common b d e l l o i d r o t i f e r species at 2.5m, 1969-72 35 13. D e n s i t i e s of the two common h a r p a c t i c o i d copepod species at 2.5m, 1970-72, 36 14. Number of female h a r p a c t i c o i d copepods c a r r y i n g eggs at 2.5m, 1970-72 37 X LIST OF FIGURES Page 15. Numbers of immature Bryocamptus hiemalis, at 2.5m, 1970-72 40 16. Simulation model of Bryocamptus hiemalis population. Rates of transfer determined from laboratory culture results 62 17. The e f f e c t of temperature on population growth of two meiobenthic chydorid cladoceran species in culture 64 18. A comparison of population growth by two common species of meiobenthic r o t i f e r s i n mass culture at 20°C, and the e f f e c t of food concentration on one species 67 19. The influence of temperature on development rate of Dissotrocha macrostyla embryos 68 20. A comparison of Dissotrocha population growth rate i n Marion Lake, with b i r t h rate predicted from culture studies (Figure 20A), and calculated death rate (Figure 20B) 70 21. The e f f e c t of temperature on growth rates of immature stages of Bryocamptus hiemalis 72 22. The e f f e c t of temperature on mortality rates, reproductive maturation rates and egg production rates for Bryocamptus hiemalis 74 23. Population density of Marion Lake Bryocamptus" hiemalis adults as predicted by a simulation model, compared with actual numbers at 2.5m i n 1971 75 24. The e f f e c t of two levels of inorganic f e r t i l i z a t i o n (10:10:0, N:P:K) on meiofaunal population densities i n 4 m2 enclosures, July-August, 1971 91 25. Radioactivity of in d i v i d u a l Bryocamptus hiemalis feeding on fresh l a b e l l e d sediment, and on pre-grazed l a b e l l e d sediment 96 x i LIST OF FIGURES Figure Page 26. Radioactivity i n water above the sediment i n undisturbed cores at two temperatures following addition of l^c-giucose 126 27. Radioactivity of benthic faunal components following addition of -^C-glucose to undisturbed sediment cores at two temperatures 128 28. Radioactivity of benthic faunal components per unit weight, following addition of l^C-glucose to undisturbed sediment cores at two temperatures 13 2 29. Radioactivity of three meiofauna and one macrofaunal groups per unit weight, following addition of •^C-glucose to undisturbed sediment cores at two temperatures 134 30. Benthos standing crops and carbon flow i n A p r i l -May 13 8 31. Major and minor pathways of energy flow i n the Marion Lake food web 159 32. Theoretical increase i n r a d i o a c t i v i t y of animals feeding on 1 4 c _ i a D e n e c j food, as DPM per i n d i v i d u a l (Figure 3 2A) and DPM per unit weight carbon (Figure 32B) 195 x i i ACKNOWLEDGEMENT The research for t h i s thesis was supervised by Dr. I.E. Efford, whose help and generous support i s g r a t e f u l l y acknow-ledged. Many people gave assistance but special thanks are due to Dr. Pierre Kleiber for computer expertise. Discussions with Dr. Gerry Marten and Mr. Richard Kool were stimulating and h e l p f u l i n c l a r i f y i n g ideas. The writing of the thesis was supervised by Dr. T.G. Northcote, without whom i t would not have been completed. Dr. P.A. Larkin's encouragement and suggestions were most welcome. F i n a l l y , I express my gratitude to my wife Carolyn, for sharing rainy days i n a cold boat at the beginning, and for her understanding patience through years of " f i n i s h i n g up". INTRODUCTION - 2 -Meiofauna i s loosely defined as the group of metazoans less than 1.0 mm i n length which inhabit either freshwater or marine mud and sand sediments (Hulings and Gray, 1971). Taxon-omic groups included i n freshwater are harpacticoid and cyclopoid copepods, cladocerans, r o t i f e r s , nematodes, gastrotrichs, t u r b e l l a r i a n s , tardigrades, and halacarine mites. Meiofauna (from the Greek meion, l e s s ) , microfauna (protozoa, e s p e c i a l l y c i l i a t e s ) , and macrofauna together comprise the zoobenthic community. The role played by meiofauna i n the t o t a l benthic community i s not well understood. Recent reviews of the ecology of marine meiofauna (Mclntyre, 1969; Gerlach, 1971; Coull , 1973) have emphasized the lack of knowledge about t h i s faunal component i n ocean sediments, and there i s even less knowledge concerning the community ecology of freshwater meiofauna. A recent major limnology textbook (Wetzel, 1975) only b r i e f l y mentions meio-fauna. The small size of meiofauna might lead to the assumption that the meiofaunal role i s i n s i g n i f i c a n t i n the t o t a l benthic community. A l t e r n a t i v e l y , small size could be related to high reproductive fates and rapid turnover of metabolic carbon, and meiofaunal organisms might be important because they process a disproportionately large amount of energy. The carbon/energy accumulated by meiofauna may be passed on to higher trophic lev e l s (Gerlach, 1971, 1978; Brown and Sibert, 1977; Evans and Stewart, 1977) or meiofauna may be a trophic dead end - 3 -(Mclntyre, 1969; Mclntyre and Murison, 1973; C o u l l , 1973; Giere, 1975), thus making a certain amount of energy unavailable to the rest of the fauna. The work described i n t h i s thesis was undertaken to determ-ine the d i s t r i b u t i o n and abundance of meiofauna i n a small oligotrophic lake i n southwestern B r i t i s h Columbia, to suggest reasons for the observed d i s t r i b u t i o n and abundance using experimental techniques, and to investigate the role of meio-fauna i n the t o t a l benthic community. This study was part of an International B i o l o g i c a l Programme project focussed on Marion Lake, B.C., which began i n 1963 and involved a large team of research s c i e n t i s t s and graduate students over the following 10 years. According to Efford and H a l l (197 5), the project had three main objectives. The f i r s t was to describe pathways by which energy was transferred through the t r o p h i c . l e v e l s . The second and main objective was to determine what controlled rates of energy transfer between various components of the lake ecosystem. Thirdly, the knowl-edge gained was to be used to predict accurately the r e s u l t s of disturbances to Marion Lake, thus testing the v a l i d i t y of conclusions. There was also the hope that detailed knowledge about the functioning of t h i s ecosystem would have some general a p p l i c a b i l i t y , and would aid the development of ecological theory. Early work on the lake (Efford, 1967) indicated that the planktonic contribution to lake energetics was small and - 4 -attention was s h i f t e d to the benthos where the major carbon/ energy flow takes place (Dickman, 1969). Detailed studies of the ecology of benthic vertebrates (salamanders, frog tadpoles), macrofaunal invertebrates (amphipods, chironomid and other insect larvae), and microfauna ( c i l i a t e d protozoa) were carried out. My work on lake meiofauna was designed to investigate a component of the benthic community not previously studied. There was also a unique opportunity to use the detailed informa-tion available on other benthic components to gain understanding of the meiofaunal r o l e . A complete l i s t of Marion Lake studies i s given i n H a l l and Hyatt (1974). This thesis i s organized into four chapters. Chapter I describes methods used to sample meiofauna and to separate the organisms from the sediment, presents results of the sampling programme, and discusses reasons for the observed d i s t r i b u t i o n and abundance. The second chapter reports the r e s u l t s of laboratory culture studies of representative meiofaunal species. Experimental work on predation and food supply as c o n t r o l l i n g agents for meiofaunal populations i s discussed i n Chapter I I I . Benthic carbon flow experiments are reported i n Chapter IV. F i n a l l y , the General Discussion and Conclusion provides an overview of the work performed and attempts a synthesis of present knowledge of Marion Lake benthos, with emphasis on the role of the meiofauna. - 5 -CHAPTER I MEIOFAUNAL DISTRIBUTION AND ABUNDANCE IN MARION LAKE - 6 -Introduction Within the l a s t ten years there have been many studies of d i s t r i b u t i o n and abundance of meiobenthic organisms, i n both marine and freshwater environments. Some studies have dealt with population dynamics over a summer, a year, or even longer. In the marine environment, work of Barnett (1968), Coull (1970), Fenchel (1967), Harris (1972), Mclntyre and Murison (1973), and Thane-Fenchel (1968) i s of note, and for freshwater studies, one may consult Daggett and Davis (1974), Fenchel (1975), Goulden (1971), Prejs (1970), Prejs and Stanczykowska (1972), and Wasilewska (1973). The pioneering study of freshwater meiobenthic population ecology was that of Moore (1939). Other workers have investigated population dynamics of chydorid cladocerans i n the freshwater l i t t o r a l water column, rather than i n the benthic substrate i t s e l f (e.g. Keen, 1973; White-side, 1974) . One r e s u l t of these studies which i s surprising i s that population densities of meiofauna seldom fluctuate by even an order of magnitude over a year. If one considers the taxonomic and size s i m i l a r i t i e s between meiofauna and zooplankton, which often show great population fluctuations, one might predict that meiofauna populations would be equally variable. This chapter presents re s u l t s of the meiofauna sampling programme and compares meiofaunal densities and population dynamics i n a shallow, oligotrophic lake with results from other aquatic environments. - 7 -Description Of Marion Lake Marion Lake i s located i n the University of B r i t i s h Columbia Research Forest, approximately 50 km east of Vancouver, B.C. It i s a small (length 0.8 km, width 0.17 km, area 13.3 ha) and shallow lake (mean depth 2.4 m, maximum depth 8 m), which l i e s i n a north-south oriented U-shaped v a l l e y at an elevation of 300 m i n the coastal mountains north of the Fraser River low-lands. The watershed area i s approximately 1300 hectares with an impermeable granite substratum covered by a layer of g l a c i a l t i l l . Located within the coastal western hemlock zone, the area's dominating vegetation now, following major logging i n the 1920's,is second-growth western red cedar, Douglas f i r , and western hemlock (Efford and H a l l , 1975). Climatic conditions are mild and wet, with annual p r e c i p i t a -tion about 240 cm. This heavy p r e c i p i t a t i o n , combined with the impermeable watershed f l o o r , often results i n large amounts of water entering the lake through i n l e t streams, and the lake i s often rapidly flushed (Hall and Hyatt, 1974). Consequently the water i s well oxygenated but low i n dissolved nutrients, and plankton communities are quite unstable. A brown s i l t - o o z e sediment (gyttja), which i s 94% water and 35-45% organic matter by weight (Hargrave, 1970c), covers the bottom of the lake except near the i n l e t and outlet streams, where sand and gravel are found. The sediment i s heterogeneous upon close inspection. At very shallow depths (0.5-1.0 m) the surface ooze i s covered with, and incorporates, chironomid - 8 -tubes and amphipod faeces and i s extremely f l o c c u l e n t . At middle depths (2.0-3.0 m) there may be t h i n mats of filamentous algae (Mougeotia sp.) covering the sediment surface. The average s i z e of sediment p a r t i c l e s at shallow and middle depths i s 50-100 um. At greater depths (4.0-5.0 m) sediment p a r t i c l e s are smaller but l a r g e pieces of s l i g h t l y decomposed veg e t a t i o n (twigs, leaves) are found o c c a s i o n a l l y . W i t h i n the sediment p a r t i c l e s , as w e l l as c o a t i n g the o u t s i d e , are b a c t e r i a and blue-green algae c e l l s (Perry, 1974). At the sediment-water i n t e r f a c e grow many species of s i n g l e c e l l e d and c o l o n i a l e p i p e l i c algae (Gruendling, 1971). Grazing on the sediments are various micro-, meio-, and macrofaunal herbivores and dep o s i t feeders. Methods Recent s t u d i e s of the r o l e played by meiofauna i n v a r i o u s marine and freshwater environments have focussed a t t e n t i o n on the techniques used to sample and e x t r a c t meiofauna from d i f f e r e n t types of sediments (Stanczykowska, 1966; Hulings and Gray, 1971; Holme and Mclntyre, 1971; deBovee, Soyer, and A l b e r t , 1974; Heip, Smol, and Hautekiet, 1974). Sampling meiofauna can pose s p e c i a l problems. Because of the o f t e n patchy d i s t r i b u t i o n of these organisms i n even small 2 (<0.2 m ) areas of sediment ( A r l t , 1973), l a r g e numbers of samples are r e q u i r e d t o determine population s i z e s a c c u r a t e l y and p r e c i s e l y . I f frequent sampling over long periods of time - 9 -i s involved, the number of samples to be extracted and analyzed becomes enormous, unless samples are pooled and subsampled. Extraction of meiofauna from sandy sediments i s not d i f f i c u l t , for one can make use of the difference i n density between the sand p a r t i c l e s and the bodies of the meiofauna. Thus a sample may be e a s i l y extracted by mixing, allowing a b r i e f period of time for the sand to s e t t l e out, and decanting the l i q u i d containing the animals. For organic sediments the problem i s more d i f f i c u l t because the density of the sediment i t s e l f i s close to that of the animals. Sampling: Samples were taken approximately monthly (more frequently at one station during the summer) along a transect running from shore toward the center of the lake (Figure 1). Sampling stations were marked with poles embedded i n the sediment at 1.0 m, 2.5 m, and 4.5 m contours (summer average depth). Because of the small size of the lake the depth sometimes increased by up to 1 m during periods of heavy r a i n f a l l . The' transect was l a i d out over open mud substrate, but the 1.0. m station was within 10 meters of submerged, f l o a t i n g , and emergent macrophyte beds (Potamogeton natans, Nuphar polysepalum, Equisetum sp.). Figure 1. Diagram of Marion Lake, B.C. showing depth contours and location of the meiofaunal sampling transect with 1.0m, 2.5m, and 4.5m stations. - 11 -From June, 1969 to A p r i l , 1970 samples were taken only from the 2.5 m station. The sampling method was to l i f t one 20 x 20 cm section of undisturbed sediment to the surface 2 using a Hargrave sampler (Hargrave, 1969) and place six 2.8 cm , 15 cm long plexiglass cores i n t h i s sediment. Cores were corked and withdrawn with t h e i r contents of sediment (approximately 4 cm) and overlying water, and samples were placed i n i n d i v i d u a l jars and fixed with 5% formalin. At the laboratory, the r o t i f -ers were extracted from t h i s sediment by sugar f l o t a t i o n and Rhodamine B staining (described below). Other meiofauna taxon-omic groups were not counted i n these early samples. Each sample was processed and counted i n d i v i d u a l l y . On each sampling date the temperature of the mud-water interface was measured at each station by placing a thermometer inside the undisturbed sample cores immediately a f t e r they were raised to the surface. Temperature data were also c o l l e c t e d in 19 71 with Ryan continuous recording thermometers positioned at the interface at the sampling stations. After one year's work the sampling method was modified so that calculated population densities would more accurately represent the average densities at the station's depth. From 2 May, 1970 to March, 1971, f i v e 20 cm cores were taken with a modified Kajak corer (McCauley, 1971 MS) at each of the three 2 stations within a 25 m area centered on the station marker 2 buoys. To reduce the amount of mud to be extracted, one 2.8 cm core sample was taken from the center of the sediment i n each - 12 -Kajak core. The top 3 cm of mud was preserved and sediment samples were extracted as before. In these and a l l subsequent samples, harpacticoid and cyclopoid copepods, cladocerans, nematodes, and mites were counted as well as r o t i f e r s . Each core sample was processed i n d i v i d u a l l y . Members of two other meiofaunal groups, oligochaetes and t u r b e l l a r i a n s , usually disintegrated when formalin was added to the samples, and these groups were not considered. In the spring of 1971 the sampling method was further modified. Analysis of samples indicated that most meiofaunal groups had contagious s p a t i a l d i s t r i b u t i o n s (see Results). These d i s t r i b u t i o n patterns were i n t e r e s t i n g i n themselves, but were a complicating factor i n accurately determining average population density on a given date. Accordingly, i n the f i n a l phase of the sampling programme more samples were taken (10) 2 within a larger area (100 m ), centered on the station marker buoys. Because of the time which would be required to extract the organisms from the additional sediment, i t was necessary to pool the samples and take subsamples. The core sampler used during the f i n a l phase of sampling 2 took a 2.8 cm section of lake sediment. The sampler was a plexiglass tube (1.9 cm I.D., 2.5 cm O.D., 30 cm long) with a bevelled bottom edge and a hinged fla p of thin (2 mm) r i g i d p l a s t i c covering the top end. The corer was weighted near the lower end with a band of lead. The r e t r i e v a l l i n e was poly-propylene cord (ca. 2 mm i n diameter). In use the corer was - 13 -lowered rapidly and as i t sank the movement of water into the bottom of the tube kept the hinged f l a p open at the top. When the corer had embedded i t s e l f i n the sediment (usually 5-10 cm) i t was pulled out and l i f t e d back to the boat. Water pressure kept the top closed and the sediment i n t a c t and r e l a t i v e l y un-disturbed. Although the sediment v e r t i c a l p r o f i l e could have been dis t o r t e d by t h i s sampler, such d i s t o r t i o n was not obvious. Moreover the water above the sediment i n each core was clear, i n d i c a t i n g l i t t l e disturbance to the very flo c c u l e n t interface sediment. 2 To check whether 10 pooled 2.8 cm samples would allow a consistent estimate of the meiofauna leve l s on a given date, sampling was ca r r i e d out i n t r i p l i c a t e on two occasions, once i n November and once i n July. On these dates three sets of 10 cores were taken at the same station on the transect. Samples were extracted and counted i n the usual way. Results (Table 1) showed that t h i s method gave repeatable counts for d i f f e r e n t meiofaunal groups, with one exception, which i s unexplained. To investigate v e r t i c a l d i s t r i b u t i o n of meiofauna, three core samples were taken i n A p r i l , 1971 at the 2.5 m station using the Kajak core sampler. Each core was sectioned into 1 cm thick layers using plexiglass rings (McCauley, 1971 MS) and the appropriate sediment layers from the three cores were pooled, extracted, and counted. - 14 -Table 1. R e l i a b i l i t y of meiofaunal sampling method: r e s u l t s of r e p l i c a t e sample sets. Meiofaunal 2 de n s i t i e s i n No/cm -f 95% Confidence L i m i t s Nov. 15, 1971 (2.5m) Sample Set A Sample Set B Sample Set C R o t i f e r s 11.4+3.8 10.4+3.0 9.9+1.6 Harpacticoids 1.5+0.7 1.8+1.0 0.9+0.7 Cyclopoids 0.4+0.3 0.7+0.4 0.4+0.6 Cladocerans 1.1+0.3 1.1+0.8 1.1+0.5 Nematodes 0.8+0.2 0.4+0.2 0.5+0.6 Mites 1.3 + 0.9 1.0 + 0.8 0.4 + 0.0 Ju l y 29, 1972 (1.0m) Sample Set A Sample Set B Sample Set C R o t i f e r s 19.1+3.3 16.6+2.5 15.3+6.4 Harpacticoids 11.2+3.7 6.6+1.6* 12.0+3.5 Cyclopoids 2.6+1.5 1.9+1.4 2.4+0.6 Cladocerans 1.3+0.9 1.1+1.1 1.6+0.5 Nematodes 2.1+1.2 1.6+0.8 2.4+0.7 Mites 1.1 + 0.5 0.9 + 0.4 0.6 + 0.4 * t - t e s t s i n d i c a t e that the ha r p a c t i c o i d density f o r set B i s s i g n i f i c a n t l y d i f f e r e n t (at'the .05 l e v e l ) from the other two sample sets. - 15 -Sample Processing: Preserved samples were allowed to s e t t l e 24 hours and excess water was decanted, leaving a mud-water sample of approximately 200 ml. This material was d i s t r i b u t e d among four 300 ml wide-mouth p l a s t i c b o t t l e s . Next, by using a funnel, 100 ml of an 80% sucrose solution was placed at the bottom of each bottle underneath the sample. Bottles were capped and centrifuged for 5 minutes at 1800 RPM. Meiofauna, along with a l l other invertebrates and some organic debris, was trapped at the sucrose/water interface while most sediment accumulated at the bottom i n the sucrose layer. To check whether t h i s procedure extracted meiofauna e f f i c i e n t l y , sediment at the bottom of the bot t l e was examined on three occasions. The extraction method removed 88%, 78%, and 94% of the meiofaunal organisms, for an average e f f i c i e n c y of 86.7%. Water and sucrose solution containing the suspended animals was sucked out of the b o t t l e using a faucet aspirator and poured into a large p l a s t i c tube (diameter 11.5 cm) covered at the bottom with 30 um nylon mesh. The l i q u i d containing the dissolved sucrose, and some fine debris, was thus removed. The remaining sample was rinsed with tap water. In the next step the sample was d i l u t e d to 100 ml i n a 250 ml beaker and s t i r r e d slowly on a magnetic s t i r r e r for 3 minutes. The slow s t i r r i n g speed was used so as not to con-centrate organisms i n the center of the beaker and so bias subsampling. Five 5 ml subsamples were taken randomly from - 16 -d i f f e r e n t parts of the beaker using a plunger-type automatic pipette with a 0.8 cm inner diameter. Subsamples were placed in small p l a s t i c tubes (diameter 4 cm) covered at one end by 30 um mesh. These tubes were set i n a staining bath of 0.1% Rhodamine B solution and l e f t for 24 hours. Rhodamine B i s a p r o t e i n - s p e c i f i c fluorescent stain which rea d i l y stains meiofauna and other invertebrates while leaving background sediment either unstained or non-fluorescent. This st a i n has been used i n examining benthos samples for macrofauna (Hamilton, 1969). During the development of t h i s technique i t was discovered that l i v e microscopic animals could also be stained and separat-ed unharmed from fresh sediment. Large numbers of many organ-isms ( c i l i a t e s , r o t i f e r s , cladocerans, copepods, etc.) could thus be gathered for culture purposes. Following staining, preserved subsamples were rinsed several times to remove excess stai n and then suspended i n 10 ml of water i n a p e t r i dish. The dish was methodically searched using a Wild M-5 stereomicroscope at 12-25 X magnification. Illumination was provided by a 100 watt long-wave u l t r a v i o l e t l i g h t source (Blak-Ray Model B 100) which causes Rhodamine B stained material to fluoresce a bright orange. To prevent fluorescence being "washed out" by white l i g h t , searching was done under a hood. A yellow f i l t e r was placed below the objective to reduce the intense blue color seen through the microscope. Examination of stained material had to be under-- 17 -taken immediately aft e r r i n s i n g as there was considerable leaching of sta i n into the surrounding water. Meiofauna could e a s i l y be distinguished against the more drab color of organic debris. Individual animals were picked up by a glass micropipette and deposited i n a depression of a p l a s t i c spot plate. After s e t t l i n g , animals were removed to a clean glass s l i d e , excess water was evaporated using a hot plate, and a drop of polyvinyl-lactophenol (Thane-Fenchel, 1968) was added, followed by a coverslip. Polyvinyl-lactophenol acted both as a mountant and clearing agent. After allowing 24 hours for clearing, the prepared s l i d e was examined using phase-contrast microscopy and organisms were i d e n t i f i e d and counted. Slides could then be stored for future reference. For long term storage, cover s l i p s had to be sealed along the edge with clear f i n g e r n a i l p o l i s h to prevent slow evaporation of the polyvinyl-lactophenol. Using the above procedures, preparation and counting of one sample (five subsamples) required about three hours of work d i s t r i b u t e d over four days, to allow the 24 hour periods needed for s e t t l i n g of the sample, staining, and clearing of prepared s l i d e s . I d e n t i f i c a t i o n s of meiofaunal species were made using Bartos (1951), Edmondson (1959), Donner (1956), and Harring and Myers (1921, 1924, 1926, 1928) for r o t i f e r s ; Wilson and Yeatman (1959) for harpacticoid copepods; Yeatman (1959), and Harding and Smith (1974) for cyclopoid copepods; and Brooks - 18 -(1959) for cladocerans. Nematodes and mites were not i d e n t i f i e d . A l l meiofauna population numbers derived from sample counts were transformed using a logarithmic transformation (Sokal and Rohlf, 1969) before geometric mean population densities and 95% confidence l i m i t s were calculated. This was done because the untransformed sample variance was c h a r a c t e r i s t i c a l l y correlated with the mean. A transformation of the sample counts was therefore necessary to make the variance independent of the mean and allow c a l c u l a t i o n of confidence l i m i t s ( E l l i o t t , 1971). Results The highest mud-water interface temperatures on the-transect were at the 1.0 m station (Figure 2), and there was a lag of up to one month between the time summer maximum temperatures were reached at 1.0 m and 4.5 m. The lake was s t r a t i f i e d from May (or before) u n t i l November i n 1970 and from A p r i l u n t i l September i n 1971. During the summer, several days of high r a i n f a l l and the re s u l t i n g i n f l u x of cold water to the lake through i t s two i n l e t streams could depress temperatures at the mud-water interface by several degrees (e.g. June, 1971). In the f a l l , high r a i n f a l l and run-off from the lake's watershed, along with wind, disrupted the weak summer thermal s t r a t i f i c a t i o n . Ice cover was present from December to March i n both 1970 and 1971. ° o !.0 molar 1S70 197! 1972 Figure 2. Mud-water interface temperature at three depths i n Marion Lake, 1970-72. - 20 -R o t i f e r s were i d e n t i f i e d t o genus, except f o r the most common forms, which were taken t o s p e c i e s l e v e l . A t l e a s t 30 sp e c i e s o f r o t i f e r s b e l o n g i n g t o 17 genera were c o l l e c t e d . M i cro-crustaceans (Copepoda and Cladocera) were r e p r e s e n t e d by 22 s p e c i e s . Two s p e c i e s o f b d e l l o i d r o t i f e r s , two s p e c i e s o f h a r p a c t i c o i d copepods, and one s p e c i e s of c y c l o p o i d copepod dominated the meiobenthos, being represented i n v i r t u a l l y a l l samples a t a l l s t a t i o n s (Table 2). When a l l taxonomic groups were added together the maximum p o p u l a t i o n d e n s i t i e s of meiofauna on any sampling date were u s u a l l y found a t the 2.5 m s t a t i o n , although each group d i d not always f o l l o w t h i s p a t t e r n (Figure 3). P r e l i m i n a r y sampling i n d i c a t e d t h a t meiofaunal organisms were con c e n t r a t e d a t the mud-water i n t e r f a c e and t h e r e f o r e the sampling procedure was designed to take o n l y the top thr e e t o fo u r c entimeters o f sediment. R e s u l t s of the v e r t i c a l d i s t r i b u t i o n Kajak core samples taken i n A p r i l , 1971 i n d i c a t e d t h a t over 75% of the meiofauna was found i n the top cent i m e t e r o f sediment and 97% i n the top two centimeters (Figure 4). The meiofauna tended t o have a patchy d i s t r i b u t i o n , even when s m a l l areas o f ap p a r e n t l y homogeneous sediment were co n s i d e r e d . In the e a r l y samples (June, 1969 to May, 1970), 2 2 sxx 2.8 cm cores were taken from the 400 cm of un d i s t u r b e d sediment l i f t e d from the lake bottom w i t h a Hargrave sampler, and o n l y r o t i f e r s were counted. An index of d i s p e r s i o n was c a l c u l a t e d by d i v i d i n g sample v a r i a n c e by sample mean u s i n g - 21 -Table 2. Marion Lake Meiofaunal species, with percentage of samples from each s t a t i o n i n which the species were found. ROTIFERA SAMPLING STATIONS (DEPTH) 1.0m 2.5m 4.5m Order Bd e l l o i d e a Dissotrocha macrostyla  Macrotrachela p l i c a t a ~ R o t a r i a spp. (including R. r o t a t o r i a ) 100% 100 75 100% 100 88 100% 100 65 Order Monogononta Aspe l t a sp. Cephalodella spp. Col l o t h e c a sp. (including C. vacuna) Dicranophorus spp. Encentrum spp. Lecane spp. (including L. Manfredium sp. s i g n i f e r a ) Monostyla spp. Notomraata spp. (including M. (including N. crenata) saccigera) Taphrocampa sp. T e s t u d i n e l l a spp. T r i c h o c e r c a spp. T r i c h o t r i a spp. 7 25 3 3 11 64 11 93 32 0 18 18 18 36 24 6 9 27 88 6 72 45 12 45 24 36 14 7 3 7 24 59 0 72 7 3 13 17 7 CRUSTACEA Order Harpacticoida A t t h e y e l l a obatogamensis  Bryocamptus~hiemali"s  Bryocamptus zschokkei Order Cyclopoida Acanthocyclops nanus  Cyclops bicuspidatus  Eucyclops a g i l i s  Macrocyclops albidus  Macrocyclops fuscus 97 100 93 97 100 97 22 15 0 100 100 100 15 18 48 56 67 45 4 3 3 37 21 45 - 22 -Table 2. (continued) Order Cl'adocera Alona a f f i n i s  AIona costata Alona guttata  Alona quadrangularis  Alona rectangula A l o n e l l a -excisa Alone11a nana BjO^p.ina l o n g i r o s t r i s Camptocercus r e c t i r o s t r i s Ce r i o d aphni a' sp. Chydorus sphaericus  Eurycercus lamellatus Ilyocryptus sordidus Sida c r y s t a l l i n a NEMATODA" ARACHNIDA1 a) Nematodes were not identified. Some were fre e - l i v i n g adult stages of species which parasitize chironomid larvae in Marion Lake (McCauley, 1973). b) Mites were not identified. Conroy (1968, 1973) l i s t s Marion Lake species. SAMPLING STATIONS (DEPTH) 1.0 m 2.5m 4.5 m 4 0 0 33 9 7 4 3 0 19 18 34 11 0 0 37 3 7 52 97 59 4 3 0 7 0 0 4 0 0 33 24 14 4 6 0 59 76 72 22 24 14 100 100 100 92 100 86 22 20 18 16 14 H o ||0 8 H 6 4 2H 0 ROTIFERS 2.5 m lm f.om A P R I L J U L Y OCTOBER - 23 -22 20-18-16-14-12-10-8-6-4-2-0-H A R P A C T I C O I D C O P E P O D S A P R I L J U L Y O C T O B E R 8 * E 6 u ^ 4 2 2H 0 C L A D O C E R A N S t L A P R I L J U L Y O C T O B E R 8 6-4-2 -0 CYCLOPOID C O P E P O D S j f m_L£Lx A P R I L J U L Y O C T O B E R 6-w 'cm 4-© 2 -0-N E M A T O D E S J1 D d A P R I L J U L Y C L O C T O B E R 6H 4 2H 0 MITES r-TU A P R I L J U L Y O C T O B E R Figure 3. Densities of Marion Lake meiofaunal taxonomic groups at three depths i n representative spring, summer and f a l l samples (1971). No./cm" 0 - 1 ?n 1 - 2 H = 2-3 LJ m 1 4-5 rn z. _ _ —I o - 6 q 6-7 7- 8 8- 9 2 .JU 3 . 5 6 ROTIFERS 7 2 3 4 HARPACTICOID COPEPODS 6 —L I 2 3 J NEMATODES • J o :< CO o -1 p > o o n > CO Figure 4. V e r t i c a l d i s t r i b u t i o n of meiofaunal taxonomic groups at 2.5m i n Marion Lake, A p r i l , 1971. - 2 5 -untransformed data ( E l l i o t t , 1971): I = s! x If the organisms were di s t r i b u t e d randomly among the samples t h e i r d i s t r i b u t i o n would follow the Poisson d i s t r i b u t i o n and I would approximate unity. If the variance became greater than the mean, the Poisson d i s t r i b u t i o n would no longer be a suitable model because the organisms would have a clumped or contagious d i s t r i b u t i o n . To test whether the sample variance was s i g n i f i c a n t l y greater than the sample mean, a chi-square value was calculated X 2 = I (n-1) where n i s the number of samples. These values were compared to c r i t i c a l chi-square values (p>0.05) i n E l l i o t t (1971). Of the r o t i f e r samples from June, 1969 to May, 1970, 88% showed s i g n i f i c a n t contagious d i s t r i b u t i o n s . Since the six cores that made up each sample set were taken approximately three to four centimeters from each other, these results suggest that r o t i f e r s , at least, have a patchy d i s t r i b u t i o n on the scale of a few centimeters. From May, 19 70 to May, 1971 samples were sets of f i v e 2.8 2 cm cores taken with a modified Kajak core sampler over an area 2 of approximately 25 m . samples were taken at a l l three samp-l i n g stations and a l l taxonomic groups were counted. The index of dispersion was calculated for these samples, and the - 26 -significance of departure from unity was tested by c a l c u l a t i o n of chi-square. Taxonomic groups and percentage of samples which showed a contagious d i s t r i b u t i o n were r o t i f e r s , 6 7%; harpacticoid copepods, 50%; nematodes, 45%; cladocerans, 36%; cyclopoid copepods, 18%; and mites, 0%. Samples taken from May, 1971 to May, 1972 were pooled and consequently no information regarding patchiness was available for t h i s sampling period. Two years of sampling results for the major meiofauna groups (three years for r o t i f e r s at 2.5 m) are presented i n Figures 5 to 10. Population densities of the various meiofauna taxonomic groups did not fluctuate by more than a factor of f i v e over the sampling period, with the exception of Cladocera, whose maxi-mum seasonal changes approximated one order of magnitude. The t o t a l r o t i f e r population at 2.5 m showed a late summer and f a l l maximum i n two out of three years (Figure 5) but no pattern was obvious i n the r o t i f e r r esults from the 1.0 m and 4.5 m stations. Harpacticoid population densities at 2.5 m reached t h e i r peak i n May of the two years these copepods were studied (Figure 6). At the other two stations (1.0 m and 4.5 m) spring maxima were not as well defined. Cyclopoid copepod popu-l a t i o n densities declined s l i g h t l y over two years at a l l depths (Figure 7). There was a tendency toward summer maxima in cyclo-poid density at the 1.0 m station. At 4.5 m the movement of planktonic. cyclopoid copepods into the sediments to encyst in September - 27 -1.0 m IB.. Figure 5. Total meiobenthic r o t i f e r s at three depths i n Marion Lake, 19 6 9-19 72. Log-transformed data, with 95% confidence l i m i t s . - 28 -Figure 6. Total meiobenthic harpacticoid copepods at three depths i n Marion Lake, 19 70-72. Log-transformed data with 95% confidence l i m i t s . 1.0 m Figure 7. Total meiobenthic cyclopoid copepods at three depths i n Marion Lake, 19 70-72. Log-transformed data with 95% confidence l i m i t s . - 30 -and from the sediment back to the water column i n A p r i l was r e f l e c t e d i n cyclopoid densities i n these months. Cladocerans showed t h e i r peak densities i n mid-summer in 1971 but i n 1970 a build-up to a summer maximum was not observed (Figure 8). Nematode (Figure 9) and mite densities were e s s e n t i a l l y constant over the two years (Figure 10). Total r o t i f e r density was not s i g n i f i c a n t l y correlated with temperature (r = 0.23, p = .05). This was due to the slow response of the abundant b d e l l o i d Dissotrocha macrostyla to increasing spring temperatures, which o f f s e t the more rapid response of non-bdelloid r o t i f e r s (Figure 11). I t i s paradoxical that Dissotrocha was so common, given i t s slow reproduction. This species, along with another equally abundant b d e l l o i d , Macrotrachela p l i c a t a (Figure 12), accounted for approximately two-thirds of r o t i f e r numbers at 2.5 m. Two species of harpacticoid copepods, ; Bryocamptus hiemalis and Attheyella obatogamensis, were found regularly on the transect. Bryocamptus was' more abundant at a l l depths, but both species reached t h e i r maximum densities at the 2.5 m st a t i o n (Figure 13). Bryocamptus females produced eggs i n the f a l l and winter while Attheyella females ca r r i e d eggs only i n spring and early summer (Figure 14). Although the two species are approximately the same size and both are deposit feeders, they d i f f e r i n that Bryocamptus i s more active than Attheyella and moves vigorously i f disturbed. - 31 -Figure 8. Total meiobenthic cladocerans at three depths i n Marion Lake, 1970-72. Log-transformed data with 95% confidence l i m i t s . Figure 9. Total meiobenthic nematodes at three depths i n Marion Lake, 1970-72. Log-transformed data v/ith 95% confidence l i m i t s . - 33 -Figure 10. Total meiobenthic halacarine mites at three depths i n Marion Lake, 1970-72. Log-transformed data with 95% confidence l i m i t s . - 34 -Figure 11. A comparison of temperature with population densities of the common b d e l l o i d r o t i f e r Dissotrocha and t o t a l non-bdelloid r o t i f e r s at 2.5m i n 1971-72. - 35 -Figure 12. Densities of the two most common b d e l l o i d r o t i f e r species at 2.5m, 1969-72. Log-transformed data with 95% confidence l i m i t s . - 36 -Figure 13. Densities of the two common harpacticoid copepod species at 2.5m, 1970-72. Log-transformed data, with 95% confidence l i m i t s . - 37 -Bryocomptus hiemalis CL *• 0) XJ 3 . E 3 Attheyella obotoqamensis ^ 1 I I t — f t I H I I I t ! ! •H- I I 1-I K J < J J W E K W t E A F t » IK J< JU « J SE CC M E JA F l ! W W 1370 1S71 Figure 14. Number of female harpacticoid copepods carrying eggs at 2.5m, 1970-72. Log-transformed data with 95% confidence l i m i t s . - 38 -Bryocamptus females probably produced f i v e to six egg clutches (50-60 nauplii) during the winter, based upon culture work (Chapter I I ) . Survival through naupliar stages to the f i r s t copepodid stage was low i n the lake. Individuals hatched from eggs at the beginning of October made the f i n a l moult to adult stage at the beginning of the following May, taking seven months at an average temperature of approximately 5°C (Figure 15). Bryocamptus produced only one generation per year. The less common harpacticoid Attheyella also produced only one generation per year. This species took barely four months (April to September) at an average temperature of 12°C, to go from egg to adult. Since Attheyella was not extensively studied i n culture, the average number of egg clutches produced by a female cannot be estimated. Survival from egg to adult was apparently low. Population densities of cyclopoid copepods were approximately the same as densities of harpacticoid copepods at the 1.0 m and 4.5 m stations. In contrast, harpacticoids were much more abundant at the 2.5 m station (cf. Figures 6 and 7). Although f i v e species of cyclopoids were found, the smallest species (Acanthocyclops nanus - 0.7 mm i n length) was most abundant, usually contributing at least 80% of cyclopoid numbers at a l l depths. Attempts to culture Acanthocyclops were unsuccessful. Unlike the two harpacticoid species, t h i s cyclopoid had a long reproductive season. Females were found carrying eggs i n - 39 -F i g u r e 15. Numbers of immature Bryocamptus h i e m a l i s a t 2.5m, 19 70-72. Log-transformed data w i t h 95% confidence l i m i t s . Number per S q u a r e C e n t i m e t e r - 41 -a l l months except June, July, and August, and copepodid stages were present a l l year round. There was a general decline i n t o t a l cyclopoid numbers at a l l depths over the two years of sampling (Figure 7). This r e f l e c t s the decline i n population density of the dominant species, Acanthocyclops nanus. The sharp increases i n t o t a l cyclopoid numbers at 4.5 m which occurred i n September and A p r i l of the two sampling years resulted from the appearance i n the samples of Cyclops  bicuspidatus, a planktonic copepod. This species moved from the plankton to deep water i n July and August as stage IV copepodids and burrowed into the mud where i t encysted (McQueen, 1969). Although the exact depth i n the sediment where t h i s copepod encysted was not determined, i t was deep enough so that none were co l l e c t e d i n the regular 3 cm deep sediment samples taken from September through March. Excysted copepods appeared at the 4.5 m station i n A p r i l , s t i l l i n the copepodid IV stage, apparently as they moved from the sediment back into the plank-ton. Average t o t a l cladoceran population densities on the benthic transect (Figure 8) were sim i l a r to cyclopoid copepod densities. Also l i k e cyclopoids, the cladocerans showed a pattern of approximately equal abundance at the 1.0 m and 2.5 m stations, i n contrast to harpacticoid copepods and r o t i f e r s which were more abundant at 2.5 m than at 1.0 m. Of 14 species of Cladocera found at the 1.0 m station, three species were - 42 -generally most abundant: Chydorus sphaericus, A l o n e l l a nana, and Ilyocryptus sordidus. At 2.5 m and at 4.5 m there were ten and seven species collected, respectively, and at both of these stations A l o n e l l a nana was c l e a r l y dominant, accounting for 80% or more of the cladoceran numbers. Nematode worms were more abundant at 2.5 m than at 1.0 m or 4.5 m. Average densities were approximately the same as for cladocerans and cyclopoid copepods and well below densities reached by harpacticoid copepods and r o t i f e r s . Female nema-todes carrying eggs were observed i n May and June at 1.0 m and 2.5 m, and i n May, June, August and October at 4.5 m. Numbers of these worms varied l i t t l e over the two year sampling period. With the exception of densities observed on a few sampling dates at the 2.5 m station, numbers of water mites were con-s i s t e n t l y very low (Figure 10). Both juvenile and adult stages of these slow moving predators were recorded i n a l l months of the year. Discussion Species Diversity: The 17 genera of r o t i f e r s l i s t e d i n Table 2 are not the only r o t i f e r s which were found i n Marion Lake benthos. Several other genera (e.g. C o l u r e l l a , Lepadella, Tetrasiphon) were found i n q u a l i t a t i v e samples of benthic sediments taken i n very shallow water (<0.5 m) and i n beds of macrophytes. Moore - 43 -(1939) l i s t e d 19 genera and 28 species i n Douglas Lake, Michigan benthic samples. Ten of these genera were also present i n Marion Lake benthos and one species of b d e l l o i d r o t i f e r which Moore collected frequently (Dissotrocha macrostyla) was the most common benthic r o t i f e r i n Marion Lake. Cole (1955) found nine species i n the shallow benthos of two Minnesota lakes, and again D. macrostyla was frequently c o l -lected. P e j l e r (1962) sampled the benthos of a number of Swedish ponds and lakes and found 53 species belonging to 30 genera i n mud sediments. Once again D. macrostyla was common, occurring i n 11 d i f f e r e n t bodies of water. A t o t a l of eight species of Copepoda (Table 2) was c o l -lected i n benthic samples i n Marion Lake. The dominant harp-a c t i c o i d copepod was Bryocamptus hiemalis, which i s a wide-spread and common species (Wilson and Yeatman, 1959). I t was found i n Douglas Lake, Michigan by Moore (1939) and i n several B r i t i s h Columbia locations by Carl (1940). The other Bryocamptus species (B. zschokkei) found occasionally i n Marion Lake i s l i s t e d i n Wilson and Yeatman (1959) as being . widely d i s t r i b u t e d i n North America but was not co l l e c t e d by Carl (1940) i n B.C. The second most common harpacticoid species i n Marion Lake was Attheyella obatogamensis, which has been reported from Quebec (Wilson and Yeatman, 1959) but not previously from B r i t i s h Columbia. - 44 -Of the f i v e c y c l o p o i d copepod species c o l l e c t e d , one i s pl a n k t o n i c f o r most of i t s l i f e (Cyclops b i c u s p i d a t u s ) and three others are commonly found i n the open water plankton and/ or the l i t t o r a l water column (Eucyclops a g i l i s , Macrocyclops  a l b i d u s , M. fus c u s ) . The most numerous c y c l o p o i d was the small Acanthocyclops nanus. This species was l i s t e d by Yeatman (19 59) and Pennak (196 3) as being rare i n North America and was not found i n B.C. by C a r l (1940). I t i s common i n B r i t a i n (Harding and Smith, 1974). The 14 species of Cladocera found on the benthic t r a n s e c t are common forms (Brooks, 1959) and a l l were c o l l e c t e d i n B.C. by C a r l (1940). The most common species was A l o n e l l a nana, a small (0.25 mm) chydorid. The second most common cladoceran species was I l y o c r y p t u s sordidus. This organism i s w e l l adapted to l i f e i n s o f t sediments, possessing broad and powerful antennae which i t uses to crawl through the sediment, r a t h e r than f o r swimming as i n most other cladocerans. A l s o common was Chydorus sphaericus which has been c a l l e d the most common cladoceran species i n the world (Brooks, 1959). Of the 14 cladoceran species found by Moore (1939) i n h i s e a r l y meio-benthic study i n Michigan, four were c o l l e c t e d i n Marion Lake. S i m i l a r l y , seven of the 25 species reported by Cole (1955) were found on the Marion Lake t r a n s e c t . I t should be emphasized that the cladoceran species l i s t e d i n Table 2 are only those found on the t r a n s e c t . Other species were found a t the mud-water i n t e r f a c e and i n the water column i n macrophyte beds - 45 -(e.g. Kurzia latissima and Ac an tho1eberi s c u r v i r o s t r i s ) by Pearlstone (1973). Di s t r i b u t i o n : On any sampling date, the greatest population densities for the various taxonomic groups were usually found at the 2.5 m station, with lower densities at the 1.0 m and 4.5 m stations (Figure 3). One possible explanation for t h i s d i s -t r i b u t i o n pattern i s that both a l g a l standing crop and a l g a l primary productivity are greater at middle depths than i n more shallow, or deeper stations (Hargrave, 1969; Gruendling, 1971). This correspondence between population densities and a l g a l standing crop and productivity suggests that the meiofauna i s food limited, a hypothesis which was not supported by experi-mental evidence (Chapter I I I ) . An explanation which has been offered by Gruendling (1971) to explain the lower standing crop of algae at shallow depths i s the presence of the highest densities of H y a l e l l a azteca, a deposit-feeding amphipod not usually found below 2-3 meters in Marion Lake. Hargrave (1970b) demonstrated that t h i s abundant amphipod processes large amounts of surface sediments. My experiments (Chapter III) indicated that "predation" by Hyalella on meiofauna i s i n s i g n i f i c a n t , but heavy amphipod grazing could disturb meiofaunal feeding or otherwise make the sediment less suitable for meiofauna. I t i s i n t e r e s t i n g that the meiofaunal group which most consistently followed the - 46 -p a t t e r n of lower d e n s i t i e s i n shallow water i s h a r p a c t i c o i d copepods, which are "miniature H y a l e l l a " i n t h a t they are d e p o s i t f e e d e r s . The copepods may be a t a c o m p e t i t i v e d i s -advantage i n t h i s s i t u a t i o n . The lower meiofauna p o p u l a t i o n d e n s i t i e s observed i n deeper water (4.5 m s t a t i o n ) as compared to middle depths are perhaps e a s i e r to understand. Standing crops of algae and a l g a l p r o d u c t i v i t y are much lower than a t mid-depths (Gruendling, 19 71). At the same time, p o t e n t i a l p r e d a t o r s such as the ca r n i v o r o u s amphipod Crangonyx richmondensis show no decrease i n numbers w i t h depth (Mathias, 1971). The most l i k e l y reason f o r lower meiofauna d e n s i t i e s i n deeper water i s the d i r e c t e f f e c t on r e p r o d u c t i o n and growth of lower temperatures (Figure 2). Deeper water s t a t i o n s are a l s o f a r t h e r from the shallow water macrophyte zone which may be a source of meiofaunal o r g -anisms ( e s p e c i a l l y mobile cladocerans and c y c l o p o i d copepods). Many workers have s t u d i e d the v e r t i c a l d i s t r i b u t i o n of meiofauna i n freshwater sediments (Moore, 1939; Stanczykowska, 1966; Sarkka and P a a s i v i r t a , 1972; Fenchel, 1975) and i n marine sediments (Fenchel and Jansson, 1966; B a r n e t t , 1968; A r l t , 1973). Except i n very shallow w a t e r - s a t u r a t e d sandy beaches, meiofauna was concentrated i n the upper few centimeters of sediment. T h i s was a l s o the case i n Marion Lake (Figure 4 ) . A probable cause f o r the v e r t i c a l d i s t r i b u t i o n p a t t e r n i s the sharp d e c l i n e i n oxygen c o n c e n t r a t i o n i n the top centimeter of sediment (Hargrave, 1970c). B e n t h i c algae, which i s one food - 47 -source for meiofauna, i s also concentrated i n the top centimeter of sediment. The p o s s i b i l i t y of v e r t i c a l migration within the sediment, either diurnal or seasonal, was not investigated i n t h i s study but diurnal v e r t i c a l migration by meiofauna seems u n l i k e l y . McCauley (1971 MS) found some evidence of s l i g h t seasonal v e r t i c a l migration by meiofauna i n Marion Lake sediments, but i t would not have affected my sampling r e s u l t s . A l l groups of Marion Lake meiofauna except the mites showed contagious or patchy d i s t r i b u t i o n s i n at lea s t some sample sets. The size of the patches was not determined but 1969-70 results suggested that small areas of high and low r o t i f e r density were located within a few centimeters of each other. Patchy d i s t r i b u t i o n of meiofauna i n very shallow (0.5 m) marine sediments was studied i n d e t a i l by A r l t (1973). He 2 2 took 64 1 cm samples 5 cm apart within an area of 1600 cm , and plotted the r e s u l t i n g data as a map with isopleths connect-ing densities of equal magnitude. Patches varied i n size and 2 the smallest patches had an area of 7-8 cm . Patches i n which 2 harpacticoid copepod density was 0-5 individuals/cm were located within 15 cm of patches of the maximum density, more 2 than 40 individuals/cm . A r l t found si m i l a r r e s u l t s for nematodes, ostracods, and large c i l i a t e d protozoa. - 48 -Whiteside (1974) s t u d i e d c h y d o r i d c l a d ocerans u s i n g a 2 p a t t e r n sampler with which he took 36 samples w i t h i n a 70 cm area. He found samples of c h y d o r i d s ranging from 1 to 204 (x = 41.5) w i t h i n t h i s s m a l l area. P o p u l a t i o n Dynamics: The s t a b i l i t y o f Marion Lake meiofauna p o p u l a t i o n d e n s i t i e s i s s i m i l a r t o the r e s u l t s found i n most s t u d i e s of freshwater and marine meiobenthos, i n c o n t r a s t t o the o f t e n l a r g e seasonal f l u c t u a t i o n s i n numbers t y p i c a l of p l a n k t o n i c c r ustaceans and r o t i f e r s (Wetzel, 1975). The r e l a t i v e constancy of the b e n t h i c environment w i t h r e s p e c t t o p h y s i c a l f a c t o r s such as temperature may p a r t i a l l y e x p l a i n the g e n e r a l phenomenon of meiobenthic p o p u l a t i o n s t a b i l i t y . In Marion Lake s p e c i f i c a l l y , the h i g h f l u s h i n g r a t e d e f i n i t e l y a f f e c t s p l a n k t o n i c organisms more than the benthos. Average p o p u l a t i o n d e n s i t i e s f o r Marion Lake meiofauna are s i m i l a r to the r e s u l t s of other s t u d i e s (Table 3), f a l l i n g between the low v a l u e s r e p o r t e d i n Moore's (1939) study and the r a t h e r h i g h v a l u e s f o r the benthos of e u t r o p h i c M i k o l a j s k i e Lake i n Poland (Wasilewska, 1973). Maximum meiofauna d e n s i t i e s f o r freshwater environments are g e n e r a l l y lower than maximum values found i n marine s t u d i e s . One or two s p e c i e s i n each taxonomic group of the Marion Lake meiobenthos were much more common than other s p e c i e s i n t h a t group. A s i m i l a r dominance p a t t e r n was a l s o found by - 49 -Table 3. A comparison of the maximum meiofauna population densities i recorded for some freshwater and marine habitats Habitat Author Locality Meiofauna group Max. No/( Li t t o r a l this Marion Lake, Rotifers 25 benthos study B.C. Harpacticoids 12 Cyclopoids 7 Cladocerans 4 Nematodes 4 Mites 3 Shallow Wasilewska, Mikolajskie Rotifers 47 l i t t o r a l 1973 Lake, Copepods 9 benthos Poland Cladocerans 3 Nematodes 44 L i t t o r a l and Prejs and Mikolajskie Copepods 7 profundal Stanczykowska, Lake, Cladocerans 1 benthos 1972 Poland Nematodes 16 Deep Sarkka and Lake Harpacticoids 1 profundal Paasivirta, Paijanna, Cyclopoids 21 benthos 1972 Finland Cladocerans 1 Nematodes 2 Arctic Fenchel, Barrow, A l l meiofauna 30 pond 1975 Alaska benthos Shallow Goulden, Lake Chydorid cladocerans 30 l i t t o r a l 1971 Lacawac, benthos Pennsylvania Intertidal Barnett, Southampton, Harpacticoids 100 mudflat 1968 U.K. Intertidal Harris, Cornwall, A l l meiofauna 200 sand beach 1972 U.K. Shallow Thane-Fenchel, Helsingor, Rotifers 10 brackish 1968 Denmark Nematodes 60 sand Harpacticoids 15 Sublittoral McLachlan et al., Algoa Bay, A l l meiofauna 200 sand 1977 S. Africa Summary of var- Mclntyre, A l l meiofauna 10-1000 ious i n t e r t i d a l 1969 studies Summary of Coull, estuary studies 1973 A l i meiofauna 50-250 - 50 -Prejs (1970) and Wasilewska (1973) for freshwater meiobenthic nematodes, by Keen (1973) for l i t t o r a l water column chydorid cladocerans, by Thane-Fenchel (1968) for brackish-water benthic r o t i f e r s , and by Barnett (1968) and Harris (1972) for marine harpacticoid copepods. The most common benthic r o t i f e r i n Marion Lake was the bd e l l o i d Dissotrocha macrostyla, a slow moving r o t i f e r which bears i t s young a l i v e . Generation times even at 15-20PC are approximately 20 days (Chapter I I ) . Once an embryo reaches an advanced stage i t w i l l be born, even i f the adult r o t i f e r i s placed at a temperature where i t normally reproduces slowly or not at a l l (e.g. 10°C). Interpretation of the population data for t h i s r o t i f e r i s that warm temperatures of summer stimulated production of eggs and embryological development proceeded at maximal rate (which was s t i l l very slow). F a l l i n g temperatures of September slowed embryological development but those embryos i n an advanced stage were born over the next month. F i n a l l y , Dissotrocha individuals became inactive when temperatures decreased. Predation on thi s abundant but slow moving species was apparently s l i g h t (Chapter I I I ) . Therefore population density remained high for most of the winter (Figure 11). Extensive culture work with the most common harpacticoid copepod (Bryocamptus hiemalis) indicated that the optimum temperature for s u r v i v a l , growth and reproduction i s approxi-mately 10°C (Chapter I I ) . Although the second most common - 51 -harpacticoid (Attheyella obatogamensis) was less extensively studied, the optimum temperature apparently i s somewhat higher than for Bryocamptus. Since the mean temperature for Marion Lake was close to 10°C i n 1970-71 (Figure 2) i t i s possible that temperature was responsible for the greater abundance of Bryocamptus. Warm temperatures of July and August were apparently as i n h i b i t o r y to egg formation i n Attheyella as they were i n Bryocamptus (Figure 14). A suitable temperature f o r egg production was shown not to be s u f f i c i e n t for Bryocamptus to produce eggs i n the lake. Rather, a decrease from a higher temperature down to 10°C i n the f a l l , or an int e r a c t i o n of temperature and photoperiod, was apparently necessary to trigger egg production (Chapter I I ) . For Attheyella a temperature of approximately 10°C was also suitable for egg production, but reproduction took place only i n the spring. The 1971 data (but not 1970) showed an increase i n t o t a l cladoceran numbers which p a r a l l e l e d the increasing interface temperature. Highest densities reached were s t i l l considerably lower than those reported by Goulden (1971) for benthic chydorid cladocerans i n very shallow (<0.5m) water. The maximum d a i l y population growth rate i n the lake (r = 0.020) was about half the rate calculated for two lake chydorid cladocerans cultured on natural sediment i n the laboratory (Chapter I I I ) . This suppression of population growth rate may have been due to predation pressure. Certainly a possible explanation for the plateau and decline i n cladoceran numbers - 52 -a t 1.0 m and 2.5 m i n l a t e summer of 1971, when temperatures were optimum f o r r e p r o d u c t i o n , i s p r e d a t i o n , p r i m a r i l y by t a n y p o i d midge l a r v a e and young predatory amphipods (Crangonyx) which appeared i n the l a k e a t t h a t time. McCauley (unpublished data) has shown t h a t Marion Lake tanypoids eat l a r g e q u a n t i t i e s of c l a d o c e r a n s . Goulden (1971) concluded t h a t t a n y p o i d preda-t i o n c o u l d s i g n i f i c a n t l y reduce b e n t h i c c h y d o r i d c l a d o c e r a n p o p u l a t i o n s and Whiteside (1974) suggested t h a t p r e d a t i o n c o u l d have caused a mid-summer r e d u c t i o n of weed-bed c h y d o r i d p o p u l a t i o n s . Keen (1973) concluded t h a t p r e d a t i o n by odonate nymphs, and s m a l l f i s h was the cause of m o r t a l i t y i n p o p u l a t i o n s of four c h y d o r i d s p e c i e s i n the water column of the weed zone of a Michigan l a k e . The c l a d o c e r a n fauna d e s c r i b e d here i n c l u d e s some s p e c i e s l i k e Chydorus sp h a e r i c u s which occur i n the plankton and among macrophytes i n the l i t t o r a l water column as w e l l as i n b e n t h i c samples. A l l the other c l a d o c e r a n s p e c i e s , w i t h the e x c e p t i o n of I l y o c r y p t u s s o r d i d u s , are as l i k e l y to be found i n the l i t t o r a l water column as i n the benthos (Quade, 1969; Keen, 1973; Daggett and Davis, 1974; Whiteside, 1974). There-f o r e an unknown p o r t i o n of the c l a d o c e r a n fauna may r e p r e s e n t i n d i v i d u a l s t h a t have l e f t the water column o n l y t e m p o r a r i l y , or i n the case of the 1.0 m s t a t i o n , i n d i v i d u a l s t h a t have wandered from the macrophyte h a b i t a t . Another d i f f i c u l t y i n i n t e r p r e t i n g c l a d o c e r a n p o p u l a t i o n dynamics i s the p o s s i b i l i t y t h a t some of the more a c t i v e l y swimming s p e c i e s may a v o i d a - 53 -small descending core sampler. Similar considerations apply to the cyclopoid copepod species co l l e c t e d on the transect. These animals are even more active swimmers than cladocerans and thus are even more l i k e l y to be found i n the water column occasionally. Evans and Stewart (1977) c l a s s i f i e d only 28-44% of the microcrustaceans they found i n sediment cores from shallow waters of Lake Michigan as true benthic species. Population densities reached by nematodes i n the Marion Lake benthos (Figure 9) were low compared to the densities reported by Prejs (1970), Prejs and Stanczykowska (1972), and Wasilewska (1973) for Mikolajskie Lake, Poland, and by Moore (1939) for Douglas Lake, Michigan. I t i s possible that some small nematodes, whose diameter i s a few microns, could have been l o s t through the fine netting used i n extraction of samples. Summary 1. Over 50 species of meiobenthic r o t i f e r s , copepods, and cladocerans, as well as an undetermined number of species of nematodes and mites, were found to occur on a sampling transect from 1.0 m to 4.5 m i n depth. The most abundant group of meio-fauna was the r o t i f e r s , followed by harpacticoid copepods. 2. Greatest population densities for the various taxonomic groups on any sampling date were usually found at the middle depth station. 3. V e r t i c a l d i s t r i b u t i o n of the meiofauna within the sediment - 54 -was s i m i l a r to results of other reported studies, with organisms concentrated i n the top one or two centimeters. 4. A l l meiofauna groups except mites showed patchy d i s t r i b u t i o n to some degree. 5. Maximum population densities observed for Marion Lake meio-benthos are comparable to other studies and as i n other studies, annual population fluctuations were usually less than one order of magnitude. 6. In the r o t i f e r , harpacticoid copepod, cyclopoid copepod, and cladoceran taxonomic groups, one or two species were much more abundant than other species. 7. The most abundant r o t i f e r species was a slow-moving b d e l l o i d r o t i f e r with a low reproductive rate. This species responded slowly to increasing water temperature and therefore tended to exhibit f a l l and winter population maxima. 8. The two common harpacticoid species showed d i f f e r e n t repro-ductive patterns, but both had only one generation per year. 9. The most abundant cyclopoid copepod species apparently had an extended reproductive period, and more than one generation was produced. 10. Cladocerans responded to increasing spring water tempera-tures with population growth. Decline i n cladoceran numbers i n late summer was probably due to predation. - 55 -CHAPTER I I LABORATORY CULTURE STUDIES ON LIFE HISTORY AND POPULATION DYNAMICS - 56 -Introduction To estimate production of meiofauna i n natural environments i t i s necessary to have information on reproductive rates. In several recent studies (Fenchel, 1968, 1975; Gerlach, 1971; Smith, 1973) i t has been assumed that generation times of these small animals must be quite short. According to a relationship between body length and generation time for a large number of organisms ranging from bacteria through various poikilothermic and homeothermic animals to large trees (Bonner, 1965), "meio-fauna sized" animals should have generation times ranging from less than a day to a maximum of a week or two. Organisms with short generation times should have high rates of increase (innate population growth rate-"r") according to Smith (1954). Fenchel (1968), using a graphical r e l a t i o n s h i p developed by Smith, indicated that micrometazoans such as harpacticoid copepods have d a i l y r values of 0.15 to about 0.42 and genera-ti o n times of 7 to 2 8 days. Five species, of micrometazoans from the benthos of Marion Lake were cultured, and reproductive rates and l i f e spans of the animals were determined under various temperature conditions. The data were then used to construct predictive models for two species and predictions were compared with f i e l d data. Methods Culture Techniques: A l l cultures were grown in constant environment chambers - 57 -at 5, 10, 15, 20, or 25°C (temperature v a r i a t i o n + 2°C) and 2 under fluorescent l i g h t s (approximately 0.10 cal/cm /min) on a 16 hours light/8 hours dark cycle. As growth experiments lasted for months i n some cases and the environment chambers were used by other workers as well, minor v a r i a t i o n i n l i g h t i n t e n s i t y and/or duration could not be avoided, but i t was not considered c r i t i c a l . The f i v e species investigated were the harpacticoid cope-pod Bryocamptus hiemalis, the chydorid cladocerans A l o n e l l a  nana and Alona quadrangularis, and two r o t i f e r s , the b d e l l o i d Dissotrocha macrostyla and the monogonont Lecane s i g n i f e r a . The harpacticoid reproduces sexually while the r o t i f e r s and cladocerans are almost exclusively parthenogenetic. The two chydorid cladoceran species carry t h e i r one to two eggs inside a brood pouch u n t i l the embryos are mature. The monogonont r o t i f e r Lecane lays single eggs while the b d e l l o i d Dissotrocha i s ovoviviparous, giving b i r t h to single o f f s p r i n g . These species were the most common members of t h e i r taxonomic groups i n the Marion Lake meiobenthos. Several unsuccessful attempts were made to culture benthic cyclopoid copepods. The harpacticoid and the two cladoceran species were grown on Marion Lake sediment, sieved to remove other organisms and p a r t i c l e s larger than 130 um. Sediment was co l l e c t e d fresh and kept at 10°C u n t i l used. Occasionally sediment older than one week had to be u t i l i z e d . Rotifers were grown on suspensions of Chiamydomonas r e i n h a r d i i (Indiana University - 58 -Algae Culture C o l l e c t i o n , Starr, 1964) because preliminary work had shown i t to be impossible to find a l l the r o t i f e r s when sediment was used as the growth medium. Chlamydomonas was cultured on soil-water agar (Starr, 1964) at 20°C and harvested one to two weeks after inoculation to fresh medium. Individual animals were placed i n single depressions (volume = 2.5 ml) of glass 9-spot plates or p l a s t i c 12-spot plates. Approximately 0.1 ml of sediment i n 1.5 ml of lake water was placed i n each depression. For r o t i f e r culture the 5 Chlamydomonas concentration was 1 X 10 .cells per ml (checked by comparing o p t i c a l density against a standard curve prepared from d i l u t i o n s of a known concentration suspension). Depression plates were placed inside large (diameter 14 cm) glass p e t r i dish moist chambers with a small amount of water to prevent evaporation of the contents of the depressions. Transfers to fresh sediment or a l g a l suspension were made frequently, some-times d a i l y , depending upon temperature. Individual animals were observed every one to two days using a stereomicroscope. Data were obtained on generation time, number of of f s p r i n g per female, hatching success, growth rate of i n d i v i d u a l animals, s u r v i v a l at various temperatures, maximum l i f e span, and other parameters. Offspring were removed from the depressions to avoid confusion with individuals under study. In addition to observations on i n d i v i d u a l animals over t h e i r entire l i f e s p a n , two cladoceran and two r o t i f e r species were grown i n mass cultures to measure d i r e c t l y maximum - 59 -population growth rates. Mass cultures were started with single recently hatched i n d i v i d u a l s . Data Analysis: H a l l (1964) has shown how the instantaneous b i r t h rate (b) can be calculated for a natural population, where b = In (1 + B) and B (the f i n i t e b i r t h rate) equals the number of newborn per i n d i v i d u a l per day during the i n t e r v a l between samples. This f i n i t e b i r t h rate can be calculated as N -E-l/D B = _J2 N o where i s the number of reproductive adults, E i s the average brood size, 1/D i s the rate of development of the eggs per day, and N q i s the population size on the f i r s t sampling date. Hall's method was used to calculate b for the population of Dissotrocha macrostyla at 2.5 m during 1970-71, using l i f e h istory data c o l l e c t e d i n the laboratory. For Dissotrocha, E i s 1.0 since t h i s animal c a r r i e s single offspring. Because very small embryos could not be detected, the development period D was defined as the length of time from formation of trophi (jaws) u n t i l b i r t h . Rotifers carrying embryos which had formed trophi could be e a s i l y detected i n cleared microscopic preparations of lake samples because trophi are composed of a hard proteinaceous material. - 60 -The development rate of Dissotrocha embryos was determined as a function of temperature. Using lake temperature data, the development rate could be calculated for each sampling date. Np was the number of r o t i f e r s carrying embryos at trophi formation stage or l a t e r , and N q was the t o t a l number of Dissotrocha i n the sample. The observed rate of increase was calculated from lake population densities (Chapter I ) , using r = In N^-ln N Q/t. Whereas b can never be less than zero, r w i l l be a negative number when the population i s declining. Since the observed population growth rate r e f l e c t s the sum of the b i r t h rate and death rate (ignoring immigration and emigration), the instant-aneous death rate for any sampling date can be calculated as d = b-r. Mortality represented by d can be caused by preda-t i o n , disease, etc. In practice, d i s used primarily as a measure of predation i n natural populations (Hall, 1964; Keen, 1973). To r e l a t e harpacticoid copepod culture r e s u l t s to the lake population a d i f f e r e n t method was used. A computer simulation model of the Bryocamptus hiemalis population at 2.5 m was constructed, using growth, reproduction and mortality rates estimated from laboratory r e s u l t s , and assuming no immigra-tion or emigration. The primary reason for construction of the model was to determine whether culture results could be used to model a natural harpacticoid population r e a l i s t i c a l l y . If successful, the model could also be used to estimate predation - 61 -on the lake population of copepods, through a comparison of predicted population density (neglecting predation) and actual lake numbers. The general plan of the model i s shown i n Figure 16. Boxes represent the number of eggs, n a u p l i i , copepodids, and adults i n the population and arrows represent rates at which individuals passed from one compartment to another or were l o s t to the system. The model was i n i t i a l i z e d with actual lake densities of the various compartments at 2.5 m on January 1, 1971. Daily temperatures at the mud-water interface at 2.5 m, as determined by a continuous recording thermometer, were used to drive the model, which calculated predicted numbers in the various compartments on a d a i l y basis for the entire year. Results The cladoceran A l o n e l l a nana i s much smaller (0.3 mm) than Alona quadrangularis (0.9 mm), but i t has a longer genera-ti o n time and l i f e span than the larger species. However the mean number of offspring over the individual's l i f e span i s less for A l o n e l l a than for Alona. Egg development times are si m i l a r for the two species (Table 4). At both 10°C and 20°C Alona population growth rates i n mass culture are higher than Al o n e l l a (Figure 17) . Values of r (Caughley and Birch, 1971) for the two s cladoceran species, and for the r o t i f e r and copepod species described below, were calculated from i n d i v i d u a l s u r v i v a l and ADULT MALES EGGS NAUPLII COPEPODID h g I • d d ADULT FEMALES FEMALES m WITH EGGS d I-e.p. Figure 16. Simulation model of Bryocamptus hiemalis population. Rates of transfer determined from laboratory culture r e s u l t s . h i s egg hatching rate; g i s growth rate; m i s maturation rate to reproductive status; e.p. i s egg production rate; and d i s death rate. - 63 -Table 4. The e f f e c t of temperature on l i f e spans and reproductive parameters f o r two meiobenthic chydorid cladoceran species. A l o n e l l a nana Alona quadrangularis A l o n e l l a nana Alona quadrangularis A l o n e l l a nana Alona quadrangularis A l o n e l l a nana Alona quadrangularis A l o n e l l a nana Alona quadrangulari s m m Mean L i f e Span (days) TO °C 20°C 127 87 90 59 Generation Time (days) 10°C 20°C 34.0 26.4 13.1 12.4 Mean Number of O f f s p r i n g per I n d i v i d u a l 10 °C 20°C 9.1 14.2 13.1 19.3 Egg Development Time (days) 10°C 20°C 10.1 10.8 3.9 3.4 Innate Rate of Population Increase (per day) 10 °C .028 .035 .044 .047 20°C .053 .068 .064 .071 -« Alonella nana at IO" C -o Alonella nana at 20° C o— — * Alono quadranqularis at 10° C — — o Alona quadranqularis at 20° C / T r— 50 DAYS / 60 i — 70 80 I 90 gure 17. The e f f e c t of temperature on population growth of two meiobenthic chydorid cladoceran species i n culture. - 65 -fecundity results according to the methods of Heip (1972) and Edmondson (1968). Values of (Caughley and Birch, 1971) were calculated from population increases i n mass cultures. Different meanings of r, and c a l c u l a t i o n of t h i s important population reproductive parameter for micrometazoans, are discussed i n d e t a i l i n Appendix I. Alonella's d a i l y r values (r , r ) at 10°C are only two-2 s m 2 thirds of Alona's, but at 20°C t h e i r r values are more s i m i l a r . The contrast between culture r e s u l t s for the b d e l l o i d r o t i f e r Dissotrocha macrostyla and the monogonont r o t i f e r Lecane  s i g n i f e r a i s s t r i k i n g . The l i f e span of Dissotrocha i s three times longer than that of Lecane, but generation time of Disso-trocha i s also three times longer, and i t produces only one-quarter to one-third the o f f s p r i n g (Table 5). Consequently the r values for Lecane are f i v e times greater than for Dissotrocha. When the two r o t i f e r species were grown i n mass culture on the same food source the low reproductive rate of the b d e l l o i d species was again c l e a r (Figure 18). Higher food concentrations served only to reduce further the growth rate of the Dissotrocha population. The development rate of Dissotrocha embryos was slow and was temperature dependent (Figure 19). With information on development rates, and knowing the temperature of the lake mud-water interface at 2.5 m on a p a r t i c u l a r day (Chapter I ) , i t was possible to estimate the development rate i n the lake on that date. Using the formulas described previously, B (the - 66 -Table 5. The e f f e c t of temperature on l i f e spans and reproductive parameters f o r two meiobenthic r o t i f e r species. Mean L i f e Span (days) 15 °C 20°C 25°C Dissotrocha macrostyla 56.0 47.5 34.8 Lecane Sign!fera 21.8 15.5 Generation Time Cdays) T5°C 20°C 25°C Dissotrocha macrostyla 23.0 16.0 13.8 Lecane s i g n i f e r a 7.9 5.1 Mean Number of O f f s p r i n g per I n d i v i d u a l 15 °C 20°C 25°C Dissotrocha macrostyla 3.0 4.8 3.0 Lecane s i g n i f e r a 12.7 13.3 Egg Development Time (days! 15 °C 20°C Lecane s i g n i f e r a 4.2 2.6 Innate Rates of Population .. Increase (per day) 15 °C 20°C 25°C Dissotrocha macrostyla rm .027 .049 .045 r s .029 .056 .053 Lecane s i g n i f e r a rm .175 .251 r s .199 .277 - 67 -Figure 18. A comparison of population growth by two common species of meiobenthic r o t i f e r s i n mass culture at 20°C, and the e f f e c t of food concentration on one species. 0.3 H 0 .2H o.H - 68 - I — i — i — i — i—p 0 5 1 — r - | — i — i — i — i — j — i — i — i — i — | — i — i — i — i — | — i — i — t 10 15 20 TEMPERATURE (°C) 25 Figure 19. The influence of temperature on development rate of Dissotrocha macrostyla embryos. D i s the development time (days) from appearance of trophi u n t i l b i r t h . - 69 -f i n i t e b i r t h rate) and b (the instantaneous b i r t h rate) were c a l c u l a t e d . Values of b and the observed Dissotrocha popula-t i o n growth r a t e are p l o t t e d i n Figure 2OA f o r two years' samples. The instantaneous death r a t e (d), c a l c u l a t e d from b and r (d = r - b ) , i s p l o t t e d against time i n Figure 20B. The r values f o r the n a t u r a l p o p u l a t i o n l i e i n the range of r values from c u l t u r e work ( c f . Table 5). G e n e r a l l y , values of b are only s l i g h t l y greater than values of r , and on o n e - t h i r d of the dates the r value exceeds the b value, and d values i n Figure 2OB are correspondingly negative. T h e o r e t i c a l l y t h i s should not happen, and p o s s i b l e reasons f o r t h i s discrepancy are considered l a t e r . The common h a r p a c t i c o i d copepod Bryocamptus h i e m a l i s i n c u l t u r e had a generation time of approximately 4 months at a constant temperature of 15°C but d i d not reproduce i f kept a t 20°C. At c o o l temperatures (5-10°C) the l i f e span was 10 months or more. A f e r t i l i z e d female copepod kept at a constant temp-erature of 10°C could produce 9 egg c l u t c h e s , three times more than at e i t h e r 5°C or 15°C. The r value was a t i t s maximum s at 10°C a l s o (Table 6). This information, combined w i t h per-centage s u r v i v a l of immature stages at v a r i o u s temperatures i n c u l t u r e , suggests t h a t a temperature of 10°C i s near the optimum. Growth r a t e s of Bryocamptus increased at higher temperatures, w i t h times from egg to a d u l t ranging from over 200 days at 5°C to l e s s than 60 days at 20°C (Figure 21), but f u r t h e r work, 70 -1970 1971 1972 Figure 20. A comparison of Dissotrocha population growth rate i n Marion Lake with b i r t h rate predicted from culture studies (Figure 20 A), and calculated death rate (Figure 20 B). r = population growth rate; b = b i r t h rate; d (death rate) = b-r. - 71 -Table 6. The e f f e c t of temperature on s u r v i v a l , l i f e span, and reproductive parameters f o r the meio-benthic h a r p a c t i c o i d copepod Bryocamptus hiemalis. Naupliar stages Copepodid stages To t a l s u r v i v a l to maturity 5°C <10% 64 <10 5°C 321 5°C 186 5°C 28 S u r v i v a l (percentage) 10°C 15°C 20°C 66% 92 8% 80 1% 83 61 7 1 Mean L i f e Span (days) 10°C 15°C 20°C 301 187 107 Generation Time (days) 10°C 15°C 20°C 126 115 Egg Development Time (days) 10°C 15°C 20°C 14 7 6 Egg Clutches Per Female (Total eggs per female i n parentheses) 5°C 3.3 (34) 5°C .002 10°C 9.2 (97) 15 °C 2.4 (25) 20 °C Innate Rate of Population Increase ( r g per day) 10°C 15°C 20°C .016 ,000 - 72 -20 40 60 80 100 120 140 160 180 200 Days Figure 21. The e f f e c t of temperature on growth rates of immature stages of Bryocamptus hiemalis. - 73 -reported below, indicated that growth rates i n t h i s species were not a simple function of temperature. Parameter values necessary to operate the Bryocamptus population computer model were obtained from Table 6 (egg hatching rates), from Figure 21 (growth rates), and from Figure 22 (sexual maturation rates, egg production rates, death rates). Results of the model are shown i n Figure 23, which compares predicted numbers of adult Bryocamptus and actual numbers found in the lake i n 1971. For the f i r s t three months of the year the model and actual densities were i n close agreement. The lake population of adult copepods began increasing i n May (when copepodid stages moult to adults) but the model lagged about one month behind in the onset of t h i s phase. The lake population of adult cope-pods then l e v e l l e d o f f and began to decline i n the f a l l while the model predicted that numbers of adults should keep r i s i n g . The reason for the increasing simulated adult population was that the model calculated recruitment to the population beginning i n May/June when in fact, female copepods did not begin to carry eggs u n t i l l a t e September. Based on the data obtained i n the laboratory and b u i l t into the model, Bryocamptus should have begun reproduction when the temperature reached 10°C i n the spring, although the model co r r e c t l y assumed that reproduction was i n h i b i t e d by high temperatures during the summer months. 0.05-1 5 0.04-ui g 0.03-£ 0.02-o 2 0 .0M - 74 • — — * nauplii O — — O copepodids /V- A adults 0.03 H lu < a: 0.02-2 O H < a: p 0.01 -- r -5 10 15 I— 20 TEMPERATURE ( °C) ©——~—& maturation to egg production O O mean reproductive rate h0.5 H0.4 m h0.3 H0.2 rO.I < UI u. >-< Q \ CO o o UI UI r-< or UI > r-O Z> Q O CC a. ui cc < UI 5 - 1 — 10 T 15 — i — 20 TEMPERATURE ( ° C ) 25 Figure 22. The e f f e c t of temperature on mortality rates, reproductive maturation rates and egg production rates for B ryo c amptus hiemalis. - 75 -25^ Figure 23. Population density of Marion Lake Bryoc amptu s hiemalis adults as predicted by a simulation model, compared with actual numbers at 2.5m i n 1971. - 76 -Since the model predicted reproduction when none occurred i n the lake, the information on maturation from adult female stage to egg production c o l l e c t e d i n the laboratory (and b u i l t into the model) was re-examined. These data were based on ind i v i d u a l females kept at constant temperature i n the laboratory (5, 10, 15, or 20°C). A hypothesis was developed that copepodid stages which over-wintered i n the lake at temperatures from 2-5°C and moulted to the adult female stage early i n the spring were retarded with respect to the onset of egg production through the normally appropriate temperature range i n the spring. High summer temperatures would then i n h i b i t egg production u n t i l a temperature of 10°C was reached i n the early f a l l . To test this hypothesis, a group of late stage copepodids was' c o l l e c t e d f rom the lake i n A p r i l of 19 72. These animals were kept b r i e f l y at 10°C u n t i l the females had moulted to the adult stage, females were then paired with males, and the time to production of eggs at 10°C was noted. A control group of recently moulted females and males, which had l i v e d a l l t h e i r l i v e s at 10°C, was also paired and the time to egg production recorded. The results were cl e a r . The time required from adult female stage to egg production was 8 8.8 + 5.7 days (95% confidence limits) for the animals which had overwintered i n the lake. The control group only required 33.9 + 9.6 days, confirming e a r l i e r results i n laboratory cultures. - 77 -The other major discrepancy between the model prediction and the lake population was that the model lagged one month behind the lake population i n the timing of the increase i n adult copepod numbers in the spring. To explain t h i s , one would have to hypothesize that exposure to cold winter temper-atures followed by rapid warming i n the spring accelerated the growth rate of the copepodid stages. To test t h i s p o s s i b i l i t y , l ate naupliar stages were col l e c t e d i n early March 1972 and were allowed to moult to the adult stage. The time required to grow from f i r s t copepodid to adult was 84.8 + 2.7 days (95% confidence l i m i t s ) at 5°C, 52.1 + 3.4 days at 10°C, and 2 4.4 + 2.2 days at 20°C. Previous laboratory work with animals raised through a l l the naupliar stages at constant temperature gave times from copepodid I to adult as being 158.7 days, 57.6 days, and 35.5 days at 5, 10, and 20°C respectively. Clearly, recently c o l l e c t e d animals could moult through f i v e copepodid stages more quickly than laboratory animals at the same temperature. This explains why the model lagged behind the natural population, because the model incorporated the growth rate data from previous studies. Although modification of the model to take into account the stimulation of copepodid growth rates and suppression of adult female maturation rates i n the spring would have resulted in predicted numbers more sim i l a r to actual numbers, i t was f e l t that further work on the model would have amounted to c u r v e - f i t t i n g . The model had served i t s purpose as an analytic t o o l . - 78 -Discussion Meiofaunal L i f e H i s t o r i e s : Relatively l i t t l e work has been done on l i f e h istory and population parameters for meiobenthic species i n culture. Results of several other studies are summarized i n Table 7 and compared with t h i s study. Generation times for most harpacti-coid copepods which have been cultured are approximately one month or less as compared with 115 days for the Marion Lake harpacticoid Bryocamptus. Short generation times for other harpacticoids are probably not t y p i c a l . In studies on marine harpacticoid populations i n nature, Barnett (1970) and Lasker et a(. (1970) concluded these animals actually have very long genera-ti o n times. Since the easy to culture species of meiofauna are not t r u l y representative (Fenchel, 1974; Heip, Smol and A b s i l l i s , 1978), i t i s important to be cautious i n extrapolating from laboratory results to the f i e l d , e s p e c i a l l y where produc-tion calculations are being made. Results from laboratory work on a freshwater harpacticoid reported here and information from marine f i e l d studies must be taken as evidence against the generalization that very small animals have short generation times, short l i f e spans, and high fecundity. The data on Bryocamptus from Marion Lake, two Platychelipus species on a marine i n t e r t i d a l mudflat (Barnett, 1968, 1970), and AseTlopsis on a marine i n t e r t i d a l sandy beach (Lasker et aj.. , 1970) gave l i f e spans of 11-13 months and only one or two generations per year. Fecundity - 79 -Table 7. Life spans and reproductive parameters for meiofauna in culture reported in the literature, compared with results for Marion Lake meiofauna. Generation Species Time (days) Marine harpacticoids Tisbe furcata 19-24 Tachidius discipes 11-12 Nitrocra spinipes 11 Longipidia s c o t t i Tigriopus fulvus 60 Tigriopus japonicus 10 Arenopcr.tia indie a 30 Nitocra typica 19-36 Freshwater harpacticoids Bryocamptus hiemalis 115 Freshwater chydorid cladocerans Pleuroxus denticulatus 6 Eurycercus lamellatus 13 Alonella nana 13 Alona quadrangular1s 12 Freshwater benthic rotifers Epiphanes brachionus 1.4 Euchlanis dilatata 1.9 Euchlanis dilatata Lecane signifera 5 Dissotrocha macrostyla 16 Li f e Span (days) r Source 40-50 .190 Mclntyre, 1969 30-60 .152 Mclntyre, 196 9 90 .085 Mclntyre, 1969 60 - Mclntyre, 1969 . - - Mclntyre, 1969 _ _ Provasoli et a l . 1959 - - Rao, 1967 - .100 .175 Lee et a l . , 1976 187 .016 this study 9-24 - Shan, 1969 38 - Smirnov, 1962 87 .068 this study 59 .071 this study Pourriot and Deluzarches, 1971 - - Pourriot and Deluzarches,1971 3-5 1.150 King, 1967 16 .277 t h i s study 48 .056 this study - 80 -for Asellopsis was 30-3 8 eggs per female and for Bryocamptus was 25-97 eggs per female. Generation times calculated for Marion Lake chydorid cladocerans are comparable to the values for two other chydorid species reported i n the l i t e r a t u r e (Shan, 1969; Smirnov, 1962) though Marion Lake chydorids tend to have longer l i f e spans. Egg development times for A l o n e l l a and Alona (Table 4) are comparable to the averages reported i n B o t t r e l l (1975) for six chydorid species (7-10 days at 10°C, 3-4 days at 20°C). Because of t h e i r smaller s i z e , r o t i f e r s would be expected to have shorter generation times and higher reproductive rates than cladocerans. Information from the l i t e r a t u r e on benthic monogonont r o t i f e r s i n culture and the data for the monogonont Lecane from Marion Lake support t h i s concept. However the results of culture work on the b d e l l o i d r o t i f e r Dissotrocha  macrostyla, which i s the most common Marion Lake benthic r o t i f e r , are evidence against the u n c r i t i c a l acceptance of t h i s general-i z a t i o n . Dissotrocha Population Analysis: In Figure 20A population growth rate (r) calculated from samples of the Dissotrocha population at the 2.5 meter station i s compared with the instantaneous b i r t h rate (b) calculated from laboratory data on development times and lake temperature on the sampling dates. One purpose of t h i s comparison i s to obtain an i n d i r e c t measure of predation on these b d e l l o i d - 81 -r o t i f e r s . If b i s higher than r on a given date, then the death rate (d) estimated from the difference w i l l l i k e l y be caused by predation, i f the l i f e span of the animals i s r e l a -t i v e l y long and the i n t e r v a l between samples i s short. Using th i s method H a l l (1964) found an average of 28% t o t a l popula-tion loss per day i n the summer for Daphnia galeata, which he attributed to predation. Keen (1973) also estimated population losses of t h i s magnitude or larger per day for chydorid clado-cera populations, on the basis of plots of r and b. The instantaneous death rates for Dissotrocha (Figure 20B) show population losses averaging only 4-5% of the population per day, much lower than H a l l and Keen found for cladocerans. I t w i l l be noted i n Figure 20B that some values of d are negative. This, of course, i s t h e o r e t i c a l l y impossible because i t implies a population growth rate higher than the b i r t h rate. Some negative values for d were also found by H a l l (1964) and Keen (1973). They may be caused by sampling error, incorrect estimates of egg development time, immigration, or rapidly increasing temperature. In the l a t t e r case, increasing tempera-tures may increase the value of r, calculated from numbers on two successive sampling dates, while the estimate of b i s based on numbers of r o t i f e r s carrying embryos and t o t a l r o t i f e r s on the f i r s t sampling date (temperature i s assumed to be constant over the sampling i n t e r v a l ) . The negative values for d found i n t h i s study are probably due to a combination of sampling error and the eff e c t s of rapid temperature change. - 82 -The b i r t h rate for Dissotrocha (Figure 20A) i s zero during the winter months, because few r o t i f e r s were carrying embryos and because of extreme retardation of embryo development caused by cold temperatures. Individual Dissotrocha probably do not die during the winter. In the laboratory these r o t i f e r s became inactive at low temperatures but could be revived upon warming. Peak reproduction occurred i n May through August when up to 50% of the Dissotrocha individuals were carrying an advanced embryo (Chapter II) . A comparison of maximal values of r and b i n Figure 20A with data i n Table 5 on Dissotrocha population growth rates shows that populations cultured on Chlamydomonas under laboratory conditions gave values of r i n agreement with natural popula-tion estimates. Bryocamptus Population Model: The purpose for constructing a computer model for Bryocamptus was to determine whether culture r e s u l t s could be used to simulate a natural population of harpacticoids and a secondary purpose was to estimate predation. Death rates determined i n the laboratory were incorporated i n the model but predation was not. Thus differences between Bryocamptus densities as pre-dicted by the, model and the actual population densities should represent losses due to predation. As expected the model predicted higher adult copepod numbers than were actually reached i n the lake (Figure 23). However, analysis of the model - 33 -population disclosed two unexpected discrepancies. F i r s t the model, based upon laboratory culture r e s u l t s , predicted egg production by copepods i n the spring as well as the f a l l . Since the lake population only reproduces i n the f a l l , i t was hypothesized that females which had overwintered as copepodids at the cold temperature of the lake (<5°C) would take much longer to produce eggs than females which had spent t h e i r copepodid stages at 10°C i n the laboratory. Experimental results supported t h i s hypothesis. A possible reason for t h i s delay i s that there was less food available i n the lake than i n laboratory cultures. However the cultures were fed natural lake sediment. A more l i k e l y explanation for the delay i s a requirement for the accumula-tion of a c r i t i c a l number of degree-days from early copepodid stages before egg production was possible, or an i n t e r a c t i o n of temperature and photoperiod, as shown for several marine amphipods by Steele (1967), a freshwater amphipod by de March (1977), and several copepods by Elgmork (1967). The other unexpected discrepancy was that the model predicted slower growth rates by copepodid stages i n the spring than were actually observed. A possible explanation i s that n a u p l i i exposed f i r s t to cold temperatures i n the winter could grow through t h e i r copepodid stages at a spring temperature of 10°C faster than n a u p l i i raised completely at 10°C. Experi-mental results supported t h i s interpretation, but the mechanism i s not c l e a r . - 84 -The slower growth rates for copepodids i n the laboratory may have been p a r t i a l l y a handling e f f e c t . Copepodids were transferred to fresh sediment every 2-3 days and i t was l a t e r discovered that frequent handling could slow down growth by 20-25%. The computer model was thus unsuccessful i n simulating the natural population of Bryocamptus, but analysis of the discrepancies between the model and the lake population led to experiments that showed an unexpected delay i n the onset of egg production and an equally unpredicted acceleration of growth of immature stages during the spring months i n the lake. As Walters and E f f o r d (1972) state, the best c r i t e r i o n for judging the success of a simulation model i s not f i t to data (because models can be "tuned" to f i t data), but rather whether the model leads to c l a r i f i c a t i o n of b i o l o g i c a l assumptions and input parameter estimates, based on i t s f a i l u r e to f i t r e a l data. By this c r i t e r i o n , the Bryocamptus model was successful. Conclusion Data presented i n t h i s chapter show that some of the common micrometazoans from the benthos of Marion Lake are exceptions to the generalization that very small animals necessarily have short l i f e spans and high reproductive rates. I t i s suggested that most culture work on micrometazoans has been conducted on species which reproduce rapidly and are - 85 -otherwise easy to work with under laboratory conditions. Data from such studies should not be taken as representative of meiobenthic organisms i n general. Comparison of population growth rates i n the lake for the b d e l l o i d r o t i f e r Dissotrocha macrostyla with b i r t h rates calculated from laboratory studies shows that t h i s species has a low reproductive rate and suffers l i t t l e predation i n Marion Lake. A simulation model for the harpacticoid copepod Bryocamptus  hiemalis i l l u s t r a t e s the d i f f i c u l t i e s i n treating a population of organisms i n a mechanistic way, and i n extrapolating from laboratory work to nature. - 86 -CHAPTER I I I EXPERIMENTAL STUDIES ON FOOD SUPPLY AND PREDATION - 87 -Introduction Work reported i n Chapter II shows that meiofaunal organisms do not necessarily have high reproductive rates. Nevertheless, something must l i m i t population sizes of such animals, as with a l l organisms. In the case of the meiobenthos, the most obvious potential c o n t r o l l i n g agents were food supply and predation. Accordingly, a series of laboratory and f i e l d experiments was designed to investigate the influence of these factors on meio-faunal populations. There i s a variety of feeding methods i n the meiobenthic community. Two of the important taxonomic groups (harpacticoid copepods and chydorid cladocerans) are primarily deposit feeders, either ingesting very small p a r t i c l e s of sediment or scraping the surface of larger p a r t i c l e s . Presumably the animals digest bacteria and micro-algae obtained i n t h i s way. Benthic cyclo-poid copepods are generally considered predatory (Fryer, 1957; Monakov, 1972) though the species i n Marion Lake have a l l been found with a l g a l material i n t h e i r guts, e s p e c i a l l y the smallest species (Acanthocyclops nanus). Bdelloid r o t i f e r s feed on bacteria and small algae (<10 um) by d i r e c t i n g a stream of water toward the mouth using t h e i r wheel organs (Donner, 1966) while monogonont r o t i f e r s are mostly herbivores and bacteriov-ores, though some are predatory. The d i e t of f r e e - l i v i n g nematodes i n the lake i s undetermined but many are probably bacteriovores. Adult stages of p a r a s i t i c nematodes are also found (McCauley, 19 73). Predatory mites are present but are - 88 -a minor numerical component of the meiobenthos. Besides the mites and cyclopoid copepods which may prey upon other meiobenthic species, the major non-meiobenthic predators are the amphipod Crangonyx richmondensis and various species of tanypoid and ceratopogonid midge larvae (Hamilton, 1965; McCauley, pers. comm.). I n i t i a l l y i t was f e l t that the smallest members of the meiobenthos ( r o t i f e r s , recently hatched harpacticoid nauplii) might be eaten accidently by Hya l e l l a  azteca, a deposit feeding amphipod (Hargrave, 1970a). In thi s sense Hyalella too could be a "predator" although there i s no evidence that t h i s amphipod hunts for micrometazoa or protozoa. I t can dis t i n g u i s h between sediments with d i f f e r e n t a l g a l or b a c t e r i a l compositions (Hargrave, 1970b). Methods and Results The d e t a i l s of the methods used i n the f i v e experiments are given along with the results below. A l l laboratory experi-ments were carried out i n controlled environment chambers, with constant fluorescent l i g h t l e v e l s of approximately 0.10 2 cal/cm /min, and temperature constant to within + 2°C. In a l l cases where meiofauna had to be extracted from sediment, the sucrose centrifugation-fluorescent staining procedure described i n Chapter I was used. - 89 -Food Supply Experiments: Experiment 1 A f e r t i l i z a t i o n experiment was carr i e d out at the lake during July/August, 1971 using three bottom enclosures situated at 1.0 meter depth. The 2m x 2m enclosures were constructed with a galvanized pipe framework and four walls of heavy poly-ethylene, and were open at the top and bottom. These enclosures were sunk i n place four weeks preceding f e r t i l i z a t i o n , with the bottom edge of the p l a s t i c walls embedded 0.5m into the mud and the top edge extending 1.0m above the water surface. One of the enclosures acted as a control, one received 10 2 2 grams/m (low level) and one received 100 grams/m (high level) 2 of a 10:10:0 (N:P:K) f e r t i l i z e r . Eight 2.8 cm core samples from each enclosure were taken immediately preceding f e r t i l i z a -t i o n , a f t e r 8 days, and after 26 days. Nitrogen and phosphate enrichment had previously been shown to cause an increase i n epibenthic a l g a l standing crop i n Marion Lake and, at least i n i t i a l l y , an increase i n primary production of the epibenthic algae (Cameron, 1973). Within a few days afte r addition of the f e r t i l i z e r , the sediment surface i n both f e r t i l i z e d enclosures was noticeably more green than that i n the control. By three weeks the water column i n the high f e r t i l i z a t i o n enclosure had turned murky. The e f f e c t of inorganic enrichment on standing crop of bacteria i n surface layers of the sediment i s less c l e a r . Inorganic nutrient f e r t i l i z a t i o n might act d i r e c t l y to stimulate b a c t e r i a l repro-- 90 -duction or i n d i r e c t l y , through increased a l g a l exudates which are substrates for b a c t e r i a l metabolism (Kleiber, 1972) . Cameron (19 73) found no s i g n i f i c a n t difference i n b a c t e r i a l plate counts between control and f e r t i l i z e d enclosures. How-ever, H a l l and Hyatt (1974) reported an increase i n sediment glucose uptake rate i n these enclosures, i n d i c a t i n g either increased a c t i v i t y per b a c t e r i a l c e l l or an increase i n b a c t e r i a l standing crop, or both. I n i t i a l population numbers for the various taxonomic groups were nearly i d e n t i c a l i n a l l enclosures, with the exception of cladocerans. The most surprising r e s u l t was a decline i n meio-benthos populations (except for nematodes) i n the high f e r t i l i z a -t i on treatment (Figure 24). By the t h i r d and f i n a l sampling date no cladocerans or cyclopoid copepods were found i n samples from the high f e r t i l i z a t i o n enclosure, and numbers of r o t i f e r s and harpacticoid copepods were very low. There are at least three possible explanations for these declines. The higher l e v e l of f e r t i l i z e r may have been d i r e c t l y toxic to the meiofauna, but t h i s seems unl i k e l y . A l g a l species which bloomed following f e r t i l i z a t i o n may have been unsuitable as food for meiofauna, or perhaps were toxic when ingested. This also seems unl i k e l y because one would expect to observe a si m i l a r e f f e c t i n the low f e r t i l i z a t i o n enclosure, where a smaller bloom also occurred. Regardless of species, a t h i r d p o s s i b i l i t y i s that the greatly increased standing crop of algae i n the high f e r t i l i z a t i o n enclosure may have reduced \ Figure 24. The e f f e c t of two le v e l s of inorganic f e r t i l i z a t i o n (10:10:0, N:P:K) on meiofaunal population densities i n 4 m^  enclosures, July-August, 1971. Numbers/m2 with 95% C L . - 92 -oxygen to a c r i t i c a l l e v e l at the sediment surface at night, when photosynthesis ceased. Because standing crops of algae r e s u l t i n g from f e r t i l i z a t i o n of enclosures i n Marion Lake are a function of amount of f e r t i l i z e r added (Cameron, 1973), the low f e r t i l i z a t i o n enclosure may not have developed a standing crop large enough to cause a c r i t i c a l oxygen depletion. Before oxygen samples were taken to check t h i s p o s s i b i l i t y a heavy r a i n f a l l raised the lake l e v e l and flooded the enclosures, thus terminating the experiment. The r o t i f e r population i n the low f e r t i l i z a t i o n and i n the control enclosures doubled during the 26 days of the experiment. This increase p a r a l l e l e d the increase i n r o t i f e r population size on a nearby sampling transect and was probably due to high water temperatures p r e v a i l i n g at the time of the experiment (approximately 24°C interface temperature). The only other taxonomic group capable of responding numerically to increased food l e v e l (or high temperature) i n so short a time period was the cladocerans. Although the beginning of a population increase was suggested i n the cladoceran data, population sizes i n control and low f e r t i l i z a t i o n enclosures were not s i g n i f i c a n t l y d i f f e r e n t . Although harpacticoid and cyclopoid copepods could not have been expected to respond to increased food with population growth i n only four weeks, these animals could have begun to produce eggs. No egg carrying copepods were observed. There was even a suggestion of a s l i g h t decline i n harpacticoid - 93 -populations i n low f e r t i l i z a t i o n and control enclosures. Since optimum temperature for the most common harpacticoid species i s approximately 10°C and t h i s species shows increased mortality i n the laboratory at temperatures above 20°C (Chapter I I ) , the high average temperature of the mud-water interface both inside and outside the enclosures may well have caused some harpacti-coid mortality. With the exception of the dramatic decline i n meiofaunal populations observed i n the high f e r t i l i z a t i o n enclosure, there seems to have been no e f f e c t on, and c e r t a i n l y no stimulation of, meiofaunal population growth which can be attributed to increased food. I f t h i s short term experiment was repeated at a d i f f e r e n t time of year the r e s u l t s might have been d i f f e r e n t , either because food might be less abundant or because meiofauna l i f e cycle stages present could more rapidly exploit increased food. If at least some of the species of algae which increased following low l e v e l f e r t i l i z a t i o n were suitable food for meiofauna,as i s l i k e l y , what can be concluded from t h i s experiment i s that r o t i f e r s and cladocerans are not food limited at t h i s time of year. Experiment 2 To test whether deposit-feeding harpacticoid copepods might be food limited, feeding experiments using lake sediment were carr i e d out i n the laboratory. I f the harpacticoids were food limited then sediment which had been heavily grazed - 94 -by h a r p a c t i c o i d s should be d e p l e t e d of b a c t e r i a and micro-algae, or a t l e a s t of t h a t p r o p o r t i o n of the b a c t e r i a and a l g a l s t a n d i n g crop which was a v a i l a b l e t o h a r p a c t i c o i d s . T h i s was i n v e s t i g a t e d by r a d i o a c t i v e l y l a b e l l i n g b a c t e r i a and algae i n n a t u r a l l a k e sediment, a l l o w i n g h a r p a c t i c o i d s to feed on t h i s sediment w h i l e m o n i t o r i n g the r a t e a t which they i n c o r p o r a t e d the l a b e l , and then r e p l a c i n g the f i r s t animals w i t h " c o l d " h a r p a c t i c o i d s . I f the second group of copepods accumulated t r a c e r a t a s i g n i f i c a n t l y slower r a t e than the i n i t i a l group, t h i s would i n d i c a t e t h a t the a v a i l a b l e component of sediment m i c r o f l o r a was reduced by h a r p a c t i c o i d g r a z i n g . The experimental procedure was as f o l l o w s . Approximately 3 mis of f r e s h l a k e sediment ( s i f t e d to remove aggregates 14 l a r g e r than 130 um) was incubated w i t h 50 u C i of C glucose f o r 11 days a t 10°C, then r i n s e d t o remove any r a d i o a c t i v e m a t e r i a l s t i l l i n s o l u t i o n . T h i s l e n g t h of time was more than enough to l a b e l most of the sediment b a c t e r i a , and through 14 a l g a l uptake of CO^ produced by the b a c t e r i a , t o l a b e l the e p i b e n t h i c algae as w e l l . Ten a d u l t Bryocamptus h i e m a l i s (0.600 - 0.700 mm, 5 males, 5 females) were p l a c e d i n each d e p r e s s i o n of a g l a s s 9-spot p l a t e along w i t h 0.1 ml of r a d i o a c t i v e l y l a b e l l e d sediment. T h i s d e n s i t y of h a r p a c t i c o i d s was e q u i v a l e n t to 100/cm and was f a r h i g h e r than d e n s i t i e s ever reached i n the l a k e . The animals were allowed to feed at 10°C under continuous l i g h t . At v a r i o u s times ranging from 1 to 218 hours animals were removed, r i n s e d w i t h non-- 95 -radioactive water, and placed i n s c i n t i l l a t i o n v i a l s with Bray's solution. At the same times, 0.001 ml samples were taken of the radioactive mud which the animals had been feeding upon. Both animal and sediment samples were dispersed and suspended within the Bray's solution using Cabosil, to prevent s e t t l i n g out during s c i n t i l l a t i o n counting. Harpacticoids became radioactive rapidly (Figure 25 - " i n i t i a l feeding"). While the f i r s t part of t h i s experiment was being conducted, a portion of the o r i g i n a l radioactive sediment was exposed to grazing by the same high density of harpacticoids. After 9 days the copepods were removed and the sediment was rinsed. Next, 0.1 ml of th i s "pre-grazed" sediment was placed i n each depres-sion of a glass spot plate and 10 adult "cold" B. hiemalis were added to each depression. . Harpacticoids were again allowed to feed for different'lengths of time and samples of the animals and sediment were taken as before. Harpacticoids from the l a s t three samples were counted i n d i v i d u a l l y to e s t a b l i s h confidence l i m i t s . Radioactivity of the experimental sediment was constant throughout both parts of the experiment. Although confidence l i m i t s cannot be established for most points,. the p a r a l l e l and only s l i g h t l y lower l i n e shown by the second feeding results as compared with the i n i t i a l feeding (Figure 25), indicates that harpacticoids exposed to pre-grazed sediments were able to obtain as much food as did the i n i t i a l group of harpacticoids. I t i s not known why the l a s t two points i n the second feeding results show a decline 9 '•—• '»•' 9 Inlttal feeding 0^W»J»^O feeding on pre-grazed sediment HOURS Figure 25. Radioactivity of ind i v i d u a l Bryocamptus hiemalis feeding on fresh l a b e l l e d sediment, and on pre-grazed l a b e l l e d sediment. DPM/individual, with 95% confidence l i m i t s for three points where replicate animals were not pooled before determination of r a d i o a c t i v i t y . - 97 -i n r a d i o a c t i v i t y accumulated per i n d i v i d u a l . I t i s possible that by 18 days a f t e r i n i t i a l l a b e l l i n g of the bacteria and algae i n the sediment, the tracer had become "diluted" by b a c t e r i a l and a l g a l reproduction. If we compare the maximum counts obtained by harpacticoids (approximately 2000 DPM per individual) with the r a d i o a c t i v i t y of the experimental sediment (approximately 10,000 DPM/.001 ml) and correct for natural densities of harpacticoids per square centimeter i n lake sediment, i t appears that the copepods do not e x p l o i t more than about 2-3% of the t o t a l microflora. Whether much more than t h i s percentage of the microflora i s available to grazing harpacticoid copepods i s not known. Microscopic observations by the author indicate that lake harpacticoids feed by scraping the surface of sediment part-i c l e s . Bacteria and micro-algae within the porous p a r t i c l e s or i n the i n t e r s t i t i a l water are probably not available to harpacticoid copepods. Since t h i s experiment showed no s i g n i f i c a n t reduction i n amount of radioactively l a b e l l e d food obtained by harpacticoid copepods feeding on sediment which was pre-grazed by unnaturally high densities of harpacticoids, these copepods cannot be food limited at normal lake densities. Experiment 3 Individual specimens of Bryocamptus hiemalis were raised from f i r s t copepodid stage to adult on unenriched lake sediment, - 98 -b a c t e r i a l enriched sediment, and a l g a l enriched sediment. If B. hiemalis was food limited i n the lake then growth rates of i n d i v i d u a l animals raised on unenriched sediment should be lower than growth rates on enriched material (unless food l i m i t a t i o n affects only fecundity and not growth). Using recently moulted (within the previous 24 hours) f i r s t copepodid stage animals, experiments were ca r r i e d out at 15°C i n continuous l i g h t using p l a s t i c 12-spot plates enclosed within p e t r i dish moist chambers. Into each depression was placed 0.1 ml of sieved lake sediment i n 2.0 ml of lake water. Ten depressions were enriched with approximately 2 x 10 Aerobacter aerogenes c e l l s , and ten other depressions received approximately 1 x 10^ C h l o r e l l a sp. c e l l s . With one 2 animal per depression the density was 10/cm , which l i e s within the range of natural population densities. There was no stimulation of harpacticoid growth rate when sediment was enriched with either bacteria or algae (Table 8) nor did addition of b a c t e r i a l or a l g a l food have any apparent negative e f f e c t s on growth rate of i n d i v i d u a l copepods. Predation Experiments: Experiment 4 To determine whether meiobenthic organisms were eaten by potential predators, several short-term experiments were carried out i n the laboratory, using radioactively l a b e l l e d meiofauna placed i n cores of freshly c o l l e c t e d lake sediment. - 99 -Table 8. The effect of added bacterial or algal food on the total duration of copepodid stages Ways from f i r s t copepodid stage to adult) in' Bryocamptus hiemalis. n x ± 95% Confidence Limits Bacterial enrichment (Aerobacter) 10 29.2 + 1.7 Algal enrichment (Chlorella) Control 10 10 27.5 + 1.6 29.2 + 2.2 - 100 -A t o t a l of 18 small (surface area 2.8 cm ) and four large 2 (surface area 20 cm ) cores were used and experiments were run i n December and January ("winter"), A p r i l ("spring") and July ("summer"). The experimental procedure was the same i n a l l cases. The meiofaunal group to be tested (harpacticoids, r o t i f e r s , cyclopoids, or cladocerans) was cultured on lake 14 sediment l a b e l l e d with C-glucose u n t i l the organisms were "hot" (usually 200-1000 DPM/individual) . Ten to 10.0 .. of the organisms, depending upon the group and core size being used, were rinsed free of radioactive sediment and placed i n the core of undisturbed lake sediment. To insure the presence of amphipod predators, one Crangonyx and three H y a l e l l a were added to the cores. The winter and spring experiments were run i n continuous l i g h t at 10°C for 6 hours, and the larger cores used i n the summer experiments were incubated for 4 hours at 20°C i n continuous l i g h t . Following incubation the top 3 cm of the cores was removed, fixed i n 5% buffered formalin, and meio-and macrobenthic invertebrates were extracted from the sediment. Members of a l l taxonomic groups were separated and poten t i a l predators were rinsed and placed i n s c i n t i l l a t i o n v i a l s with Bray's solution. Larger predators such as amphipods and large chironomids were combusted (Burnison and Perez, 1974) before l i q u i d s c i n t i l l a t i o n counting. The cases where predation occurred were few and predation rates were low (Table 9). Labelled r o t i f e r s were ingested only - 101 -Table 9. Predation rates on meiofauna i n Marion Lake as percentage of prey population eaten per. day, estimated from laboratory studies with r a d i o -a c t i v i t y l a b e l l e d meiofaunal prey. L a b e l l e d Prey Cyclopoids Mites Chironomids H y a l e l l a Crangonyx R o t i f e r s Winter (2)" Spring (3) Summer (1) Harpacticoids Winter (7) Summer (1) Cladocerans Winter (3) Summer (1) Cyclopoids Winter (3) Summer (1) 5%(5%) 0.2% (3%) 1%(15%) x x 0.1%(6%) 0.1%(7%) 0.1%(7%) 5%(11%) a -b -number of r e p l i c a t e cores predation rates corrected f o r lake predator and prey d e n s i t i e s ; numbers i n parentheses are uncorrected values. - 102 -by chironomids and Hyalella, and harpacticoids, cyclopoids, and cladocerans were eaten only by Crangonyx i n these experi-ments. The predation rates given i n Table 9 were corrected for lake predator and prey population densities, because addition of prey and amphipods to experimental cores raised densities of these organisms above usual lake conditions. The lack of po s i t i v e results for a time of year or a predator species does not prove that predation at that time or by that species was nonexistent, but only that i_f i t occurs the rates are very low. What can be said with certainty i s that some predation does occur, and at low rates, which may nevertheless be s i g n i f i c a n t to a slowly reproducing population. For example, the maximum estimated predation on r o t i f e r s (5% per day) i s s i g n i f i c a n t because the maximum population growth rate i n the lake i s less than 10% per day (Chapter I I ) . Experiments 5a and 5b Another way to test for ef f e c t s of predation i s to compare densities of various meiobenthic species before and after exposure to poten t i a l predators. Such experiments are most meaningful when carried out under natural lake conditions of temperature and l i g h t . In experiment 5a a Hargrave sampler (Hargrave, 1969) was 2 used to take twelve 20 cm black p l a s t i c cores from 1.5m i n July, 1971. Each core contained about 4-6 cm of undisturbed sediment and an equal amount of overlying water. The top 2 cm - 103 -of sediment i n six of the cores was removed and fixed i n 5% formalin. Nine juvenile Crangonyx were added to each of the other six cores, which raised the density of the predatory amphipod to approximately ten times normal. Experimental cores were sealed at the bottom with a rubber stopper and a piece of 54 um nylon mesh was fixed over the top with an e l a s t i c band. This mesh prevented emigration or immigration of a l l meiofauna except the smallest r o t i f e r s , while allowing contin-u i t y of the water with the surrounding lake water when cores were immersed. The six experimental cores were placed i n a wire rack and lowered c a r e f u l l y to 2.5m where they were l e f t for 92 hours. Weather for the four days was sunny and warm and lake temperature at 2.5m was approximately 23°C. At the end of the incubation period cores were raised and the top 2 cm of sediment was removed and fixed. Meiobenthic animals were extracted from the sediment, i d e n t i f i e d , and counted. E s s e n t i a l l y the same experiment was repeated i n October, 1971, with Hyalella rather than Crangonyx added to the cores (Experiment 5b). Twenty-five amphipods were added to each of six experimental cores, r a i s i n g amphipod density to about six times normal. Cores were incubated for 92 hours at 2.5m (temperature 12°C). Weather for the four days was cloudy. Meiobenthic densities at the beginning and at the conclu-sion of the experiments were not s i g n i f i c a n t l y d i f f e r e n t , with one exception (Table 10). Confidence i n t e r v a l s tend to be rather large because samples from d i f f e r e n t experimental cores - 104 -Table 10. The e f f e c t on meiofauna population d e n s i t i e s of i n c r e a s i n g predator number i n undisturbed 2 sediment cores. Numbers/cm + 95% C.L. Experiment 5a Crangonyx added (July) R o t i f e r s Harpacticoids Cyclopoids Cladocerans Nematodes S t a r t 6.0+2.8 5.7+3.7 1.5+1.4 3.7+1.7 1.4+1.2 F i n i s h 6.8+6.5 4.7+3.2 2.5+1.4 1.8+1.8 1.4+1.1 Experiment 5b H y a l e l l a added (October) * R o t i f e r s Harpacticoids Cyclopoids Cladocerans Nematodes S t a r t 21.2+4.8 4.0+2.6 3.8+2.7 4.5+3.5 5.6+2.5 F i n i s h 18.3+4.6 4.0+2.3 2.5+1.3 0.8+0.8 4.7+3.2 Cladocera i n Experiment 5b i s the only taxonomic group f o r which d e n s i t i e s before and a f t e r predator a d d i t i o n are s i g n i f i c a n t l y d i f f e r e n t (p<.05). - 105 -were not pooled for each treatment but counted i n d i v i d u a l l y . Therefore confidence i n t e r v a l s r e f l e c t the patchy d i s t r i b u t i o n of the meiofauna as well as error introduced by sampling and processing procedures. Discussion Food as a Limiting Factor: The p o s s i b i l i t y that food supply l i m i t s or regulates meio-benthos i s occasionally mentioned i n the l i t e r a t u r e , and opinions d i f f e r . Thus Barnett (1970) i n a two year study of fluctuating populations of harpacticoid copepods on a marine i n t e r t i d a l mudflat found no evidence of food l i m i t a t i o n . How-ever Harris (1972a, b, c) implied that food supply may a f f e c t l o c a l d i s t r i b u t i o n and abundance of meiofauna on an i n t e r t i d a l sand beach, and suggested that p o s i t i v e c o r r e l a t i o n between temperature and harpacticoid population maxima may have been due to stimulation of the copepods 1 microflora food. The experimental work of Gray (196 8), which showed that marine meiofauna select sediment with certain b a c t e r i a l species when offered a choice between such sediment and s t e r i l e sediment, i s i n d i r e c t evidence that these animals may be food limited i n natural environments. I t seems un l i k e l y that such se l e c t i o n would evolve and be maintained i f the organisms were not p o t e n t i a l l y food limited at normal densities. - 106 -In freshwater studies, Prejs (1970) found that densities of herbivorous meiobenthic nematodes were highest when densities of algae i n surface layers of sediment were greatest. On the other hand, Daggett and Davis (1974) claimed that food was not l i m i t i n g for chydorid cladocerans and cyclopoid copepods i n , and just above, the sediments i n two freshwater habitats. Fenchel (1975) found that meiofauna, together with microfauna ( c i l i a t e s ) and macrofauna, consumed only about 50% of the b a c t e r i a l and micro-algae production of an Alaska tundra pond. This would imply that food was not l i m i t i n g to populations of these grazers, assuming that 100% of the microbial production was available. Fryer (1957) stated that food of herbivorous cyclopoid copepods (including species found i n Marion Lake benthos) i s always superabundant, but he implied that predatory cyclopoids are p o t e n t i a l l y food limited. However, Brandl and Fernando (1975) found that such "carnivorous" copepods can survive on algae. Meiobenthic harpacticoid copepods and chydorid cladocerans of Marion Lake are deposit/detritus feeders, deriving t h e i r nourishment from the bacteria and algae associated with the material which they ingest. Levinton (1972) argued that for such organisms, food would be a l i m i t i n g factor. He hypothes-ized that due to r e l a t i v e l y constant and predictable food l e v e l s , species would s p e c i a l i z e e v o l u t i o n a r i l y and would compete for food. Fenchel, Kofoed, and Lappalainen (1975) accepted Levinton"s argument concerning food l i m i t a t i o n and - 107 -concluded that while larger deposit/detritus feeders may s p e c i a l i z e on d i f f e r e n t sizes of sediment p a r t i c l e s , meio-and microfauna can s p e c i a l i z e on d i f f e r e n t kinds and size groups of micro-organisms. They explained high d i v e r s i t y of marine microfauna Cciliates) i n terms of niche d i v e r s i f i c a -t i o n i n choice of food. According to Kool (19 75) there i s a general consensus among protozoan ecologists that benthic c i l i a t e populations, whether marine or freshwater, are food limited, although Fenchel's (196 9) monograph on c i l i a t e ecology does not e x p l i c i t -l y state acceptance of the food l i m i t a t i o n hypothesis. For the s i m i l a r l y sized freshwater benthic r o t i f e r s there i s no published evidence for or against food l i m i t a t i o n , although Edmondson (1965) makes a strong case for the r e l a t i o n s h i p between food supply and population reproductive rate i n planktonic r o t i f e r s . In short term enrichment experiments i n the shallow benthos of Marion Lake, Kajak and Kajak (1975) used small enclosures 2 (60 x 60 cm) and cylinders (20 cm ) with large mesh covers which allowed immigration and emigration of meiofauna. Experi-ments lasted two weeks and food was added (powdered milk and baker's yeast). Although chironomid larvae and H y a l e l l a showed increases i n the experiments, meiofauna showed no response. An untested assumption i n Experiment 1, i n which natural sediment was f e r t i l i z e d , i s that algae and bacteria species - 108 -which were stimulated were suitable food for meiofauna. The importance to population growth of the i d e n t i t y or qu a l i t y of food (as opposed to quantity) has been demonstrated for lab-oratory populations of c i l i a t e s (Taylor and Berger, 1976), r o t i f e r s (King, 1967), freshwater planktonic cladocerans, calanoid and cyclopoid copepods (Schindler, 1971), and marine harpacticoid copepods (Provasoli, S h i r a i s h i , and Lance, 1959). Gray and Johnson (1970) were able to show that density of the species of bacteria which was most a t t r a c t i v e to a marine meio-benthic gastrotrich i n the laboratory was s i g n i f i c a n t l y c o r r e l a t -ed with the gastrotrich's density i n the f i e l d . The d i s t r i b u t i o n of meiobenthic animals along the sampling transect i n Marion Lake generally showed higher populations at intermediate depths (Chapter I ) . This d i s t r i b u t i o n i s i n d i r e c t evidence i n favor of the food l i m i t a t i o n hypothesis because Hargrave (1969) and Gruendling (1971) have shown highest a l g a l productivity and standing stocks at intermediate depths. Other explanations for the d i s t r i b u t i o n are also possible, e.g. temperature preferences. With respect to b a c t e r i a l food, Marten (pers. comm.) carried out radiotracer experiments to study carbon flow i n Marion Lake sediment and concluded that only 0.2% of t o t a l sediment bacteria were consumed by meiofauna per day. Thus even i f the available microflora i s only 2-3% of the t o t a l food present i t would be more than s u f f i c i e n t to support natural densities of harpacticoid copepods, a conclusion - 109 -which was supported by the results of Experiment 2. Stachurska (1975MS) estimated that only about 2% of Marion Lake sediment bacteria were available to c i l i a t e d protozoans, and Kool (1975) concluded that c i l i a t e s i n the lake were not f u l l y e x p loiting the bacteria which were available. Experimental results reported i n t h i s chapter suggest that meiobenthic invertebrate groups i n Marion Lake are not food limited i n either sense of the term (Krebs, 1978), i . e . with respect to determination of average density or carrying capacity, or causes of short term fluctuations i n population size. Predation as a Limiting Factor: It i s generally assumed that predation on marine meiofauna i s i n s i g n i f i c a n t (Mclntyre, 1969; Gerlach, 1971; Mclntyre and Murison, 1973; Giere, 1975), although estuarine harpacticoids may be an important food source for juvenile salmonids -(Kaczynski et a l . , 1973; Sibert et a l . , 1977). A few workers indicate that predation may help control abundance (Barnett, 1970; Hulings and Gray, 1976). Studies on freshwater meio-benthos have suggested that predation may be important i n l i m i t i n g populations of certain groups (Stanczykowska and Przytocka-Jusiak, 1968; Whiteside, 1974) but d e f i n i t e evidence of predation e f f e c t s on meiofauna i s limited to two reports dealing with chydorid cladoceran populations (Goulden, 1971; Daggett and Davis, 1974). - 110 -The predation experiments described i n t h i s chapter (Ex-periments 4 and 5) show that predation rates on meiofauna are c e r t a i n l y low i n Marion Lake. However, i t seems possible that even these low predation rates could regulate populations of meiobenthic b d e l l o i d r o t i f e r s . Although addition of amphipod predators to undisturbed sediment cores i n the lake showed no e f f e c t , a very low "predation" rate was shown by the deposit feeding amphipod Hy a He'll a (Experiment 4) . The most common benthic r o t i f e r , the b d e l l o i d Dissotrocha macrostyla, has an extremely slow reproductive rate for a micrometazoan. Maximum recorded values of " r " , the innate population rate of increase, are 0.090 in lake samples and 0.078 i n laboratory studies (Chapter I I ) . A predation rate on r o t i f e r s of even 5% of the population per day, as estimated for chironomids i n Experiment 4, would have a major e f f e c t on the r o t i f e r popula-ti o n . This implication of chironomid larvae as r o t i f e r preda-tors i s supported by the results of gut analyses on tanypoid chironomids which occasionally showed the presence of r o t i f e r s (McCauley, pers. comm.). Kool (1975) car r i e d out experiments si m i l a r to Experiment 4, using r a d i o a c t i v e l y l a b e l l e d benthic c i l i a t e s from Marion Lake. Predation rates on these protozoa were found to be higher than for meiofauna, with up to 26% of the c i l i a t e population l o s t to predators per day i n the spring months. I t i s a paradox that a slow reproducing b d e l l o i d r o t i f e r i s most numerous i n the samples while the benthic monogonont - I l l -r o t i f e r s which have higher rates of increase (e.g. Lecane sp.) are r e l a t i v e l y scarce. I t i s tempting to say that the more active monogononts are s e l e c t i v e l y hunted by predators while the r e l a t i v e l y inactive bdelloids are overlooked. There i s l i t t l e evidence to support t h i s idea other than the observation that monogonont remains were found more often i n cyclopoid copepod guts than b d e l l o i d r o t i f e r remains, although both were rare. These observations also prove that cyclopoids w i l l take r o t i f e r s , although results of Experiment 4 (Table 9) indicated no predation. The only experimental evidence for predation on harpacti-coid copepods i s a low rate for the predatory amphipod Crangonyx i n Experiment 4. Possible i n d i r e c t evidence of predation by Crangonyx i s the s l i g h t population decline of harpacticoids i n June and July (Chapter I) when young Crangonyx are produced i n the lake (Mathias, 1971). McCauley (pers. comm.) found harpacticoids i n a few tanypoid chironomids from Marion Lake. Harpacticoid copepods are active animals and are more abundant i n Marion Lake benthos than other microcrustaceans—cyclopoid copepods and chydorid cladocerans (Chapter I ) . Thus the lack of evidence of predation on them i s surprising. The clue to understanding what factors l i m i t population numbers of harpacticoids comes from laboratory culture studies on Bryocamptus hiemalis (Chapter I I ) . Although t h i s copepod has a high reproductive p o t e n t i a l , reproduction i s suppressed by high summer temperatures at the sediment-water interface. - 112 -B. hiemalis w i l l not form eggs at temperatures of 20°C or higher, and mortality i s high for n a u p l i i , copepodids, and even adults at 20°C. Optimum temperature for survival of a l l stages and for production of eggs i s approximately 10°C. Although spring water temperatures of about 10°C are maintained i n the lake for one to two months, B. hiemalis does not produce eggs u n t i l a temperature of 10°C i s reached i n the f a l l . This delay of reproduction means that there i s only one generation per year. Moreover, naupliar s u r v i v a l rate i s low at winter temperatures (5°C or l e s s ) . Thus, temperature caused natural mortality of n a u p l i i i n winter, and adults i n summer, coupled with a repro-ductive delay caused by high summer temperatures may be s u f f i c i e n t to l i m i t the population of the most important harpacticoid species. Any predation on these animals, however s l i g h t , would therefore be s i g n i f i c a n t . A s i m i l a r s i t u a t i o n i s described for a t e r r e s t r i a l isopod by McQueen and Carnio (1974) and McQueen (1976). The popula-tion of the isopod remained r e l a t i v e l y constant over a three year period and i t ..."appeared to be limited by temperature conditions"... acting on growth, reproduction, and s u r v i v a l . In t h i s way, numbers were kept low enough that density dependent regulation did not come into play. Enright (1976) discussed the theory of population l i m i t a t i o n (as opposed to "control" in a cybernetic sense) by c l i m a t i c factors such as temperature. There i s some evidence that cyclopoid copepods are eaten by Crangonyx (Experiment 4, Table 9) although Experiment 5 did - 113 -not show predation by the amphipod on cyclopoids. In addition cyclopoids have been found i n tanypoid chironomid guts (McCauley, pers. comm.) and the more numerous small copepods belonging to Acanthocyc1ops nanus are probably eaten by the less numerous large predatory cyclopoids such as Macrocyclops  fuscus and M. albidus (Fryer, 1957). Population densities of cyclopoids were always lower than those of harpacticoids even though a few Acanthocyclops nanus, the most abundant cyclopoid, were carrying eggs i n a l l months except for June, July and August. The only d e f i n i t e experimental evidence for predation on meiobenthic cladocerans was found i n Experiment 4 (Table 9). The predator was the carnivorous amphipod Crangonyx. Apparent predation on cladocerans by Hyalella seen i n Experiment 5 (Table 10) must be discounted because there i s no way t h i s deposit feeding amphipod could ingest l i v i n g , active chydorid cladocerans. Since i t i s known that these cladocerans rapidly pass food through t h e i r guts (Fryer, 1970), i t i s possible that some radioactive material i n cladoceran guts was defecated and then ingested by Hyalella. There i s strong, but not experimental evidence that tany-poid chironomids i n the Marion Lake benthos are predators on benthic cladocerans although Experiment 4 results did not indicate such predation. Gut analyses of tanypoids show the cladocerans to be the second most important prey item for predatory t h i r d and fourth instars (McCauley, unpublished data). - 114 -These l a r v a e are most abundant i n the l a k e benthos from May to August, a t a time when c h y d o r i d p o p u l a t i o n growth r a t e s are p o t e n t i a l l y very h i g h . At temperatures p r e v a i l i n g d u r i n g these months (12 to 25°C), r e p r e s e n t a t i v e c h y d o r i d s p e c i e s have gen e r a t i o n times ranging from 10 to 30 days (Chapter I I ) . I t i s a l s o p o s s i b l e t h a t newborn pr e d a t o r y Crangonyx, which are produced i n June and J u l y , may prevent c h y d o r i d s from develop-i n g l a r g e r p o p u l a t i o n s . Kajak and Kajak (1975) c a r r i e d out experiments on Marion Lake benthos s i m i l a r t o Experiment 5 r e p o r t e d i n t h i s chapter. The major d i f f e r e n c e i s t h a t the u n d i s t u r b e d cores they used d i d not have Crangonyx added. Rather the n a t u r a l l y o c c u r r i n g Crangonyx and predatory chironomids were "trapped" w i t h i n the cores and f o r c e d to feed f o r 4 8 hours on the food w i t h i n the core. D e n s i t i e s of p o t e n t i a l prey s p e c i e s were then compared f o r cores where more or fewer p r e d a t o r s had been trapped. From these data the authors c a l c u l a t e d the biomass of meio-benthos eaten by p r e d a t o r s and, comparing t h i s biomass wi t h the standing crop, d e r i v e d a turnover time f o r a l l meiofauna to t h e i r p r e d a t o r s of 4-15 days a t 10-15°C. T h i s r e p r e s e n t s a p r e d a t i o n r a t e of some 7-25% o f the p o p u l a t i o n per day and exceeds even the maximum value s found i n Experiment 4. In Experiment 5, which most c l o s e l y resembles the Kajaks' e x p e r i -ments, one would expect meiofauna p o p u l a t i o n s t o be decimated because of the a r t i f i c i a l l y i n c r e a s e d number of p r e d a t o r s , but meiofauna p o p u l a t i o n s a t the beginning and end of - 115 -the experiment were not s i g n i f i c a n t l y d i f f e r e n t . Unfortunately, Kajak and Kajak did not subject t h e i r meiofauna date to s t a t -i s t i c a l treatment. Of the meiobenthic animals which have been cultured i n the laboratory only the uncommon monogonont r o t i f e r Lecane has a generation time which would allow i t to withstand the predation pressure postulated by Kajak and Kajak. The chydorid cladocer-ans A l o n e l l a nana and Alona quadrangu1aris have short genera-ti o n times, but not quite short enough, and the harpacticoid copepod Bryocamptus hiemalis, with generation times of over 100 days, couldn't survive i f predation i n the lake was t h i s intense over long periods of time. Thus the r e s u l t s of Kajak and Kajak must be questioned i n l i g h t of culture work with meiobenthic organisms from the lake (Chapter II) and the r e s u l t s of Experiments 4 and 5 reported i n t h i s chapter. Kool (1975) and Stachurska (19.75. .MS) undertook a series of experiments to investigate the causes of population l i m i t a t i o n i n Marion Lake benthic c i l i a t e s . Stachurska was unable to show that food was l i m i t i n g to the benthic c i l i a t e s but she also could not r e j e c t the hypothesis of food l i m i t a t i o n . Kool's experiments indicated that predation on c i l i a t e s by cyclopoid copepods was s i g n i f i c a n t . Moreover Kool showed a s i g n i f i c a n t c o r r e l a t i o n between c i l i a t e population density and the experimentally determined predation rate for various times of the year, implying density dependent population regulation. However, given the generation times for Marion - 116 -Lake c i l i a t e s grown on natural sediment i n the laboratory, Kool concluded that predation could not completely explain the declines seen i n c i l i a t e populations i n the lake. Both Kool and Stachurska emphasized that t h e i r conclusions were dependent upon extrapolating laboratory population growth rates, a practice which they recognized can be misleading. Thus i f the benthic c i l i a t e s i n the lake did not reproduce as quickly as they assumed, then predation might have been regulating c i l i a t e populations. Tanner (19 66) suggested that i f a population was regulated by density dependent parameters, then a negative c o r r e l a t i o n should be found between"population density and " r " (population rate of growth) at any time. Kool (1975) found such a negative c o r r e l a t i o n for c i l i a t e populations i n Marion Lake. When I tested the t o t a l meiobenthic r o t i f e r data for three years, a negative c o r r e l a t i o n was also found (r = -0.519, p<0.01, Spearman's cor r e l a t i o n of rank c o e f f i c i e n t i n Siegal, 1956). S i m i l a r l y , the population density and " r " were s i g n i f -i c a n t l y and negatively correlated for two years' sampling data on Dissotrocha macrostyla, the most common r o t i f e r species. If we accept Tanner's t h e o r e t i c a l argument, then t h i s i s strong evidence that the meiobenthic r o t i f e r population i n the lake was being regulated i n a density dependent manner. Tanner's interpretation may not be the only i n t e r p r e t a t i o n for such negative correlations. Consider the following s i t u a -t i o n . Weather conditions moderate as summer begins; lake - 117 -temperature r i s e s and organisms such as benthic c i l i a t e s and r o t i f e r s begin to reproduce rapidly. In t h i s case, r e l a t i v e l y low densities w i l l be correlated with high population growth rates. After a couple of weeks of good weather, during which time the c i l i a t e s or r o t i f e r s have increased t h e i r population s i z e , there i s a heavy r a i n f a l l and lake temperature drops. As a r e s u l t , the population w i l l grow very slowly or even decline. High population density would then be correlated with a low value f o r population growth rate. If t h i s t y p i c a l summer pattern continued, one would fi n d a negative c o r r e l a -t i o n between population density and rate of population growth, even though no density dependent process had taken place. On the other hand, Tanner found s i g n i f i c a n t negative correlations between " r " and population density for 47 of 64 populations from widespread taxonomic groups (insects, f i s h , birds, mammals) and i t i s unl i k e l y that a l l these correlations could be attributed to physical factors varying seasonally. Conclusion I t i s impossible to make any c o l l e c t i v e statement con-cerning population regulation of the Marion Lake meiobenthos as a whole. If we consider major taxonomic categories, i t i s s t i l l d i f f i c u l t to be d e f i n i t i v e . I t seems l i k e l y that r o t i f e r populations are not food lim i t e d , either i n terms of average density or short term fluctuations i n density, and may be controlled by predation. Such predation need not - 118 -involve more than a small percentage of the population, given the low reproductive rate of the most common b d e l l o i d species. There i s s t i l l the paradox of the monogonont species, with much higher reproductive rates, being less common than the '. bdelloids. Perhaps they are more a t t r a c t i v e to predators. As for harpacticoid copepods, the most common species does best i n terms of survival and reproduction at a tempera-ture of around 10°C. Lake temperatures are not i n the optimum range long enough to allow more than one generation per year. Low winter temperatures cause much mortality of n a u p l i i and high summer temperatures cause some mortality of adults and prevent the onset of egg production. Any predation during the summer, no matter how minor, w i l l further reduce the number of adults which reproduce i n the f a l l . Factors l i m i t i n g or regulating populations of the re-maining meiobenthic groups are less clear. Cyclopoid copepods are present i n lower numbers than harpacticoids throughout the year and apparently have a long reproductive period. I t i s possible that predation on a c t i v e l y swimming n a u p l i i and early copepodids by older stages as demonstrated for Cyclops  bicuspidatus i n Marion Lake plankton (McQueen, 1969) may be a self-regulatory mechanism. Because some benthic cyclopoid copepods also are found i n the water column above the sediment surface, they may suffer some predation from water column predators (e.g. juvenile salmonids). In the sediment, tany-poid chironomid larvae take some cyclopoids and are also - 119 -predators on chydorid cladocerans. Such predation may l i m i t chydorid cladoceran population size during the summer. - 120 -CHAPTER IV EXPERIMENTAL STUDIES ON BENTHIC CARBON FLOW - 121 -I n t r o d u c t i o n R e c e ntly t h e r e has been much i n t e r e s t i n t o t a l b e n t h i c metabolism i n marine environments (Pamatmat, 1968; Smith e t a l . , 1972; Smith, 1973) and a l s o i n freshwater (Hargrave, 1969, working on Marion Lake). The r o l e played by meiofauna i n t o t a l b e n t h i c carbon flow and e n e r g e t i c s has been c o n s i d e r e d f o r marine environments by Fenchel (1969), G e r l a c h (1971, 1978), Vernberg and C o u l l (1974), and M i l l s (1975). To date, the c o n t r i b u t i o n o f meiofauna t o t o t a l b e n t h i c metabolism i n freshwater has been s t u d i e d i n d e t a i l o n l y by Fenchel (1975). In none of the marine or freshwater s t u d i e s were m i c r o f a u n a l , meiofaunal, and macrofaunal carbon flow a l l measured independ-e n t l y . T h i s chapter presents r e s u l t s o f s e v e r a l experiments on carbon flow i n the b e n t h i c community and on the carbon budget of the most abundant h a r p a c t i c o i d copepod s p e c i e s . D e t a i l s o f methods used are d e s c r i b e d w i t h the r e s u l t s of each experiment. Methods and R e s u l t s Community Carbon Flow Experiments: Experiment 1 To study the movement o f carbon through the zoobenthic community an experiment u s i n g u n d i s t u r b e d sediment cores and r a d i o a c t i v e l y l a b e l l e d l a k e b a c t e r i a was c a r r i e d out i n November, 1971. Cores o f sediment were o b t a i n e d by pushing 2 2 g l a s s c y l i n d e r s ( c r o s s - s e c t i o n a l area 20 cm ) i n t o the 225 cm - 122 -block of sediment l i f t e d from 1.5 m i n the lake u s i n g a sampler designed by Hargrave (1969). The c o r e s , c o n t a i n i n g 7-8 cm of sediment and an e q u i v a l e n t amount of water, were c a r e f u l l y stoppered a t both ends and r e t u r n e d t o the l a b o r a t o r y , where they were kept a t 10°C o v e r n i g h t (lake temperature was 5°C). A mixed p o p u l a t i o n of two u n i d e n t i f i e d s p e c i e s of Marion Lake b a c t e r i a ( i s o l a t e d by F r a k e r , unpublished) was c u l t u r e d f o r 3 days a t 20°C i n a f l a s k of n u t r i e n t c u l t u r e medium 14 c o n t a i n i n g C-acetate as a carbon source. The b a c t e r i a l suspension was harvested by c e n t r i f u g a t i o n and resuspended i n lake water. A p o r t i o n of t h i s suspension was f i l t e r e d (0.45 um M i l l i p o r e ) f o r d e t e r m i n a t i o n of r a d i o a c t i v i t y , and another p o r t i o n was counted u s i n g a hemocytometer. One ml of r a d i o a c t i v e b a c t e r i a l suspension ( c o n t a i n i n g 7 7 x 10 c e l l s ) was added by s y r i n g e t o the sediment-water i n t e r f a c e of the three c o r e s , and the cores were capped. A f t e r 1, 14, and 25 hours of i n c u b a t i o n a t 10°C (+ 2°C) i n a dark environment chamber, the top 2 cm of each core was removed and f i x e d i n 5% f o r m a l i n . Meio- and macrofauna were e x t r a c t e d and counted as d e s c r i b e d i n Chapter I, r i n s e d f r e e of sediment, and p l a c e d i n s c i n t i l l a t i o n v i a l s c o n t a i n i n g Bray's s c i n t i l l a -t i o n s o l u t i o n . C a b o s i l was a l s o added t o suspend organisms i n the s o l u t i o n . R a d i o a c t i v i t y was determined u s i n g a New England N u c l e a r Mark I s c i n t i l l a t i o n counter. Meio- and macrofauna accumulated o n l y about 1% of the r a d i o a c t i v i t y added as l a b e l l e d b a c t e r i a , even a f t e r 25 hours - 123 -(Table 11). Ingestion of bacteria would have been a l i t t l e greater than t h i s , allowing for faunal r e s p i r a t i o n of ingested l a b e l , but the amount of available bacteria exploited was small, supporting the r e s u l t s of Chapter I I I . Meiofauna accounted for 10-22% of the faunal r a d i o a c t i v i t y . Experiments 2a and 2b The l a b e l l e d bacteria added to sediment cores i n Experiment 1 represented only about 0.1-0.2% of the normal standing crop 10 2 of bacteria i n surface sediment (1.0-3.2 X 10 cells/20 cm according to Perry, 1974). I t i s possible that only a small portion of sediment bacteria are located on the surface of the sediment p a r t i c l e s and available to grazers. Therefore the bacteria added i n Experiment 1 might have s i g n i f i c a n t l y i n -creased the b a c t e r i a l biomass available to the meiofauna or macrofauna or both. To overcome th i s possible problem, and to insure that b a c t e r i a l species which were l a b e l l e d were the ones actually found i n the p a r t i c u l a r cores, two experiments were conducted 14 m which bacteria i n s i t u were l a b e l l e d with C-glucose, rather than adding previously l a b e l l e d bacteria. These experi-ments were carr i e d out i n A p r i l and May, 1973. Six cores were taken from 1.0 m i n the lake i n mid-April using the method previously described. Cores were kept at 10°C for one week before the experiment (2a) was run at 10°C. Six other cores were taken from 1.0 m i n mid-May and kept at 20°C - 124 -Table 11. R a d i o a c t i v i t y of meiofauna and macrofauna following a d d i t i o n of l a b e l l e d b a c t e r i a to undisturbed sediment cores. 1 hour 14 hours 25 hours DPM per group: Meiofauna 55 Macrofauna 454 P a r t i t i o n i n g of accumulated DPM: Meiofauna 10.8% Macrofauna 89.2% Proportion of b a c t e r i a l DPM accumulated: Meiofauna 0.03% Macrofauna 0.23% 518 1757 22.8% 77.2% 0.26% 0.89% 264 1669 13.7% 86.3% 0.14% 0.85% - 125 -for one week before being used i n an experiment (2b) at 20°C. In both experiments a l l water above the sediment was removed, except for 1.0 cm. Radiotracer was added to both sets of 14 cores at a rate of 50 uCi of C-glucose per core, which was di s t r i b u t e d across the sediment surface by syringe. The glass 14 cores were stoppered t i g h t l y (to prevent the escape of c 0 2 ) and placed i n environment chambers i n constant l i g h t (0.10 c a l / 2 cm /min) at 10 or 20°C (+2°C) for 1, 2, 3, 24, 48, and 70 hours. At the end of the incubation period a 0.1 ml sample of the water above the sediment i n each core was taken for analysis of r a d i o a c t i v i t y . The top 2 cm of sediment was s l i c e d o f f and a small sample sorted immediately for microfauna ( c i l i a t e s ) by Richard Kool. The sediment was then fixed i n 5% formalin. Benthic invertebrates were extracted i n the usual way, counted and rinsed. Meiofauna was „suspended i n Bray's solution and Cabosil i n precounted s c i n t i l l a t i o n v i a l s . Macrofaunal animals were combusted and the r e s u l t i n g radioactive CC>2 trapped i n s c i n t i l l a t i o n v i a l s according to the method of Burnison and Perez (1974). There was a very rapid drop i n r a d i o a c t i v i t y i n the water above the sediment i n the early stages of the experiment (Figure 26). Kleiber (unpublished) has shown that t h i s i s primarily due to rapid b i o l o g i c a l uptake of the glucose by sediment bacteria, with only about 25% of the uptake due to adsorption onto sediment p a r t i c l e s . The shape of the curve over 70 hours results not only from uptake of glucose by - 126 -Figure 26. Radioactivity i n water above the sediment i n undisturbed cores at two temperatures following addition of x 4C-glucose. - 127 -sediment bacteria but also from release into the water of radioactive carbon dioxide and dissolved organic carbon from b a c t e r i a l , a l g a l , and faunal r e s p i r a t i o n and excretion. After 5-10 hours, depending upon temperature, r a d i o a c t i v i t y i n the water was only 10% of i n i t i a l counts. Radioactivity appeared i n microfauna, meiofauna, and macrofauna within one hour and increased rapi d l y (Figure 27). Although microfauna showed an unexplained decrease i n radio-a c t i v i t y between 2 and 3 hours at 10°C and 1 and 2 hours at 20°C, and macrofaunal r a d i o a c t i v i t y did not change between 1 and 2 hours and declined between 24 and 48 hours at 10°C, the o v e r a l l pattern for a l l groups was a rapid increase i n radio-a c t i v i t y , followed by a gradual increase, and f i n a l l y a plateau where r a d i o a c t i v i t y no longer increased, or began to decline. This plateau i s interpreted as being the stage at which equilibrium was reached between the r a d i o a c t i v i t y of the organism and that of i t s food, i . e . the s p e c i f i c a c t i v i t i e s of the two were the same, assuming no growth during the feeding period. The data indicate that t h i s stage was reached by microfauna within 24 hours at 10°C, but not u n t i l 48 hours at 20°C. Total meiofauna r a d i o a c t i v i t y l e v e l l e d o f f by 48 hours at both 10°C and 20°C, but t o t a l macrofauna r a d i o a c t i v i t y was s t i l l increasing at 70 hours at both temperatures. The r e l a t i v e amount of r a d i o a c t i v i t y i n major faunal groups i n the f i r s t hour approximates t h e i r p a r t i t i o n i n g of b a c t e r i a l food i n the sediment. The microfaunal share of Figure 27. Radioactivity of benthic faunal components follow-ing addition of x^C-glucose to undisturbed sediment cores at two temperatures. - 129 -carbon uptake i n the f i r s t hour was 12%, the meiofaunal share ranged from 3-20%, and the macrofaunal share from 67-84%. Only 0.1-0.5% of the l a b e l l e d food was incorporated by a l l three groups i n the f i r s t hour. To compare r a d i o a c t i v i t y per unit biomass for d i f f e r e n t faunal components, i t was necessary to determine standing crops i n the sediment cores. Microfauna ( c i l i a t e ) standing crops were calculated from l i t e r a t u r e biomass values by Richard Kool. Standing crops of meiofauna were calculated from weights of representative organisms (Table 12). These weights were ob-tained using a Cahn electrobalance (accuracy +1 jag) aft e r drying the organisms for 3 days at 50°C on pre-weighed 0.8 cm diameter discs of M i l l i p o r e f i l t e r paper. Macrofaunal standing crops were determined d i r e c t l y by weighing animals from each core aft e r drying. The only macrofauna found consistently i n the cores was amphipods and chironomid larvae, and macrofauna results are based on these two groups only. The t o t a l invertebrate dry weight standing crop was 1.8-2 2 2.4 mg/20 cm (900-1200 mg/m ), of which 0.6% was due to microfauna and 5.9-7.5% to meiofauna (Table 13). Macrofauna was under-represented because only chironomids and amphipods were included, but s t i l l contributed 92-94% of faunal standing crop. Radioactivity (in DPM/mg dry weight) increased most rapidly i n the microfaunal component at both 10°C and 20°C, followed by meiofauna and then macrofauna (Figure 2 8). - 130 -Table 12. Lengths and dry weights of representative meiofaunal animals. Units are um and ug per i n d i v i d u a l . B d e l l o i d r o t i f e r s 350-500 um Harpacticoid copepods 500-600 600-700 Cyclopoid copepods 400-800 800-1000 1000-2000 1200-1400 Chydorid cladocerans 200-400 Nematodes 800-1000 Mites 400-700 0.15 ug/ind. 0.45 0.82 0.55 2.80 3.33 S.17 0.88 0.85 2.54 - 131 -Table 13. Average Standing crops of microfauna, meio-fauna, and macrofauna i n sediment cores. 2 Units are mg dry weight per 20 cm core. Experiment 2a Experiment 2b A p r i l , 1973 May, 1973 (10°C) (20°C) Microfauna ( c i l i a t e s ) .010 mg .012 mg Meiofauna R o t i f e r s .010 .017 Harpacticoids .050 .093 Cyclopoids .032 .039 Mites .007 .011 Nematodes .006 .010 Cladocerans .003 .007 T o t a l .108 mg .177 mg Macrofauna Chironomids .322 1.119 Amphipods 1.397 1.070 T o t a l 1.719 mg 2.189 mg T o t a l Standing Crop 1.837 mg 2.378 mg Percentage of Standing Crop Microfauna 0.6% 0.6% Meiofauna 5.9% 7.5% Macrofauna 93.5% 91.9% - 132 -Figure 28. Radioactivity of benthic faunal components, per unit weight, following addition of 1 4C-glucose to undisturbed sediment cores at two temperatures. - 133 -Equilibrium levels were higher for microfauna than for meio-fauna. Macrofauna did not reach equilibrium i n the 70 hours. Because Figure 28 lumps various benthic taxonomic groups together, while they i n d i v i d u a l l y demonstrated d i f f e r e n t responses, results for three meiofaunal groups ( r o t i f e r s , harpacticoid copepods,. cyclopoid copepods) and one macrofaunal group (chironomid larvae) are presented i n Figure 29 to show the d i v e r s i t y within faunal components. Rotifer and cyclopoid copepod r a d i o a c t i v i t y had l e v e l l e d o f f by 70 hours but harp-a c t i c o i d r a d i o a c t i v i t y was s t i l l increasing. Thus, although the meiofauna as a whole appeared to reach equilibrium by 7 0 hours, one important group of the meiofauna - the harpacticoids - had not. Chironomid r a d i o a c t i v i t y had s t a b i l i z e d at 10°C, but was s t i l l increasing at 20°C, aft e r 70 hours. Two important carbon flow parameters can be estimated from the results of the experiments. Turnover rate of the sediment can be defined as the rate at which b a c t e r i a l carbon in the sediment passes to a component of the fauna and may be calculated as T = x a s sr s where x i s r a d i o a c t i v i t y i n the faunal group a f t e r 1 hour and cl x g i s r a d i o a c t i v i t y i n the b a c t e r i a l food, estimated from the decrease of tracer observed i n the f i r s t hour (Figure 26). The reci p r o c a l of T i s the time (in hours) required for the faunal component to ingest an amount of biomass equivalent to the - 134 -ir-rr™ • • ~L «r-itn 1 1 1 l t » M 48 ?0 129 24 <8 TO Hours Figure 29. Radioactivity of three meiofauna and one macrofauna groups per unit weight, following addition of 14c-glucose to undisturbed sediment cores at two temp-eratures . - 135 -biomass of the food. Turnover rate of the animals i s the rate at which a p a r t i c u l a r faunal component accumulates carbon from i t s food, and may be defined as T = X l a — x e where x^ i s the counts per milligram i n the faunal group a f t e r 1 hour and x g i s the counts per milligram i n the group at equilibrium. The counts had to be weighted to take into account standing crop v a r i a b i l i t y between experimental cores but growth over the 3 days was assumed to be n e g l i g i b l e . Although not a l l taxonomic groups had enough time to reach equilibrium during the course of the experiments, for these groups the value x g was assumed to be the same as for the groups which did s t a b i l i z e (5 X 10 5 DPM/mg dry weight). The r e c i p r o c a l of T i s the time required for the group to ingest cl an amount of biomass equal to i t s own biomass. Turnover rates of sediment (T ) to major faunal components s -4 were low (Table 14), with values ranging from 2.0-6.7 X 10 -4 -4 for microfauna, 1.8-3.3 X 10 for meiofauna, and 11-45 X 10 for macrofauna. In Experiment 1, l a b e l l e d bacteria were added to the surface sediment, i n cores and these bacteria were pos-s i b l y more available to grazing fauna than in. s i t u bacteria. However turnover rates of these bacteria to meio- and macro-fauna were approximately the same as rates for i n s i t u bacteria. Because turnover rates of sediment to fauna were - 136 -Table 14. Turnover rates (per hour) of sediment (T g) and animals (T ) based on r a d i o t r a c e r e x p e r i -a ments with undisturbed cores. s a Experiment 1 (10°C) — 4 Meiofauna 2.8 X 10 -Macrofauna 23.1 X 10~ 4 Experiment 2a (10°C) Microfauna 6.7 X 10~ 4 .45 Meiofauna 1.8 X 10~ 4 .012 Macrofauna 45.0 X 10~ 4 .017 Experiment 2b (20°C) Microfauna 2.0 X 10~ 4 .27 Meiofauna 3.3 X 10~ 4 .031 Macrofauna 11.0 X 10~ 4 .008 - 137 -so low, turnover times would be large, on the order of months. This supports the conclusion of Chapter III, that non-predatory meiofauna are probably not food-limited, and suggests the same conclusion for non-predatory micro- and macrofauna. Turnover rates for faunal components ( T a) followed the expected pattern, with microfaunal turnover rates much greater than meior or macrofauna rates (Table 14). Microfauna turnover times (1/T ) ranged from 2-4 hours, meiofauna from 1-3 days, ct and macrofauna from 2-5 days. The results of Experiments 2a and 2b, along with values for standing crop of bacteria (Perry, 1974) and algae (Gruendling, 1971), and predation rates on microfauna (Kool, 1975) and meio-fauna (Chapter III) may be used to estimate carbon standing crops and carbon flow i n the benthic faunal community on a spring day (Figure 30). Carbon flow from bacteria and micro-2 algae to microfauna i s 6-19 mg C/m /day, to meiofauna i s 4-16 2 2 mg C/m /day, and to macrofauna i s 41-120 mg C/m /day. The lower values for each faunal component were calculated by multiplying average sediment turnover rate (T ) times standing crop of bacteria. The higher values were calculated by multiplying average turnover rate f o r the faunal component (T ) times standing crop of that component. Carbon flow from algae to benthic fauna i s undetermined but probably smaller than carbon flow from bacteria (see Discussion). Microfauna Figure 30. Benthos standing crops and carbon flow i n April-May. Units are mgC/m2/day. - 139 -Bryocamptus Carbon Budget Experiments: Experiment 3 To investigate p a r t i t i o n i n g of ingested carbon by a t y p i c a l meiofaunal species, experiments were carried out i n the labora-tory using the common harpacticoid copepod, Bryocamptus  hiemalis. The f i r s t experiment was designed to determine feeding rate by measuring egestion at 5, 10, 15, and 20°C. At each temperature, 18 adult copepods (9 male, 9 female) were placed i n d i v i d u a l l y i n depressions of glass 9-spot plates to which had been added 0.1 ml of fresh lake sediment sieved to remove p a r t i c l e s larger than 250 jum and smaller than 130 um. The plates were placed inside large (diameter 14 cm) glass p e t r i dish moist chambers to prevent evaporation and incubated for 2 4 hours at each temperature. After incubation each depres-sion of the 9-spot plate was searched under a stereoscope (25 X magnification) and faecal p e l l e t s counted. Microscopic examination of cleared specimens indicated that the content of the gut when f u l l was equivalent to the volume of three faecal p e l l e t s . Consequently, information on the number of faecal p e l l e t s produced per unit time allowed ca l c u l a t i o n of gut f i l l i n g time and number of times the gut could be f i l l e d i n one day. The number of p e l l e t s egested in 24 hours was much greater at 10, 15, and 20°C than i t was at 5°C (Table 15), but numbers of p e l l e t s produced at the three higher temperatures were not s i g n i f i c a n t l y d i f f e r e n t from each other (t-test, p < .05). At 5°C i t took over 8 - 140 -Table 15. The e f f e c t of temperature on egestion rates of Bryocamptus hie m a l i s . 5°C 10°C 15°C 20°C Faecal p e l l e t s 8.4 + 4.7 32.4 +3.6 41.6+6.4 37.7+10.1 produced i n 24 hours (+ 95% C.L.) Time to f i l l the 8.6 2.2 1.7 1.9 gut (hours) Number o f times 2.8 10.9 14.1 12.6 gut i s f i l l e d per day - 141 -hours to f i l l the gut, w h i l e at 10, 15, and 20°C the time r e q u i r e d was only about 2 hours. Experiments 4a,b and 5a,b In these experiments B. h i e m a l i s was fed sediment i n which the m i c r o f l o r a had been l a b e l l e d w i t h r a d i o t r a c e r . Experiments 5a and 5b were i d e n t i c a l to 4a and 4b, except t h a t the animals i n the 20°C treatment were fed on l a b e l l e d sediment f o r 3 hours i n s t e a d of 1.5 hours (to insure the gut was f i l l e d ) , and the animals were counted i n i n d i v i d u a l s c i n t i l l a t i o n v i a l s to allow the c a l c u l a t i o n of confidence l i m i t s . Experiment 5 was run 3 days a f t e r Experiment 4. Fr e s h l y c o l l e c t e d Marion Lake sediment was sieved t o remove p a r t i c l e s and organisms l a r g e r than 130 um i n s i z e , 14 and approximately 25 ml was incubated w i t h C-glucose at 10°C fo r 7-10 days. The in c u b a t i o n time was s u f f i c i e n t l y long t h a t not only b a c t e r i a but a l s o algae would have become l a b e l l e d , 14 through f i x a t i o n of C0 2 r e s p i r e d by b a c t e r i a . Two ml of l a b e l l e d sediment was f i l t e r e d (0.45 um M i l l i p o r e ) to remove any r a d i o a c t i v i t y i n the water and then resuspended i n lake water. In each experiment, l a b e l l e d sediment (approximately 1.0 ml i n 2.0 ml of sediment-water suspension) was added to a small (volume 4.0 ml) Stender d i s h f i t t e d w i t h a ground g l a s s cover. Twenty adu l t B. h i e m a l i s (.10 male, 10 female) were added to each d i s h and dishes were placed i n constant environment - 142 -chambers at 10 or 20°C where the copepods were allowed to feed for 1.5 hours (Experiment 4b at 20°C) or 3 hours (Experiments 4a, 5a at 10°C; 5b at 20°C). The 20 copepods i n each dish were then removed by micropipette under a stereoscope and rinsed free of any sediment by several transfers through clean lake water. Ten of the copepods were placed i n Bray's solution i n a s c i n t i l l a t i o n v i a l and the other 10 were transferred to another Stender dish containing non-radioactive, sieved, s t e r i -l i z e d lake sediment. Inside the dish l i d was taped an aluminum f o i l cup holding a CC^ trap composed of a glass f i b e r f i l t e r (2.4 cm diameter) saturated with 0.1 ml of 1 M hyamine hydroxide. The ground glass l i d was sealed with petroleum j e l l y to prevent loss of radioactive CG^ • After 3 hours incubation at 10°C or 20°C i n non-radioactive sediment, copepods were k i l l e d by addition of 0.1 ml of 5 N H 2 S 0 4 ' wk-*-ch a l s o released C0 2 dissolved i n the water. The covered dish was swirled and l e f t for an additional 2 hours to allow absorption of CG^ by the hyamine hydroxide. The CC^ trap f i l t e r was then placed i n a s c i n t i l l a t i o n v i a l , and the dead copepods picked out of the sediment, rinsed, and placed in another v i a l . The sediment-water mixture l e f t i n the dish was f i l t e r e d (0.45 um Millipore) and the sediment, containing material defaecated by the copepods, was placed i n a t h i r d s c i n t i l l a t i o n v i a l . F i n a l l y the f i l t r a t e containing dissolved organic matter excreted by the copepods was evaporated to dryness at 50°C i n a fourth v i a l . Bray's solution was added - 143 -to a l l v i a l s , along with Cabosil to prevent s e t t l i n g out i n v i a l s containing animals or pa r t i c u l a t e matter, and the v i a l s were counted i n a l i q u i d s c i n t i l l a t i o n counter. The above procedures allowed measurement of radioactive food ingested, and p a r t i t i o n i n g of ingested carbon into carbon retained, r e s p i r a t i o n , excretion, and egestion over the next 3 hours (Table 16). Carbon which was respired, excreted, or egested during the i n i t i a l 1.5-3.0 hour feeding on l a b e l l e d sediment could not be measured, and values for these processes are therefore underestimated. Of radioactive carbon ingested, 18-32% was respired over the 3 hour incubation i n unlabelled sediment, 16-22% was excreted, and 5-14% egested. If i t i s assumed that the copepods had f i l l e d t h e i r guts with unlabelled sediment, and had egested any l a b e l l e d sediment remaining i n the gut 3 hours aft e r transfer, then subtracting r a d i o a c t i v i t y of the egested faeces from i n i t i a l r a d i o a c t i v i t y of the animal allows the c a l c u l a t i o n of percentage radioactive carbon assimilated. The assimilation e f f i c i e n c y of B. hiemalis i n these experiments was high - 85-95%. Copepods incorporated d i f f e r e n t numbers of counts at d i f -ferent temperatures, but where these differences could be sub-jected to a t - t e s t (in Experiments 5a and 5b) they were not found to be s i g n i f i c a n t (p<.05). Theoretically, the DPM/ in d i v i d u a l after feeding on radioactive sediment should equal the combination of DPM/individual which was retained, respired, egested and excreted after feeding for 3 hours on unlabelled - 14 4 -Table 16. P a r t i t i o n i n g of r e c e n t l y ingested carbon by Bryocamptus hiemalis, based on short-term feeding experiments using r a d i o a c t i v e l y l a b e l l e d sediment. Units are DPM per i n d i v i -dual copepod, with 95% C.L., where a p p l i c a b l e . DPM/individual 4a (10°C) 4b (20°C) 5a (TQ°C) 5b (20°C) Incorporated 233 195 155 + 66 242 + 95 a) Retained 79 71 73 + 31 60 + 35 b) Respired 49 63 46 44 c ) . Excreted 37 41 34 37 d) Egested 24 20 7 34 T o t a l a,b,c,d 189 195 160 175 - 145 -sediment. However i n d i v i d u a l v a r i a b i l i t y i n f e e d i n g r a t e s and i n r e s p i r a t i o n , e x c r e t i o n , and e g e s t i o n makes t h i s u n l i k e l y , e s p e c i a l l y over the s h o r t i n c u b a t i o n p e r i o d s used i n t h i s experiment. The c l o s e agreement between i n i t i a l and f i n a l summary counts i n Experiments 4b and 5a i s t h e r e f o r e remarkable. D i s c u s s i o n Community Carbon Flow: I n t e r p r e t a t i o n of r a d i o t r a c e r experiments i s not a simple task (Sorokin, 1966). One must take i n t o account v a r i o u s processes happening simultaneously, and a number of assumptions must be made. The t h e o r e t i c a l p a t t e r n of uptake i n r a d i o t r a c e r f e e d i n g experiments i s d e s c r i b e d i n Appendix I I , along w i t h a l i s t o f assumptions made i n such experiments. To i l l u s t r a t e one d i f f i c u l t y of r a d i o t r a c e r methodology, the h i g h c o n c e n t r a t i o n of r a d i o i s o t o p e i n the water d u r i n g the i n i t i a l stages of Experiments 2a and 2b might have caused animals t o i n c o r p o r a t e some r a d i o a c t i v i t y , from the water, as w e l l as through t h e i r food. Marten (1975 MS)found t h a t H y a l e l l a , 14 when p l a c e d i n C-glucose alone, p i c k e d up l e s s than 10% of the counts accumulated i f sediment was p r e s e n t . However, i n p r e l i m i n a r y experiments u s i n g twice the c o n c e n t r a t i o n of r a d i o -i s o t o p e used i n Experiments 2a and 2b, and i n the absence o f sediment, I found t h a t H y a l e l l a c o u l d p i c k up s i g n i f i c a n t r a d i o a c t i v i t y , as c o u l d m i c r o c r u s t a c e a n meiofauna. The mechan-ism was probably not d i r e c t uptake of glucose by the organisms - 14.6 -(Efford and Tsumura, 1973b) but rather physical adsorbtion of the glucose by the body wall (K. H a l l , pers.comm.) and/or uptake by bacteria carried on the organism's exterior (Hargrave, 1971). This d i f f i c u l t y i s uncontrollable, and i t could have affected the determination of turnover rates, which were calculated from r a d i o a c t i v i t y accumulated during the f i r s t part of Experiments 2a and 2b. In a previous study on Marion Lake, Hargrave (1969) estimated standing crops and attempted to p a r t i t i o n benthic community re s p i r a t i o n . He found that microfauna represented 7%, meiofauna 1%, and amphipod and chironomid macrofauna 92% of faunal biomass. My results are i n agreement with Hargrave's standing crop r e s u l t s , except that the r e l a t i v e contributions of microfauna and meiofauna are reversed, i . e . microfauna were 1%, meiofauna 6-8%, and macrofauna 92-94% of standing crop. When the re s u l t s of t h i s study on p a r t i t i o n i n g of b a c t e r i a l carbon by benthic fauna are compared with Hargrave 1s p a r t i t i o n -ing of community res p i r a t i o n there i s basic agreement. Har-grave calculated that microfauna contributed 34% of faunal community re s p i r a t i o n and I found that 12% of b a c t e r i a l carbon taken up by benthic fauna went to microfauna. Meiofauna accounted for 5% of faunal r e s p i r a t i o n i n Hargrave's data, and 3-20% of b a c t e r i a l carbon accumulated i n my experiments. Amphipod and chironomid macrofauna, according to Hargrave, contributed 61% of faunal community re s p i r a t i o n and I found that t h i s component accounted for 67-84% of b a c t e r i a l carbon ingested. - 147 -In a study of b e n t h i c carbon flow i n an Alaskan tundra pond, Fenchel (1975) found percentage s t a n d i n g crops of micro-, meio-, and macrofauna to be 2%, 5%, and 93% r e s p e c t i v e l y . B a c t e r i a l and m i c r o - a l g a l carbon was p a r t i t i o n e d approximately 12% to microfauna, 11% to meiofauna, and 77% to macrofauna. Fenchel's r e s u l t s f o r percentage s t a n d i n g crop and carbon a l l o c a t i o n are thus very s i m i l a r t o my r e s u l t s f o r Marion Lake. The a c t u a l s t a n d i n g crops which he found i n the A l a s k a pond are somewhat h i g h e r than Marion Lake benthos however. In Fenchel's study the carbon i n g e s t e d per day by a l l components o f the fauna was l e s s than 20% of b a c t e r i a l and a l g a l s t a n d i n g crops.. T h i s i s s i m i l a r to my estimates f o r Marion Lake (Figure 30). Fenchel concluded t h a t a f r a c t i o n o f b a c t e r i a and algae r e g u l a r l y becomes b u r i e d i n the sediment, becoming i n a c t i v e or b eing decomposed by other b a c t e r i a . I t i s i n t e r e s t i n g t h a t a depth p r o f i l e o f b a c t e r i a i n Marion Lake sediment ( H a l l and Hyatt, 1974) shows o n l y a g r a d u a l decrease w i t h depth, w i t h numbers at 6 cm, w e l l below the oxygenated s u r f a c e l a y e r , 40% of numbers at the mud-water i n t e r f a c e . In a l a r g e and d e t a i l e d study of marine benthos i n shallow water, Fenchel (1969) attempted to p a r t i t i o n community metab-o l i s m among microfauna, meiofauna, and macrofauna. To do t h i s he c a l c u l a t e d r e l a t i v e m e t a b o l i c r a t e per u n i t body weight f o r the d i f f e r e n t f a u n a l groups u s i n g the formula c a l o r i e s , T T. 67 — r = kW hour - 148 -where W i s body weight. A decrease i n body weight by a factor 3 . . . of 10 would r e s u l t i n an increase i n metabolic rate per unit weight by a factor of 10 according to t h i s r e l a t i o n s h i p , which Fenchel cautioned does not hold s t r i c t l y for a l l animals. By using r e l a t i v e metabolic rates for the d i f f e r e n t faunal groups and numbers and biomass data he c o l l e c t e d i n a regular sampling programme, Fenchel calculated r e l a t i v e numbers, r e l a -t i v e biomass, and r e l a t i v e contribution to faunal community metabolism for three marine s i t e s i n Denmark. One of these s i t e s , i n Niva Bay, had a shallow (<lm) s i l t y bottom and i s more sim i l a r to Marion Lake i n bottom c h a r a c t e r i s t i c s than the other two s i t e s , which were an i n t e r t i d a l sand beach and a 10m deep station with a sand substrate. In Niva Bay Fenchel found microfauna: meiofauna: macrofauna numbers to be 50: 10: 1, while biomass r a t i o s were 1: 10: 170. Community metabolism rat i o s for microfauna: meiofauna: macrofauna were 1: 2: 4. Vernberg and Coull (1974) questioned Fenchel's use of the r e l a t i v e metabolic rate formula, and recalculated the r e l a t i v e community metabolism for the Danish s i t e s using Fenchel's biomass data and actual oxygen consumption rates for c i l i a t e s and meio- and macrofauna. Their community metabolism r a t i o s for the Niva Bay s i t e were 1: 3.4: 1.9 for microfauna, meio-fauna, and macrofauna, thus increasing the r e l a t i v e importance of meiofauna and decreasing the importance of macrofauna compared to Fenchel"s r e s u l t s . - 149 -I applied the same techniques to the data from Experiments 2a and 2b. Relative metabolic rates per unit body weight calculated according to the formula used by Fenchel were 17: 4: 1 for microfauna, meiofauna, and macrofauna respectively. 14 This can be compared to the r e l a t i v e C ingestion rates per unit body weight measured i n the f i r s t hour of the experiments, which gave a r a t i o of 29: 2: 1 for micro-, meio-, and macro-fauna. The numbers ra t i o s i n the experimental cores for micro-fauna: meiofauna: macrofauna were 27: 6: 1 while biomass r a t i o s were 1: 12: 170. Relative community metabolism estimated from 14 the biomass r a t i o and the r a t i o of C ingestion rates per unit biomass, was 1: 1: 6 for the three groups. Using r e l a t i v e metabolic rates per unit biomass calculated according to Fenchel's method, the r e l a t i v e community metabolism was 1: 3: 10 for the three groups. When Vernberg and Coull's oxygen consumption rates for amphipod and chironomid macrofauna were used to calculate r e l a t i v e community metabolism, the r a t i o s were 1: 4: 5 for microfauna: meiofauna: macrofauna. The r a t i o s for Niva Bay and for Marion Lake are summarized i n Table 17. The d i f f e r e n t estimates for r e l a t i v e community metabolism i n Marion Lake show how the technique of analysis applied may a f f e c t the interpretation s i g n i f i c a n t l y . Based on the amount of l a b e l l e d b a c t e r i a l food ingested, the meiofaunal contribu-tion to faunal community metabolism i s approximately 10%, while i f Fenchel's (1969) concept of r e l a t i v e metabolic rates - 150 -Table 17. A comparison of r e l a t i v e numbers, biomass, and community metabolism r a t i o s f o r microfauna, meiofauna, and macrofauna i n Niva Bay, Denmark, and Marion Lake, B.C. Numbers Biomass Community Metabolism Community Metabolism (Vernberg and Coull, 1974) Niva Bay, Denmark Microfauna Meiofauna 50 1 1 1 10 10 2 3.4 Macrofauna 1 170 4 1.9 Numbers Biomass Community Metabolism {Radiotracer method) Community Metabolism (Metabolic rate method of Fenchel, 1969) Community Metabolism (Oxygen consumption method of Vernberg and C o u l l , 1974) Microfauna 27 1 1 Meiof atir.a 6 12 1 Macrofauna 1 170 6 10 - 151 -i s applied the meiofauna contribution r i s e s to 30%. If oxygen consumption rates taken from the l i t e r a t u r e (Vernberg and Coull, 1974; Hargrave, 1969) are used, the meiofaunal contribu-tion r i s e s s t i l l further to 40%. My estimates of r e l a t i v e community metabolism are based upon two assumptions. The f i r s t i s that r e l a t i v e metabolic rate per unit biomass i s proportional to r e l a t i v e ingestion rates per unit biomass, as measured by incorporation of radio-a c t i v e l y l a b e l l e d food. The second assumption i s that inges-tion rates measured i n Experiments 2a and 2b apply to ingestion of both a l g a l and b a c t e r i a l food, although they were determined 14 from r a d i o a c t i v i t y accumulated within one hour aft e r C-glucose was added, and most lab e l picked up by the microflora was probably s t i l l i n the b a c t e r i a l component. In fact, non-predatory microfauna and meiofauna i n Marion Lake probably are more dependent upon b a c t e r i a l than a l g a l food. In the microfauna, more c i l i a t e species feed on bacteria than algae (Kool, pers. comm.). Among the meiofaunal r o t i f e r s only some numerically unimportant species are primarily a l g a l feeders. Intact algae were occasionally found i n cyclopoid copepod gut contents (as were animal remains), during micro-scopic examination of transect samples (Chapter I ) . Usually however, only an indistinguishable mixture of material was observed. Harpacticoid and cladoceran guts contained a compact mixture of unid e n t i f i a b l e material but never i n t a c t algae or animal remains. Brown and Sibert (1977) found estuarine deposit - 152 -feeding harpacticoids ingested radioactive bacteria nine times faster than radioactive algae. Non-predatory macrofauna may be r e l a t i v e l y more dependent upon algae for food than are micro- and meiofauna, although carbon flow from algae to macrofauna i s probably s t i l l less than from bacteria. Hamilton (1965) found most Marion Lake chironomid species which ingested algae also ingested "detr i t u s " , and another study of chironomids (McCauley, unpublished) sug-gested more dependence upon sediment/detritus than upon algae. The deposit-feeding amphipod Hya l e l l a has been shown to ingest algae (Hargrave, 1970b) but other evidence (Marten, 19 75 MS) indicated that bacteria i s more important than algae i n t h i s animal's d i e t . P a r t i t i o n i n g of Carbon by Bryocamptus: The balanced carbon budget equation i s C = P + R+ U + F where C i s consumption, P i s production (growth and repro-duction) , R i s r e s p i r a t i o n , U i s excretion of dissolved organic matter, and F i s egestion of faeces (Mann, 1969). Assimilation (A) i s the difference between C and F, i . e . i t i s the sum of P plus R plus U. Assimilation e f f i c i e n c y i s A/C X 100 (Gulati, 1974). The short term Bryocamptus feeding experiments (4a, 4b, 5a, and 5b) demonstrated high assimilation e f f i c i e n c i e s for these copepods (85-95%), feeding on sediment. Hargrave (1970b) - 153 -fed Hyalella azteca on Marion Lake sediment enriched with radio-active Pseudomonas sp. bacteria. He found the amphipod1s assimilation e f f i c i e n c y was 89%. I t i s tempting to apply the results of the harpacticoid experiments to the balanced carbon budget. Of the radioactive carbon ingested, 25-47% was retained for 3 hours following transfer to unlabelled sediment ("production"), 18-32% was released as CO2 ("respiration"), 15-22% was released as DOM ("excretion"), and 5-14% was defaecated ("egestion"). Such application of the experimental results would unfortunately be misleading because the s p e c i f i c a c t i v i t y of the carbon released i n various forms would not be the same as the s p e c i f i c a c t i v i t y of the carbon ingested. What can be concluded from the experiments i s that 85-95% of the microflora carbon ingested i s assimilated and about half of this assimilated carbon i s immediately respired or excreted. Assimilated carbon which was retained a f t e r 3 hours of incubation i n unlabelled sediment cannot a l l go into production, for t h i s would imply an extreme-l y large growth rate or immediate reproduction for these adult copepods, which normally only reproduce i n the f a l l months. Presumably a small portion of the carbon retained was diverted to growth or storage of high energy compounds, and most was passed into the main carbon pool of the animals' bodies where i t would be respired or excreted at a l a t e r time, whenever feeding rate decreased or locomotion was required. - 154 -The rapid r e s p i r a t i o n and excretion of recently ingested carbon suggests that there i s a short-term pool of carbon i n the copepods which has a faster turnover rate to r e s p i r a t i o n and excretion than the main body carbon pool. Such an arrangement was postulated by Conover and Francis (1973) who discussed the implications for radiotracer feeding studies of a two-pool system. Recently, Brandl and Fernando (1975) found evidence for the two-pool carbon system i n two fresh-water cyclopoid copepod species. In his experiment with Hyalella Hargrave (19 70b) also found that approximately 50% of recently assimilated carbon was respired or excreted within 5 hours at 15°C, which suggests there may be a two-pool system i n t h i s amphipod. In summary, radiotracer techniques are promising tools for community carbon flow and carbon/energy budget investiga-tions, but interpretation of experimental r e s u l t s i s often complicated (Conover and Francis, 1973). Fortunately, analyt-i c a l methods are being developed to deal with t h i s complexity (Marten et a l . , 1975). - 155 -GENERAL DISCUSSION AND CONCLUSION - 156 -The b e n t h i c f a u n a l community of Marion Lake i s abundant and d i v e r s e , and i s c h a r a c t e r i z e d by o b v i o u s l y complex i n t e r -r e l a t i o n s h i p s . Food f o r the b e n t h i c primary consumers i s pro-v i d e d by the m i c r o f l o r a (algae and b a c t e r i a ) . There are about 185 s p e c i e s of b e n t h i c algae found i n the lake w i t h an average 2 standing crop of approximately 0.2-0.4 g C/m and annual 2 primary p r o d u c t i o n of 40-44 g C/m (Hargrave, 1969; Gruendling, 1971). E x t e n s i v e work on b e n t h i c b a c t e r i a ( H a l l e t a l . , 1972; 2 Perry, 1974) has i n d i c a t e d standing crops of 0.6 g C/m and 2 average carbon f l u x o f 20 g C/m /year. B a c t e r i a are d i s t r i b u t e d throughout the sediment p r o f i l e and, because oxygen i s d e p l e t e d below 1 cm, much of the b a c t e r i a l p o p u l a t i o n may be f a c u l t a t -i v e l y anaerobic. In c o n t r a s t t o b a c t e r i a , most a l g a l biomass i s c o n c e n t r a t e d i n the top centimeter of the sediment. Feeding on the b e n t h i c m i c r o f l o r a and on each other are a t l e a s t 42 s p e c i e s of c i l i a t e s (Kool, 1975). An unknown number of other protozoans ( f l a g e l l a t e s , s a r c o d i n i a n s ) i s present. Meiofauna i s represented by a t l e a s t 40 s p e c i e s of r o t i f e r s , 8 s p e c i e s of h a r p a c t i c o i d and c y c l o p o i d copepods, 14 s p e c i e s of c l a d o c e r a n s , and an unknown number o f nematodes, h a l a c a r i n e mites, g a s t r o t r i c h s , t a r d i g r a d e s , o s t r a c o d s , and t u r b e l l a r i a n s (Chapter I ) . The i n s e c t component of the herb-i v o r o u s , d e t r i t i v o r o u s , and c a r n i v o r o u s macrofauna i s r e p r e s e n t -ed by 55 s p e c i e s of d i p t e r a n chironomid l a r v a e (Hamilton, 1965), f o u r s p e c i e s o f ephemeropteran nymphs (Reynolds, u n p u b l i s h e d ) , four s p e c i e s o f odonate nymphs (P e a r l s t o n e , 1973), and 25 - 157 -species of trichopteran larvae (Winterbourne, 1971). Crustacean macrofauna includes one herbivorous amphipod (Hyalella azteca) and one primarily carnivorous amphipod (Crangonyx richmondens1s). There are f i v e small bivalve molluscan species i n the benthos (Efford and Tsumura, 1973a) and an unknown number of pulmonate mollusk species. Oligochaete and hirudinean annelids are present, but the number of species has not been determined.. The macrofauna i s dominated by. chironomid larvae and amphipods (Mathias, 1971). One benthic vertebrate herbivore species - tadpoles of Rana aurora - occupies the lake for part of the year (Calef, 19 73). Vertebrate predators include two species of salamanders, Ambystoma g r a c i l e and Taricha granulosa, whose populations p a r t i a l l y leave the lake seasonally (Neish, 1971). The two species of salmonid f i s h , Salmo gairdneri and Oncorhynchus  nerka, although l i v i n g i n the water column, feed heavily on the benthos at d i f f e r e n t ages (Ware, 1972; H a l l and Hyatt, 1974) . The known food relationships i n the Marion Lake benthos are summarized i n a food web (Figure 31). As many as six trophic le v e l s may be i d e n t i f i e d although most food chains are shorter. This food web i s by no means complete. Some organisms are not included because t h e i r food relationships are completely unknown and some possible transfers are not indicated because evidence i s lacking. - 158 -Figure 31. Major (dark lines) and minor pathways of energy flow i n the Marion Lake food web. Ver tebra te P reda to rs ( F i s h , Sa lamanders) - 160 -The observations and experiments on the meiofaunal compon-ent of the benthos reported i n th i s thesis have raised many-more questions than have been answered. The meiofaunal com-munity of a small oligotrophic lake has been shown to be composed of many species, some of which are numerically abund-ant. Each taxonomic group of the meiobenthos i s dominated by one or two species, for reasons that are not cl e a r . Perhaps the lack of heavy predation on meiofauna allows a species with strong competitive advantages to become dominant, as suggested by H a l l et al.(1970) for planktonic and benthic communities. This might account for the observed r e l a t i v e abundance of harpacticoid species, although i t requires that some resource (food, space) be l i m i t i n g , which could not be demonstrated. I t also seems possible that the observed species d i v e r s i t y and dominance i n the meiofauna may largely be due to r e l a t i v e tolerance to a b i o t i c conditions, e s p e c i a l l y temp-erature, or to the history of species introductions to t h i s p a r t i c u l a r lake. The meiofauna has a fine scale patchy d i s t r i b u t i o n i n what i s s u p e r f i c i a l l y a homogeneous habitat. This could be a r e s u l t of patchy d i s t r i b u t i o n of food supply, or of preferred food species. Unfortunately there i s l i t t l e quantitative evidence for or against the concept of patchiness i n m i c r o f l o r a l stand-ing crop. Gruendling's (1971) study of Marion Lake benthic algae reported l i t t l e patchiness i n t o t a l a l g a l standing crop but patchiness of d i f f e r e n t a l g a l species was not mentioned. - 161 -Because of d i f f i c u l t i e s i n i d e n t i f y i n g and counting m i c r o f l o r a l bacteria i n Marion Lake (Hall and Hyatt, 1974), information on b a c t e r i a l patchiness i s lacking. Reasons for the observed patchy d i s t r i b u t i o n of meiofauna are therefore unknown. Population densities of meiofaunal groups fluctuated l i t t l e over time. Attempts to explain t h i s observation led to culture studies of the reproductive potential of represent-ative meiofauna species. Contrary to the expectation that these very small animals would have high reproductive rates and short l i f e spans, i t was found that dominant r o t i f e r and harpacticoid copepod species reproduced slowly for t h e i r sizes and had l i f e spans l a s t i n g many months. The dominant chydorid cladocerans, on the other hand, had t y p i c a l reproductive potentials for t h e i r sizes. Evidence from these culture studies suggested that the annual temperature regime was of c r i t i c a l importance i n l i m i t i n g population densities of dominant r o t i f e r and harpacticoid species i n the lake. S p e c i f i c tests of the influence of predation and food supply on meiofauna populations were not conclusive. However, evidence supported the suggestion that neither factor i s re-sponsible for l i m i t i n g ultimate population densities found i n the lake. Whether either or both factors serve to control short term density fluctuations i s unknown. Low predation rates on meiofauna could be s i g n i f i c a n t i f meiofaunal popula-tions were otherwise reduced due to temperature e f f e c t s . I t seems l i k e l y that r e a l understanding of the r e l a t i v e importance - 162 -of a b i o t i c factors such as temperature, and b i o t i c factors such as predation and food supply (and food q u a l i t y ) , i n l i m i t i n g and c o n t r o l l i n g meiofaunal populations w i l l require detailed study of every species i n the community. Radiotracer techniques allowed investigation of the role played by meiofauna i n carbon flow i n the undisturbed benthic faunal community. Although results of such studies must be interpreted with care, i t appears that meiofauna, representing about 7% of benthic faunal biomass, accounted for approximately 10% of carbon flow from bacteria to the t o t a l benthic fauna. Evidence also indicated that microfauna, meiofauna, and macro-fauna combined could consume 6-25% of b a c t e r i a l standing crop per day. Radiotracer methodology was also used to investigate the way harpacticoid copepods p a r t i t i o n recently ingested carbon. Evidence suggested that the bodies of these animals contain two pools of carbon between which recently ingested carbon i s divided. One carbon pool i s small and carbon i s rapidly turned over to excretion and r e s p i r a t i o n , while the main body pool i s larger and turns over less r a p i d l y . In these radiotracer studies, as i n the culture studies, there i s thus a reminder that even small animals have a complicated physiology and interpretation of experimental re s u l t s must take this complexity into account. What then i s the role played by the meiofauna i n the t o t a l benthic community of Marion Lake? Herbivorous and - 163 -detritivorous macrofauna i n the lake are probably not food-lim i t e d (Efford and H a l l , 19 75) and the microfauna i s also probably not food-limited (Kool, 1975) . Therefore the small amount of b a c t e r i a l and a l g a l carbon taken by meiofauna would not have a s i g n i f i c a n t impact on the other components of the benthic fauna i n terms of competition for food, and i n fact, herbivorous and detritivorous meiofauna are themselves prob-ably not food-limited. The predatory species of macrofauna (Crangonyx, large tanypoid chironomid larvae, odonate larvae, e t c . ) , meiofauna (a few r o t i f e r species, large cyclopoid copepods), and micro-fauna (a few predatory c i l i a t e species) may however be food-lim i t e d and competition may take place between these species. To the degree that predatory macrofauna are dependent upon meiofauna prey, the l a t t e r may have an influence on the former. It does not follow that meiofaunal populations are limited or controlled by predation, and they probably are not, although cladocerans may be an exception. It appears that meiofauna are an energetic dead end i n Marion Lake, i . e . because there i s l i t t l e predation on meio-fauna, l i t t l e carbon/energy passes through the meiofaunal component of the benthos d i r e c t l y to macrofauna and then to the lake's vertebrate predators. If t h i s view i s correct, and i f meiofaunal grazing removes only a small portion of the b a c t e r i a l or a l g a l standing crop, i s i t correct to conclude - 164 -that meiofauna play an i n s i g n i f i c a n t r o l e i n the benthic com-munity? The same question applies to the role of microfauna, whose grazing impact on microflora i s si m i l a r to meiofauna's and which contributes l i t t l e energy to higher trophic l e v e l s . The answer i s that the primary importance of meiofauna and microfauna may l i e i n t h e i r role i n recycling nutrients to bacteria and algae and as "gardeners" of the sediment micro-f l o r a . Johannes (1965) and Barsdate et a l . (1974) have stressed the importance of marine protozoa to inorganic nutrient regen-eration, and Mclntyre (1969) and Coull (1973) concluded that the main role of meiofauna i n shallow water marine environments was to a s s i s t i n the re c y c l i n g of nutrients. Micro-, meio-, and macrofauna a l l release dissolved organic compounds (Johannes and Webb, 1970) which serve as carbon and energy sources for heterotrophic bacteria, carbon dioxide which i s a carbon source for autotrophic algae, and inorganic nutrients (e.g. nitrogen and phosphorous compounds) which are needed by both bacteria and algae and which are i n short supply i n Marion Lake (Gruend-l i n g , 1971). Detritus i s made available to the benthic community when leaf l i t t e r i s washed into the lake, when dead phyto- and zoo-plankton sink from the water column, or when algae or animals i n the benthos die. The f i r s t stage i n decomposition of th i s organically r i c h material i s colonization by bacteria and fungi, which remove inorganic nutrients and e a s i l y assimilated carbon compounds from the surface of the d e t r i t u s , and increase t h e i r - 165 -standing crops i n the process. When the detritus i s grazed some bacteria and fungi are removed, thus opening up space for recolonization by more decomposers. In addition, release of dissolved organic and inorganic compounds by grazers stimulates b a c t e r i a l (and algal) growth and further decomposition of detritus can take place. The mechanical e f f e c t of grazing by deposit feeding macro- and meiofauna also breaks up larger pieces of detritus into smaller p a r t i c l e s with a corresponding increase i n surface area for b a c t e r i a l colonization. Physical s t i r r i n g of the sediment by grazers probably also provides more oxygen to decomposer, microflora. In these ways grazers actually can cause an increase i n t h e i r food supply, as pointed out for Marion Lake by Hargrave (1970a) and Efford and H a l l (1975), and more generally by Fenchel (1972) and Gerlach (1978). At the same time, detrit u s which enters the system i s stripped of i t s u t i l i z a b l e carbon and inorganic nutrients, leaving refractory compounds (especially from plant materials) which are incorporated into the sediment (Hall and Hyatt, 1974). It i s suggested that the ecological importance of meio-fauna i n th i s small oligotrophic lake l i e s not so much i n s t r i c t l y energetic considerations or position i n a food web, but i n i t s physical working of the sediment and i n helping to recycle scarce nutrients. Meiofauna i n other environments may also be important as food for higher trophic l e v e l s , as has been shown for juvenile salmonids feeding on benthic - 166 -harpacticoids i n estuarine environments (Kaczynski et a_l. , 1973). Recently, sticklebacks (Gasterosteus aculeatus) were introduced into Marion Lake. These small f i s h , which can exploit meiofaunal sized prey, w i l l probably channel more meiofaunal carbon into the main food chain as sticklebacks are i n turn the prey of rainbow trout. What w i l l happen to meio-faunal populations as a r e s u l t of increased exploitation? This i s only one of many possible questions for future research. - 167 -REFERENCES - 168 -A r l t , G. 1973. V e r t i c a l and h o r i z o n t a l m i c r o d i s t r i b u t i o n o f the meiofauna i n the G r e i f s w a l d e r Bodden. Oikos Suppl. 15: 105-111. Bar n e t t , P.R.O. 1968. D i s t r i b u t i o n and ecology of h a r p a c t i -c o i d copepods oh an i n t e r t i d a l mudflat. I n t . Revue ges. H y d r o b i o l . 53: 177-209. Ba r n e t t , P.R.O. 1970. The l i f e c y c l e s o f two s p e c i e s of Platyche11pus Brady (Harpacticoida) on an i n t e r t i d a l mudflat. I n t . Revue ges. H y d r o b i o l . 55: 169-195. Barsdate, R.J., R.T. P r e n t k i , and T. Fenchel. 1974. Phos-phorus c y c l e o f model ecosystems: s i g n i f i c a n c e f o r decomposer food chains and e f f e c t of b a c t e r i a l g r a z e r s . Oikos 25: 239-251. Bartos, E. 19 51. The Czechoslovak R o t a t o r i a o f the Order B d e l l o i d e a . V e s t n i k Ceskoslovenske Zool. S p o l e c u n o s t i 15: 241-500. Bonner, J.T. 1965. S i z e and C y c l e . P r i n c e t o n Univ. P r e s s , P r i n c e t o n , N.J. 219 pp. B o t t r e l l , H.H. 1975. The r e l a t i o n s h i p between temperature and d u r a t i o n of egg development i n some e p i p h y t i c Clado-c e r a and Copepoda from the R i v e r Thames, Reading, w i t h a d i s c u s s i o n of temperature f u n c t i o n s . O e c o l o g i a (Berl.) 18: 63-84. deBovee, F., J . Soyer, and P. A l b e r t . 1974. The importance of the mesh s i z e f o r the e x t r a c t i o n o f the muddy bottom meiofauna. Limnol. Oceanog., 19: 350-354. - 169 -B r a n d l , Z. and C H . Fernando. 1975. Food consumption and u t i l i z a t i o n i n two freshwater c y c l o p o i d copepods (Me'socyclops' edax and Cyclops v i c i n u s ) . I n t . Revue ges. H y d r o b i o l . 60: 471-494. Brooks, J.L. 1959. Cl a d o c e r a . In W.T. Edmondson (ed.), Freshwater B i o l o g y , 2nd e d i t i o n , pp. 587-656. John Wiley and Sons, N.Y. Brown, T . J . and J.R. S i b e r t . 1977. Food o f some b e n t h i c h a r p a c t i c o i d copepods. J . F i s h . Res. Board Can. 34: 1028-1031. Burnison, B.K. and K.T. Perez. 1974. A simple method f o r the 14 dry combustion of C - l a b e l l e d m a t e r i a l s . Ecology 55: 899-902. C a l e f , G.W. 1973. N a t u r a l m o r t a l i t y of tadpoles i n a popula-t i o n o f Rana aurora. Ecology 54: 741-758. Cameron, R.L. 1973. A comparison of the responses of b e n t h i c and p l a n k t o n i c communities t o the enrichment of i n o r g a n i c f e r t i l i z e r s . M.Sc. T h e s i s , Univ. of B r i t i s h Columbia. 77 pp. C a r l , G.C. 1940. The d i s t r i b u t i o n o f some Cladocera and f r e e -l i v i n g Copepoda i n B r i t i s h Columbia. E c o l . Monogr. 10: 55-110. Caughley, G. and L . C B i r c h . 1971. Rate of i n c r e a s e . J . W i l d l i f e Management 35: 658-663. - 170 -Cole, G.A. 1955. An e c o l o g i c a l study of the microbenthic fauna of two Minnesota la k e s . Amer. M i d i . Nat. 53: 213-230. Conover, R.J. and V. F r a n c i s . 1973. The use of r a d i o a c t i v e isotopes to measure the t r a n s f e r of m a t e r i a l s i n aquatic food chains. Mar. B i o l . 18: 272-283. Conroy, J.S. 196 8. The water-mites of western Canada. Nat. Mus. Canada B u l l . 223: 23-24. Conroy, J.S. 19 73. Ecology of water-mites i n Marion Lake. Ph.D. Thesis, Univ. of Manitoba. 155 pp. C o u l l , B.C. 19 70. Shallow water meiobenthos of the Bermuda platf o r m . Oecologia (Berl.) 4: . 325-357. C o u l l , B.C. 1973. Estu a r i n e meiofauna: a review: t r o p h i c r e l a t i o n s h i p s and m i c r o b i a l i n t e r a c t i o n s . In L.H. Stevenson and R.R. C o l w e l l (eds.), E s t u a r i n e M i c r o b i a l Ecology, pp. 499-511. Univ. of S. C a r o l i n a Press, Columbia. Daggett, R.F. and C.C. Davis. 1974. A seasonal q u a n t i t a t i v e study of the l i t t o r a l Cladocera and Copepoda i n a bog pond and an a c i d marsh i n Newfoundland. I n t . Revue ges. Hydrobiol. 59: 667-683. Dickman, M.D. 1969. Some e f f e c t s of lake renewal on phyto-plankton p r o d u c t i v i t y and species composition. Limnol. Oceanog., 14: 660-666. Donner, J . 1966. R o t i f e r s . . Translated by H.G.S. Wright. F. Warne and Co., London. 75 pp. - 171 -Edmondson, W.T. 1959. R o t i f e r a . In W.T. Edmondson (ed.), Freshwater B i o l o g y , 2nd e d i t i o n , pp. 420-494. John Wiley and Sons, N.Y. Edmondson, W.T. 1965. Reproductive r a t e of p l a n k t o n i c r o t i f e r s as r e l a t e d to food and temperature i n nature. E c o l . Monogr. 35: 61-111. Edmondson, W.T. 1968. A g r a p h i c a l model f o r e v a l u a t i n g the use of the egg r a t i o f o r measuring b i r t h and death r a t e s . Oecologia (Berl.) 1: 1-37. Edmondson, W.T. and G.G. Winberg. 1971. A Manual on Methods f o r the Assessment of Secondary P r o d u c t i v i t y i n Fresh Waters. IBP Handbook No. 17. B l a c k w e l l , Oxford. 358 pp. E f f o r d , I.E. 1967. Temporal and s p a t i a l d i f f e r e n c e s i n phyto-plankton p r o d u c t i v i t y i n Marion Lake, B r i t i s h Columbia. J . F i s h . Res. Board Can. 24: 2283-2307. E f f o r d , I.E. and K. Tsumura. 1973a. A comparison of the food of salamanders and f i s h i n Marion Lake, B r i t i s h Columbia. Trans. Amer. F i s h . Soc. 102: 33-47. E f f o r d , I.E. and K. Tsumura. 1973b. Uptake of d i s s o l v e d glucose and g l y c i n e by P i s i d i u m , a freshwater b i v a l v e . Can. J . Zool. 51: 825-832. E f f o r d , I.E. and K.J. H a l l . 1975. Marion Lake — An a n a l y s i s of a lake ecosystem. In,. T.W.M. Cameron and L.W. B i l -l i n g s l e y (eds.), Energy Flow - I t s B i o l o g i c a l Dimensions: A Summary of the IBP i n Canada, ppJ 199-219. Royal Soci e t y of Canada, Ottawa. - 172 -Elgmork, K. 1967. Ecological aspects of diapause i n copepods. Proc. Symp. Crust. Mar. B i o l . Assoc. India. Part I I I , pp.. 947-954. E l l i o t t , J.M. 1971. Some methods for the s t a t i s t i c a l analysis of samples of benthic invertebrates. Freshwater B i o l . Assoc. S c i . Publication No. 25. 144 pp. Enright, J.T. 1976. Climate and popualtion regulation. Oecologia (Berl.) 24: 295-310. Evans, M.S. and J.A. Stewart. 1977. Epibenthic and benthic microcrustaceans (copepods, cladocerans, ostracods) from a nearshore area i n southeastern Lake Michigan. Limnol. Oceanog. 22: 1059-1066. Fenchel, T. 1967. The ecology of marine meiobenthos. I. The quantitative importance of c i l i a t e s as compared with metazoans i n various types of sediments. Ophelia 4: 121-137. Fenchel, T. 196 8. The ecology of marine microbenthos. I I I . The reproductive pot e n t i a l of c i l i a t e s . Ophelia 5: 123-136. Fenchel, T. 1969. The ecology of marine microbenthos. IV. Structure and function of the benthic ecosystem, i t s chemical and physical factors and the microfauna communi-t i e s with special reference to the c i l i a t e d protozoa. Ophelia 4: 1-182. Fenchel, T. 19 72. Aspects of decomposer food chains i n marine benthos. Verh. d. Dtsch. Zool. Ges. 65: 14-22. - 173 -Fenchel, T. 1974. I n t r i n s i c r a t e of n a t u r a l i n c r e a s e : the r e l a t i o n s h i p w i t h body s i z e . O e c o l o g i a (Berl.) 14: 317-326. Fenchel, T. 19 75. The q u a n t i t a t i v e importance of the b e n t h i c microfauna o f an A r c t i c tundra pond. H y d r o b i o l o g i a 46: 445-464. Fenchel, T. and B.O. Jansson. 1966. On the v e r t i c a l d i s t r i -b u t i o n o f the microfauna i n the sediments of a b r a c k i s h -water beach. O p h e l i a 3: 161-177. Fenchel, T., L.H. Kofoed, and A. Lappalainen. 1975. P a r t i c l e s i z e - s e l e c t i o n o f two d e p o s i t f e e d e r s : the amphipod Corophium v o l u t a t o r and the prosobranch Hydrobia uTv'ae. Mar. B i o l . 30: 119-128. F r y e r , G. 1957. The food of some freshwater c y c l o p o i d copepods and i t s e c o l o g i c a l s i g n i f i c a n c e . J . Anim. E c o l . 26: 263-286. F r y e r , G. 1970. De f a e c a t i o n i n some m a c r o t h r i c i d and c h y d o r i d c l a d o c e r a n s , and some problems of water i n t a k e and d i g e s -t i o n i n the Anomopoda. Z o o l . J . Linnean Soc. 49: 255-270. Gerlac h , S.A. 1971. On the importance o f marine meiofauna f o r benthos communities. O e c o l o g i a (Berl.) 6: 176-190. Gerlac h , S.A. 1978. Food-chain r e l a t i o n s h i p s i n s u b t i d a l s i l t y sand marine sediments and the r o l e of meiofauna i n s t i m u l a t i n g b a c t e r i a l p r o d u c t i v i t y . O e c o l o g i a (Berl.) 33: 55-69. - 174 -Giere, 0. 1975. Population structure, food r e l a t i o n s and ecological role of marine oligochaetes, with special reference to meiobenthic species. Mar. B i o l . 31: 139-156. Goulden, C.E. 1971. Environmental control of the abundance and d i s t r i b u t i o n of the Chydorid Cladocera. Limnol. Oceanog. 16: 320-331. Gray, J.S. 196 8. An experimental approach to the ecology of the harpacticoid Leptastacus constrictus Lang. J. exp. mar. B i o l . E c o l . 2: 278-292. Gray, J.W. and R.M. Johnson. 1970. The bacteria of a sandy beach as an ecological factor a f f e c t i n g the i n t e r s t i t i a l g astrotrich Turbanella hyalina Schultze. J. exp. mar. B i o l . Ecol. 4: 119-133. Gruendling, G.K. 1971. Ecology of the e p i p e l i c a l g a l commun-i t i e s i n Marion Lake, B r i t i s h Columbia. J. Phycol. 7: 239-249. Gulati, R.D. 1974. Laboratory methods i n secondary production. Hydro. B u l l . 8: 255-268. H a l l , D.J. 1964. An experimental approach to the dynamics of a natural population of Daphnia galeata mendotae. Ecology 45: 94-112. H a l l , D.J., W.E. Cooper, and E.E. Werner. 1970. An experi-mental approach to the production dynamics and structure of freshwater animal communities. Limnol. Oceanog. 15: 839-928. H a l l , K.J., P.M. Kleiber, and I. Yesaki. 1972. Heterotrophic uptake of organic solutes by micro-organisms i n the sediment. Mem. 1st. I t a l . I d robiol. Suppl. 29: 441-471. H a l l , K.J. and K.D. Hyatt. 1974. Marion Lake (IBP) - from bacteria to f i s h . J. Fish. Res. Board Can. 31: 893-911. Hamilton, A.L. 1965. An analysis of a freshwater benthic community with special reference to the Chironomidae. Ph.D. Thesis, Univ. of B r i t i s h Columbia. 94 pp. Hamilton, A.L. 1969. A method of separating invertebrates from sediments using longwave u l t r a v i o l e t l i g h t and fluorescent dyes. J. Fish. Res. Board Can. 26: 1667-1672. Harding, J.P. and W.A. Smith. 1974. A key to the B r i t i s h freshwater cyclopoid and calanoid copepods. Freshwater B i o l . Assoc. S c i e n t i f i c Publication No. 18. 55 pp. Hargrave, B.T. 1969. Epibenthic a l g a l production and community res p i r a t i o n i n the sediments of Marion Lake. J. Fish. Res. Board Can. 26: 2003-2026. Hargrave, B.T. 1970a. The e f f e c t of a deposit-feeding amphipod on the metabolism of benthic microflora. Limnol. Oceanog. 15: 21-30. Hargrave, B.T. 1970b. The u t i l i z a t i o n of benthic<microflora by Hy a l e l l a azteca (Amphipoda). J. Anim. Ecol. 39: v - 176 -Hargrave, B.T. 1970c. D i s t r i b u t i o n , growth, and seasonal abundance of Hy a l e l l a azteca (Amphipoda) i n r e l a t i o n to sediment microflora. J. Fish. Res. Board Can. 27: 685-699. Hargrave, B.T. 19 71. An energy budget for a deposit-feeding amphipod. Limnol. Oceanog.. 16: 99-103. Harring, H.K. and F.J. Myers. 1921. The r o t i f e r fauna of Wisconsin. Trans. Wisconsin Academy of Sciences, Arts and Letters 20: 553-663. Harring, H.K. and F.J. Myers. 1924. The r o t i f e r fauna of Wisconsin—II. A r e v i s i o n of the notommatid r o t i f e r s , exclusive of the Dicranophorinae. Trans. Wisconsin Academy of Sciences, Arts and Letters 21: 415-573. Harring, H.K. and F.J. Myers. 19 26. The r o t i f e r fauna of Wisconsin—III. A r e v i s i o n of the genera Lecane and Monostyla. Trans. Wisconsin Academy of Sciences, Arts and Letters 22: 315-423. Harring, H.K. and F.J. Myers. 1928. The r o t i f e r fauna of Wisconsin—IV. The Dicranophorinae. Trans. Wisconsin Academy of Sciences, Arts and Letters 23: 667-808. Harris, R.P. 1972a. Horizontal and v e r t i c a l d i s t r i b u t i o n of the i n t e r s t i t i a l harpacticoid copepods of a sandy beach. J. mar. b i o l . Ass. U.K. 52: 375-387. Harris, R.P. 1972b. Seasonal changes i n the meiofauna population of an i n t e r t i d a l sand beach. J. mar. b i o l . Ass. U.K. 52: 389-403. - 177 -Harris, R.P. 1972c. Seasonal changes i n population density and v e r t i c a l d i s t r i b u t i o n of harpacticoid copepods on an i n t e r t i d a l sand beach. J. mar. b i o l . Ass. U.K. 52: 493-505. Heip, C. 19 72. The reproductive potential of copepods i n brackish water. Mar. B i o l . 12: 219-221. Heip, C., N. Smol, and W. Hautekiet. 1974. A rapid method of extracting meiobenthic nematodes and copepods from mud and d e t r i t u s . Mar. B i o l . 28: 79-81. Heip, C , N. Smol, and V. A b s i l l i s . 1978. Influence of temp-erature on the reproductive potential of OnchoTaimus  oxyuris (Nematoda: Oncholaimidae). Mar. B i o l . 45: 255-260. Holme, N.A. and A.D. Mclntyre (eds.). 1971. Methods for the Study of Marine Benthos. IBP Handbook No. 16. Blackwell, Oxford. 334 pp. Hulings, N.C., and J.S. Gray. 1971. A manual for the study of meiofauna. Smithson. Contrib. Zool., 78: 1-83. Hulings, N.C. and J.S. Gray. 1976. Physical factors control-l i n g abundance of meiofauna on t i d a l and a t i d a l beaches. Mar. B i o l . 34: 77-83. Johannes, R.E. 1965. Influence of marine protozoa on nutrient regeneration. Limnol. Oceanogr. 10: 434-442. - 178 -Johannes, R.E. and K.L. Webb. 1970. Release of dissolved organic compounds by marine and freshwater invertebrates. In D. Hood (ed.), Organic Matter i n Natural Waters, pp. 257-273. Univ. of Alaska, College. Kaczynski, V.W., R.J. F e l l e r , J. Clayton and R.J. Gerke. 1973. Trophic analysis of juvenile pink and chum salmon (Oncor- hynchus gorbuscha and 0. keta) i n Puget Sound. J. Fish. Res. Board Can. 30: 1003-1008. Kajak, Z. and A. Kajak. 1975. Some trophic r e l a t i o n s i n the benthos of shallow parts of Marion Lake. Ekol. pol. 23: 573-586. Keen, R. 19 73. A p r o b a b i l i s t i c approach to the dynamics of natural populations of the Chydoridae (Cladocera, Crust-acea) . Ecology 54: 524-534. King, C.E. 1967. Food, age, and the dynamics of a laboratory population of r o t i f e r s . Ecology 48: 111-128. Kleiber, P.M. 1972. The dynamics of e x t r a c e l l u l a r , dissolved organic material i n the sediments of Marion Lake, B r i t i s h Columbia. Ph.D. Thesis, Univ. of C a l i f o r n i a , Davis. 93 pp. Kool, R. 1975. The ecology of the c i l i a t e d protozoa of Marion Lake, B r i t i s h Columbia. M.Sc. Thesis, Univ. of B r i t i s h Columbia, 55 pp. - 179 -Krebs, C.J. 1978. Ecology: The Experimental A n a l y s i s of D i s t r i b u t i o n and Abundance, 2nd E d i t i o n . Harper and Row, New York. 678 pp. Lasker, R., J.B.J. W e l l s , and A.D. Mclntyre. 1970. Growth, reproduction, r e s p i r a t i o n and carbon u t i l i z a t i o n of the sand-dwelling h a r p a c t i c o i d copepod, A s e l l o p s i s intermedia. J . mar. b i o l . Ass. U.K. 50: 147-160. Lee, J . J . , J.H. T i e t j e n , and J.R. Gar r i s o n . 1976. Seasonal switching i n the n u t r i t i o n a l requirements of N i t o c r a  t y p i c a , a h a r p a c t i c o i d copepod from s a l t marsh.Aufwuchs communities. Trans. Amer. Micro. Soc. 95: 628-637. Levinton, J . 1972. S t a b i l i t y and t r o p h i c s t r u c t u r e i n depo s i t - f e e d i n g and suspension feeding communities. Amer. Nat. 106: 472-486. McCauley, V.J.E. 1971 MS.' A corer f o r studying the v e r t i c a l d i s t r i b u t i o n of benthos i n r i v e r i n e and l a c u s t r i n e sediments. Unpublished manuscript i n Marion Lake F i l e , S p e c i a l C o l l e c t i o n s D i v i s i o n , Univ. of B r i t i s h Columbia L i b r a r y . McCauley, V.J.E. 1973. Mermithid (Nematoda) p a r a s i t e s of Chironomidae (Diptera) i n Marion Lake, B r i t i s h Columbia. J . I n v e r t . P a t h o l . 22: 454-463. Mclntyre, A.D. 1969. Ecology of marine meiobenthos. B i o l . Rev. 44: 245-290. - 180 -Mclntyre, A.D. and D.J. Murison. 1973. The meiofauna of a f l a t f i s h nursery ground. J . mar. b i o l . Ass. U.K. 53: 93-118. McLachlan, A., P.E.D. Winter, and L. Botha. 1977. . V e r t i c a l and h o r i z o n t a l d i s t r i b u t i o n of s u b - l i t t o r a l meiofauna i n Algoa Bay, South A f r i c a . Mar. B i o l . 40: 355-364. McQueen, D.J. 1969. Reduction of zooplankton standing stocks by predaceous Cyclops b l c u s p i d a t u s thomasi i n Marion Lake, B r i t i s h Columbia. J . F i s h . Res. Board Can. 26: 1605-1618. McQueen, D.J. 1976. P o r c e l l i o s p i n i c o r n i s Say (Isopoda) demography. I I . A comparison between f i e l d and la b o r a -t o r y data. Can. J . Zool. 54: 825-842. McQueen, D.J. and J.S. Carnio. 1974. A l a b o r a t o r y study of the e f f e c t s of some c l i m a t i c f a c t o r s on the demography of the t e r r e s t r i a l isopod P o r c e l l i o s p i n i c o r n i s Say. Can. J . Zool. 52: 599-611. Mann, K.H. 1969. The dynamics of aquatic ecosystems. Advances i n E c o l o g i c a l Research 6: 1-81. de March, B.G.E. 1977. The e f f e c t s of photoperiod and temper-ature on the i n d u c t i o n and te r m i n a t i o n o f , r e p r o d u c t i v e r e s t i n g stage i n the freshwater amphipod H y a l e l l a azteca (Saussare). Can. J . Zool. 55: 1595-1600. Marten, G.G. 1975 MS. The e f f e c t of grazing by a sediment feeding amphipod. Unpublished manuscript i n Marion Lake F i l e , S p e c i a l C o l l e c t i o n s D i v i s i o n , Univ. of B r i t i s h Columbia L i b r a r y . - 181 -Marten, G.G., P.M. K l e i b e r , and J.A.K. Reid. 1975. A computer program f o r f i t t i n g t r a c e r k i n e t i c and other d i f f e r e n t i a l equations to data. Ecology 56: 752-754. Mathias, J.A. 1971. Energy flow and secondary production of the amphipods H y a l e l l a azteca and Crangonyx richmondensis o c c i d e n t a l i s i n Marion Lake, B r i t i s h Columbia. J . F i s h . Res. Board Can. 28: 711-726. M i l l s , E.L. 1975. Benthic organisms and the s t r u c t u r e of marine ecosystems. J . F i s h . Res. Board Can. 32: 1657-1663. Monakov, A.V. 1972. Review of stud i e s on feeding of aquatic i n v e r t e b r a t e s conducted at the I n s t i t u t e of B i o l o g y of Inland Waters, Academy of Science, USSR. J . F i s h . Res. Board Can. 29: 363-383. Moore, G.M. 1939. A l i m n o l o g i c a l i n v e s t i g a t i o n of the microscopic benthic fauna of Douglas Lake, Michigan. E c o l . Monogr. 9: 537-587. Neish, I.C. 1971. Comparison of s i z e , s t r u c t u r e and d i s t r i -b u t i o n a l patterns of two salamander populations i n Marion Lake, B r i t i s h Columbia. J . F i s h . Res. Board Can. 28: 49-58. Pamatmat, M.M. 1968. Ecology and metabolism of a benthic community on an i n t e r t i d a l sand f l a t . I n t . Revue ges. Hydr o b i o l . 53: 211-298. Pea r l s t o n e , P. 1973. Food of damselfly l a r v a e i n Marion Lake, B r i t i s h Columbia. Syesis 6: 33-39. - 182 -P e j l e r , B. 1962. On the taxonomy and ecology of benthic and p e r i p h y t i c r o t a t o r i a . Zool. B i d r a g . , Uppsala. 33: 327-422. Pennak, R.W. 1963. Species i d e n t i f i c a t i o n of the freshwater Cyclopoid Copepoda of the United States. Trans. Amer. Micro. Soc. 82: 353-359. Perry, E. 19 74. The biomass and a c t i v i t y of benthic b a c t e r i a i n Marion Lake, B r i t i s h Columbia. M.Sc. Thesis, Univ. of B r i t i s h Columbia. 98 pp. P o u r r i o t , R. and M. Deluzarches. Recherches sur l a b i o l o g i e des r o t i f e r s . I I . Influence de l a temperature sur l a duree du developpement embryonnaire et post-embryon-n a i r e . Annales de Limnologie 7: 25-52. P r e j s , K. 19 70. Some problems of the ecology of benthic nematodes (Nematoda) of M i k o l a j s k i e Lake. E k o l . p o l . 18: 225-242. P r e j s , K. and A. Stanczykowska. 1972. S p a t i a l d i f f e r e n t i a t i o n and changes of zoomicrobenthos i n three Masurian lak e s . E k o l . p o l . 20: 734-745. P r o v a s o l i , K., K. S h i r a i s h i , and J.R. Lance. 1959. N u t r i t i o n a l i d i o s y n c r a s i e s of Artemia and T i g r i o p u s i n monoxenic c u l t u r e . Ann. N.Y. Acad. S c i . 77: 250-261. Quade, H.W. 1969. Cladoceran faunas a s s o c i a t e d w i t h aquatic macrophytes i n some lakes i n northwestern Minnesota. Ecology 50: 170-179. - 183 -Rao, C.G. 1967. On the l i f e - h i s t o r y of a new sand d w e l l i n g h a r p a c t i c o i d copepod. Crustaceana 13: 185-199. Sarkka, J . and L. P a a s i v i r t a . 1972. V e r t i c a l d i s t r i b u t i o n and abundance of the macro- and meiofauna i n the profundal sediments of Lake Paijanne, F i n l a n d . Ann. Zool. F e n n i c i 9: 1-9. S c h i n d l e r , J . 1971. Food q u a l i t y and zooplankton n u t r i t i o n . J . Anim. E c o l . 40: 589-595. Shan, R.K. 1969. L i f e c y c l e of a chydroid cladoceran, PTeuroxus d e n t i c u l a t u s B i r g e . Hydrobiologia 34: 513-523. S i b e r t , J . , T.J. Brown, M.C. Healey, B.A. Kask, and R.J. Naiman. 1977. Detritus-based food webs: e x p l o i t a t i o n by j u v e n i l e chum salmon (Oncorhynchus k e t a ) . Science 195: 649-650. S i e g e l , S. 1956. Nonparametric S t a t i s t i c s f o r the B e h a v i o r a l Sciences. McGraw-Hill, Toronto. 312 pp. Smirnov, N.N. 1962. Eurycercus l a m e l l a t u s (O.F. Muller) (Chydoridae, Cladocera): f i e l d observations and n u t r i t i o n . H ydrobiologia 20: 280-294. Smith, F.E. 1954. Q u a n t i t a t i v e aspects of population growth. In E.J. B o e l l (ed.), Dynamics of Growth Processes, pp. 277-294. P r i n c e t o n Univ. Press, P r i n c e t o n , N.J. Smith, K.L. 1973. R e s p i r a t i o n of a s u b l i t t o r a l community. Ecology 54: 1065-1075. Smith, K.L., K.A. Burns, and J.M. T e a l . 1972. In s i t u r e s p i r a t i o n of benthic communities i n C a s t l e Harbor, Bermuda. Mar. B i o l . 12: 196-199. - 184 -Sokal, R.R. and F.J. Rohlf. 1969. Biometry. The P r i n c i p l e s and P r a c t i c e of S t a t i s t i c s i n B i o l o g i c a l Research. W.H. Freeman and Co., San Fra n c i s c o . 776 pp. 14 Sorokin, J . I . 196 8. The use of C i n the study of n u t r i t i o n of aquatic animals. I n t e r n a t . Assoc. Theor. and Appl. Limnol., Comm. No. 16. 40 pp. Stachurska, T. 1975 MS. Ecology of c i l i a t e d protozoa i n Marion Lake, B r i t i s h Columbia. Unpublished manuscript i n Marion Lake F i l e , S p e c i a l C o l l e c t i o n s D i v i s i o n , Univ. of B r i t i s h Columbia L i b r a r y . Stanczykowska, A. 1966. Some methodical problems i n zoomicro-benthos s t u d i e s . E k o l . p o l . 16: 385-393. Stanczykowska, A. and M. Przytocka-Jusiak. 1968. V a r i a t i o n s i n abundance and biomass of microbenthos i n three Mazurian lake s . E k o l . p o l . 16: 539-559. S t a r r , R.C. 1964. The c u l t u r e c o l l e c t i o n of algae at Indiana U n i v e r s i t y . Amer. J . Botany 51: 1013-1044. S t e e l e , V.J. 196 7. Resting stage i n the reproductive c y c l e s of Gammarus. Nature (London) 214: 1034. Tanner, J.T. 1966. E f f e c t s of population d e n s i t y on growth ra t e s of animal populations. Ecology 47: 733-745. Taub, F.B. and A.M. D o l l a r . 1968. The n u t r i t i o n a l inadequacy of C h l o r e l l a and Ch1amydomonas as food f o r Daphnia pulex. Limnol. Oceanog. 13: 60 7-617. - 185 -Taylor, W.D. and J . Berger. 1976. Growth responses of co-h a b i t i n g c i l i a t e protozoa to various prey b a c t e r i a . Can. J . Zool. 54: 1111-1114. Thane-Fenchel, A. 196 8. D i s t r i b u t i o n and ecology of non-p l a n k t o n i c brackish-water r o t i f e r s from Scandinavian waters. Ophelia 5: 273-297. Vernberg, W.B. and B.C. C o u l l . 19 74. R e s p i r a t i o n of an i n t e r s t i t i a l c i l i a t e and benthic energy r e l a t i o n s h i p s . Oecologia (Berl.) 16: 259-264. Walters, C.J. and I.E. E f f o r d . 1972. Systems a n a l y s i s i n the Marion Lake IBP P r o j e c t . Oecologia (Berl.) 11: 33-44. Ware, D.M. 1972. Predation of rainbow t r o u t (Salmo g a l r d r i e r i ) : the i n f l u e n c e of hunger, prey d e n s i t y , and prey s i z e . J . F i s h . Res. Board Can. 29: 1193-1201. Wasilewska, B.E. 1973. Microfauna of a few e u l i t t o r a l h a b i t a t s of M i k o l a j s k i e Lake w i t h s p e c i a l c o n s i d e r a t i o n to the nematodes (Nematoda) . E k o l . p o l . 21: 57-72. Wetzel, R.G. 1975. Limnology. Saunders, Toronto. 743 pp. Whiteside, M.C. 1974. Chydorid (Cladocera) ecology: seasonal patterns and abundance of populations i n E l k Lake, Minnesota. Ecology 55: 538-550. Wilson, M.S. and H.C. Yeatman. 1959. H a r p a c t i c o i d a . In W.T. Edmondson (ed.), Freshwater B i o l o g y , 2nd e d i t i o n , pp. 815-861. John Wiley and Sons, N.Y. - 186 -Winterbourne, M.J. 1971. The l i f e h i s t o r i e s and t r o p h i c r e l a t i o n s h i p s of the T r i c h o p t e r a of Marion Lake, B r i t i s h Columbia. Can. J . Zool. 49: 623-635. Yeatman, H.C. 1959. Cyclopoida. In W.T. Edmondson (ed.), Freshwater B i o l o g y , 2nd e d i t i o n , pp. 795-815. John Wiley and Sons, N.Y. - 187 -Appendix I C a l c u l a t i o n o f . r f o r Micrometazoans - 188 -Data A n a l y s i s : When a population i s allowed to increase without r e s t r a i n t , the growth of the population at any i n s t a n t i s p r o p o r t i o n a l to the s i z e of the popu l a t i o n , or: N t = N e r t t o where N Q and N f c are the population numbers at time 0 and time t , e i s the base of n a t u r a l logarithms and r i s a constant known as the in n a t e , i n t r i n s i c , or maximum r a t e of population i n c r e a s e . S o l v i n g f o r r , we have: N t r = o t I f we l e t t = T, the minimum generation time, N m ( / ) r = o T Note th a t the f a c t o r N T / N q i n t h i s equation i s the net repro-d u c t i v e r a t e per generation. For protozoa, which m u l t i p l y by simple d i v i s i o n , t h i s f a c t o r i s 2/1 so the numerator on the r i g h t side of the equation becomes In 2 or 0.693 (Fenchel, 1968) . For micrometazoans such as r o t i f e r s , cladocerans, and copepods which undergo a growth phase and then s t a r t producing eggs or o f f s p r i n g , e i t h e r s i n g l y or i n c l u t c h e s , the s i t u a t i o n i s more complex. I f one l e t s the f a c t o r N T / N q equal 2 ( f o r - 189 -the micrometazoans which produce o f f s p r i n g one at a tim e ) , then the a c t u a l maximum r a t e of population increase i s under-estimated, because d i v i d i n g by T, the generation time, i m p l i e s t h a t a l l the next o f f s p r i n g of an i n d i v i d u a l w i l l be spaced e x a c t l y one generation time l a t e r . This i s of course not true because the time between o f f s p r i n g f o r almost a l l small animals w i l l be l e s s than the time i t takes to grow from egg to reproductive a d u l t . The d i f f i c u l t y i s the same f o r micrometazoans which produce eggs i n c l u t c h e s . For example, an animal might take 10 days to grow from egg to reproductive a d u l t and then might produce 5 egg clutches c o n t a i n i n g 8 eggs each, one c l u t c h every 5 days. I f we say t h a t the net reproductive r a t e i s 8, because t h a t i s the number of eggs produced a f t e r one genera-t i o n time (10 days), and c a l c u l a t e r on t h i s b a s i s , we underestimate i t s value because we d i s r e g a r d the 4 X 8 or 32 a d d i t i o n a l o f f s p r i n g which w i l l be added i n j u s t 20 days. One p o s s i b l e way to solve t h i s problem i s to determine the t o t a l l i f e s p a n (LS) of the animal and change N t to N L g or number of o f f s p r i n g produced over the e n t i r e l i f e s p a n . This would g i v e : r = l n N L S LS The d i f f i c u l t y w i t h t h i s f o r m u l a t i o n i s t h a t i t too would underestimate the true value of r because i t would give - 190 -the same value f o r an animal t h a t l i v e d 35 days and produced one l a r g e c l u t c h of 40 eggs on the 35th day as f o r an animal which l i v e d 35 days, producing 5 c l u t c h e s of 8 eggs every 5th day a f t e r day 10. C l e a r l y the l a t t e r case would have a higher value f o r r , because recruitment to the population would occur e a r l i e r . Heip (19 72) uses a compromise method. He c a l c u l a t e s an average generation time which equals (T + LS)/2. The equation f o r r then becomes: T '+• LS 2 Caughley and B i r c h (1971) discuss three d i f f e r e n t concepts of "rate of i n c r e a s e " . The f i r s t " r " i s the observed r a t e of increase of a n a t u r a l population c a l c u l a t e d as: In N -In No r = t t and i n c l u d i n g m o r t a l i t y caused by disease, p r e d a t i o n , e t c . The second type of r a t e i s " r , which i s the r a t e of population increase i m p l i e d by the p r e v a i l i n g schedules of f e c u n d i t y and s u r v i v a l . This r a t e i s c a l c u l a t e d from l i f e t a b l e data as: I n E l m r = x x E l m x x x E l m x x where 1 i s the p r o b a b i l i t y at b i r t h of a reproductive - 191 -i n d i v i d u a l s u r v i v i n g to age x, and m i s the mean number of reproductive o f f s p r i n g produced i n the age i n t e r v a l x. The method used by Heip (1972) gives an approximation of r as c a l c u l a t e d by Caughley and B i r c h . The t h i r d type of r a t e of increase i s 11 r " , the maximum or i n t r i n s i c r a t e of increase m of a population i n a s p e c i f i e d environment. According to the authors, t h i s r a t e i s best c a l c u l a t e d by measuring the r a t e at which a newly e s t a b l i s h e d population i n i t i a l l y i n -creases . A c l o s e r approximation to Caughley and B i r c h ' s r can be c a l c u l a t e d using Edmondson's (1968) g r a p h i c a l method. To use t h i s method a time s c a l e i s chosen and a l i n e repre-senting the l i f e span of a s i n g l e parthenogenetic female i s drawn. Using data from l a b o r a t o r y s t u d i e s , t h i s l i n e i s marked to show times when eggs are produced (or when an advanced embryo appears, i n the case of the b d e l l o i d r o t i f e r Dissotrocha) and when hatching occurs. Every time an o f f -s p r i n g i s produced, a new l i n e i s drawn below the o t h e r s , representing the l i f e s p a n and reproduction of the new i n d i v i -d u al. The process i s continued u n t i l a l a r g e simulated population i s produced. The population at any time can be determined by counting l i n e s i n a v e r t i c a l column and r i s c a l c u l a t e d (r = In N^-l n N /t) from numbers of animals i n two d i f f e r e n t columns o a f t e r the population age d i s t r i b u t i o n has s t a b i l i z e d . An advantage of t h i s method i s t h a t the f i n i t e b i r t h r a t e :(.B). - 192 -can be determined from the numbers of egg bearing animals i n one column and the t o t a l number of animals on that date. Once B has s t a b i l i z e d , the instantaneous b i r t h r a t e (b) can be c a l c u l a t e d f o r the simulated population. - 193 -Appendix I I I n t e r p r e t a t i o n of Radiotracer Feeding Experiments - 194 -The h y p o t h e t i c a l changes i n r a d i o a c t i v i t y of a group of 14 animals feeding on C l a b e l l e d food are shown i n Figure 32A ( a f t e r Edmondson and Winberg, 1971). Animals are placed i n t o , or r e c e i v e l a b e l l e d food at time t ^ . From t 1 to t 2 the animals' guts are f i l l i n g w i t h l a b e l l e d food, and at t 2 the f i r s t r a d i o a c t i v e faeces are egested and the f i r s t r a d i o a c t i v e carbon i s r e s p i r e d and excreted. The slope of the feeding curve from t ^ to t 2 i s a measure of i n g e s t i o n r a t e . The growth r a t e i s the slope of the feeding curve a f t e r the p o i n t (t.j) where the s p e c i f i c a c t i v i t y of the animals has reached the a c t i v i t y of the food, determined from a p l o t of s p e c i f i c a c t i v i t y of animals against time (Figure 3 2B). Unfortunately t h i s simple i n t e r p r e t a t i o n i s dependent upon a number,of assumptions, some of which are d i f f i c u l t to v a l i d a t e : 1. The food i s uniformly l a b e l l e d w i t h r a d i o i s o t o p e . 2. The food i s present i n excess and evenly d i s t r i b u t e d . 3. L a b e l l e d food does not gain or l o s e r a d i o a c t i v i t y during the experiment. 4. Animals feed on l a b e l l e d food as they would on u n l a b e l l e d food. 5. Animals pic k up r a d i o a c t i v i t y only by i n g e s t i n g food. 6. Animals feed continuously at a f i x e d r a t e and egest-i o n r a t e s are constant. 7. Animals do not r e s p i r e or excrete ingested r a d i o -a c t i v i t y i n the time i n t e r v a l t1 to t0 (Figure 32A, - 195 -Figure 32. Theoretical increase i n r a d i o a c t i v i t y of animals feeding on -^ 4C-labelled food, as DPM per i n d i v i -dual (Figure 32 A) and DPM per unit weight carbon (Figure 32 B). - 196 -B). R e s p i r a t i o n and e x c r e t i o n of r e c e n t l y a s s i m i l a t e d carbon begins at and proceeds at a constant r a t e . 8. Recently a s s i m i l a t e d carbon immediately enters the general carbon pool of the animal. In p r a c t i c e , few i f any r a d i o t r a c e r feeding experiments can meet a l l these c o n d i t i o n s . Perhaps assumptions 1, 2, 3, 4, and 5 can be v a l i d i n very c a r e f u l experimental p r e p a r a t i o n s , but assumptions 6, 7, and 8 r e l a t e to the animals' physiology and are u n r e a l i s t i c . 

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