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The ecology of the ciliated protozoa of Marion Lake, British Columbia Kool, Richard 1975

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THE ECOLOGY OF THE CILIATED PROTOZOA OF MARION LAKE, BRITISH COLUMBIA by RICHARD KOOL B.A., University of New Hampshire, 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF • MASTER OF SCIENCE i n the department o f X \ Zoology We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1975 In present ing th is thes is in p a r t i a l fu l f i lment of the requirements for an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that I fur ther agree that permission for extensive copying of th is thes is for scho la r ly purposes may be granted by the Head of my Department or by his representa t ives . It is understood that copying or pub l i ca t ion of th is thes is for f inanc ia l gain sha l l not be allowed without my wr i t ten permission. the L ibrary sha l l make it f ree ly ava i l ab le for reference and study. Department of The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 0-Abstract The population dynamics of the c i l i a t e d Protozoa i n Marion Lake 2 sediment are examined. Densities of c i l i a t e s range from 10-100/cm , 2 with the yearly mean being 51/cm . C i l i a t e density i s not correlated with r a i n f a l l , but i s correlated with temperature. However, when the data i s detrended, no correlations appear. The number of individuals and the number of species present i n a sample are correlated, A negative correlation i s found between c i l i a t e density and the populations i n t r i n s i c rate of increase at both 1 and £ meters depth. I t i s concluded that the c i l i a t e population cannot be controlled by food l i m i t a t i o n as the c i l i a t e s cannot influence the size of the b a c t e r i a l population, and the predation rate i s not large enough to have a regulatory influence on the c i l i a t e population. The c i l i a t e s make an energetic contribution to higher trophic l e v e l s , but i t probably unimportant when compared to that of the bacteria and microalgae. For deposit feeders, the c i l i a t e s are energetically unimportant. However, benthic meiofaunal predators such, as cyclopoid copepods and t h e i r n a u p l i i may- be supplied with a considerable amount of t h e i r daily energy needs by the c i l i a t e s . Table of Contents i i i Abstract. .. i i Table of Contents , i i i L i s t of Tables v L i s t of Figures v i The Relationship between C i l i a t e d Protozoa and th e i r Predators i n Marion Lake Abstract • 1 Introduction. .... 2 Methods 3 1. Radiotracer experiments , 3 2. Predator addition experiments 4 Results 5 1. Predator addition experiments... 5 2. Radiotracer experiments. 5 3. Energetic contribution of the c i l i a t e s to predators 11 Discussion , 12 Acknowledgements, , , 18 References , 19 The Population of C i l i a t e s i n Marion Lake Abstract ,. 22 Introduction 23 Methods 24 1. Sampling 24 2. Analysis 24 3. Slide preparation... 25 iv 4. Taxonomy 25 5 5. Physical parameters 26 Results.. * 26 1. General population data 26 2. Species composition 29-3. Ciliate populations and meteorological factors 35 4. Population growth data . . . 40 Discussion. 45 1. Food limitation hypothesis. 45 2. Predator limitation hypothesis 49-3. Conclusion • 49. Acknowledgements 52 References 53 V L i s t of Tables The Relationship Between C i l i a t e d Protozoa and t h e i r Predators i n Marion Lake I. Results of.Hyalella azteca addition experiments 6 I I . Percent of c i l i a t e population eaten per day by in d i v i d u a l predator groups 9 I I I . Correlation between c i l i a t e f i e l d density and predation rate........ 10 The Population of C i l i a t e s i n Marion Lake I. Taxonomic l i s t of species found i n Marion Lake 32 I I . Rank data for c i l i a t e s found at 1 meter 34 I I I . Minimum and maximum densities of c i l i a t e s reported i n the l i t e r a t u r e 37 IV. Correlations between c i l i a t e density and various environmental factors , 38 V. Detrended correlations between c i l i a t e density and various environmental factors, . 39 VI. Spectral correlation between c i l i a t e density and various physical factors 41 VII. I n t r i n s i c rate of increase of the c i l i a t e population at 1 meter 42 VII I . Values of r, b, and d, calculated from the c i l i a t e population at 1 meter • 43 IX. Correlation between i n t r i n s i c rate of increase and c i l i a t e density. 50 The Relationship Between C i l i a t e d Protozoa and thei r Predators i n Marion Lake, B r i t i s h Columbia Richard Kool I n s t i t u t e of Resource Ecology-University of B r i t i s h Columbia Contribution to the Canadian International B i o l o g i c a l Programme lb Abstract The c i l i a t e s make an energetic contribution to higher trophic levels, but i t i s probably unimportant when compared to that of the bacteria and microalgae. For deposit feeders, the ci l i a t e s are energetically unimportant, however, benthic meiofaunal predators such as cyclopoids and their nauplii may be supplied with a considerable amount of their daily energy needs by the c i l i a t e s . Based on the experiments performed, we cannot conclude that there is a density dependent predatory mechanism controlling the size of the c i l i a t e population. 2 Introduction C i l i a t e d protozoa have a cosmopolitan d i s t r i b u t i o n (Cairns and Ruthven, 1972), but reports of metazoans eating c i l i a t e s are uncommon. Maguire e_t ail, (1968) have demonstrated the importance of dipteran larvae eating c i l i a t e s i n Heliconia bracts. Gray (1952) observed a negative correla t i o n between chironomid and s i m u l i i d larvae and c i l i a t e numbers i n a B r i t i s h chalk stream. More recently, Addicott (1974) found the dipteran Wyeomyia sp. important i n determining the species d i v e r s i t y of the protozoan communities i n pitcher plants. Lawton (1970) has re-ported that instars 2 and 3 of Pyrfhosoma nymphula (Odonata: Zygoptera) eat Paramecium caudatum and Stylonychia sp. i n feeding experiments. Thane-Fenchel (1968) observed a few genera of predatory marine r o t i f e r s eating c i l i a t e s , while Straarup (1970) gave instances of predation on c i l i a t e s by marine t u r b e l l a r i a n s . Hopper and Meyers (1966) observed predation by marine nematodes. Sushkina e_t a l . (1968) have used paramecia as food for a l l stages of the cyclopoid copepod l i f e cycle. Monakov (1972), i n reviewing recent work on feeding of aquatic invertebrates, mentions a few groups which feed on c i l i a t e s , including bivalves, cyclo-poids, r o t i f e r s , and chironomids. I have performed a series of experiments concerned with examining the role predators have i n regulating the size of the c i l i a t e population, and with the energetic relationships between the c i l i a t e s and t h e i r predators. This work was performed as part of a large scale ecosystem study of Marion Lake, carried out under the auspices of the Canadian International B i o l o g i c a l Programme. Other work done on Marion Lake i s described by Efford and H a l l (in press). 3 Methods 1. Radiotracer experiments These experiments were conducted i n small (diameter = 2 cm) undis-turbed sediment cores taken from a depth of 1 m i n Marion Lake. The cores were transported from the lake to our laboratory with a minimum of d i s t u r -bance and allowed to stand for several days before use. Incubation was at either 5, 10, 15, or 20°C, whichever was closest to the lake tempera-ture. H y a l e l l a azteca (Amphipoda) was added to some cores to ensure the presence of t h i s grazer. A large number of healthy Paramecium bursaria (Ciliophora) were iso l a t e d from cultures and placed i n a small Stender dish with 2 ml of lake water. P. bursaria was chosen to be the tracer c i l i a t e as i t harbours photosynthetically active zoochlorellae, which become l a b e l l e d when incu-bated with H-^C03 added to the culture water. The dish with tracer and c i l i a t e s was sealed and placed i n the l i g h t at 20°C. P e r i o d i c a l l y , a few P_. bursaria were removed, rinsed and placed on a glass f i b e r f i l t e r to be counted for a c t i v i t y using l i q u i d s c i n t i l l a t i o n methods. In a check of the r i n s i n g procedures, i t was found that three rinse baths would re-move a l l but a very small amount of tracer outside of the c i l i a t e s . When the F. bursaria were la b e l l e d (greater than 100 cpm/individual) they were removed from the radioactive l i q u i d , rinsed, and placed on top of the core sediment at the desired density. I f a cold incubation was to be used, the c i l i a t e s were acclimated at the lower temperature for 2 hr. After the incubation period i n the sediment core (either 4 or 6 h r ) , the top 2 cm of mud and overlying water was removed from the core and placed i n a b o t t l e , 10 ml of buffered formalin added, and the sample quickly frozen. When the sample was to be examined, the b o t t l e was thawed and the organisms extracted using a sugar f l o t a t i o n method (M. Hoebel, pers. comm.). The extracted organisms were then stained with rhodamine-b and examined using a dissecting microscope with UV i l l u m i n a t i o n . The organisms were separated into taxonomic groups, rinsed, and placed on glass f i b e r f i l t e r s . In the case of small meiofaunal organisms, the f i l t e r s were put d i r e c t l y into Bray's solution. The larger organisms were ashed i n a tube furnace and the trapped using a toluene f l u o r (Burnison and Perez, 1974). The samples were counted using a l i q u i d s c i n t i l l a t i o n method. The a c t i v i t y of the sample was a d i r e c t i n d i c a t i o n of the number of labelled c i l i a t e s . eaten i n the incubation period. 2. Predator addition experiments In J u l y , 1972, 5 cm diameter cores were taken at a depth of I m, 1/3 of these cores remained controls, with only a th i n screen placed over the top to prevent immigration or emigration of macrofauna. To 1/3 of the cores were added 10 times the normal density of H_. azteca. The remaining cores were covered so that water could c i r c u l a t e , but no l i g h t could penetrate to the sediment surface. The cores were allowed to incubate for 45 days at a depth of 1 m. After the incubation period, the c i l i a t e s were removed and counted i n representative samples of the di f f e r e n t treatments and the control. Marten (1975) discussed the design of t h i s experiment further, and also described the radiotracer studies done after the incubation period. In August, 1972, I placed 40 ml of sieved surface sediment into each of three dishes. One remained a control and the others had five times the normal density of H_. azteca added. After 48 hr at 15°C, the c i l i a t e densities were determined and compared against the i n i t i a l values. A similar experiment was done in December, 1972. However, at that time, a small dish was used and ten times the normal density of H_. azteca was present as the treatment, with no macrofauna present in the control. In'May, 1973, I added 25 cyclopoid copepods to a 2 cm sediment core (this being five times the normal spring density of cyclopoids). After a five day incubation period, the number of c i l i a t e s in the core was determined, and the predation rate calculated from a radiotracer experi-ment (see section 1). Results 1. Predator addition experiments The f i r s t experiments were done by adding E. azteca to either intact cores or mixed sediment and allowing them to incubate for a varying number of days. In a l l cases, the number of c i l i a t e s present in the treatment was lower than in the controls (Table 1), but when a median test was performed (Sokal and Rolf, 1969), the treatments were a l l found to be insignificant. In the cyclopoid addition experiment, the treatment actually had more c i l i a t e s in i t than did the control, but again the treatment was not a significant one. 2. Radiotracer experiments The predation results can be broken into two groups; l ) a fall/winter Table I Results of Hya l e l l a azteca addition experiments, using 10 times the normal density. Data i s expressed as numbers of ciliates/cm^. Date Control Treatment August, 1972 123 134 105 108 September, 1972 39 34 December, 1972 26 27 27 16 group, and 2) a spring/summer group (Table 2, Fig. 1). The winter group had _H. azteca and cyclopoid copepods as the major predators, with the former the most important. Minor predators included nematodes, mites, cyclopoid n a u p l i i and l a t e instar chironomid larave. The only t u r b e l -l a r i a n found i n a l l the samples had eaten two labelled c i l i a t e s . The average predation rate expressed as percent of the population l o s t to predators per day was about 5%/day (Table 2). The spring group had a much higher predation rate than the winter group. During t h i s period, the major predators were the cyclopoid cope-pods (mainly Cyclops sp., M. Hoebel, pers. comm.), which ate an average of 14% of the c i l i a t e population/day. This figure corresponded to 65% of a l l the c i l i a t e s eaten i n t h i s time period. One d i f f i c u l t y with t h i s figure i s that i t i s an estimate of the cyclopoid population predation rate per core, however, the number of i n d i v i d u a l predators varied i n d i f -ferent cores. In most cases, a l l of the cyclopoids were counted for a c t i v i t y together. In the one case where the cyclopoids were counted i n d i v i d u a l l y for a c t i v i t y , only two out of eleven had eaten l a b e l l e d c i l i a t e s . H. azteca ate more c i l i a t e s i n the spring (5% of the population/day) than i n the f a l l (1.2% of the population/day). But the proportion of the t o t a l population i n the spring was l e s s , dropping from 40% of the t o t a l eaten/day i n the winter to 17%/day i n the spring. When the chironomid larvae were separated into early and l a t e i n s t a r stages, only the l a t e instars were found to have tracer i n them. They were probably deposit feeding i n the same manner as H_. azteca. In December, 1972 and February, 1973, I performed experiments to see To f a c e Page 8 Figure 1 Percent of total c i l i a t e s eaten per season by various predators, based on radiotracer experiments. j ! ° / 0 of total c i l iates eaten per season, ,;" I f a l l , w in ter , spr ing 8 Table & Percent of c i l i a t e population eaten per day by i n d i v i d u a l predator groups, with the t o t a l percent eaten per day for each experiment. harpact-acoid cyclo-poid nema-tode mite naup-l i i • chiron-omid amphi-pod tu r b e l -l a r i a n t o t a l % 24 Sept "72 1.3 0.4 1.7 12 Oct 0.72 1.5 0.72 0.72 2.2 5.7 14 Nov 2.4 1-2 2.4 6.0 14 Feb '73 1.9 1.9 1.9 1.9 0 3.8 11.0 15 March 1.9 1.9 3.8 7.6 8 May 18.0 ' 6.0 1.9 26.0 11 May 4.0 16.0 0 20.0 17 May 9.0 3.0 9.0 21.0 28 June 3.0 3.0 • 3.0 3.0 15.0 Table I I I Correlation of c i l i a t e f i e l d density (individuals/cm 2), and predation rate Date Density Predation 21 Sept '72 10 1.7% 12 Oct '72 30 5.7 14 Nov '72 30 6.0 14 Feb '73 40 11.4 15 March '73 65 7.6 8 May '73 80 26 11 May '73 80 20 17 May * 73 60 21 28 June '73 50 15 r = 0.81, p < .01 11 i f i t would be possible to induce higher predation rates by adding larger numbers of P_. bursaria to cores. In the December experiments, although fewer c i l i a t e s were eaten i n the low density cores than i n cores with f i v e times the number of c i l i a t e s , the predation rate was the same i n both cores (5%/day and 6%/day). This was owing to the predation of R. azteca which being a non-selective predator, removed only a fix e d propor-t i o n of the prey present. A l l of the predation experiments were done on lake sediment that had natural c i l i a t e population densities ranging from very low (20/cmz) to very high (80/cm ). I f some sort of density dependent regulatory mechanism was regulating the size of the c i l i a t e population, we would expect to see higher predation rates when the c i l i a t e populations were high, and lower predation rates when the population was low. Predation and c i l i a t e f i e l d densities at the time of experimentation were s i g n i f i c a n t l y corre-lated (r = 0.81, p 4. .01; Table 3). This res u l t i s contrary to the exper-imental results described above, and would imply some sort of density dependent predation acting on the c i l i a t e population. 3. Energetic contribution of the c i l i a t e s to predators Work has been done on the bioenergetics of the two major c i l i a t e predators i n Marion Lake; H. azteca and cyclopoid copepods. From the work of Mathias (1971) and Shushkina et al_. (1968) we can estimate the pot e n t i a l contribution of the c i l i a t e s to the d a i l y energy needs of these predators. The following calculations are based on the assumption of a single g c i l i a t e weighing 10 grams dry weight, and one gram of c i l i a t e s equalling 6000 c a l o r i e s . 12 Shushkina e_t a l . (1968) derived a regression that relates body weight of cyclopoid copepods to t h e i r O2 requirements: Q Q 2 = 0.134 W + 0 ' 8 4 , where O2 = ml 02/hour W = grams wet weight. The average cyclopoid i n Marion Lake benthos weighs 10 grams wet weight, and would consume 7 X 10 ^ ml 02/day. From Hargrave (1971) 1 ml 0^ = _3 4.8 c a l , so a cyclopoid would need about 3.57 X 10 cal/day. Assuming a 2 conservative predation rate of 4% of the c i l i a t e population i n a 3 cm 2 core/day/cyclopoid, and a c i l i a t e density of 80/cm , a single predator would eat 10 c i l i a t e s per day. This would equal 6 X 10 ^ cal/day, which i s equal to about 20% of the cyclopoids d a i l y energy need. As cyclopoid copepods have a very high assimilation e f f i c i e n c y (90%) , t h i s may be a r e a l i s t i c estimate of the energy contribution to them by the c i l i a t e s . Mathias (197l) has shown that during the warmer part of the year, H. azteca needs about 1 cal/day. I have shown that an i n d i v i d u a l H. azteca 2 can crop at most 4% of the c i l i a t e population'in a 3 cm core/day. This would equal 6 X 10 ^'cal/day, or about .06% of the enrgy needed d a i l y . However, Hargrave (1971) has pointed out that H. azteca has a very low assimilation e f f i c i e n c y (15%) so t h i s value must be a d d i t i o n a l l y lowered. Discussion In the Marion Lake benthos, a l l meiofauna with the exception of r o t i f e r s , tardigrades, and gastrotrichs, have been shown to be p o t e n t i a l predators on the c i l i a t e s . The most important of these are the cyclopoid 13 copepods. As these copepods are v i s u a l hunters who search and s t r i k e at moving objects, they could be s i g n i f i c a n t predators and could act i n a density dependent fashion when c i l i a t e numbers are high. However, although the c o r r e l a t i o n does exi s t between predation rate and f i e l d density, the predation rate at high prey densities i s not nearly enough to control the growth of the c i l i a t e population. This may indicate 1) that the cyclopoid predation a b i l i t y i s e a s i l y saturated at r e l a t i v e l y low c i l i a t e d e n sities, or 2) that the complexity of the environment makes hunting very d i f f i c u l t . So many refuges may e x i s t for the c i l i a t e prey that the predators can only s l i g h t l y respond to even high c i l i a t e densities. - I think that the l a t t e r explanation best f i t s the available data. M. Hoebel (pers. comm.)'has performed a feeding experiment with Cyclops sp., i n which he placed a few animals i n a dish with no sediment, and then added a large number of l a b e l l e d _P_. bursaria. He found that an i n d i v i d u a l cyclo-poid could eat 2 c i l i a t e s / h o u r . This figure of 24 c i l i a t e s / d a y i s more than twice the number I arrived at from the predation experiments i n natural sediment. Since Hoebel's experiment was done without refuges for the prey, i t may be that the complexity of the sediment surface offers substantial refuges for the c i l i a t e s from predators. H_. azteca has been reported by Hargrave (1970) to eat r o t i f e r s , as w e l l as microalgae and bacteria. This i s the f i r s t report of H_. azteca eating c i l i a t e s . As i s clear from the amount of energy i t gets from c i l i a t e s , H. azteca i s not gaining much by eating them. As a deposit feeder eating detritus with bacteria and microalgae, H. azteca w i l l probably eat a c i l i a t e only by accident. I t seems u n l i k e l y that they could actually hunt for c i l i a t e s , therefore i t i s also u n l i k e l y that H. azteca could have 14 much of an influence on the size of the c i l i a t e population. My data on chironomid feeding i s counter to that reported by MacCauley (Marion Lake Report, 1970) and Lawton (1970), and others. They state that the early i n s t a r s feed on c i l i a t e s . In a l l cases, the only larvae having tracer i n them were late i n s t a r classes, which probably are deposit feeding. However, as the number of chironomids seen with l a b e l l e d c i l i a t e s i s low, I may have missed early i n s t a r predation. The Halacarid mites are primarily predators, but according to Efford (pers. comm.) have not been known to eat c i l i a t e s . This would be due to the lack of i d e n t i f i a b l e remains i n the guts of the predators, i n p a r t i c u l a r as these mites suck t h e i r food out of the prey. The only d i r e c t observation of a nematode eating c i l i a t e s i s by Hopper and Meyers (1966). They observed juvenile Melonicholaimus sp. (a marine , nematode) feeding on c i l i a t e s which were growing next to a decomposing worm. They noticed a decrease i n number of c i l i a t e s and an increase i n the size of young worms. Perkins (1958) found that nematodes could survive longer i f grown i n culture medium containing bacteria and c i l i a t e s than i f kept i n pure sea water. Webb (1956), even though she includes nematodes as c i l i a t e predators, f a i l e d to see any dir e c t predation by t h i s group. In Marion Lake, a small number of nematodes were found to have eaten c i l i -ates. Turbellarians are r e l a t i v e l y uncommon i n Marion Lake, and probably are i n s i g n i f i c a n t as predators on c i l i a t e s . However, the one t u r b e l l a r i a n found i n the radiotracer experiments had eaten c i l i a t e s . This confirms Straarups (1970) observation that some turb e l l a r i a n s eat c i l i a t e s . Webb (1956) also mentions that rhabdocoels may eat c i l i a t e s . 15 In the only core where Pisidium (Mollusca) was found, i t appeared that one c i l i a t e was eaten. Pisidium i s reported to eat bacteria and algae (Efford and Tsumura, pers. comm.), and Monakov (1972) reports that "many Sphaerium and Pisidium draw small Infusoria into the mantle cavity and reject big ones when feeding on c i l i a t e d plankton." Fenchel (1969) implies that marine lamellibranchs must eat c i l i a t e s when eating sediment or siphoning surface water, but he had no evidence that t h i s was the case. Shushkina at a l . (1968) fed Paramecium to cyclopoid n a u p l i i as part of a study i n the bioenergetics of cyclopoid copepods. This study also indicates that c i l i a t e s are pot e n t i a l prey for the n a u p l i i . We are now able to refute Muus's (1967) contention that the c i l i a t e s do not play any traceable role i n the food chain leading to higher animals. Picken (1937) also mentions "The protozoa are ecol o g i c a l l y a very i n t e r -esting group inasumch as they have very few metazoan enemies... and t h e i r communities are not therefore linked up with metazoan forms". As t h i s study has shown, at least nine d i f f e r e n t groups of metazoa prey on c i l i a t e s . C i l i a t e s may make up an important part of the energy input i n the carniv-orous cyclopoid copepods, a point which was stressed by Monakov and Sorokin (1971). This study has ignored the role of predatory c i l i a t e s i n the possible regulation of the t o t a l c i l i a t e population. Predatory c i l i a t e s found i n Marion Lake are Dileptus sp., Lacrymaria sp., Loxophyllum sp., and Stentor spp. Due to the nature of these experiments, i t was impossible to examine the importance of these predators. From my population data, i t appears as i f 10% of the species of c i l i a t e s found and 9% of the individuals found at 1 m i n Marion Lake are predatory. This i s very s i m i l a r to Fenchel' 16 (1969) r e s u l t s , where he found about 10% of the c i l i a t e s he examined i n a marine i n t e r s t i t i a l environment to be predatory. There has been l i t t l e work done i n the role of predators i n regula-t i n g the size of natural populations of c i l i a t e s . The only f i e l d work of t h i s sort i s by Hairston (1967), examining the population dynamics of Paramecium au r e l i a i n a small seep i n a hardwood forest. He concluded that the death rate observed i n the population was constant, and the pop-u l a t i o n was responding to changes i n the d i v i s i o n rate. These changes i n d i v i s i o n rate, he concluded, were based upon varying levels of food. He maintains that since the "observed loss rates (were not) related to the density of paramecia at the start of the relevant observation periods", density dependent predation could not be invoked as the regulatory mecha-nism. Webb (1956) b r i e f l y states " c i l i a t e populations are apparently l i t t l e r e s t r i c t e d by the attack of metazoan predators". In the f a l l and winter, the c i l i a t e population i n Marion Lake i s 2 r e l a t i v e l y stable at about 25 c i l i a t e s / c m . The measured predation rate i s very clase to the population growth rate, 8%/day (Stachurska, 1975). When the water temperature i s low and l i g h t a v a i l a b i l i t y i s reduced by clouds and i c e , lake production i s reduced, and by a combination of a l l these factors ( i f growth rate and predation rate are the same) and low food a v a i l a b i l i t y , we would expect a stable population s i z e . L u c k i n b i l l (1973, 197A) has performed a series of experiments that i n d i r e c t l y test t h i s hypothesis. After examining the s t a b i l i t y properties of a Paramecium—  Didinium system, he concluded that "enrichment of predator prey systems creates i n s t a b i l i t y " . His studies have shown that a coexistence of pre-dator and prey with small predator-prey o s c i l l a t i o n s i s possible under 17 low food densities for the prey. This s i t u a t i o n may be what i s control-l i n g the c i l i a t e population during the winter, and i s not due to density dependent predation. In the summer, predation i s at least 2-3 times greater than i n the winter, but the growth rate of the c i l i a t e s i s almost 10 times greater than what i t was i n the winter. With the warmer temperatures the c i l i a t e growth rate goes up (Stachurska, 1975), and we could also expect the bac-t e r i a l growth rate to go up. With the c i l i a t e population seemingly unbound by predation, we would expect to see o s c i l l a t i o n s between c i l i a t e s and i t s b a c t e r i a l food, si m i l a r to what L u c k i n b i l l (197.3, 1974) found when he i n -creased the number of paramecia. However, Stachurska (pers. comm.) has shown that even at high c i l i a t e density, the b a c t e r i a l population i n the sediment i s not affected by c i l i a t e grazing. She concludes that she has not been able to show that the c i l i a t e populations are controlled by a food l i m i t a t i o n . I have not been able to show that the c i l i a t e s are con-t r o l l e d by a predatory mechanism. Based on the data of Stachurska, i t seems un l i k e l y that predation can have much of an influence on the c i l i a t e population at temperatures above 10°C. The population i n t r i n s i c rate of increase at 15°C i s r = 0.315, which i s a higher rate of increase than mortality due to predation. The maximum predation observed (20%/day) i s much lower than the p o t e n t i a l rate of growth which may be between 50-70%/day. However, a problem with the data i s that the growth rate of the population was measured i n the lab-oratory i n cultures with lake sediment. F i e l d conditions may give higher or lower values of r. Acknowledgements I am indebted to Dr. Ian Efford for the opportunity to work with the Marion Lake group. Ideas, advice and assistance were received from Drs. Gerry Marten, Teresa Stachurska, Ken H a l l , Pierre K l e i b e r , Ken Burnison, and Mr. Mike Hoebel and Rob Powell. 1 9 References Addicott, J.F. i Predation and prey community structure: An experimental study of the effect of mosquito larvae on the protozoan communities of pitcher plants. Ecology 55, 475-492 (1974) Burnison, B.K., Perez,'K.P.: A simple, method for the dry combustion of 1 4 C - l a b e l l e d materials. Ecology 55, 899-902 (1974) Cairns, J , Ruthven, J.A.: A study of the cosmopolitan d i s t r i b u t i o n of freshwater protozoa. Hydrobiologia 3_9_, 405-427 (1972) Efford, I.E., H a l l , K.J.: Marion Lake- an analysis of an ecosystem. Proceedings of the Royal Society of Canada (in press) Fenchel, T.: The ecology of marine microbenthos. IV. The structure and function of the benthic ecosystem, i t s chemical and physical factors, and the microfauna communities with specieal reference to the c i l i a t e d protozoa. Ophelia 1-182 (1969) Gray, E.: The ecology of the c i l i a t e fauna of Hobsons Brook, a Cambridge-shire chalk stream. J . Gen. Micro. 108-122 (1952) Hairston, N.G.: Studies on the l i m i t a t i o n of a natural population of Paramecium a u r e l i a . Ecology 48, 904-910 (1967) Hargrave, B.T.: An energy budget for a deposit feeding amphipod. Limnol. Oceanog. 16, 99-103 (1971) Hargrave, B.T.: The effect of a deposit feeding amphipod on the metabolism of benthic microflora. Limnol. Oceanog. _15, 21-30 (1970) Hopper, B.E., Meyers, S.F.: Observations on the bionomics of the marine nematode, Melonicholaimus ;sp. Nature 209, 899-900 ( 1966) 20 Lawton, J.H.: Feeding and food energy assimilation i n larvae of the damsel-f l y PyjrrJmr£Ojiia nympjnila_ (Sulz.) (Odonata: Zygoptera). J. Anim. Ecol. 39, 669-689 (1970) L u c k i n b i l l , L.S.: Coexistance i n laboratory populations of Paramecium a u r e l i a and i t s predator, Didinium nasutum. Ecology 5_4, 1320-1327 (1973) L u c k i n b i l l , L.S.: The effects of space and enrichment on a predator-prey system. Ecology 55, 1142-1147 )1074) Maguire, B., Belk, D., Wells, G.: Control of community structure by mosquito larvae. Ecology 4£, 207-210 (1968) , Marten, G.G.: The effect of grazing by a sediment feeding amphipod. (unpublished, 1975) Mathias, J.A: Energy flow and secondary production of the amphipods Hyalella azteca and Crangonyx richmondensis occidentalis i n Marion Lake, B.C. J. Fish. Res. Bd. Can. 28, 711-726 (1971) Monakov, A.V.: Review of studies on feeding of aquatic invertebrates conducted at the I n s t i t u t e of Biology of Inland Waters, Academy of Science, USSR. J. Fish. Res. Bd. Can. 29_, 363-383 (1972) Monakov, A.V., Sorokin, Y.I.: Role of Infusoria as food of Cyclopoida of Rybinsk Reservoir. Trans. Inst. B i o l . Inland Waters, Acad. S c i . USSR 21, 37-42 (1971) Muus, B . J . : The fauna of Danish estuaries and lagoons. Medd. Dan. Fisk. Hauv. 5, 9-316 (1967) Perkins, E . J . : The food relationships of the microbenthos with p a r t i c u l a r reference to that found at Whitestable, Kent. Ann. Mag. Nat. H i s t . 12, Ser. 10, 37-42 (1958) 21 Picken, L.E.R.; The structure of some protozoan communities. J . Ecol. 25, 368-384 (1937) Shushkina, E.A., Anisimov, S.I., Klekowski, R.Z.: Calculation of production e f f i c i e n c y i n planktonic copepods. P o l . Arch. Hydrobiol. 15, 251-261 (1968) Sokal, R.R., Rolf, S.F.: Biometry, 775pp. San Francisco, C a l i f o r n i a : W.H. Freeman and Company 1969 Stachurska, T: The ecology of c i l i a t e d protozoa i n Marion Lake, B.C. I. (unpublished, 1975) Straarup, B-J.: On the ecology of turb e l l a r i a n s i n a sheltered brackish water bay. Ophelia ]_, 185-216 (1970) Thane-Fenchel, A.: The ecology and d i s t r i b u t i o n of nonplanktonic r o t i f e r s from Scandinavian waters. Ophelia 5_, 273-297 (1968) Webb, M.G.: An ecological study of brackish water c i l i a t e s . J . Anim.. Ecol. 25, 148-175 (1956) The Population of C i l i a t e s i n Marion Lake, B r i t i s h Columbia Richard Kool I n s t i t u t e of Resource Ecology University of B r i t i s h Columbia Contribution to the Canadian International B i o l o g i c a l Preogramme 22b Abstract The population dynamics of the c i l i a t e d Protozoa i n Marion Lake 2 sediment are examined. Densities of c i l i a t e s range from 10-100/cm , 2 with the yearly mean being 51/cm . C i l i a t e density i s not correlated with r a i n f a l l , but i s correlated with temperature. However, when the data i s detrended, no co r r e l a t i o n appears. The number of individuals and the number of species present i n a sample are correlated. A negative corre l a t i o n i s found between c i l i a t e density and the populations i n t r i n s i c rate of increase at both 1 and 4 meters depth. I t i s concluded that the c i l i a t e population cannot be controlled by food l i m i t a t i o n as the c i l i a t e s cannot influence the size of the b a c t e r i a l population, and the predation rate i s not large enough to have a regulatory influence on the c i l i a t e population. The mechanism of population regulation i n c i l i a t e populations i s s t i l l unkown. Introduction. As part of the large scale ecosystem study of Marion Lake (see Efford, 1967, H a l l and Hyatt, 1975, and Efford and H a l l , i n press, for additional information about Marion Lake), I have studied the temporal and s p a t i a l d i s t r i b u t i o n of the c i l i a t e d Protozoa i n the s u b l i t t o r a l sediment. The major alms of this research were to determine the role of the c i l i a t e s i n the sediment ecosystem, and to examine mechanisms c o n t r o l l i the dynamics of the c i l i a t e s populations. Methods 1 • Sampling Mud samples for quantitative studies of c i l i a t e density were taken using a gravity core designed by M. Hoebel. The core has an inside diameter of 2 cm., and the top 2 cm. of sediment plus the overlying water was saved for examination. Ten cores were taken at every s t a t i o n , with each station being an area enclosed by a c i r c l e (diam. 2 meters) around a fixed point. A l l ten samples were mixed together i n a b o t t l e and taken back to the laboratory for enumeration. Stations were along an east-west transect at the northern end of the lake, at depths of 1, 2, and 4 meters depth. 2 . Analysis In the lab, the j a r s with sediment and water were kept at lake temperatures, and the sediment allowed to s e t t l e for at least one hour before analysis was begun. The supernatant water was carefully pipetted off leaving only .25 cm. of water. The sediment was then thoroughly mixed and 5 ml. was removed The sample was then placed into an extraction column made of dif f e r e n t sized Nitex f i l t e r s ( 405 um, 253 urn, and 130 urn). The funnels were arrainged i n a seri e s , and the sediment washed through with 35 ml. of f i l t e r e d lake water. The f i l t r a t e was collected i n a beaker and the volume determined. C i l i a t e s were counted by removing 0.5 ml. of the mixed f i l t r a t e with a mouth pipette, to a 1 ml. hemispherical glass depression s l i d e w e l l . Eighteen 0.5 ml. samples were counted. The number of c i l i a t e s in each depression was determined, and each in d i v i d u a l i d e n t i f i e d and 25 removed for l a t e r s l i d e preparation. Using this method, we could estimate the number of c i l i a t e s i n our o r i g i n a l sample of 5 ml. However, because there i s good evidence that i n mud bottom sediments, at least 90% of a l l the c i l i a t e s are i n the top centimeter (Cole, 1955, Goulder, 1971a), and as we wished to express 2 our results i n ciliates/cm , we divided the answer by 2.5 rather than by 5. 3• Slide preparation The isolated c i l i a t e s were concentrated with a fine micropipette and placed on a clean glass s l i d e . The Nigrosin- HgC^- formalin s t a i n - f i x a t i v e (Borror, 1968a) was used, and the sl i d e s were dehydrated i n the normal fashion. The finished s l i d e s were then examined and the c e l l s were i d e n t i f i e d , measured, and the contents of t h e i r food vacuoles recorded. 4^  Taxonomy A l l c i l i a t e s were examined l i v e using a Wild M-5 dissecting microscope. Most magnifications were 40X, thus small organisms were hard to i d e n t i f y . Unlike most phytoplankters, benthic algae or meiofaunal organisms, c i l i a t e s do not, i n general, withstand f i x a t i o n very w e l l . For every type of f i x a t i v e , there w i l l be a different proportion of the c i l i a t e fauna destroyed. Therefore complete morphometric data i s not available for a l l species. The i d e n t i f i c a t i o n from l i v e materials makes accurate i d e n t i f i c a t i o n to species very d i f f i c u l t i n most cases. In some genera, species are easy to di s t i n g u i s h , such as Paramecium, Spirostpmum and Blepharisma. In many smaller organisms (e.g. Coleps, Metopus and many small hypotrichs) genera can e a s i l y be assigned, but s p e c i f i c i d e n t i f i c a t i o n i s d i f f i c u l t . 26 F i n a l l y , i n some genera (e.g. Prorodon) taxonomy i s not clear. Unless the species was c l e a r l y i d e n t i f i e d , the generic name i s used only. The monograph by Kahl (1930-1934) was used as the basis of the nomenclature. 4 . Physical parameters Continuous temperature records were kept at 1 and 4 meters depth by the use of Ryan temperature recorders.Precipitation ; data was taken from the records of the UBC Research Forest Spur #17, located on a ridge about two mile from Marion Lake. Results 1. General population data The trend of the population at 1 meter i s clear, with two population maxima during the year. The f i r s t maxima was at the end of May, with the tendency for the peak densities during the summer to be less than the peak at the end of May (Fig. 1). The population density remained low during the f a l l and early winter u n t i l the ice l e f t the lake i n early Febuary. At that time the population "bloomed", and then declined, only to r i s e again i n May back to the cha r a c t e r i s t i c summer density. The mean density. 2 2 of c i l i a t e s at 1 meter i s 50/cm , with a range of 6/cm i n l a t e September 2 to a high of 100/cm i n early June. The population trends of important species at 1 meter show s i m i l a r trends, with high densities i n spring and summer, and low densities i n f a l l and winter (Fig. 2). The 4 meter population also shows a clear increase i n the early summer, but the number of c i l i a t e s seems to o s c i l l a t e throughout the f a l l and never reaches the low densities of the 1 meter population i n winter. *3 To face Page 27 Figure 1 Population dynamics of c j l i a t e s at 1 meter depth i n Marion Lake, units expressed as c i l i a t e s / c m . Bars i n d i c a t e 95% confidence l i m i t s of sample To face Page 28 Figure 2 Population dynamics of^golepsMetropus, 'Prorodon and Paramecium bursaria at 1 meter depth., i n Marion Lake, units expressed as ciliates/cm2. 29 A ."bloom" at 4 meters i n Febuary i s s i m i l a r to the 1 meter bloom (Fig. 3). 2 Themean density of c i l i a t e s ' a t 4 meters i s 52/cm , with a range of 2 2 13/cm i n l a t e July to 96/cm i n early May (. F i g . 4). 2, Species composition , Thirty two genera of c i l i a t e s were found i n Marion Lake. Of these, the most common were Coleps, Prorodon and an unkown c i l i a t e (put i n the Gymnostomatida, but possibly Cinetochilum sp.). Coleps contributed about 30% of the t o t a l number of c i l i a t e s found at 1 meter (Tables 1 and 2). Following the scheme of Grabaka (1971), the c i l i a t e s can be c l a s s i f i e d into four groups of species: 1) very frequent- found i n 51-100% of the samples 2) frequent - found i n 21-50% of the samples 3) rare - found i n 11-20% of the samples 4) very rare - found i n <^10% of the samples. Based on this scheme, only f i v e species of c i l i a t e s were very frequently found i n Marion Lake (Coleps, Prorodon, Unid. gymnostome, Metopus, and an Unid. hypotrich). These species contributed most to the o v e r a l l v a r i a b i l i t y of the population at 1 meter (Fig. 2). Grabaka (1971) found a s i m i l a r number of frequent species i n the f i n g e r l i n g ponds she studied (Coleps, Prorodon, Cinetochilum, Uroleptus and Aspidisca). About 50% of the species found i n Marion Lake were very rare (Fig. 5). These species were always found i n low numbers and do not indivudually have a large impact on the size of the c i l i a t e population. This i s also s i m i l a r to Grabaka's (1971) data, where she found 50% of the species to be very rare. There i s a correlation between the number of individuals and numbers of species present at 1 meter i n Marion Lake (r=.55, p^.,01). This would indicate that as the number of c i l i a t e s increases, more rare species are To f a c e Page 30 Figure 3 Population dynamics of the c i l i a t e s at 4 meters depth i n Marion Lake, units expressed as c i l i a t e s / c m 2 . Bars indicate 9.5% confidence l i m i t s for the sample. To face Page 31. Figure 4 Population dynamics of Coleps and Metopus at 4 meters i n Marion Lake, units expressed as c i l i a t e s / c m z • 32 Table I Taxonomic l i s t of species found i n Marion Lake Order Gymnostomatida Prorodon spp. Prorodon v i r i d i s  Coleps spp. Dileptus spp. Holophrya sp. Loxophyllum sp. Mesodinium sp. Lacrymaria sp. Placus sp. Loxodes magnus  Nassula sp. Order Hymenostomatida Tetrahymena sp. Paramecium a u r e l i a P_. caudatum P_. bursaria  Frontonia e l l i p t i c a F_. accuminata l e u c a s  Monochilum frontatum Cinetochilum margaritaceum Order O l i g i t r i c h i d a Strombidium sp. Ha l t e r i a c h l o r e l l i g e r a Order P e r i t r i c h i d a V o r t i c e l l a sp, E p i s t y l i s sp. Order Heterotrichida Spirostomum ambiguum S. minor S. teres  Stentor r o e s e l i S_. mul l e r i S. coerulus  Metops spp. Blepharisma muscorum  Bursaria sp. Condylostoma sp. Order Odontostomatida Caenomorpha sp. Order Hypotrichida Euplotes sp. 8 x y t r i c h a sp. Stylonychia mytilus  Parurostyla weissei  Uroleptus violaceus  Aspldisca sp. xHolostlcha sp. Table I I Rank data for c i l i a t e s found at 1 meter i n Marion Lake Rank Name Number % of Total found 1 Coleps 580 27.8 2 unid. gymnostome 218 10.4 3 Prorodon 206 9.9 4 unid. hypotrich 150 7.2 5 Metopus 132 6.3 6 Paramecium bursaria 73 3.5 7 Loxophyllum 61 2.9 8 Frontonia leucas 51 2.4 9 unid. gymnostome #2 44 2.1 10 Holophrya 42 2.0 11 Spirostomum 36 1.7 12 Blepharisma muscorum 34 1.6 13 Lacrymaria 34 1.6 14 Stentor 33 1.6 15 Dileptus 30 1.4 16 V o r t i c e l l a 30 1.4 17 Stromidium 28 1.3 18 Aspidisca 25 1.2 19 Spirostomum minor 23 1.1 20 Stentor igneus 22 1.0 21 unid. hymenostome 19 .92 22 Paramecium aure l i a 19 .92 23 Loxodes 18 ,90 24 Spirostomum teres 18 .89 25 unid. heterotrich 16 .78 26 Spirostomum ambiguum 15 .71 27 Uroleptus violaceus 12 .56 28 Holosticha 11 .51 29 Frontonia accuminata 9- ,45 30 F. e l l i p t i c a 8 ,36 31 Ha l t e r i a c h l o r e l l i g e r a 7 .35 32 Caenomorpha 7 .35 33 Nassula 7 .35 34 Homalozoon 6 .29 35 Parurostylaxweissei 5 .24 36 unid. pleuronematine 5 .24 37 Tetrahymena 4 .21 38 Euplotes 4 .21 39- Blepharisma 4 .21 40 . Bursaria 3.4 .16 41 unid. hymenostome #2 3 .15 42 Strombidium 2 .11 35 added to the enumeratable population. There i s also a correlation between the number of Coleps and the t o t a l number of c i l i a t e s (r=.75, p< .01), number of Prorodon and number of c i l i a t e s (r=.61, p< .01), and Metopus and the number of c i l i a t e s (r=.5, p<.01). 3 . C i l i a t e populations and meteorological factors The c i l i a t e population i n Marion Lake i s s i m i l a r to other c i l i a t e populations, i n that the densities remain roughly within an order of magnitude less than the highest reported value (Table 3). Given the potential rate of increase of the c i l i a t e s (Fenchel, 1968, Stachurska, 1975), these populations vary l i t t l e throughout the year. One possible way to evaluate patterns we saw i n population dynamics was to look for correlations between physical factors such as temperature and r a i n f a l l , and c i l i a t e density. No correlation exists between c i l i a t e density and r a i n f a l l , as reported by Hairston (1968). A positive correlation however exists between c i l i a t e density and temperature at 1 meter (Table 4). By using a modified sign test (Marten, pers. comm.), we can examine the short term correlation between population density and temperature. In the Marion Lake data, there was no short term correlation between these two variables (Table 5), Temperature may affect primary productivity (Greundling, 1971) and t o t a l benthic respiration (Hargrave, 1969), but i t was not a primary factor influencing the c i l i a t e populations. This compares we l l with Fenchel's (1969) data, as he also found no correlation between c i l i a t e density and temperature, either i n the long or short run. This lack of correlation might be expected, however, as most ecological factors w i l l involve some lag periods before the population i s able to To f a c e Page 36 Figure 5 D i s t r i b u t i o n of species found i n samples i n Marion Lake 2 0 -1 8 -14-10-6-2 -1 4 -1 2 -1 0 -CO 8 -spec 6 -H— o 4 -number 2 -1 Meter 36 2 Meters 18-14-1 0 -6 -4 Meters "^3 10 20 3 0 4 0 5 0 60 70 8 0 9 0 100 ° / Q samples found 37 Table I I I Minimum and maximum densities of c i l i a t e s reported i n the l i t e r a t u r e , values are the maximum reported i n that paper. Single Author Density Location Goulder (1971a) Grabaka (1971) Fenchel (1969) Fenchel (1975) Pieczynska (1972) A r l t (19-73) Borror (1963)-Moore (1939)-Kool (present study). 2500-8000/cm2 500-5000/cm2 900-4000/cm2 60-100/cm2 30-r550/cm2 20-200/cm2 54/cm2 51/cm2 10-100/cm2 Eutrophic lake, 3m, England F e r t i l i z e d f i s h pond, Poland I n t e r s t i t i a l sand beach Denmark A r c t i c tundra pond Alaska, USA E u l i t t o r a l eutrophic lake, Poland Subtidal i n t e r s t i t i a l sand, Germany I n t e r t i d a l sand, F l o r i d a , USA Anaerobic profundal muck, Michigan, USA S u b l i t t o r a l oligotrophic lake, B.C., Canada Table IV Correlation co e f f i c i e n t s (Spearman's r') between c i l i a t e density and various environmental factors. Factor Depth r' n P Temperature 1 meter ,45 51 <.01 Temperature 4 meters .18 20 n.s. R a i n f a l l 1 meter .2 25 n.s. R a i n f a l l 4 meters .06 23 n.s. Table .V Detrended (sign test) correlations between c i l i a t e density and various physical factors (correlation as chi-square) Factor Depth n P Temperature 1 meter .72 51 n.s. Temperature 4 meters .06 20 n.s. R a i n f a l l 1 meter 1.5 25 n.s. R a i n f a l l 4 meters 3.86 23 n.s. 40 respond to the environmental change. I have examined the importance of time lags by using spectral correlation analysis on detrended data (data which has had a t h i r d degree poynomial f i t t e d through i t ) (Fig.6). The correlation i s done on the matched pairs of residuals from the polynomial and the correlation can be performed with any lag period of one variable desired ( Marten, pers. comm., Blackman and Tukey, 1958). There was no correlation between c i l i a t e d protozoan density and either temperature, r a i n f a l l or lake discharge rate, at any lag period (Table 6). S i m i l a r l y , when spectral analysis was done on the data of Fenchel (1969), no lagged correlations appeared between c i l i a t e density and temperature. 4,. Population growth data Tables 7 and 8 give the calculated values of r , the population i n t r i n s i c rate of increase f o r 1 and 4 meters. The equation N =N e r t t ° was used to calculate the value of r between the two sample dates, N o and Nt» The i n t r i n s i c rate of increase i s made up of two components, the b i r t h rate b, and the death rate d. From Kool (1975), I can estimate the predation rate (equal to d) for various times of the year. I f r and d are known, then the b i r t h r a t e can be calculated, b=r+d (Table 7). The b i r t h r a t e calculated for the f i e l d data can then be compared with the data of Stachurska (1975) for c i l i a t e s grown i n the laboratory i n lake sediment at different temperatures. Table 8 gives the value for r, b, and d of the f i e l d data (when r i s p o s i t i v e ) , and then compares those values with Stachurska's at the equivalent temperature. A l Table VI Spectral correlation between c i l i a t e density and various physical factors (correlation i s Product-moment r) Factor Depth r n p Temperature 1 meter .lA 51 n.s. R a i n f a l l 1 meter -.18 25 n.s. Table VII I n t r i n s i c rate of increase (r) for the c i l i a t e population at 1 meter i n Marion Lake. Date r 8 May '72 -.015 18 May .024 25 May .12 30 May .089 8 June -.02 24 June -.05 30 June -.028 7 July .074 16 July -.11 26 July .083 4 August .022 18 August -.024 24 August -.086 3 September -.097 18 September .05 2 October -.054 19 October .074 30 October .003 27 November -.015 29 December .003 12 January '73 •T.OI 26 January .035 14 Febuary .06 27 Febuary ^.034 14 March ^.031 4 A p r i l .03 18 A p r i l -.02 30 A p r i l .105 7 May r.04 18 May .04 25 May -.016 Table VIII Values of r, b, and d calculated from the ciliate population at 1 meter in Marion Lake, contrasted with the lab data from Stachurska (1975). T is generation time in days.. Field data Dates Temp. r b d T b T 25-30 May, '72 15 9C. .12 .25 ,13 2.7 - .32 2,2 8-16 July 15 °C .07 ,15 .08 4.5 ,32 2.2 26 July-4 August 20°C .08 .17 .08 4.1 .51 1.4 18 September-2 October 10°C .06 .09 .03 8.1 .19 3.7 19-30 October 5°C .07 .11 .03 6.5 .12 5.6 14-27 Febuary, '73 5°C .06 .14 .08 5.1 .12 5.6 30 Aprils May 10°C .11 .21 .10 3,3 ,19- 3,7 To face Page 44 Figure 6 An example of a t h i r d degree polynomial f i t t e d through, the temperature data for May, June and J u l y , 1972. 45 Discussion 1 . Food l i m i t a t i o n hypothesis of population regulation After a review of the l i t e r a t u r e regarding population regulation of the c i l i a t e d Protozoa, i t seems clear that the general consensus of workers i n the f i e l d i s that food l i m i t a t i o n i s the most l i k e l y factor involved. Hairston (1968) feels that food l i m i t a t i o n i s the prime factor for two reasons; 1) that the dates of the major population peaks i n his study occur at a l l times of the year (as happens i n Marion Lake), thus eliminating weather as an important factor, and 2) the observed loss rate i n the population i s independent of density at the s t a r t of the observation period, thus eliminating the density dependent predation argument. He found that the population increases were at times associated with r a i n f a l l , and he could duplicate this effect by watering an area with a garden hose. The increase i n density of Paramecium was due, he maintains, to the presence of more food carried by the water from the surrounding s o i l to the small seep he studied. Gray (1952) also reported that the c i l i a t e s were found to "increase i n numbers after heavy rains or during prolonged drought, when the banks (of the stream) tend to crumble." He f e l t that the c i l i a t e population was regulated by the quality and quantity of bacteria i n the water, but that they are "made available as food by c l i m a t i c conditions..." Johnson (1941) b r i e f l y reports that "the studies (of protozoan population growth) seems to indicate that a depletion of the food supply i s more important as a l i m i t i n g factor i n population growth than are waste products." Grabaka (1971) and Goulder (1971a) imply that food i s the most important factor i n determining the size of c i l i a t e populations. Grabaka (1971) 46 found the highest densities of c i l i a t e s i n f i n g e r l i n g ponds to which the greatest amount of f e r t i l i z e r had been added, while the lowest densities were found i n the control ponds. Goulder (1971a) states that the eutrophic condition of one lake studied was the cause of the greater c i l i a t e density found there than i n a less eutrophic pond. Pieczynska (1972) reports that after a large mass of planktonic algae was washed up on a sandy shore of a Po l i s h lake, the c i l i a t e 2 2 population increased from 292/10 cm to 2880/10 cm i n three days. This i s a population growth rate of .76, with a generation time of .9 days; Stachurska (1975) found a maximum mean generation time of 1.03 days for c i l i a t e s growing at 25°C. Pieczynska (1972) also states that after a short time, the algae had been decomposed and the numbers of c i l i a t e s decreased. Fenchel (1969) , i n the most s i g n i f i c a n t study on the ecology of the c i l i a t e s done to date does not d i r e c t l y adress the question concerning what factors control the size of the microfaunal populations. However, he does indicate his preference for the food l i m i t a t i o n hypothesis i n a number of ways. In his discussion of laboratory ecosystems, a l l references to blooms of c i l i a t e s are associated with descriptions of diatom or bacteria blooms, and never with the decrease i n number of predators, or a decrease i n t h e i r rate of feeding on the c i l i a t e s . Fenchel (1968) demonstrates how the i n t r i n s i c rate of increase (r) of Aspidisca varies with concentration of food. This would indicate that the growth rate of the population i s dependent on the food supply, which i s contrary to the results of Stachurska (1975). She found that increasing the amount of bacteria offered to Stylonychia growing i n lake sediment only increased the carrying capacity of the sediment, but 47 did not increase the growth rate of the c i l i a t e s . However, Fenchel's work was done at very high concentrations of bacteria growing i n proteose peptone, while Stachurska's was done under more r e a l i s t i c conditions with much lower concentrations of food. Fenchel (1969) concludes that "the growth rate of the populations are lower than t h e i r p o t e n t i a l rate i n pure culture", and t h i s i s probably due to food l i m i t a t i o n . Stachurska (1975) performed experiments examining the possible role of food l i m i t a t i o n i n regulating the population of c i l i a t e s i n Marion Lake. She found that only 2% of the t o t a l bacteria present i n the lake were available for consumption by the c i l i a t e s . After l a b e l l i n g sediment 14 bacteria with C-glucose, she allowed either 20 or 50 c i l i a t e s to graze on 0.1 ml of the labeled sediment. Each day she she determined the dpm/ in d i v i d u a l c i l i a t e . After four days, she removed a l l the c i l i a t e s , and then added the o r i g i n a l number back to the already grazed sediment and repeated her procedure. She found much less r a d i o a c t i v i t y i n the l a t t e r groups as compared to the former. The consumption rate (of radioactive material) declined 37% i n the sample with 20 c i l i a t e s , and declined 61% i n the sample with 50 c i l i a t e s . She concluded that possibly "the consumption rate was lower as the amount of available food decreased". Another method for examining the p o s s i b i l i t y of food l i m i t a t i o n i n Marion Lake sediment i s to estimate the number of bacteria i n a volume of sediment, and then compare this with the number of bacteria the c i l i a t e s may eat i n a day. H a l l and Hyatt (1974) using unpublished data of g P. Fraker, W. Ramey and B.K. Burnison, estimated that at least 2X10 2 b a c t e r i a l cells/cm are present i n the sediment, while Perry (1975) 9 10 2 calculated that there are between 5X10 and 1.6X10 bacteria/cm . Tezuka (1974) calculated that Paramecium caudatum consumes 4.2X10^ 48 bacteria/day, or 1700/hour. Fenchel (1975) found Tetrahymena to consume 500-600 bacteria/hour during logarithmic growth, but during the stationary phase only 180-200 bacteria/hour. If 75% of the c i l i a t e s at 1 meter eat bacteria, and they eat roughly 1000 bacteria/hour (based on the above data), the summer density of 2 6 2 c i l i a t e s (80/cm ) would consume 1.9X10 bacteria/day/cm . If we assume 9 2 a density of 2X10 bacteria/cm , and according to Stachurska (1975) only 2% of these are available, then the c i l i a t e s could consume 4X10^ bacteria/ 2 day / cm . Based on these calculations, the c i l i a t e s could eat only 5% of the available bacteria/day, and only 0.1% of the total bacteria/day. In radiotracer experiments done to examine the carbon flow in the Marion Lake sediment (Marten, 1975), we have estimated that the cil i a t e s were taking 0.5% of the total bacteria/day (see also Marten et a l , 1975, for methods of analysis). Fenchel (1975) has presented a picture of the carbon flow in a small tundra pond. He based his estimates of carbon flow from bacteria and microalgae to cil i a t e s by calculating from measured feeding rates. -He found that the c i l i a t e s ate only .03% of the total bacterial population/day. Even assuming that only 2% of the bacteria are available to the c i l i a t e s , they would s t i l l have eaten only 1.4% of the available bacteria. Goulder (1972), in a study of feeding of Loxodes magnus on the green algae Scenedesmus sp. calculated that the c i l i a t e could eat at most .68% of the alga's standing crop. Although he maintains that "grazing by a l l invertebrates could be significant", i t is unlikely that L. magnus (the numerically dominant c i l i a t e in his study) could influence the standing crop of Scenedesmus, and was not food limited. 49 2 . Predation l i m i t a t i o n hypothesis of population regulation There are a number of reports i n the l i t e r a t u r e of predation being important i n c o n t r o l l i n g the c i l i a t e s populations. Gray (1952) reported a negative corre l a t i o n between insect larvae and c i l i a t e s i n a stream. Maguire et a l (.1968) and Addicott (1974) also demonstrated the importance of insect larvae i n reducing the number of c i l i a t e s i n small aquatic environments (plant bracts). Kool (1975) reviewed the l i t e r a t u r e regarding c i l i a t e predation, and presented evidence that although the predation rate may equal the population growth rate during part of the winter i n Marion Lake, during the summer months the predation rate i s much lower than the potential rate of increase of the population, as determined by Stachurska (1975). If density dependent predation was involved i n regulating the population, then, according to Hairston (1968), we should f i n d a correlation between r (population i n t r i n s i c rate of increase) and the population density p r i o r to a decline. No correlation was found (r=.07); the same result that Hairston found. . However, some sort of density dependent factor must be involved, as there are highly s i g n i f i c a n t negative correlations between population density and r i n Marion Lake at both 1 and 4 meters. When the data of Fenchel (1969) and Grabaka (1971) i s put to the same analysis, a negative correlation i s also found (Table 9). Tanner (1966) , while examining records of population growth, performed correlations as described above, and found that i n 47 out of 66 populations examined, a s i g n i f i c a n t negative correlation existed. 3.. Conclusion I have t r i e d to apply three standard mechanisms of population / Table IX Correlation (Spearman's r') between the i n t r i n s i c rate of increase (r) and c i l i a t e density. The Helsing^r location i s from Fenchel (1969), and the P o l i s h location i s from Grabaka (1971). Location r n P Marion Lake 1 meter -.36 32 .025 Marion Lake 4 meters -.7 20 < .01 Helsing^r -.38 27 < .025 Poland -.96 7 < .001 51 regulation, i e . weather and density independent factors, and food and predation, to explain the dynamics of the populations of c i l i a t e s i n Marion Lake. A l l three explanations are unsatisfactory by themselves, and each cannot s u f f i c i e n t l y explain the observations. I t seems highly u n l i k e l y that the c i l i a t e s can deplete t h e i r food supply, and Fenchel (19751 calculates that a l l benthic invertebrates can consume only 50% of the bacteria present i n the sediment. Possibly the quality rather than quantity of bacteria may influence the growth, of the c i l i a t e s . The. sediment bacteria may have to have an extremely adaptable biochemisty to deal with the sporadic inputs of organise^matter (Kleiber, pers. comm), and consequently may be of higher n u t r i t i o n a l quality at certian times of the year, while of poorer quality at other times. Waste product i n h i b i t i o n was not examined as a possible factor i n c o n t r o l l i n g the c i l i a t e population. I t was unlikely that at the r e l a t i v e l y low densities present i n the f i e l d (compared to densities common i n cultures) and the rapid flushing of the lake (Efford, 19.671 that an i n h i b i t i n g concentration of waste products could ever b u i l d up. Although the predation rate seems to be to low to be able to control the p o t e n t i a l rate of reproduction of the c i l i a t e s , i f the f i e l d reproductive rate i s lower than the rate measured by Stachurska (1975). i n the lab, then predation may be more important i n c o n t r o l l i n g the population than I now assume. The data indicate that factors c o n t r o l l i n g the population act i n a density dependent fashion. However, the standard density dependent mechanisms do not seem to apply. Possibly some interaction between the various factors not yet studied are responsible for the observed population dynamics. Acknowlegements I must thank Dr. Ian Efford for his interest and assistance. Dr. Jim Berger and Michael Hoebel gave most useful c r i t i c i s m . Dr. Tom Fenchel kindly provided the data from his 1969 paper. Dr. A.C. Borror f i r s t gave me the ideas for the extraction process. Dr. Teresa Stachurska, Dr. Gerry Marten and Michael Hoebel a l l assisted i n the planning and execution of the work, and made the time spent very pleasant. 53 References Addicott, J.F.: Predation and prey community structure: An experimental study of the effect of mosquito larvae on the protozoan communities of pitcher plants. Ecology 55, 475-492 (1974) A r l t , G.: V e r t i c a l and horizontal microdistribution of the meiofauna i n the Greifswalder Bodden. Oikos (suppl) 15_, 105-111 (1973) Blackman, R.B., Tukey, J.W.: The measurement of power spectra. Dover Press, New York, N.Y. (1958) Borror, A.C.: Morphology and ecology of the benthic c i l i a t e d Protozoa of A l l i g a t o r Harbor, F l o r i d a . Arch. P r o t i s t . 106_, 465-534 (1963) Borror, A.C.: Nigrosin-HgC^-formalin; a st a i n f i x a t i v e for c i l i a t e s (Protozoa, Ciliophora). Stain Tech. 43, 293-294 (1968a) Borror, A.C.: Ecology of i n t e r s t i t i a l c i l i a t e s . Trans. Am. Micr. Soc. 87_, 233-243 (1968b) Efford, I.E.: Temporal and s p a t i a l difference i n phytoplankton productivity i n Marion Lake, B.C. J. Fish. Res. Bd. Can. 24_, 2283-2307 (1967) Efford, I.E., H a l l , K.J.: Marion Lake-analysis of an ecosystem t ± n Royal Society volume on Candian I.B.P. ( i n press) Fenchel, T.: The ecology of the marine microbenthos I I I . The reproductive potential of c i l a i t e s . Ophelia 5_, 123-136 (1968) Fenchel, T.: The ecology of marine microbenthos IV. Structure and function of the benthic ecosytem, i t s chemical and physical factors and the microfauna communities with special reference to the c i l i a t e d protozoa. 0pheliax6, 1-182 (1969) Fenchel, T.: The quantitative importance of the benthic microfauna of an A r c t i c tundra pond, Hydrobiol. 46s 445-464 (1975) Goulder, R.: V e r t i c a l d i s t r i b u t i o n of some c i l i a t e d protozoa i n two freshwater sediments. Oikos 22., 199-203 (1971a) 5.4". Goulder, R.: The effects of saprobic conditions on some c i l i a t e d protozoa i n the benthos and hypolimnion of a eutrophic pond, Freshl B i o l . 1, 307-318 (1971b) Goulder, R.: Grazing by the c i l i a t e d protozoan Loxodes magnus on the alga Scenedesmus i n a eutrophic pond. Oikos 23, 109-115 (1972) Grabaka, E.: C i l i a t a i n bottom sediments of f i n g e r l i n g ponds, P o l , Arch. Hydrobiol. 18, 225-233 (1971) Gray, E.: The ecology of the c i l i a t e fauna of Hobsons Brook, a Cambridge-shire chalk stream. J . Gen. Micro. 6_, 108-122 (1952). Gruendling, G.H.: Ecology of the ep i p e l i c a l g a l communities i n Marion Lake, B.C. J. Phycol. ]_, 239-249- (1971). Hairston, N.G.: Studies on the l i m i t a t i o n of a natural population of Paramecium au r e l i a . Ecology 4£, 904-910 (1968)-H a l l , K.J., Hyatt, K. : Marion Lake (IBP)- from bacteria to f i s h . J . Fish. Res. Bd. Can. 31, 89-3-911 (1974) Hargrave, B.T.: Epibenthic a l g a l production and community resp i r a t i o n i n the sediments of Marion Lake. J . Fish. Res. Bd. Can. 26., 2003-2026 (1969) Johnson, W.H.: Populations of c i l i a t e s . Am. Nat. 75, 438-457 (1941) Kahl, AL: Urtiere oder Protozoa I. Wimpertiere oder C i l i a t a (Infusoria), eine Bearbeitung der freilebenden und ectocommensalen Infusorien der Erde, unter Asschluss der marinen Tintinnidae. Tierwelt D t l . 1_8_ (1930), 21 (1931)., 25 (1932), 30 (1934) Kool, R.: The relationship between c i l i a t e d Protozoa and th e i r predators i n Marion Lake, B r i t i s h Columbia, unpubl. manuscript (1975) Maguire, B., Belk, D., Wells, G.: Control of community structure by mosquito larvae. Ecology 49, 207-210 (1968) Marten, G.G.: A carbon budget for Marion Lake, unpubl. manuscript (1975) Marten, G.G., Kleiber, P.M., Reid, J.A.K.: A computer program for f i t t i n g tracer 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 (1975) Moore, G.M.: A limnological investigation of the microscopic benthic - fauna of Douglas Lake, Michigan . Ecol. Monogr. 9, 538-582 (1939) Perry, E.: B a c t e r i a l biomass and a c t i v i t y i n lake sediment: A comparison of methods, unpubl. manuscript (1975) Pieczynska, E.: Ecology of the e u l i t t o r a l zone of lakes. Ekol. Polska 20, 637-732 (1972) Stachurska, T.: Ecology of the c i l i a t e d protozoa i n Marion Lake, B.C. unpubl. manuscript (1975) Tanner, J.T.: Effects of population density on growth rates of animal populations. Ecology 47, 733-745 (1966) Tezuka, Y.: An experimental study on the food chain among bacteria, Paramecium and Daphnia. Int. Rev. ges. Hydrobiol. 59_, 31-37 (1974) 

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