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The distribution and abundance of the intertidal prosobranchs Littorina scutulata (Gould 1849) and L.… Behrens, Sylvia 1971

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THE DISTRIBUTION AND ABUNDANCE OF THE INTERTIDAL PROSOBRANCHS LITTORINA SCUTULATA (GOULD 1849) AND L. SITKANA (PHILIPPI 1845) by Sylvia Behrens B.Sc,, Honors, University of British Columbia, 1968 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OP THE REQUIREMENTS FOR THE DEGREE OP MASTER OP SCIENCE in the Department of Zoology We accept this thesis as conforming to the required standard THE UNIVERSITY OP BRITISH COLUMBIA July, 1971 In presenting t h i s thesis in p a r t i a l f u l f i l m e n t of the requirements for the Library shall make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis for s c h o l a r l y purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or p u b l i c a t i o n o f t h i s thesis f o r f i n a n c i a l gain shall not be allowed without my written permission. an advanced degree at the University of B r i t i s h Columbia, I agree that The University of B r i t i s h Columbia Vancouver 8, Canada Depa rtment i ABSTRACT An attempt was made to explain the distribution and abundance of the intertidal prosobranch snails Littorina scutulata (Gould, 1649), and £. sitkana (Philippi, 1845) on beaches near the c i t y of Vancouver, i n the Gulf Islands and on the west coast of Vancouver Island, B r i t i s h Columbia. L. scutulata has a planktonic dispersal stage and i s widely distributed. L. sitkana develops directly from benthic egg masses and tends to be more restricted i n i t s distribution. The egg masses of L. sitkana are susceptible to desiccation at low tide, and consequently this species thrives best i n damp places such as mud f l a t s , tide pools and crevices. L. sitkana appears to be selected against i n wave-swept places, because i t offers more resistance to wave action than does the comparatively streamlined L. scutulata. Experimental manipulation of densities and species composition indicated that food limitation may take place i n the summer (decreased growth rates at higher densities of snails and low food abundance) but not i n the winter. Density dependent survivorship and natality were found for L. sitkana, indicating that a regulatory mechanism may be oper-ating. L. scutulata showed no such density dependent response at the densities examined. The presence of scutulata reduced the survival of JL. sitkana and vice versa i n comparison to control populations consisting of each species alone. Possible evolutionary survival strategies and competitive relation-ships of these two species are discussed. TABLE OF CONTENTS ABSTRACT LIST OF FIGURES LIST OF TABLES ACKNOWLEDGMENTS GENERAL INTRODUCTION EXTERNAL MORPHOLOGY OF L. SITKANA AND L, SCUTULATA GEOGRAPHIC DISTRIBUTION SOME ASPECTS OF THE REPRODUCTIVE BIOLOGY OF L. SITKANA AND £. SCUTULATA Introduction Description of juvenile stages Breeding Season Desiccation of juvenile stages as a possible factor restricting L. sitkana's distribution 19 Materials and Methods 19 Results 21 Discussion 23 General Discussion 23 LOCAL DISTRIBUTION OF LITTORINES 25 A. HORIZONTAL DISTRIBUTION 25 Introduction 25 Survey of Beaches 27 Materials and Methods 29 Results 30 Responses of L. sitkana and L. scutulata to Physical factors 34 Materials and Methods 34 Results 37 Submergence of L. scutulata 57 Wave exposure 38 Desiccation 38 ^ Temperature 39 Salinity 39 Crevices 39 Discussion 42 B. VERTICAL DISTRIBUTION 43 Introduction 43 I. Upper Distribution 44 Materials and Methods 44 Results 45 i i Page i i T v i v i i i 1 5 8 10 10 10 16 i i i II. Limits to the Lower Distribution 45 Materials and Methods 48 Results 51 Acmaea scutum. L. sitkana interaction 51 Effect of Leptasterias hexactis predation on Acmaea paradigitalis and L. scutulata 51 Summary 51 THE ABUNDANCE OP LITTORINES 53 A. BEHAVIORAL RESPONSES 53 Introduction 53 Materials and Methods 54 Results 55 Densities 55 Pood Levels 57 Pood Detection 57 Shelter (crevices) 57 Discussion 58 B. DENSITY-SPECIES INTERACTION EXPERIMENT 58 Introduction 58 Materials and Methods 59 Food Abundance 67 Growth Rates 73 Methods 73 Results and Discussion 77 L. sitkana Natality 84 Survivorship and Mortality 90 Materials and Methods 90 Results 92 Discussion 103 DISCUSSION AND CONCLUSIONS 105 LITERATURE CITED 111 APPENDIX, Tables 1 to 56 114 i v LIST OP FIGURES Page 1 Shell morphology of L. scutulata and L. sitkana 6 2 Map of study areas between Tofino and Coos Bay 9 3 IJ. scutulata egg capsule containing 5 eggs 11 4 L. scutulata eggs showing one-cell to eight-cell stages 12 5 L. scutulata veliger just before hatching 13 6 L. sitkana eggs inside an egg mass 14 7 Newly hatched L. sitkana 15 8a Number of L. sitkana egg masses produced inside experimental cages as a function of time 17 8b High splash pool on Edward King Island 26 9 Map of study areas between Sunset Marina and Victoria 27 10 Map of study areas on San Juan Island 28 11 Size frequency distributions of L. sitkana and L. scutulata 31 12 Size frequency distributions of L. sitkana and L. scutulata 32 13a Number of animals of both species found on rocks of different roughness 40 13b Tolerance of lit t o r i n e s to d i s t i l l e d water 41 14a Transect from Bowman's Bay 46 14b Length of Acmaea scutum versus length of L. sitkana of equal dry weight 49 15 Cages used for Acmaea-littorine interaction experiment 50 16 Modification of water table for food detection experiment 56 17 Cement stepping stones removed from vexar cages 60 18 Arrangement of cages at the Cantilever Pier Beach 61 19 Optical density versus wet weight and dry weight versus wet weight of Fragellaria 64 20 The relationship of subjective and objective estimate of standing crop of algae 66 21 Numerical estimate of standing crop of algae at three snail densities as a function of time 69 V 22 Numerical estimate of algae abundance on control slabs as a function of time 71 23 Diagram i l l u s t r a t i n g the relationship between l i p increment and length increment and between o r i g i n a l length and f i n a l length of L. scutulata 74 24 Relationship between length and l i p increment of L. sitkana 75 25 Relationship between length and l i p increment of L. scutulata 76 26 to Growth indices under different density and species 78 to 29 treatments 82 30 Number of egg masses produced from September 17 to December 9» 1969 under the three density treatments (uncorrected f o r equal density of L. sitkana) 86 31 Number of egg masses produced from September 17 to December 9, 1969 under the three density treatments (corrected for equal density of L. sitkana) 87 32 Spring n a t a l i t y for L. sitkana as a function of density 88 33 Mortality index of L. sitkana and L. scutulata as a function of time 93 34 Original number of l i t t o r i n e s surviving one year as a function of density 94 35 L. sitkana mortality data i n summer and winter 95 36 L. scutulata mortality data i n summer and winter 96 37 V a r i a b i l i t y of summer mortality i n ri g h t and l e f t cages 97 38 V a r i a b i l i t y of winter mortality i n righ t and l e f t cages 98 39 Crushed s h e l l mortality as a function of density 99 40 Number of non-sheltered animals as a function of density 101 vi LIST OP TABLES Page 1 Time sequences for the developmental stages of L_. scutulata 115 2 Hatching success of L. sitkana egg masses suspended 116 from a boat moored in Vancouver Harbor 116 3 Survival of two size classes of juvenile L. sitkana caged at the 9 foot and 13 foot t i d a l levels at Lilly-Point, from May 17 to May 18, 1969 117 4 Hatching success of L. sitkana egg masses at L i l l y Point 118 5 Position of L. sitkana egg masses found i n 16 cages at Cantilever Pier Beach 119 6 Local distribution of lit t o r i n e s 120 7 Number of animals of both species found on the surface and in crevices of a quadrat taken at Marvista Resort 122 8 A b i l i t y of the two species of lit t o r i n e s to resist wave exposure i n the f i e l d 124 9 A b i l i t y of the two species of litto r i n e s to resist being washed off the substrate with a jet of sea water 125 10 Tolerance of the two species of littorines to 3 and 4 days of desiccation at room temperature 126 11 Tolerance of litto r i n e s to high water temperature 127 12 Tolerance of litto r i n e s to sal i n i t y extremes 128 13 Elect i v i t y coefficients for Searlesia dira 129 14 Electi v i t y coefficients for Leutasterias hexactis 130 15 Pood choice by Leptasterias hexactis as determined by contact with prey 131 16 Survival of L. scutulata caged i n high intertidal and splash zone at L i l l y Point 132 17 Mean growth increments of Littorina sitkana and Acmaea scutum from single and mixed species cages 133 18 Starfish predation on lit t o r i n e s and limpets at two tide levels 134 19 Dispersal behavior of L. sitkana under two densities 135 20 Number of li t t o r i n e s of both species found on cement slabs with and without algae 136 v i i 21 Total number of l i t t o r i n e s of both species leaving diatom covered and clean slabs 137 22 Position of L. sitkana 14 hours a f t e r introduction into modified water table 138 23 Behavioral response of l i t t o r i n e s to crevices 139 24 Comparison between abundance of food i n L. sitkana and L. scutulata cages throughout the year 140 25 Biomass and length increment relationships f o r L. sitkana and L. scutulata i n August from single species low density treatments 141 26 The effects of density on L. sitkana n a t a l i t y 142 27 Tests on the effect of species composition on the n a t a l i t y rate of L. sitkana 143 28 Comparisons between the n a t a l i t y rate i n single and mixed species cages and between l e f t and r i g h t cages 144 29 Comparison of survivorship curves i n 24 cages for species and density effects 145 30 L. sitkana survivorship and mortality data 147 31 Lf scutulata survivorship and mortality data 148 32 Incidence of cercaria shedding experimental animals 149 33-56 Friday Harbor density-species interaction experiment 150 33-40 Demography and food abundance from July 1969 to June 1970 150-159 41-48 L. sitkana growth data from July 1969 to June 1970 160-167 49-56 L. scutulata growth data from July 1969 to June 1970 168-175 v i i i ACKNOWLEDGMENTS I thank my advisor, Dr. Robin Harger for allowing me to formulate and attack my own research problems. His advice and criticisms were extremely helpful during the writing phase of this study. I am grateful to Dr. John Stimpson for his interest i n my work and his many valuable suggestions. I would like to thank the faculty, staff and graduate students of the University of Washington Marine Laboratories and the Zoology Department of the University of B r i t i s h Columbia for their cooperation. Dr. Pu-shing Chia, Dr. N. Gilbert, Dolores Lautiente, Bruce Menge, Dr. N.J. Wilimovsky, Dr. A.G. Lewis and Dr. D. McPhail were especially helpful. This research was financed by the National Research Council of Canada Grant # 67660 to Dr. J.R.E. Harger. 1 GENERAL INTRODUCTION Littorines, or periwinkles are cosmopolitan i n their distribution, being found on rocky shores throughout the intertidal regions of the world (Stephenson and Stephenson, 1949). At low tide they can be found between barnacles, under rocks and seaweed and i n crevices. Since they are ubiquitous and easy to collect, l i t t o r i n e s have been the object of many studies. As early as 1911 Baseman attempted to describe the physical factors responsible for the oscillatory movements of Littorina, l i t t o r e a . located on vertical surfaces, which corresponded to t i d a l cycles. In 1916 Kanda looked at the negative geotrophic response of li t t o r i n e s to a combination of factors such as light, angle of inclination, sub-mergence and emergence, texture and moisture of substrate. He noted, that animals appeared to be sensitive to desiccation; moving upward i f the substrate was dry. Hertling and Ankel (1927) described the mode of development of various Atlantic Lacuna and Littorina species. Littorina littorea and Jj. neritold.es, both have planktonic egg capsules and veliger larvae. L. l i t t o r a l i s fasten their gelatinous egg masses to the fronds of fucoids. The veliger stage i s passed inside the egg and the young snails hatch as miniature adults. L. saxatilis on the other hand i s viviparous. Struhsaker and Costlow (1968) reared the Hawaiian Littorina picta from egg capsules to miniature adults by feeding the veligers on the phyto-plankton Phaeodactylum tricornutum. Just prior to metamorphosis the 2 veligers were observed to prefer substrates with algal cover to sub-strates without algae. Although much attention has been devoted to the development of Atlantic and Hawaiian li t t o r i n e s , no one has studied the mode of development of the north-eastern Pacific l i t t o r i n e s . In the present study I describe the development of L. sitkana and L. scutulata for the f i r s t time. In California, L. scutulata i s found i n the i n t e r t i d a l zone and ]J, p3,anaxis lives i n the spray zone, above the high water mark. Bock and Johnson (1968) fe e l that this zonation can be attributed to L,. planaxis', greater tolerance to desiccation and an i n a b i l i t y of this species to obtain the right kind of food (e.g. lichens) i n the inter-t i d a l . On be°:hes '•-^ •'ind Vancouver and on the Gulf Islands L. sitkana and L. gcutoilata occur together without differentiation i n pattern of ver t i c a l zor- ; -\. On exposed coasts of Vancouver Island however, one finds L. scutulata inhabiting the intertidal and L. sitkana l i v i n g i n splash pools which are isolated from the ocean for most of the year. The present study attempts to explain this and other distribution patterns of L. sitkana and L. scutulata,. Littorines are grazers on microscopic and macroscopic marine algae (Dahl, 1964; Poster, 1964). The effect of their grazing activity i n reducing the standing crop of marine diatoms has been reported by Castenholz (l96l). In the present study l i t t o r i n e s were caged at three densities and their effect on the standing crop of algae for one year was measured. The investigation of factors limiting the number of animals i n a 3 population forms a topic of central interest i n ecology. Animals need shelter from environmental extremes and from predators, as well as food fo r body maintainance, growth and reproduction. As the density of animals increases, both shelter and food generally become r e s t r i c t e d i n a v a i l a b i -l i t y and an increased mortality from exposure, predation, starvation and s u s c e p t i b i l i t y to diseases usually follows as well as a decrease i n n a t a l i t y . Such density dependent responses by animal populations to the f a v o r a b i l i t y of t h e i r physical and b i o l o g i c a l environment has the effect of allowing populations to increase when densities are low and resources abundant and decrease when densities are high and resources scarce. According to Murdoch (1970) long-lived species, such as elephants, generally are more independent of environmental changes and thus tend to be numerically constant over time. Shortlived species such as bacteria react faster to fluctuations i n environmental f a v o r a b i l i t y by increasing or decreasing t h e i r numbers. In the present study a comparison of the numerical responses of two species of l i t t o r i n e s to three density l e v e l s i s made. The competitive exclusion p r i n c i p l e , or Gause's p r i n c i p l e states that two ecologically s i m i l a r species using the same resource, be i t food or shelter, cannot coexist i n d e f i n i t e l y for one species would be more e f f i c i e n t at u t i l i z i n g that resource and thus would increase i n numbers and displace the other species (Hardin, I960). This was the case with Paramecium caudatum and P. a u r e l i a grown i n culture v i a l s (Gause, 1934). In single species cultures both species survived i n d e f i n i t e l y but when grown together, the smaller species P. caudatum, with a 4 greater rate of increase, could acquire food more ef f i c i e n t l y than P. aurelia and thus _P. caudatum increased i n numbers and displaced P. aurelia. In nature, however environmental conditions are more variable i n time and space and coexisting species u t i l i s i n g the same resource are not uncommon (Low, 1970; Harger, 1967). L. sitkana and L_. scutulata eat the same food and overlap i n their distribution i n most habitats. In the present study lit t o r i n e s were caged in the f i e l d i n single and mixed species treatments for a year i n an attempt to determine whether competitive relations exist between the two species. 5 EXTERNAL MORPHOLOGY Unweathered specimens of the two l i t t o r i n e species may be dis-tinguished by their external shell morphology (see P i g . l ) . The shell of L. scutulata i s smooth and has a pointed apex, that of L. sitkana i s roundish and has transverse grooves. L. sitkana i s the faster growing of the two species and as a rule i s larger than ,L. scutulata. Both species may reach up to 2 cm i n length. Size however varies with loca-tion and i s not particularly useful i n l i t t o r i n e taxonomy. Shells of both species usually appear black when wet and grey when dry. L, sitkana i s often more variable i n colour, sculpture and shape than L. scutulata. Shells of L. sitkana can be white, grey, orange, yellowish, brown or black. Complex banding patterns of one, two, three or more grey, brown or black stripes on a white background are found in L. sitkana. The characteristic grooves of L. sitkana are sometimes eroded away in older specimen. The ratio of the height of spire to maximum width i s approximately 1 . 2/l. L. scutulata does not appear to be as variable i n shell colour and morphology. This l i t t o r i n e as i t s Latin name indicates, i s often speckled with many white dots. The occasional white L. scutulata with one black or brown band has been noted, but the elaborate banding and colour patterns of L. sitkana i s absent in this species. Strong surf erodes the apex of the spire, thus giving L. scutulata on exposed beaches the squat shape of L. sitkana. Height of spire to maximum width ratio i s approximately I . 4 / 1 . Littorina sitkana Dorsal view Ventral view Littorina scutulata Figure 1. Shell morphology of Littorina sitkana and Littorina scutulata. (Magnif«c*Hor\ 7 Erosion and attack by boring algae often imbue l i t t o r i n e shells with a perforated appearance. Lightly pigmented specimens may also be coloured by the epiphytic growth of green and brown algae. 8 GEOGRAPHICAL DISTRIBUTION Only three species of littorines occur on the west coast of North America (Urban,1962). Littorina scutulata has the widest distribution, occurring from Alaska to Baja, California (58°N to 19°N latitude). Orldroy (1929) and Keen (1937) state that L. sitkana is present from the Bering Sea to Puget Sound (48°N) and that L. planaxis occurs from Puget Sound southward. Thomas (1966) found L. sitkana in bays just north and south of Lincoln City, Oregon. I confirmed the presence of Littorina sitkana in Siletz Bay just south of Lincoln City where this species was found on scattered basaltic rocks on the island near Schooner Creek Bridge. Thomas also claimed to have found L. sitkana at Sunset Bay and Winchester Bay near Coos Bay and North Bend, Oregon. I however did not find L. sitkana at Sunset Bay. The photographs he took of these littorines looked like striped L. scutulata. IJ. sitkana does however occur much further south than Puget Sound. I have never found L. planaxis in Puget Sound. The specimens of L. planaxis in the Friday Harbor museum are those of L. sitkana with the grooves eroded. Neither Thomas in 1966 nor I have found L. planaxis north of Coos Bay. 10 SOME ASPECTS OP THE REPRODUCTIVE BIOLOGY OF L. SITKANA AND L. SCUTULATA Introduction Hertling, 1927 reports on the diverse modes of development of the Atlantic l i t t o r i n e species. Littorina l i t t o r e a and L. neritoides both have planktonic egg capsules and veliger larvae. L. l i t t o r a l i s fasten their gelatinous egg masses to the fronds of fucoids. The veliger stage i s passed inside the egg and the young snails hatch as miniature adults. L. saxatilis on the other hand i s viviparous. There appears to be no information i n the literature concerning the development of IJ. sitkana and L_. scutulata. L. scutulata released floating egg capsules (Fig. 3) i n the laboratory during the week of June 22, 1970 and juvenile L. sitkana hatched from gelatinous egg masses (Fig. 6) collected from Brockton Point (Fig. 9) i n March of 1969. These observations confirmed that L. scutulata (like L. l i t t o r e a and L. neritoides) has planktotrophic development and L. sitkana (like L. l i t t o r a l i s ) has le cithotrophic development. Description of Juvenile Stages of L. scutulata and L. sitkana Materials_and Methods 0 0 Three female L. scutulata were kept at 13 to 15 C i n separate stacking dishes (5 cm i n diameter) with a l i t t l e sea water. The water was changed at least once a day and the number of newly lai d egg 11 a. capsules noted. Egg capsules were followed through the developmental stages to the hatched veligers at two temperatures (l3° to 15° and at 22 C). Five IJ. sitkana egg masses in different stages of development were collected from Brockton Point on March 12, 1969. Each egg mass was divided into four more or less equal sections. One quarter of each of the five egg masses was placed in the bottom of a petri dish (5 cm in diameter) with a section of fine plankton netting wrapped around i t . Pour such dishes were prepared. Two nylon lines (lOO lb tested)' were suspended from a boat moored in Vancouver harbour. Two petri dishes-were attached with rubber bands to each line at points 50 cm and 100 cm below the surface of the water. After 13 days these dishes were examined. Results In a period of one week three female L_. scutulata produced from 749 to 1034 egg capsules each. L_. scutulata egg capsules are 840/(in diameter, resemble trans-parent saucers and may contain from 1 to 6 eggs measuring 100 /\,±n diameter (Fig. 3). The veligers hatched from the egg capsules in 7 to 8 days after laying in 13° to 15°C water and after 3 days in 22° water. Newly hatched larvae measured l60/{_in length. L. sitkana egg masses (Fig. 6) vary in length from 5 mm to 15 mm and contain about 50 to 150 eggs. Eggs range from 0.9 mm to 1.0 mm in lib F i g . 3 L. scutulata egg capsule containing 5 eggs. Fig.4 L. scutulata eggs showing one-cell, two-cell, f o u r - c e l l and e i g h t - c e l l stages. Note the micromeres and macromeres i n the top ri g h t hand egg. F i g . 5 L. s c u t u l a t a v e l i g e r j u s t b e f o r e h a t c h i n g . Note the dense s h e l l and the velum. 14 15 F i g . 7 Newly hatched L. sitkana. Note the foot and tentacles of the uppermost s n a i l . 16 diameter and embryo sizes range from 0.33 to 0.40 mm in width. Newly hatched snails are approximately 0.45 mm wide. The jelly encasing the embryos is transparent and relatively hard. As the shell of the embryo develops, the colour and consequently the colour of the entire egg mass changes from white to yellow to pink and finally to red. Sometimes the whole egg mass is covered with diatoms and will appear opaque brown in colour. Less than half of the eggs in the petri dishes hatched into •roundish snails having a dark brown and smooth shell (Table 2). The older snails showed the characteristic grooves of L. sitkana (Fig. 7). Breeding Season L. scutulata may breed for most of the year. Copulation was ob-served in the f a l l and early winter of 1969 and 1970 and in the summer of 1969. Newly settled individuals were found in February 1968 and in spring 1969. Egg capsules were produced in June 1970 at Friday Harbour Marine Laboratories and in November 1970 at Sunset Bay near Coos Bay, Oregon (Fig. 2). L. sitkana egg masses can be found at various beaches throughout the year except during the summer months. Four egg masses were found in the cages by Cantilever pier (to be discussed in the last section) on June 22, 1970, but these had dried out, (Table 40). Peaks of egg mass abundance occur in the f a l l and early spring (Fig.8a). An extreme-ly mild spring in 1970 may have been responsible for a peak of abun-dance occurring earlier than in the previous year. (E.g. egg masses F i g . ^ a Number o f L . s i t k a n a e g g m a s s e s p r o d u c e d i n s i d e e x p e r i m e n t a l c a g e s a s a f u n c t i o n o f t i m e . 18 were collected from the Montague Harbour mud flat, Galiano Island, on May 16, 1969 whereas on May 19, 1970 none were found, but young snails were already 2 mm in length.) Egg laying is not synchronous from beach to beach; for example the first egg masses on San Juan Island were found at Pile Point in August of 1969, whereas at Cantilever pier they did not appear until September. ' Observations made on L. sitkana caged on a cement slab suspended at the 1 foot tide mark (U.S. tables) at the Friday Harbour Labora-tories pier from September 20 to October 12, 1969 indicated, that a fe-male L.sitkana can lay at least three egg masses in a three week period. 19 Desiccation of Juvenile Stages as a possible Factor Restricting  L. sitkana's Distribution Survival of juvenile L. sitkana in a location inhabited naturally by L. scutulata only was investigated at L i l l y Point (Fig. 9). The rocky foreshore in this area is characterised by barnacle covered cobble and rocks not larger than 15 cm in diameter resting on sandy bottom. The low intertidal area is mostly sand interspersed with four barnacle covered concrete blocks (50 cm by 50 cm by 50 cm). I worked on the site of an abandoned fish cannery where an a r t i f i c i a l substrate consisting of compressed tin can scraps and cobble is completely covered with barnacles and extends from the mid to the high intertidal region. Numerous barnacle covered pilings (the remains of the cannery's pier) run in rows from the mid to high intertidal. Absence of shade, as well as good drainage tends to make the L i l l y Point site a dry beach at low tides in sunny weather. Animals cannot find shelter under the cobble and rocks for these are resting on sand. To determine the critical l i f e history stage preventing _L. sitkana from living at L i l l y Point, adults, newly hatched snails and egg masses were transplanted to the area. Egg masses recovered from experimental cages containing L. sitkana yielded information on the preferred sites for egg laying. Materials and Methods a) Transplant Experiments To determine whether adult _L. sitkana could live at Li l l y Point, 20 five hundred young L. sitkana (ca. 5 mm in length) were released on the "compressed tin can rock" and on one piling stump in May of 1969. On May 16, 1970 newly hatched L. sitkana were collected from the Montague Harbor mud flat on Galiano Island (Fig. 9 ). The oyster shells and l i t t l e neck clam shells on which the egg masses were attached were kept moist with sea water. The following day eight "cages" were pre-pared by pulling a square of fine plankton netting over the concave half of the l i t t l e neck clam shells. Four of the cages contained 10 newly hatched snails each and 4 cages contained five older snails ( l mm or longer). One of each type of cage was set up in the following location: on pilings at the 13 foot tidal level, in a r t i f i c i a l tide pools (32 oz orange juice jars) at the 13 foot tidal level, on pilings at the 9 foot tidal level and in ar t i f i c i a l tide pools at the 9 foot tidal level. The "tide pools" and cages were attached to the piling stumps using rubber bands cut from an inner tube. The number of surviving animals, salinity and temperature of the tide pools and air and water were recorded the next day. L. sitkana egg masses were collected from False Bay, San Juan Island (Fig. 10) on August 21, 1969 and taken to L i l l y Point on August 23. A l l egg masses were sectioned into two parts. Each half was placed into a plastic petri dish l i d and fine plankton netting was wrapped around the dishes. The dishes were attached to the pilings at the high tide levels and to the concrete blocks at the low tide levels so that half of each egg mass was represented at each tidal level. The 21 number of hours the 5 foot and 12 foob tide level was exposed to direct mid-day sunshine was estimated from weather data and a tide table. The condition of the egg masses and the number of hatched snails were recorded on September 1 and September 7 (Table 4). b) Site preference for egg laying ,L. sitkana were retained in 16 cages located at the 2 foot tide level (U.S. tables) at Cantilevel pier beach. The cages consisted of cement stepping stones (l9 cm by 4 cm by 39 cm) sewn into plastic mesh (vexar) bags (Fig. 18). The location of a l l the egg masses laid by the snails in the cages was noted and grouped into 7 position categories (Table 5). Results After one year six L. sitkana were recovered on the tin can rock. A l l the animals had grown to roughly 10 cm in length. The rest of the animals had either died or dispersed from the immediate area. One yellow egg mass located on the wave and sun sheltered side of a piling stump was found in May 1970. The egg mass, however, dried up before hatching. The fact that the transplanted L_. sitkana survived for a year, grew and even demonstrated reproductive potential would indicate that no major selective factor was operating during this period of time preventing adult L_. sitkana from living at L i l l y Point. Lack of shelter coupled with the abrasive action of shifting sand in this area may prevent L. sitkana egg masses and newly hatched snails from devel-oping. 22 A l l the young L. sitkana caged for 26 hours at the mid tidal level and those retained inside the high tide pool survived (Table J>). However a l l the small snails (less than 1.0 mm) caged to the high piling stump were dead. The cages and pool at the high tide level (l3 ft) were calculated to be exposed to roughly 11 hours of direct sunshine, those at the mid tide level (9 foot) for roughly 6 hours during the duration of the experiment. It would seem that desiccation and not the high temperatures per se killed the small snails at the high tide level since the temperature in the high tide pool was 7° higher than air temperature at the time of measurement (Table 3 ) . From weather and tide data for the period August 23 to September 1, the 5 foot tidal level was estimated to be exposed to 'a total of 6 hours to direct mid-day sun and the 12 foot level to at least 30 hours. A total of 161 young L_. sitkana hatched at the 5 foot level as opposed to only 2 at the 11 foot level. A l l the egg masses at the high tide level had dried out by September 7, (Table 4). This correlation suggests that desiccation was responsible for egg mass mortality at the high tide level but not at the lower. Wo eggs were laid on the wave exposed side of the experimental slabs and only one on top of the slab, whereas 29 egg masses were re-covered from the wave sheltered side of the slab and 26 from the bottom of the slabs (Table 5). Fourty seven egg masses were laid in cievices of the cage seams which were on the wave sheltered side of the slabs. It therefore appears as i f L. sitkana prefer to lay their eggs in wave sheltered and dark places. 23 Discussion - Desiccation acting on egg masses and newly hatched individuals of L. sitkana may be a critical factor preventing this species from living at L i l l y Point and other dry beaches. It is conceivable,, that a perma-nent population of L. sitkana could be established at L i l l y Point i f tide pools or damp crevices were added. Egg masses hatched at low tide levels, but the abrasive action of shifting sand and s i l t , especially during storms seems to prevent any grazers from living there permanent-ly. The preference L_. sitkana shows in laying their egg masses in sheltered places appears to be an adaptive trait. General Discussion Thorson (l950) showed that a greater proportion of northern prosobranch species pass the veliger stage inside the egg capsules than do their southern counterparts. He suggests that this form of develop-ment may be an adaptation to the unpredictability of the phytoplankton food for the veligers in northern waters. This trend 'appears to hold for littorines. Both JJ. sitkana and the European L./littoralis have benthic egg masses and are considered northern species. These two species do not extend into warmer climates as do L_. scutulata. L. planaxis (imai, 1964) and the European L. neritoides with plankto-trophic development. Susceptibility of egg masses of L. sitkana to desiccation at low tide may be one reason why this species does not extend further south. Such susceptibility combined with a limited dis-persal potential restricts L. sitkana to beaches which offer protection 24 from desiccation. L. scutulata with its planktonic dispersal stage appears to be able to invade more habitats (Table 6). 25 LOCAL DISTRIBUTION PATTERNS OF LITTORINES A. HORIZONTAL DISTRIBUTION Introduction Littorina scutulata and L. sitkana coexist on beaches near Vancouver, B.C., on the islands in the Gulf of Georgia and on Vancouver Island. Vertical distribution of these snails, unlike that of the California littorines (Bock and Johnson, 1968) and the Atlantic littorines (Gowanloch and Hayes, 1926) does not f a l l into discrete bands along the intertidal exposure gradient. This absence of any obvious pattern in the vertical distribution of these two species was also noted by Urban (l962). In the San Juan Archepel^go and at Port Renfrew Urban (op. cit.) noted, that L. scutulata was the more numer-ous and more widespread species. He attributed this to a greater ability of L. scutulata to tolerate environmental extremes such as low salinity and surf action, but did not test the idea experimentally. The two species of littorines were found separated into two horizontal zones only on extremely exposed surf-swept beaches of Vancouver Island such as Chesterman's Island near Tofino. There L. scutulata occupied the intertidal zone and L. sitkana was found only in extremely high splash pools. These pools receive ocean water only during the winter storm tides (Andreas Schroeder, personal communi-cation). In the summer the pools are isolated from the ocean and both water level and salt concentration probably fluctuate between dry and rainy periods. In the spring of 1970 the pools dropped one inch in F i g . 8b High splash pool on Edward King Island near Bamfield, containing numerous newly hatched L. sitkana. 9 Taken from Chart # 3001, Vancover Island Published by the Canadian Hydrographic Service Marine Science Branch, Department of Mines and Technical Surveys, Ottawa 6-vtN\ Reef- 28 Cove N SAN DUAN ISLAND JDegcitnaii's Bay X UniVersi °f U^ shWo, La bom furies o GiUii't Cove. >nHlever Pier FRIMY PILE POINT BAY' Harsjista O Resort SCALE MILES F i g u r e 10 Cat t le Poin t 29 height from May 5 to May 6. Many snails were stranded in the salt crust at the edges of the pools, however they were not dead for they opened their operculum and moved their foot when immersed in the pool. During the week of July 1, 1970, Schroeder noted,that the water level was extremely low and that many snails were stranded. Twenty-eight beaches were surveyed and presence of the two species of littorines was correlated with type of substrate, degree of wave exposure and salinity. A series of experiments was performed to deter-mine whether the distribution patterns could be explained on the basis of differential adaptation by the two species to aspects of wave action, submergence,desiccation, water temperatures and salinity. Survey of Beaches Materials and Methods Tidal levels were estimated by reference to biological zones or else measured from the low water mark at the time of the survey. Popu-lation densities were estimated using standard quadrats of 1 meter by 1 meter or 5 cm by 5 cm. Size frequency distributions of animals were noted either by measuring animals with calipers to the nearest mm or else by sieving animals through a series of soil test sieves (mesh sizes 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm). Animals retained by the 6 mm mesh diameter were called size 8 animals, those by the 5 mm mesh size 7, those by the 4 mm mesh size 6, those by the 3 mm mesh size 5, those by the 2 mm mesh size 4, those by the 1 mm mesh size 3 , those by the 0.5 mm mesh size 2 and those passed through the 0.5 mm mesh size 1. Salinity measurements were taken with a hydrometer and wave 30 exposure ranked subjectively according to the degree of water movement at the time of the survey. Results A number of generalizations regarding population densities, size frequency distributions as well as distribution patterns of the two species of littorines were determined from the survey. 1. L, sitkana in any one place are larger than L. scutulata. Frequency distributions based on shell length do not always show differences in size since at any given length L. sitkana is bulkier and heavier than L. scutulata. For example dry body weight of a 5 mm L_. scutulata is .0018 grams and a 5 mm L. sitkana .0030 grams (data courtesy of Menge). Greater growth rate of L. sitkana may in part explain this size difference (Fig. 26). 2. Populations of L_. scutulata at any one place are character-ised by a unimodal size frequency distribution and populations of L_. sitkana by a bimodal distribution (Figs. 11, 12 ). The presence of reproductive peaks in the spring and f a l l combined with more rapid growth may make season classes detectable. Evidence indicates that L. scutulata larvae settle from at least late winter to early f a l l . Such continual settlement combined with slow growth may obscure season classes. 3- L. scutulata live at higher densities than L. sitkana. Evidence from a density-species interaction experiment to be discussed later indicates that JL. scutulata survive better at higher than at I«*> 31 70 5» Ho-01 e •H cs o n 0) io -L . s c u t u l a t a j 1 1_ •4 • i 0 I 1 I H S" t 7 g S io i» 12 13 IV ir <fe 17 to Xo IO L . s i t k a n a t l l J- 5 H >5* 6 1 1 10 II 12. 13 J * I f /fe I ? F i g . i i s i z e F r e q u e n c y D i s t r i b u t i o n s f o r L . s i t k a n a a n d L. s c u t u l a t a . • L . s c u t u l a t a was c o l l e c t e d a t L i l l y P o i n t o f J a n u a r y 27, 1968; L . s i t k a n a was c o l l e c t e d f r o m J e k e l ' s L a g o o n O c t o b e r 12, 1969. 32 i6r xo > 10 • L . s c u t u l a t a 3 H r "> 1 <\ lo CO H e •H IOO r 8o * U_l o loh * 6 • 50 Ho 30 10 10 L . s i t k a n a 8 ^ io » F i g . 12 S i z e F r e q u e n c y D i s t r i b u t i o n s o f l i t t o r i n e s f r o m Montagaue H a r b o u r Mud F l a t J u l y 30, 1969. 33 lower densities. 4. L. scutulata is more widespread than L. sitkana. occurring in 36 of the 40 sites, whereas L. sitkana occured in only 28 of them (Table 6). 5 . The ratio of L. scutulata to L. sitkana increases as exposure increases. For example only L_. scutulata were present on the heavily exposed transect on Chesterman's Island and on the Victoria Break-water (Table 6 ) . 6. The size of littorines varies inversely with wave exposure. At Chesterman's Beach exposed transect, the largest L. scutulata was 4 mm in length, at Deception Pass State Park relatively sheltered transect, they were 20 mm in length. 7. The highest densities of L. sitkana occur in sheltered damp beaches with many crevices. For example at Brockton Point there were more L. sitkana under boulders and seaweed than on the dry seawall (Tables 6,7). 8. Vertical shores tend to have higher ratios of L. scutulata to L_. sitkana. than horizontal ones. (See Saxe Point horizontal versus vertical site, and pilings versus cobbles at the Anacortes Ferry landing, Table 6 ) . 9. The lower the salinity ( surveying beaches from the Maritime Museum to Jericho to Spanish Banks) the lower the ratio of L. sitkana to L. scutulata (Table 6 ) . 34 Responses of L. sitkana and L. scutulata to Physical Factors Materials and Methods a) Continual Submergence Jekel's Lagoon on San Juan Island (Fig. 11) i s similar to the splash pools of the west coast of Vancouver Island i n that i t contains L. sitkana but no L. scutulata and i s relatively isolated from ocean water which flows into the lagopn only during high high tide. To determine whether L. scutulata could live submerged for an extended period, 50 marked animals were released into the lagoon i n February 1970 and three hundred marked L. scutulata were added to the very high splash pools on Chesterman's Island on May 6 1970. b) Wave Exposure Extremely small L_. scutulata only are found on wave swept beaches such as Chesterman's Island near Tofino. To investigate the action of intense surf as possible factor acting selectively against L. sitkana and larger L_. scutulata the following series of laboratory and f i e l d tests were performed. An equal number of similar sized animals (matched for biomass) were collected and painted with cellulose base paint. The animals were then wetted and allowed to attach to the rock or barnacle substrate of the beach, and then subjected to the wave action of the incoming tide. After a t r i a l period (from 6 hours to two days) the test site and ad-jacent areas were carefully searched and a l l the missing animals w e r e assumed to have been dislodged by waves. Laboratory experiments using 35 cement slabs as a substrate and a running sea water jet to simulate wave force were performed to check field results. c) Temperature Since both species of littorines occur in Alaska, i t was assumed, that differential adaptation to cold temperatures would not be a key-factor in explaining their local distribution patterns. Since L. sitkana is found in higher proportions than L. scutulata in high tide-pools and mud flats, this species might be expected to be more tolerant than L. scutulata to summer high temperatures. To test this, four lots of 20 animals (size 5) of each species were placed into four pyrex finger bowls (lO cm in diameter), containing sea water at 30°C, 30°C, 44°0, and 45°C. Animals were left in the water for 3 minutes after which they were tested for viability by putting them into room temperature sea water. The number of animals showing signs of l i f e after 2 minutes and after 24 hours recovery time was noted. Since a l l the animals exposed to the 30°C water were active after 2 minutes they were subjected to higher temperatures. The water in the finger bowls was heated gradually (from 30°C to 40°C in three hours) and continually stirred. Animals were removed from the warm water periodically and tested for viability. One dish was raised to 42°C, another to 45°C. Animals were then put into room temperature water and the number showing signs of l i f e after 2 minutes and after 19 hours recovery time was noted. d) Desiccation To determine which species of littorines was more tolerant to 36 desiccation size 4 animals of both species were collected from Lonesome Cove, San Juan Island (Pig.10 ) in January 1970. These animals were allowed to dry on paper at room temperature and after 3 days desicca-tion 20 animals of each species were put into sea water and the number of animals showing signs of lif e after 24 hours recovery time noted. Animals ranging in size from 4 mm to 11 mm in length were also collected from Brockton Point in April 1971 and exposed to 4 days desiccation at room temperature, e) Salinity Tolerance A survey of the beaches down a salinity gradient from Second Beach to Maritime Museum to Jericho Beach to Spanish Banks (Fig. 9) indicated that L. sitkana disappeared between Maritime Museum and Jericho Beach. A few L. scutulata occur as far as Spanish Banks. This distribution pattern may indicate that L. sitkana is less tolerant to low salinities than L. scutulata. The following tests were performed to determine the tolerance of littorines to salinity extremes. Specimens of both species from Brockton Point were matched for equal biomass. Ten animals of each species were placed into each of 14 finger bowls. Animals in-fen of the bowls were exposed to distilled water at room temperature and animals in the other 4 finger bowls to sea water at room temperature. At intervals the water in a l l the bowls was drained and replaced with fresh sea water. A l l animals which showed activity after 5 minutes recovery time were placed into clean distilled water. Those animals which did not show signs of lif e were given another hour to recover in the sea water after which they were considered dead. 37 f) Crevices In the Marvista Resort quadrat (Table 7), significantly more L. sitkana than L. scutulata were found in crevices. To determine whether L. sitkana has a superior ability to find these crevices fif t y animals of both species were introduced into a dishpan containing sea water and 15 rocks (not larger than 5 cm in diameter) of different roughness*. Five of the rocks were extremely smooth, 5 were extremely jagged with many crevices and 5 were of medium roughness. After 24 hours the number of snails of each species on each type of rock was noted. Results a) Submergence Most of the fi f t y marked L. scutulata which were released into Jekel's Lagoon in February were recovered two months later. A l l of these animals had grown, indicating that continual submergence did not harm them. The marked L_. scutulata released in the high splash pools on Chesterman's Island on May 6, 1970 were s t i l l alive during the first week in July (Schroeder, personal communication). It would seem that the physical factors measured do not prevent adult L. scutulata from living in high splash pools and lagoons. The absence of this species from the splash pools and lagoons could perhaps be explained by the inability of the planktonic larvae to reach these pools. The larvae are in the plankton from at least February to early f a l l (see p. 16 ) and i f these pools are flushed only during winter storm tides, then the larvae may not have a change 38 to enter. Struhsaker and Costlow (1968),working with Littorina picta larvae in the laboratory,state: "Removal of water from the covered rearing bowls after approximately 3 weeks of development appears to be one of the major stimulii to settlement (of L. pieta larvae). Preliminary results show that larvae settle earlier when they are damp, but not submerged at this period of development." If such drainage action is also necessary for the settlement of L. scutulata larvae, in the field, then one would not expect to find newly settled individuals in tide pools or lagoons at any level. b) Wave Exposure Both field and laboratory data indicate that L. scutulata are less likely to be dislodged by waves than L. sitkana (Tables 8 and 9). L. sitkana with its round shape and many grooves perhaps offers more resistance to wave action than the more streamlined JL. scutulata. Large L,. sitkana were more easily dislodged by wave impact than the smaller ones (Table 9b). However large L_. scutulata appeared as resistant to such forces as smaller ones (Table 8, see Port Renfrew . Nov. 21 to 22). The effect of wave force on littorines would depend on the slope of the beach and the number of crevices. L_. sitkana can live on moderately exposed horizontal beaches with crevices, but not on vertical rock walls experiencing the same type of wave action. c) Desiccation Both species of littorines were equally resistant to desiccation 39 (Table 10). After having been exposed to air for 4 days most animals of both species were extremely active when returned to sea water. It is unlikely that adult animals are ever exposed to such desiccation stress in the field. As mentioned earlier the susceptibility of the egg masses and newly hatched snails to desiccation tends to restrict L. sitkana to beaches which offer some protection. d) Temperature li' scutulata was significantly more resistant to high water temperatures than L. sitkana (Table 11). Temperature sensitivity therefore does not appear to be the factor preventing L. scutulata from living in high tide pools and lagoons. e) Salinity Tolerance Littorina sitkana survived exposure to low and high salinities significantly better than L. scutulata (Table 12, Fig. 13b). The time at which 50 percent of the Brockton Point animals died due to exposure to distilled water was 63 hours for L. scutulata and 89 hours for L. sitkana. The presence of L. scutulata closer to the mouth of the / Fraser River is not related to this species' greater tolerance to low salinity. Planktonic dispersal would allow a few L. scutulata to periodically invade marginal habitats such as Spanish Banks. However these individuals may not have the ability to reproduce and may be killed during periods of low salinity. f) Crevices Significantly more L. sitkana were found on the extremely jagged rocks than L. scutulata (Fig. 13a). This may suggest that L. sitkana 40 smooth medium r o u g h F i g . 13a Number o f a n i m a l s o f b o t h s p e c i e s f o u n d on r o c k s o f d i f f e r e n t r o u g h n e s s . C o n t r o l A n i m a l s K ^ t « ^ ^ . — v Jfc • > ^ ^ \ N=40 0 N ^ \ \ \ \ \ \ L . s c u t u l a t a \ L. s i t k a n a N=100 \ ^ N = 1 0 ° %o 3 0 kO sro fco TO 8© <*o \°» E x p o s u r e Time t o D i s t i l l e d W ater a t Room T e m p e r a t u r e ( H o u r s ) . F i g u r e 13 b T o l e r a n c e o f L i t t o r i n e s t o D i s t i l l e d W a t e r 42 is better able to find shelter than L_, scutulata. Discussion Littorina scutulata is the more widespread species, presumably because i t has planktonic dispersal. Even marginal or unstable habitats probably receive recruitment every year. This would not be the case for L. sitkana with its le ci tH orophic development. One bad season in a year (for example low salinity due to river run off such as at Spanish Banks) could have the effect of eliminating a species with such devel-opment. It would seem that L. sitkana needs crevices for two reasons: 1) in providing shelter from direct wave force (especially on exposed beaches); 2) in providing a damp place for egg mass development. L_. scutulata displays no such dependence on crevices. L. sitkana may attempt to compensate for this disadvantage by having a greater ability to find crevices. High temperatures, continual submergence, and desiccation are not factors preventing L. scutulata from living in the high splash pools and lagoons since this species is equally or more tolerant than L. sitkana. A lower tolerance to salinity extremes could prevent L. scutulata from living in the high splash pools at some time of the year. L_. scutulata survived in these pools from May 6 to at least July 1, 1970. High salinities encountered in the late summer due to desic-cation or low salinities encountered during the winter rains could 43 select against L. scutulata. Planktonic larvae probably prevent L. scutulata from living in these pools since these may be absent during the winter when the pools have communication with the ocean. Low salinities and a lack of planktonic recruits cannot explain the absence of L. scutulata in Jeckel's Lagoon, for i t receives fresh ocean water every high high tide. In this case i t appears as i f the L. scutulata veliger larvae do not settle when submerged. B. VERTICAL DISTRIBUTION Introduction The most striking observation one makes when visiting a rocky sea shore is that the various species of organisms are distributed in horizontal bands between the low and the high tide mark. Thus an eel grass zone, a kelp zone, a barnacle zone, a littorine zone and a black lichen zone can easily be distinguished. The higher an organism is on the shore, the greater will be the time it. is exposed to air. Environ-mental stresses such as desiccation, extreme temperatures and extreme salinities in the case of tide pools become increasingly important as one moves up the intertidal gradient. As a rule, the upper distribu-tion of intertidal organisms is limited by their tolerance to physical factors such as desiccation and high temperatures and their lower distribution is limited by biological factors such as predation or interspecific competition (Connell, 1961). 44 I. The Upper Distribution of Littorines Littorines become extremely rare in the splash zone. Desiccation must ultimately limit their upper distribution however limitation of available food also seems to become increasingly important up the shore. Littorines migrate up the shore in early f a l l probably in response to an easing of the desiccation stress encountered in the summer as well as in response to an increased abundance of diatoms (which in turn also is a result of decrease in desiccation) at high tidal levels. Two pilot experiments were undertaken in an attempt to evaluate the relative importance of food limitation and desiccation in setting the upper limit -to,littorine distribution. Materials and| Methods a) Survival of L. scutulata in the splash zone The first test was to determine whether littorines can survive higher on the shore than they are normally found. On February 26, 1970, three cages containing 10 L. scutulata each were attached to the pilings at Lil l y Point, Point Roberts (Fig. 9) from to l-j feet above the highest observed littorine. After 38 days the cages were examined for live snails. b) Response of Littorines to Food in the Upper Intertidal Region To determine the response of littorines to the presence of food at high tide levels, two slabs were set up on a shelf just below the black lichen zone at Cantilever pier San Juan Island (Fig. 10). One 45 of the slabs was clean and the other was surfaced by a mat of diatoms. Ten littorines of each species were allowed to attach on each of the slabs. On the next low tide (the high tide just washed the slabs), the number of littorines on each slab was noted. Results a) Survival of L. scutulata in the splash zone After being caged for 38 days in the black and yellow lichen zone, 18 out of 23 L. scutulata were s t i l l alive. This indicates that desic-cation at these levels does not k i l l the animals. However limited algal abundance combined with a limited time available for feeding would make the high intertidal and splash zone an unfavorable habitat. b) Response of Littorines to Food in the Upper Intertidal Region Two L. scutulata and 3 out of 10 L. sitkana remained on the diatom covered slab in the high intertidal zone at Cantilever pier after one high tide. No animals remained on the claan slab. Unfortunately, this* experiment was of short duration and desiccation was not a factor in that the atmosphere was. noist. This test indicated only that littorines may tend to stay in places where there is food. (Responses of littorines to food will be discussed in the next section). II. Limits to the Lower Distribution of Littorines When taking transects at Saxe Point, Victoria and at Deception Pass State Park i t 'was observed that limpets of the genus Acmaea (especially Acmaea scutum) become more abundant and littorines become less abundant at the bottom of the shore (Fig. 14s). Similarly, at 46 Figure 14a 47 Cantilever pier around the 0 ft. tidal level (U.S. tables) smooth bolders resting in the gravel, appeared to be without algae but bore many Acmaea scutum and no littorines. Fencing off an area and removing the limpets resulted in abundant algal growth within a month. It was conceivable that the grazing action of Acmaea scutum could make these bolders unattractive to littorines. To test this hypothesis a littorine-Acmaea interaction experiment was set up. The drop in littorine abundance at lower tidal levels is also correlated with an increase in intertidal predators such as the star-fish Leptasterias hexactis and Pisater ochraceus and the snail Searlesia  dira (M. Lloyd, B. Menge, personal communication). A l l these species have been observed to feed on littorines in the field. The calculated electivity coefficients of the prey species for the predators Leptasterias hexactis (Table 14, courtesy of Menge) and Searlesia dira (Table 13, courtesy of M. Lloyd), indicate that littorines are always taken at greater proportions than they are found in the environment. Menge (personal communication) is of the opinion that littorines are a convenient food source for Leptasterias in that this starfish can be digesting a littorine', Cand at the same time be foraging for more food. Perhaps the increased abundance of Acmaea and decreased abundance of littorines at lower tidal levels can in part be explained by dif-- . ferential predation pressure. Menge (1970) suggests, that Leptasterias can catch littorines more easily than Acmaea spp. since littorines cannot clamp down and have relatively weak escape responses when com-pared to Acmaea spp. (Table 15). 48 To determine whether predators feed selectively on littorines as opposed to limpets, experimental cages containing Acamea paradigitalis, L. scutulata and Leptasterias hexactis were set up in the mid and low intertidal. Materials and Methods a) Acmaea scutum, L. sitkana Interaction A cement slab (50 cm by 50 cm by 4 cm) was suspended from the Friday Harbor Laboratories pier on August 16, 1969 between the 0 and 2 foot tide mark (U.S. tables). Six stainless steel cages (Fig. 15) (10 cm by 20 cm) were screwed to the slab using plastic washers and stainless steel screws. Limpets (Acmaea scutum) between 9-5 and 16 mm in length and L. sitkana between 7 and 12 mm in length were matched for biomass by using information contained in Fig. 14b. The limpets were marked by tagging their shell with self-sticking wire markers (Brady Micro Markers, W.H. Brady Co. 727 W.Glendale Avenue, Milwaukee 9, Wis.) and adding a drop of decophane technical cement (Rona Pearl Corporation, Bayonne, New Jersey). Twenty animals, either a l l A.scutum, a l l L. sitkana or 10 of each species were then put into the cages. On September 20, 1969 the growth increments of the animals were measured. b) Effect of Leptasterias hexactis predation on A.- paradigitalis and L_. scutulata On July 16, 1969 eight mesh bags, sewn from plastic screening, with a medium sized rock placed in each, together with 10 small L.-scutulata. 10 small A. paradigitalis and two Leptasterias hexactis L e n g t h ( mm ) o f L i t t o r i n a s i t k a n a F i g . 1 5 Cages used for Acmaea-Littorine int e r a c t i o n experiment. Cement slab and st a i n l e s s s t e e l cages were suspended from the Friday Harbour Marine Laboratories p i e r . 51 were closed with rubber bands. Four of the bags were placed at the -0.5 foot tidal level and four at the +2 foot tidal level (U.S. tables), at Cantilever Pier. After three days the number of live animals and empty shells were noted. Results a) Acmaea scutum. L. sitkana interaction There was no significant difference in the growth rate of A. scutum grown alone and grown with L. sitkana, nor was there a signifi-cant difference in the growth rate of L. sitkana grown by themselves and with A. scutum (Table 17). However the direction of the growth rates may indicate that in mixed species cages A. scutum was growing at the expense of L_. sitkana. More data is needed to clarify this point. b) Effect of Leptasterias hexactis predation on Acmaea  paradigitalis and L. scutulata. Under the experimental conditions L_. hexactis appeared to feed on L_. scutulata and A. paradigitalis at the same rates (Table 18). How-ever predation pressure was significantly more intense at the low tide level than the mid tide level (Table 18J. Summary It would seem that the upper distribution of littorines is set by desiccation acting on the animals directly and/or indirectly in decreasing their food abundance. In either case the intertidal habitat becomes increasingly less favorable up the shore. 52 If i t is true that the drainage action encountered in the inter-tidal is a major stimulus to the settlement of littorine larvae then one would not expect L. scutulata to settle subtidally. The maximum density of this species then should be found in the intertidal. The lower distribution of littorines is correlated with an in-creasing abundance of predators such as Pisaster ochraceus, .,L;e_ptasterias hexactis and Searlesia dira. A l l these species have been observed to feed on littorines in the field, and evidence is presented that the intensity of predation of L. hexactis on littorines and limpets increases down the shore. The abundance of limpets such as Acmaea scutum increases down the shore as the abundance of littorines decreases. Positive evidence was not found that competitors limit the lower distribution of littorines. 53 THE ABUNDANCE OF LITTORINES A. Behavioural Responses Introduction The abundance of sessile organisms such as barnacles and dandelions is a function of the number of juveniles (barnacle larvae or dandelion seed) reaching a particular habitat and their subsequent survival success. In the case of mobile animals abundance is also affected by their ability to migrate from unfavorable to favorable habitats. The highest densities of adult and recently settled L. scutulata were found on barnacle covered beaches such as those on Chesterman's Island and at L i l l y Point. Newly settled L. scutulata are strongly associated with barnacle interstices which probably act to trap the larvae. None were ever found on smooth rock surfaces. The number of new recruits entering a L_. sitkana population is directly dependent on the number of egg masses the females in that area lay, their hatching success and subsequent survival. Such mortality factors as food scarcity, desiccation, predation, surf action etc. act to thin out littorine populations. Particular responses by the animals may mitigate the effect of such factors. Migration from an unfavorable habitat (e.g. one without food or shelter) to a more favorable habitat would be such a response. In order to study such behaviour a number of experiments was performed to determine the response of littorines to food abundance, shelter and crowding. 54 Materials and Methods a) Behavioural Response to Crowding To investigate the possibility of dispersal behaviour in response to overcrowding, a number of L. sitkana (l2 or 36) were allowed to attach to the center of four concrete paving slabs (l9.5 cm by 19.5 cm). These slabs were submerged in a water table in the laboratory and the number of animals reaching the edge of the slabs after 5 minute tr i a l periods was noted. b) Behavioural Response to Food Levels 1. Field Observation On August 11, 1969 an observation was made while diving at high tide over the cement slabs used in a density-species interaction experiment (to be discussed later). Many littorines had moved on to cement slabs covered with diatoms and very few had moved on to clean slabs although equal access to both types was possible. The number of littorines of each species was counted on 6 clean slabs and 6 diatom covered slabs. 2. Laboratory Study During September an experiment was set up to investigate the responses of littorines to a clean and a diatom covered slab. The slabs were put into a tank with running sea water. Ten L. scutulata and 10 L. sitkana were placed into the center of each slab and the times at which the animals reached the edges were noted. Those animals reaching the edge were replaced to the center of the slab as soon as their tentacles protruded over the edge. 55" c) Response of L. sitkana to the presence of food To investigate the capacity of L. sitkana to use sensory stimulii in finding food, a glass plate was used to divide a water table into two sections (Fig. 16). A cement slab (l9.5 cm by 39 cm by 4 cm), covered with diatoms was introduced into one section and a clean slab into the other section. The water level was 8 cm deep (enough to cover the slabs and the snails). Fresh sea water was run over each slab to' the drain at the other end. Fifty L. sitkana were distributed evenly between the edges of the glass plate and the drain so that 25 snails were in each section. The whole water table was covered with black plastic so that light gradients would not play a role in the orienta-tion. d) Behavioural Response to Crevices To test the idea that crevices are more attractive to littorines than smooth surfaces four oyster shells (length 12 cm) were placed in a finger bowl (diameter 10 cm). Two of the oyster shells were com-pletely covered with dead barnacle shells (therefore possessing many crevices) and two were smooth and devoid of barnacles. Water was poured into the bowls and 5 littorines of each species were placed on each of the shells. After 10 minutes, the number of littorines remain-ing on each shell was noted. The same tests was run 3 more times changing the order of the oyster shells and using new animals. Results a) Behavioural Response to Density The results of Table 19 indicate that dispersal of L. sitkana D i r e c t i o n of r u n n i n g sea water I No \\ Food Food — G l a s s p l a t e P o s i t i o n of 50 L i t t o r i n a s i t k a n a 0 " ~ 'Drain Fig.JJ-6 M o d i f i c a t i o n of a water t a b l e t o t e s t the h y p o t h e s i s t h a t l i t t o r i n e s can d e t e c t the presence of food a t a d i s t a n c e . S c a l e : 1mm = 1cm 57 was significantly greater at low densities than at high density. At high density the animals tended to attach and move over each other more so than at low density. b) Behavioural Response to Food Levels 1. Field Observation Littorina sitkana appears to be sensitive to food levels in that they move onto diatom covered slabs at a significantly greater rate than onto clean slabs. L_. scutulata did not show this trend (Table 20). 2. Laboratory Experiment After one hour significantly more animals had reached the edges of the clean slab than the diatom covered one. Both species spend more time on the diatom covered slab than the clean ones (Table 21). c) Response of L. sitkana to the presence of Food After 14 hours the positions of the snails in the food choice tank were noted (Table 22). There was no difference between the number of snails located in each section, therefore i t would seem, that L. sitkana does not use water born chemical stimulii to detect food. d) Behavioural Response to Crevices The results in Table 23 indicate that oyster shells with barnacles are more attractive to both littorine species than are smooth oyster shells without barnacles. 58 Discussion When L. sitkana were crowded they did not disperse because crowded animals exhibited a tendency to attach to one another. Animals of both species reacted to the presence of food in that they dispersed less on diatom covered slabs than on clean slabs.. L. sitkana does not appear to use chemical stimulii in finding food. Animals may move randomly with respect to food and when finding i t stay there. Both species of littorines react to crevices in that they dis-perse less when put on barnacle covered oyster shells than on smooth ones. Crevices would protect littorines from predators, direct wave force and provide a damper subhabitat thus decreasing desiccation and possibly increasing algal productivity. B. Density-Species Interaction Experiment Introduction If density dependent factors operate to regulate littorine densities at a certain level, greater mortality rates and perhaps lower growth and reproductive rates would be expected at densities higher than normally found whereas the reverse might be true at lower densities. To test this^an experimental investigation into the effects of density on survival, growth and reproduction of littorines was i n i -tiated. This investigation also helped to determine i f food limitation affected littorines in the course of a year and i f competitive 59 relationships existed between the two species. Materials and Methods To manipulate both densities and specific composition of littorine populations over a period of time, i t was necessary to retain the animals in cages. The cages used were plastic mesh cylinders constructed of vexar (Crown Zellerbach Co.) height 45 cm., circumference 100 cm and bottom diameter 33 cm sewn together with 20 lb tested nylon monofilament. The cages were weighted down by concrete stepping stones (4 cm by 19.5 cm by 39 cm) which also provided grazing surfaces for the littorines (Fig. 17). Twenty-six stepping stones were placed at the 2 to 3 food tidal level (U.S. tables) near Canti-lever Pier close to the Friday Harbor Laboratories.. This site was chosen because i t offered medium wave exposure and because both species of littorines were abundant. The slabs were left on the shore for 5 days prior to the animals being placed into the cages so that they would weather naturally and so that algae could settle on them. Animals of both species were collected at Cantilever Pier and on Gull Reef (north of San Juan Island) on June 15, 1969. A series of screens was used to match animals for size in a l l the treatments. Measurements indicated that sieving was a convenient method of sepa-rating animals of similar biomass. The lips of a l l experimental animals were marked with tech pen paint (Mark-Tex Corp. 161 Coolide Ave., Englewood, N.J.) so that new 6o Fig.17 Cement stepping stones removed from vexar cages used i n the density-species i n t e r a t i o n experiment. Note the diatom matts on the r i g h t bottom slabs. F i g . 18. Arrangement of cages at Cantilever p i e r beach. 62 growth could be measured by lip increment (Fig. 2 3 ) . Either 20, 40, or 80 animals (all L. sitkana, a l l L_. scutulata or half of each species) were put into the 24 cages on June 18, 1969. Twice as many mixed species cages as single species cages were used so that an equal number of animals would be subjected to mixed and single species treatments. A l l mixed species treatments were replicated four times and single species twice. All experimental animals were moistened so that they could attach to the slabs before the cages were sewn up. One cage was used as a control giving an indication of the quantity of algae produced in the absence of grazers . The associated slab was turned over at each checking .time giving a rough estimate of algal productivity during the period of littorine growth. Another slab which had broken in two served as an uncaged control giving an indication of the standing crop of algae under a natural density of grazers, which corresponded roughly to the medium density treatments. At each inspection measurements of lip increment and final length of a l l snails were obtained. The total number of individuals per cage was recorded together with the number of empty and broken shells. Surviving snails were repainted with a contrasting colour at each inspection and dead or missing animals replaced with new ones every two months to maintain original densities. A chlorophyll extraction method was used to estimate the standing crop of diatoms (Castenholz, 196l). Two standard samples were taken for each slab. Each sample consisted of scraping an area 63 (5 cm by 1.3 cm) five cm from the edge of the slab five times. Algal scrapings and rock chips were placed in screw-cap vials (18 mm by 100 mm) containing 20 cc of absolute ethanol. The samples were allowed to extract at room temperature for 48 hours. The relative abundance of algae was estimated by determining the absorption of the chlorophyll extract in a Bechman D.U. spectrophotometer at s l i t width 0.3 and wave length of 665 m,A. A visual estimate of standing crop of algae was made concurrently with the chlorophyll estimate of standing crop by scoring each slab on a numerical scale. Heavy mat of algae (diatoms mostly) 5 Medium thick mat of diatoms 4 Thin mat of diatoms 3 Brown film 2 Faint Brown film 1 Clear Surface 0 In July 1969. a l l the diatoms were found to belong to the genus Fragellaria. The relationships between optical density at 665 m-/t6 versus wet weight of Fr.agellaria and between wet and dry weight of Fragellaria were obtained by use of regression analysis (Fig. 19). ' From December 1969 to June 1970, visual estimates of the standing crop of algae were used since a high correlation (R=0.88 p <.00l) was found to exist between subjective and objective measurements (Fig. 20). An additional piece of information was obtained from this experiment when L. sitkana commenced laying egg masses in the cages. F i g u r e 19. OPTICAL DENSITY vs. W E T WEIGHT aw* J?RV WEIGHT vs. W E T WEIGHT of Frajellaria <0 . , O-iO o.xo a. so O.HO 0.10 Wet Wei^ Kb o£ FrageUaria sp.. in grams * O p l - i c a l3 ) e n s i o f Standard algal Scrap ing C S c m v I .Scm) exhrac l fed in 20 m\ o f a b s o t a r e e - f t a n o l . 65 Pig. 20. The r e l a t i o n s h i p of subjective estimate of standing crop of algae ( Numerical estimate squared ) and objective estimate ( o p t i c a l density of chlorophyll extract at 6 6 5 m/t). The c o r r e l a t i o n c o e f f i c i e n t was 0.880 NUMERICAL E ST IMATE OF STANDING CROP SQUARED 67 The position of the egg masses and their colour were noted. Colour of the egg masses is indicative of the stage of development of the embryos.- Egg masses were not disturbed, but unfortunately, not one young snail was recovered, presumably because they were washed off the slabs and through the coarse mesh. FOOD ABUNDANCE The standing crop of algae in an area depends on the settling rate and growth of the algae minus the grazing intensity minus physi-cal removal by such factors as wave wash. The algal cover in the cages was monitored for a year using the subjective numerical system described previously. Castenholz (l96l) found that in the colder seasons carpets of dark brown diatoms cover the rocky intertidal of the southern Oregon coast. In the summer these rocky surfaces were almost devoid of dia-toms except for patches correlated with low grazer abundance. The same phenomenon seemed to occur at Cantilever Pier. In the winter (September, October and December) food was abun-dant in a l l the density treatments (Fig. 2l). This was probably due to a high productivity of the diatoms combined with low grazing rates. In February and April i t appears as i f the grazing activity of the littorines in the high density cages was beginning to reduce the standing crop of algae. In the summer (July, August and June) three distinct food levels were maintained by the three snail densities. A great amount of food was present in the low density cages and the 68 F i g u r e 21 N u m e r i c a l e s t i m a t e o f s t a n d i n g c r o p o f a g a e a t t h r e e s n a i l d e n s i t i e s a s a f u n c t i o n o f t i m e . One s t a n d a r d e r r o r i s p l o t t e d o n e a c h s i d e o f t h e mean. s o l i d l i n e d a s h e d l i n e d o t t e d l i n e l o w d e n s i t y medium d e n s i t y h i g h d e n s i t y 69 A 70 70 F i g . 22 N u m e r i c a l e s t i m a t e o f d i a t o m a b u n d a n c e on c o n t r o l s l a b s . U n c a g e d c o n t r o l s ( mean a n d r a n g e ) g i v e a n i n d i c a t i o n o f s t a n d i n g c r o p o f d i a t o m s u n d e r n a t u r a l c o n d i t i o n s ; t h e c a g e d c o n t r o l s l a b was t u r n e d o v e r e a c h c h e c k i n g t i m e t h u s g i v i n g a r o u g h e s t i m a t e o f p r o d u c t i v i t y . s o l i d l i n e U n c a g e d c o n t r o l s ( s t a n d i n g c r o p o f d i a t o m s ) d a s h e d l i n e C a g e d c o n t r o l ( p r o d u c t i v i t y o f d i a t o m s ) 73 • high density cages were devoid of food with the middle density cages supporting a greater amount of food than the high density cages (Fig.2l). High grazing intensities may have prevented macroscopic algae from establishing themselves in the high density cages (twice natural density). Ulva appeared in the medium and low density cages by Septem-ber and Enteromorpha and Coilodesme were found in October (Tables 35, 36). The abundance of diatoms on the two uncaged control slabs was within the range of that of the experimental cages with a low standing crop in the summer and high standing crop in the winter (Fig. 22). The rough estimates of diatom productivity ranged from scale 2 to 4 with no seasonal trend (Fig. 22). This observation may suggest that the low observed standing crop of diatoms in the summer is due to grazing pressures. GROWTH RATES Methods For the purposes of analysis i t was necessary to convert growth data representing l i p increment and final length to original length and length increment. Lip and length increment are directly proportional since the angle subtended by the whorl at the axis of the animals remains constant regardless of snail size (Fig. 23). Regression of l i p increment on length increment was obtained for both L. sitkana and L. scutulata (Figs. 24, 25). These relationships were then used to convert a l l l i p increment data to length increment. The length increments were 73 F i g . 23 D i a g r a m i l l u s t r a t i n g t h e r e l a t i o n s h i p b e t w e e n l i p i n c r e m e n t a n d l e n g t h i n c r e m e n t a n d b e t w e e n o r i g i n a l l e n g t h a n d f i n a l l e n g t h o f L . s c u t u l a t a . 75 F i g . 24. R e l a t i o n s h i p b e t w e e n l e n g t h a n d l i p i n c r e m e n t o f L . s i t k a n a . GRAPH NO- 1 L - s i V K a n a Y = -0-5011E 00 + 0-4055E 01X N = 42G THE PROBABILITY OF THE SLOPE BEING ZERO IS 0.0000 2 0 4-. 1 6 o H h3 S 0 X X X XX X>K )K X X-)SKX >K. XX X XX X X M X X X X/ X X XX3KXX/ X XX X X / XSK>iK>B80p6o< X X X w X >B8K X,>&<X X X XX30&X >B3KX X X 0 3 4 LENGTH INCREMENT (mm) 76 F i g . 2 5 . R e l a t i o n s h i p between.length and l i p increment of L. s c u t u l a t a . GRAPH NO" 2 - L . s c u > u l a l & Y = 0-2791E.00 + 0°3137E OIX N = 395 THE PROBABILITY OF THE SLOPE BEING ZERO . IS 0.000 . 2 0 + LENGTH INCREMENT (am) 77 then subtracted from the final length of animals to yield the original length. Growth indices were calculated for a l l species and density treatments by dividing the adjusted mean growth increment by the number of days growth. These indices were then plotted against time (Fig. 26 to 29). Results and Discussion Growth rates in L. sitkana are much greater than for In scutulata at a l l times of the year and at a l l densities. This trend holds when length increment is converted to increment in biomass. For example, in low single species cages from July to August L_. sitkana (biomass .01225 grams) increased 82$ in biomass whereas the same dry weight L. scutulata increased jfo in biomass (Table 25). Since as mentioned previously the measured effect of the two species on the diatom standing crop was similar i t would indicate that Li. sitkana is more efficient than L. scutulata in converting food to biomass under the conditions of this experiment. Maximum growth for both species occured in the summer months (April to September) and a minimum growth occured in the winter (October through February). Low growth was associated with low temperatures? however food was actually more abundant during the winter than the summer months. Activity was much less in the winter than in the summer. In the summer most of the animals were found crawling on the slabs and on the vexar, whereas in the winter most of them were found aggregated under or on the sides of the slabs. This behaviour is doubtless 78 Figures 26,27, 28, 29. Growth indices ( length increment x 1000 mm/ number of days ) under density and species treatments as a function of time. Legend Density comparisons Low density Medium density High density Species Comparisons Single species Mixed species Stars between two adjacent data points indicate the l e v e l of s i g n i f i c a n c e at wich the n u l l hypothesis of no difference between the values has been rejected. Absence of a star indicates no s i g n i f i c a n t d i f f e r e n c e . . 0 5 . 0 1 . 0 0 1 79 •j^H Aug. SepV- Oc-V- 2>ec. Feb. April 3u.ne-82 83 adaptive serving to offer the snails protection from storms and winds. In the summer (July, August, September and June) L. sitkana grew at different rates under the three density treatments. The high density, low food availability treatments produced the lowest growth rate and the low density treatment having high food availability showed the highest growth rate (Fig. 26). L. scutulata responded similarly, however, in this case, there was no difference between medium and low densities (Fig. 26). This would indicate that L. scutulata grew at its physiological maximum at medium densities and that increasing food-abundance did not result in a growth response. Although algae could not be detected in the high density cages in July, August and June, the animals contained therein continued to grow over this period indicating some nutrient input. This suggests, that the animals were removing the algae at ;he rate of production. Since L. scutulata shrank in size during July (Fig. 26) i t is apparent that erosion must have been responsible. This could conceivably be associated with the fact that this species just recovered from re-production. The differences in growth rates among the three densities for Jj. sitkana in October, December, and February are apparently not direct-; ly related to food abundance, as during this time food was equally abundant under a l l densities. An explanation of these differences could either be due to individual interaction effects, whereby increased competition for sheltered places as density increased could result in 84 lower observed growth rates, or perhaps as a consequence of a delayed response to differences in food availability over the previous summer.. There was no difference in growth rates between single and mixed species treatments for either species at low densities (Fig. 27)*-''j«-.. sitkana survived better with animals of their own species than with L_. scutulata at medium densities in the f a l l (September, October, December) and poorer in the spring (April and June) (Table 28). There was no difference in the food availability between mixed and single species treatments. However L_. sitkana experienced a reproductive peak in the f a l l and the presence of L. scutulata may in someway have interfered • with the reproductive behaviour and food foraging ability of L. sitkana at this time. In the spring the situation was reversed, indicating that intraspecific effects were more important than interspecific effects-at this time. A similar effect was observed in September for high density L_. scutulata when animals in mixed species treatments grew better than in single species treatments (Fig. 29). L. SITKANA NATALITY "\ ^ . In both the f a l l and in the spring proportionately fewer egg masses were laid by L. sitkana in single species treatments at high densities than at lower densities (Figs. 30, 32a and Table 26). This densitiy dependent effect was more pronounced in spring than in the f a l l in that numerically fewer egg masses were laid in high density cages than in low density cages (Fig. 32a). In the f a l l such a density dependent response could have been 85 mediated through food limitation of the adult snails in the high density cages during the summer, since at low densities animals' had more food and also grew more (Figs. 21, 26). It is unlikely that direct availability of food resulted in the density dependent natality in the spring because even in the high density cages there was abundant food in the winter and early spring (Fig. 2l). Since, as already mentioned, littorines tend to aggregate in sheltered sites which are also prefered for egg deposition, i t is possible, that increased interference with egg laying occured as the densities increased. The number of egg masses produced at 20 and 40 L. sitkana per cage (uncorrected for equal density of animals per cage) were signifi-cantly greater for single species than for mixed species cages in the f a l l and spring (Figs. 30, 32a, Table 27). This would indicate that the presence of L. scutulata has an effect on the natality of L. sitkana. However such a comparison does not take account of total snail densi-ties per cage. In Figures 31 and 32b natality rates for pure L. sitkana populations have been halved to estimate production as influenced by an equal number of animals of the same species. Thus in a cage con-taining a total of 20 L_. sitkana producing 50 egg masses, yield the estimated natality of 25 egg masses for 10 L. sitkana in competition with an equal number of their own kind. A greater number of egg masses were laid per individual L. sitkana in single species cages than in mixed species cages in the f a l l 86 F a l l N a t a l i t y o f L. s i t k a n a 40 r ON 10 20 40 80 Number of L. sitkana per cage (uncorrected f o r equal density) F i g . 30 The number of egg masses produced from September 17 to December 9 1969 under the three density treatments. Note that the L. sitkana d e n s i t i e s for mixed species cages are 10. 20, and 40 L. sitkana per cage. O Single species X Mixed species F a l l N a t a l i t y Of L . s i t k a n a 87 A Number o f L, s i t k a n a p e r Cage ( c o r r e c t e d f o r e q u a l d e n s i t y ) F i g . 3 1 . The Number o f E g g M a s s es P r o d u c e d f r o m S e p t e m b e r 1 7 t o December 9 1 9 6 9 a s a F u n c t i o n o f D e n s i t y . N o t e t h a t t h e v a l u e s i n t h e s i n g l e s p e c i e s c a g e s were d i v i d e d i n h a l f t o c o r r e c t f o r a n e q u a l number o f a n i m a l s a n d a n e q u a l number o f L . s i t k a n a p e r c a g e . The number o f e g g masses p r o d u c e d was s i g n i f i c a n t l y g r e a t e r i n t h e two l o w e r d e n s i t y t r e a t m e n t s i n s i n g l e t h a n i n m i x e d s p e c i e s c a g e s . S i n g l e S p e c i e s M i x e d S p e c i e s 88 0 N 0» 0.10 3 2 10 v> in L _Q 10 i •i 2 |2 Spring N a t a l i t y of L. sitkana -lew-Nunber of L. sitkana per Cage (uncorrected for equal density) Number of L. sitkana per Cage (corrected for equal density) F i g . 32 The Number of Egg Masses Produced by L. sitkana by A p r i l 17, 1970 as a Function of Density. Single species Mixed species 89 (Tables27 ,28, Fig. 3 l ) . This discrepancy was greatest at low and medium densities (lO and 20 animals per cage). This could be related either to the fact that there were only half the number of L. sitkana in each mixed species cage and individual animals may have had a greater difficulty in finding a mate at lower densities or to direct inter-specific interference. At 40 animals per cage there was no significant difference between production of egg masses in mixed and single species cages. The reason for this seems to be associated with generally reduced egg mass production in the high density pure _L. sitkana cages. If interspecific interference rather than mate finding ability is responsible for depressed natality at lower densities, then at high densities intraspecific interference would appear to equal interspecific interference. In the spring the same trend was observed. Both at 20 and at 40 L. sitkana per cage (corrected for equal density of animals) signifi-cantly fewer egg masses were produced per individual .L. sitkana in mixed species cages than in single species cages (Fig. 32b, Table 27). This indicates that L. scutulata in some way interfered with egg mass production or deposition at these higher densities. Significantly fewer egg masses were found in the spring in the more wave exposed cages (Table 28) than in the more sheltered cages. This phenomenon was not oberved in the f a l l indicating that exposure to winter storms may have influenced natality. 90 SURVIVORSHIP AND MORTALITY Methods and Materials Mortality and survivorship data should complement each other. However a few animals were always lost, possibly by emigration through tears in the cage fabric. Losses by this means were most pronounced in December when storm action resulted in large rips in cages 6 and 21 (Table 38). Survivorship data was analysed (courtesy of Dr. Niel Gilbert) by plotting survivorship curves Log Original Number of Animals versus Time) for a l l 24 cages. Analysis of co-variance was used to compare the slopes of these curves (representing rate of survival) between single and mixed species treatments and among density treatments. Since snails have hard shells, mortality can be measured by counting the number of empty and crushed shells directly. It was assumed that the causes of mortality for crushed shells were due to physical factors (e.g. being hit by water born logs and rocks) and these data were considered separately from empty shell mortality. Since food availability differed from summer to winter, the empty shell mortality data was partitioned into two parts. As mentioned previously, winter food was not limiting at any density but in the summer distinct food levels were maintained by the three snail densi-ties. To test the idea that shelter may have been limiting at high' densities, the number of animals in exposed places (the top of the slabs and on the exposed cage walls) were counted on March 3 and March 6,1970 . 91 Al l the low numbered cages ( l to 12) were situated on one side of the beach, whereas the higher numbered cages (l3 to 24) were on the other side (Fig. 18). The right cages were resting on a shelf, whereas the.left cages were resting on a cobble gradient which sloped into deeper water. The left cages were thus exposed to direct wave action, whereas the shelf on the right side of the beach tended to break the wave force, and thus offered these cages more protection. Data was stratified into two groups to test for position effects. Chi-squared tests were performed to determine whether mortality-data and survivorship data and the number of non-sheltered animals conformed to the assumptions that no difference between the single and mixed species treatments existed and further that there was no differ-ence among the proportional mortality rates of the three density treatments (Figs. 35, 36; Tables 30, 3l). The total number of animals was split equally between single and mixed species cages and parti-tioned among the density treatments in the ration of 1 to 2 to 4 for the overall goodness of f i t to the two assumptions. Further chi-squared tests were performed to determine whether species effects and or density effects could explain the discrepancy from the expected values (Tables 30, 31). Animals of both species often released fluke larvae. Upon dissection i t was revealed that these parasites had taken over the entire digestive gland and gonad. It was conceivable that such heavy parasitism could lead to death of the snails. To determine whether species composition and density of snails had an effect on the 92 proportion of animals parasitised, original animals of both species and from a l l densities were isolated in individual stacking dishes in June 1970 in an attempt to observe the release of fluke larvae. Results The comparison of the slopes of survivorship curves showed that neither species nor density effect were detectable (Table 29). However the number of original experimental animals surviving one year is greater for L . sitkana under single species treatments than under mixed species treatments and also greater under lower than under higher densities (Fig. 34; Table 30). L . scutulata showed no difference between survival in mixed and single species treatments at a l l densi-ties. However survival in the high density single species treatments was proportionately higher than in the single species lower density treatments. This indicates that survival improved as the density was increased (Table 31; Fig. 34). In this location JJ. scutulata appeared to live longer than L_. sitkana for 49$ of the original L . scutulata survived one year, where-as only 9$ of the L . sitkana did. No species or density effects were detected for the crushed shell mortality of either species. The overall chi-squared tests for goodness of f i t of observed values to the two assumptions of even mortality with regard to species composition and density treatment was poor for both species (Tables 30,' 3 l ) . None of this discrepancy however could be attributed to species or density effects. The summer empty shell mortality for both species was smaller 93 luly Aug. Sept. Oc*. Secamfeer Feb. Apri l 3 u n e -Fig.33 M o r t a l i t y I n d e x o f L. s i t k a n a and L . s c u t u l a t a as a f u n c t i o n o f T i m e . ZO 40 80 Number o f A n i m a l s p e r Cage F i g . 3 4 O r i g i n a l Number o f L i t t o r i n e s s u r v i v i n g one Y e a r a s a f u n c t i o n o f D e n s i t y . S i n g l e S p e c i e s Cages M i x e d s p e c i e s C ages 95 i_ 1 • 2 0 **-0 80 Number of Animals per Cage F i g . 35 Number of Empty S h e l l s of L. s i t k a n a found i n Winter and Summer as a F u n c t i o n of D e n s i t y . In mixed s p e c i e s treatments s i g n i f i c a n t l y more animals d i e d i n the w i n t e r . 96 io bo SO 30 </> "S io a £ in 0 i-J) 5b io-2o •o W i n t e r io Summer M o r t a l i t y D a t a L . s c u t u l a t a to xo HO Number o f a n i m a l s p e r cage .A M i x e d s p . S i n g l e s p e c i e s 90 M i x e d s p e c i e s S i n g l e s p e c i e s 80 p i g « 3 6 . Number o f Empty S h e l l s o f L . s c u t u l a t a f o u n d i n W i n t e r a n d Summer a s a F u n c t i o n o f D e n s i t y . I n t h e w i n t e r L . s c u t u l a t a a t h i g h d e n s i t i e s s u r v i v e d s i g n i f i c a n t l y b e t t e r i n s i n g l e s p e c i e s c a g e s t h a n i n m i x e d s p e c i e s c a g e s . P r o p o r t i o n a t e l y f e w e r a n i m a l s d i e d u n d e r h i g h d e n s i t i e s s i n g l e s p e c i e s t r e a t m e n t t h a n u n d e r l o w e r d e n s i t i e s s i n g l e s p e c i e s t r e a t m e n t s i n t h e w i n t e r . Summer M o r t a l i t y L . s i t k a n a 2o Ho — i 80 L . s c u t u l a t a .. * ^ . . . . . ^ > > ^ t ^ ' T B ' < a ! • " — " r 1 lt> HO SO Number o f A n i m a l s p e r Cage M o r t a l i t y P a t t e r n s i n r i g h t a n d l e f t c a g e s . F i g . 3 7 Number o f Empty S h e l l s f o u n d i n t h e summer a s a f u n c t i o n o f D e n s i t y . N o t e , t h a t t h e r e i s no d i f f e r e n c e b e t w e e n l e f t a n d r i g h t c a g e s . R i g h t Cages L e f t C a g e s ^ S i n g l e s p e c i e s c a g e s X M i x e d s p e c i e s c a g e s 98 Winter M o r t a l i t y L. s i t k a n a Mixed s p e c i e s L e f t cages S i n g l e s p e c i e s L e f t Cages Mixed s p e c i e s R i g h t Cages S i n g l e s p e c i e s R i g h t cages HO 80 L. s c u t u l a t a Niunber of Animals per Cage .X Mixed sp. L e f t Mixed sp. R i g h t S i n g l e sp, L e f t S i n g l e sp, Righ t P i g . 38 Number of Empty S h e l l s found i n the Winter as a F u n c t i o n of D e n s i t y . Note, t h a t the animals i n the r i g h t cages s u r v i v e d b e t t e r than those i n the l e f t cages. 99 Crushed S h e l l M o r t a l i t y 2zo 0) S. n lis 0* «> 110 n 2$ V 3 c. L, s i t k a n a ..•X Mixed sp. • A S i n g l e sp. 3LO MO to lOr 2 _ ST L. s c u t u l a t a Mixed S p e c i e s A S i n g l e s p e c i e s F i g . 3 9 . 20 MO ZO Number of Animals per Cage T o t a l Number of crushed s h e l l s from June 1 9 6 9 t o June 1 9 7 0 as a F u n c t i o n of D e n s i t y . 100 F i g . 40. T o t a l Number of animals found i n exposed p l a c e s i n the experimental cages on two o c c a s i o n s ( March 3 and March 6 1 9 7 0 ) as a f u n c t i o n of d e n s i t y . P r o p o r t i o n a t e l y more animals were found i n n o n - s h e l t e r e d p l a c e s as the d e n s i t y i n c r e a s e d ( T a b l e s 3 0 , 3 1 ). The top of the s l a b s and the r o o f of the mesh cages were c o n s i d e r e d exposed s i t e s . 101 Number of Animals per Cage 102 than the winter mortality (Pigs. 33> 35, 36), this data conformed to the assumptions of no density or species effects, whereas the winter mortality did not, since in this case both species survived better under single species treatments than under mixed species treatments (Figs. 30, 35; Tables 30, 3 l ) . Mortality proportional to density was observed for L. sitkana at single and mixed species treatments and for L.. scutulata for mixed species treatments. L_. scutulata single species treatments had proportionately more animals dying at medium density than at high density. In the summer there was no difference in the mortality between left and right cages for either species. In the winter however, animals of both species at a l l the densities did not survive as well in the exposed (left) cages as in the sheltered (right) cages (Fig.38). On March 3 and March 6, 1970 there were more animals of both species in exposed sites in higher than in lower densities (Tables 30, 31; Fig. 40). This may indicate that shelter became less and less available as densities increased. Two types of fluke larvae were released by the snails,a large echinostome cercaria and a smaller microphallid cercaria (Table 32). Ten percent of both species of littorines released microphallids cercariae and 7 percent of the L_. scutulata released echinostome cercaria. Hilda Ching (personal communication) reports absence of echinostome larvae in L. sitkana. There was no difference in the pro-portion of microphallids affecting snails at high density and at medium and low density. 103 Discussion At any density L. sitkana mortality was greater than L. scutulata mortality regardless of the season. Survivorship data showed the reverse. A shorter l i f e span combined with a faster growth rate would indicate: that L. sitkana had a greater turnover rate than JL. scutulata. Since a l l the cages contained abundant food in the winter, i t does not appear that food limitation could account for most of the mortality. Starvation appeared not to play a direct role in the summer mortality because animals in the high density treatments (which were devoid of food) did not survive less well than those at lower densities. Species interaction effects likewise were not directly related to food limitation, for these effects were only measurable in the high density mixed species cages in the winter. There is some evidence that shelter from storms may be a clue in explaining the mortality patterns. The highest mortality rates were observed in the storm season. Also i t can be noted, that during this time animals of both species did not survive as well in the more wave exposed cages than animals in the more sheltered cages (Fig. 3 8 ) . In the summer, x^ hen storms did not occur, no such difference between left and right cages could be detected (Fig. 3 7 ) . Animals of both species survived less well in high density mixed species treatments than in high density single species treatments (Figs. 35t 36; Tables 30, 3 l ) . Neither food nor shelter appeared to be less abundant in mixed species cages. Perhaps the mutual inhibitory effects these two species have on each other is related to their 104 social behaviour. An equal proportion of L. sitkana died at a l l densities but pro-portionately fewer original animals survived one year as the density increased (Fig. 34). This would indicate that living conditions remained as favorable or else became less favorable as densities increased. The opposite trend held for _L. scutulata especially in single species treat-ments (Fig. 38b; Table 3 l ) . Littorines have been observed aggregated in sheltered places during the winter and perhaps this behaviour is beneficial in protecting animals from cold winds, surf and ice formation as their densities increased. More experimental data is needed to clarify the observed density and species interaction effects. 105 DISCUSSION AND CONCLUSIONS Hairston, Smith and Slobodkin (i960), suggest, that as a rule, grazing populations are not food limited and are prevented from over-exploting their food supply by the action of predators and parasites. Benthic marine predators seem to thin out littorines at low tidal level where algal food is most abundant, but these predators were never found in the mid and high tidal zones. Stomach samples of crows and ducks revealed littorine shells (Low, personal communication), however no estimate of their effect on littorine populations was made. Two species of fluke larvae were found in the digestive gland and gonad of littorines, but these parasites did not appear to exert a density dependent mortality. Both L_. sitkana and L. scutulata appear to be food limited in the high density cages (twice the natural density) in the summer, in that they grew significantly less in these cages than in the low density cages with a high standing crop of algae. Decreased growth due to a scarcity of food however did not affect numbers directly. It is possible that a nutritional limitation in the summer and possibly competition for sheltered places in the f a l l was responsible for the decreased natality rate shown by L. sitkana in the high density cages. Eisenberg (l966, 1970) demonstrated that nutritional limitation in high density cages of the pond snail Lymnaea elodes had the effect of reduc-ing the number of eggs produced but had no effect on adult mortality. Natality rates for L_». scutulata could not be measured, but mortality 106 rates decreased with density. The lower the density of L. sitkana and the higher the availabi-l i t y of food, the greater were growth rates, natality and survivorship'. These trends indicate that density responsive mechanisms may be prevent-ing this species from overexploiting its food supply. Such mechanisms would be important to a species such as L. sitkana with direct develop-ment and limited dispersal potential, for i f i t became extinct in one place, the chances of i t reinvading that place might be very small. L. scutulata grew less but survived better at higher than at lower densities. L. scutulata can live at much higher densities and"can utilise much lower food levels than L. sitkana. Extremely high densities of L. scutulata (l68 animals per 25 cm ) were observed on the exposed transect at Chesterman's Beach. These high densities were maintained possibly because these sites were very favorable for settlement of the larvae. These animals however were extremely stunted and the oldest animals (at least one year old) were not more than 4 mm long. High densities of stunted adult L. sitkana were never found. Prom the density species interaction experiment and from growth data gathered at other sites i t was found that L. scutulata would often shrink in size (Fig. 29) whereas L. -qi tkana would either maintain its size or else die. Higher growth rates together with a greater locomotory activity indi-cates that _L. sitkana may have a greater metabolic rate and may require more food per individual than L_. scutulata and thus cannot maintain as dense a population. L. scutulata, at high densities, may contribute l i t t l e i f any energy to reproduction. This is perhaps unimportant for a 107 species with planktotrophic development since recruitment can take place from a more favorable area. The competitive exclusion p r i n c i p l e leads to the expectation that two ec o l o g i c a l l y s i m i l a r species using the same resource cannot co-exi s t i n d e f i n i t e l y , f o r one species would be more e f f i c i e n t at u t i l i s i n g that resource and thus would increase i n numbers and displace the other species (Hardin, I960). When two such species overlap i n t h e i r d i s t r i -bution i t i s often assumed that competition keeps them apart and that coexistence implies lack of competition. Resource partitioning whereby both s p e c i e specialise on d i f f e r e n t aspects of the same resource i s one way whereby such competition can be minimised. For example, f i v e species of northeastern warblers i n mature, homogeneous, coniferous forests each feed i n one of f i v e locations i n the same tree (MacArthur, 1958)* Since both species of l i t t o r i n e s feed on benthic diatoms and shelter i n the same places, resource p a r t i t i o n i n g does not appear to play a r o l e . No two species are exactly a l i k e i n t h e i r ecological requirements and thus habitats exist where only one of a species pair can l i v e . This i s the case with L. sitkana and L. scutulata. L. scutulata does not l i v e i n high splash pools or lagoons, presumably because i t s planktonic larvae cannot s e t t l e there. L. sitkana cannot l i v e on exposed coasts without shelter from waves and sun, as adults tend to be dislodged by wave action and juvenile stages tend to die from desiccation. In intermediate habitats both species can co-exist. Lack of competitive interactions i s not responsible f o r the co-existence of 108 L. sitkana and L. scutulata in the intermediate habitat at Cantilever Pier, for at high densities both species died at faster rates in mixed species cages than in single species cages and L. scutulata inter-fered with the natality of L. sitkana .The degree to which two species overlap in their distribution would depend on the extent of the inter-mediate habitats and the degree of balance in their respective adaptive advantages. Hutchinson (1957) suggests that i f the advantage of one species over the other is constantly reversed by environmental fluctuations, co-existence might be possible. This was shown by Harger (1968, 1970a, 1970b) for mixed population of mussels consisting of Mytilus  califomianus and M. edulis. M. edulis had the ability to crawl to the outside of mussel clumps thus preventing themselves from getting smothered and crushed in the matrix of the clump. M. califomianus were attached to the substrate by stronger b3gsal threads. During storms M. edulis would get washed off, thus freeing the formerly inprisoned M. califomianus. Calm weather would allow M. edulis to re-establish themselves. This phenomenon did not appear to apply to L. sitkana and L. scutulata grown at Cantilever Pier, a site equally favorable to L. sitkana and L. scutulata, for growth and mortality patterns showed the same trends (Figs. 26, 33). L. sitkana. however, suffered a greater mortality during the winter and produced fewer egg masses in the spring in the more exposed (left) cages than in the more sheltered (right) cages (Table 28). This together with susceptibility to wave action, would select against L. sitkana during storms. In the summer the 109 advantage of L. sitkana over L. scutulata may be associated with i t s • greater growth rates. Williamson (l957)> postulates that two ecologically similar species can co-exist i f they do not have the same controlling factor. Predators such as Leptasterias hexactis and Searlesia dira seem to prefere L_. sitkana to L. scutulata (Tables 13, 14). The preference of these predators for L. sitkana. counterbalanced by the apparent preference of the echinostome fluke larvae for L. scutulata, may very well contribute to the maintenance of both species of lit t o r i n e s i n an area. Unfortunately, there i s no information bearing on the degree to which parasites and predators control l i t t o r i n e populations. Nicholson (1954) points out that continual recolonization from species specific refuges would allow two similar species to live i n the same habitat. The co-existence of L_. sitkana and L. scutulata at Cantilever Pier beach however does not depend on species specific refuges for both species demonstrated reproductive potential. Co-existence i s possible i f each species inhibits i t s e l f more than the other species when i t becomes numerically more abundant. Drosophila w i l l i s t o n i and D. pseudoobscura exhibit such a balance situation (Ayala, 197l). At high D. wiT)istoni and low D. pseudoobscura densities I), w i l l i s t o n i was at a disadvantage and D_. pseudoobscura at an advantage as far as natality was concerned. At high D. pseudoobscura and low D. w i l l i s t o n i densities D. pseudoobscura was at a disadvantage and D. w i l l i s t o n i at an advantage as far as survivorship was concerned. As densities increased the number of egg masses produced per individual 110 L. sitkana decreased i n single species cages but not i n mixed species cages (Fig. 3 0 ) . This may inidcate that intraspecific competition but not interspecific competition became more important as densities i n -creased. L_. scutulata appears to be the generalist of the two species of lit t o r i n e s i n that they are found almost everywhere. The highest densities of L. scutulata adults and juveniles were associated with barnacle cover whose interstices may act to trap the larvae. L. scutulata larvae do not appear to settle i n pools and mud fl a t s to any great extent and thus this species would not inhibit L_. sitkana i n these areas. In more exposed locations L,. i:\ear\p showed greater mortality and lower natality. This together with their susceptibility of being dislodged by waves would select against L. sitkana i n exposed places. L. scutulata had the advantage of planktonic recruitment, longevity, resistance to wave action and a b i l i t y to graze on a lower standing crop of algae. L. sitkana apeears to be a specialised species in that i t does best i n areas such as mud-flats, high tide pools, (where L_. scutulata does not appear to settle in large numbers) and rough shale rocky beaches. A l l these habitats offer protection to adults from being dislodged by waves and to egg masses and juvenile snails from desiccation. In such habitats L. sitkana appears to be more efficient than L_. scutulata in finding food and crevices, in converting food to biomass and i n having a less wasteful mode of development (leicithotrophic as opposed to planktotrophic). I l l LITERATURE CITED Ayala, F.J., 1971. Competition between Species: Frequency Dependence. Science, February 1971, 820-824. Bock, C.E., R.E. Johnson, 1968. The Role of Behavior in Determining the Intertidal Zonation of Littorina planaxis and Littorina  scutulata. Veliger, 10; No. 1:42-54. Castenholz, R.W., 1961. The Effect of Grazing on Littoral Diatom Populations. Ecology, 42:783-794. Connell, J.H., 1961. Effects of Competition, Predation by Thais  lapillus and other Factors on Natural Populations of the Barnacle Balanus balanoides. Ecol. Mon. 31:61-104. Dahl, A.L., 1964. Macroscopic Algal Food of Littorina planaxis and Littorina scutulata. Veliger, 7; No. 2:139-143. Eisenberg, R.M., 1966. The Regulation of Density in a Natural Population of the Pond Snail, Lymnaea elodes. Ecology 47:889-906. — 1970. The Role of Food in the Regulation of the Pond Snail, Lymnaea elodes. Ecology 51:680-684. Foster, M.S., 1964. Microscopic Algal Food of Littorina planaxis and Littorina scutulata. Veliger, 7; No. 2:149-152. Gause, G.F., 1934. The Struggle for Existence. Wilkins Co., Baltimore. Gowanloch, J.N., F.R.Hayes, 1926. Contributions to the Study of Marine Gastropods. The Physical Factors, Behaviour and Intertidal Life of Littorina. Contr. Canad. Biol.Fish. N.S. 133-165. Hairston, N.G., F.E.Smith, and L.B. Slobodkin, I960. Community Structure Population Control, and Competition. American Naturalist 94:421-425. Hardin, G., I960. The Competitive Exclusion Principle. Science, 131:1292-1297. Harger,J.R.E., 1967. Population Studies on Mytilus Communities. Ph.D. thesis, Biology Department, University of California at Santa Barbara. 112 Harger, J.R.E., 1968. The Role of Behavioral Traits in Influencing the Distribution of Two Species of Sea Mussels, Mytilus californianus and Mytilus edulis. Veliger 11:45-49• , 1970a. The Effect of Wave Impact on some Aspects of the Biology of Sea Mussels. Veliger 12:401-414. , 1970b. The Effect of Species Composition on the Survival of Mixed Populations of Sea Mussels, Mytilus californianus and Mytilus  edulis. Veliger 13:147-152. Baseman, J.D., 1911. The Rhythmic Movements of Littorina littorea Synchronous with Ocean Tides. Biol. Bull., Woods Hole, 21: 113-121. Hertling, H., W.E.Ankel, 1927. Bemerkungen uber Laich und Jugendformen von Littorina und Lacuna. Wissenschaftliche Meeresuntersuchungen-Kommission zur Untersuchung der Deutschen Meere in Kiel und der Biologischen Anstalt auf Helgoland. Neue Polge. Abteilung Helgo-land, XVI. Band, Abhandlung Nr. 7. Hutchinson, G.E., 1957. Concluding Remarks, Cold Spring Harbor Symposia on Quantitative Biology 22:416-427. Imai, E., 1964. Some aspects of Spawning Behavior and Development in Littorina planaxis and L. scutulata. Student Spring Report, Hopkins Marine Station, Monterey, California. Kanda, S., 1916. Studies on the Ceotropism of the Marine Snail Littorina littorea. Biol.Bull., Woods Hole, 39:57-84. Keen, M.A., 1937. An Abridged Check-List and Bibliography of West North American Marine Mollusca. Standford University Press, Stanford, California. Low, C., 1970. Factors Affecting the Distribution and Abundance of Two Species of Beach Crabs Hemigragsus oregonensis and H. nudis M. Sc. Thesis, Zoology Department, University of British Columbia, Vancouver. Mac Arthur, R.H., 1958. Population Ecology of some Warblers of North Eastern Coniferous Forests. Ecology, 39:599-619. Menge, B., 1970. Ph.D. Thesis, Zoology Department, University of Washington. Murdoch, W.W., 1970. Population Regulation and Population Inertia. Ecology 51:497-502. 113 Nicholson, A.J., 1954. An Outline of the Dynamics of Animal Populations. Australian J. Zool. 2:9- -5. Orldroy, I.S., 1929. The Marine Shells of the West Coast of North America. Stanford University Press, Stanford, California. Siegel, S., 1956. Nonparametric Statistics for the Behavioural Sciences. McGraw-Hill Book Company Inc., New York. Sokal, R.R., F.J. Rohlf, 1969- The Principles and Practice of Statistics in Biological Research. W.H. Freeman Co., San Francisco. Stephenson, T.A., A. Stephenson, 1949. The Universal Features of Zonation between Tide Marks on the Rocky Shores. J.Ecology, 37:289-305. Struhsaker, J.W., J.D. Costlow Jr., 1968. Larval Development of Littorina picta reared in the Laboratory. Proc. Malac. Soc. Lond. 38:153-160. Thomas, R.I., 1966. The Distribution and Zonation of Prosobranch Molluscs of the Genus Littorina on the Central Oregon Coast. Student Summer Report, Newport Marine Station. Thorson, G., 1950. Reproductive and Larval Ecology of Marine Bottom Invertebrates. Biol.Rev., 25, pp.1-45. Urban, E.K., 1962. Remarks on the Taxonomy and Intertidal Distri-bution of Littorina in the San Juan Archipelago, Washington. Ecology, 32:320-323. Williamson, M.H., 1957. An Elementary Theory of Interspecific Competition. Nature 180:422-425. APPENDIX TABLES 1 t o 5 6 S i g n i f i c a n c e L e v e l s S t a r s were u s e d t o i n d i c a t e t h e l e v e l o f s i g n i f i c a n c e a t w h i c h t h e n u l l h y p o t h e s i s o f no d i f f e r e n c e b e t w e e n v a l u e s h a s b e e n r e j e c t e d . A b s e n c e o f a s t a r o r N.S. i n d i c a t e s n o s i g n i f i c a n t d i f f e r e n c e . . 0 5 . 0 1 . 0 0 1 115 TABLE 1 . Time sequences for the developmental stages of L i t t o r i n a scutulata. Egg Laying Polar body formation Two c e l l stage Four c e l l stage Late cleavage B l a s t u l a Gastrula Young v e l i g e r Pre-hatched v e l i g e r Hatching 0 hours 2 hours 3 hours 12 to 24 hours 2 1 hours 3 days 4 days 7 to 8 days at 1 3 ° to 15°C 3 days at room temperature (22°C) 116 TABLE 2. H a t c h i n g success of L i t t o r i n a s i t k a n a egg masses suspended from a boat moored i n Vancouver Harbor. Number of Eggs Hatched not hatched Higher 'cages' 5 0 cm below s u r f a c e of the water l i n e 1 l i n e 2 40 47 40 40 Lower 'cages 1 100 cm below s u r f a c e of the water l i n e 1 l i n e 2 1 5 8 5 0 5 0 T o t a l 110 180 117 TABLE 3 . S u r v i v a l o f two s i z e c l a s s e s o f j u v e n i l e L . s i t k a n a c a g e d a t t h e 9 f o o t a n d 1 3 f o o t t i d a l l e v e l s a t L i l l y P o i n t f r o m May . 1 7 t o May 18, 1 9 6 9 . POSITION OF CAGES S A L I N I T Y OF POOLS TEMPERATURE RECOVERY OF L.SITKANA medium t i d a l 3 e v e l ( 9 f t . ) p o o l 2 7 ° C w a t e r 7 s m a l l ( n e w l y h a t c h e d ) s n a i l s a l l w i t h t h e i r f o o t m o v i n g . c a g e w i t h l a r g e r ( 1 . 0 mm o r l o n g e r ) s n a i l s was l o s t medium t i d a l l e v e l ( 9 f t . ) d r y 2 0 ° C a i r 9 s m a l l s n a i l s , a l l a l i v e 5 l a r g e s n a i l s , a l l b u t one o p e n e d o p e r c u l u m when m o i s t e n e d . h i g h t i d a l l e v e l ( 1 3 f t . ) p o o l 2 5 £ 2 7 ° C w a t e r 8 s m a l l s n a i l s , a l l a l i v e 5 l a r g e s n a i l s , a l l a l i v e h i g h t i d a l l e v e l ( 1 3 f t . ) d r y 2 0 ° C a i r 9 s m a l l s n a i l s , a l l d e a d k l a r g e s n a i l s , 3 a l i v e one w i t h b r o k e n s h e l l 118 TABLE 4 . H a t c h i n g s u c c e s s o f L . s i t k a n a e g g masses a t L i l l y P o i n t . F i v e L . s i t k a n a e g g masses were s e c t i o n e d i n two. H a l f o f e a c h e g g mass was a t t a c h e d t o p i l i n g s a t t h e h i g h t i d e l e v e l a n d h a l f were a t t a c h e d t o c o n c r e t e b l o c k s a t t h e l o w t i d e l e v e l a t L i l l y P o i n t . I N I T I A L T I D A L NUMBER OF HATCHED LITTORINA SITKANA COLOR OF HIGHT OF EGG MASS CAGE S e p t e m b e r 1 S e p t e m b e r 7 p i n k l i g h t p i n k d a r k p i n k l i g h t p i n k l i g h t p i n k { ( 5 f t . 1 1 f t . 5 f t . 1 3 f t . 6 f t . 1 3 f t . f 6 f t . V 1 3 f t . (9 f t . 1 1 3 f t . n o t s a m p l e d r e d e g g mass n o t s a m p l e d y e l l o w a n d d r y 2 5 h a t c h e d r e d a n d d r y r e d e g g mass 2 h a t c h e d l o s t c o v e r e d w i t h s e d i m e n t 5 0 a l i v e * G a l i v e 7 a l i v e * 0 a l i v e 3 2 a l i v e 0 a l i v e 4 7 a l i v e 0 a l i v e c o v e r e d w i t h s i l t * i n d i c a t e s p u n c t u r e i n c a g e T a b l e 5 . 119 P o s i t i o n o f L . s i t k a n a e g g masses f o u n d i n 1 6 c a g e s a t C a n t i l e v e r p i e r b e a c h . S u r f a c e A r e a P o s i t i o n ( c n r ) 1 . wave e x p o s e d s i d e 7 6 o f s l a b 2 . wave s h e l t e r e d s i d e 7 6 o f s l a b 3 . t o p o f s l a b 7 6 0 4 . b o t t o m o f s l a b 7 6 0 5 . r i g h t o r l e f t s i d e 3 2 0 o f s l a b 6 . i n c r e v i c e o f c a g e seam ( wave s h e l t e r e d ) s m a l l 7 . on s i d e o r b o t t o m o f c a g e l a r g e Number o f egg masses on O c t . 2 2 0 2 9 1 2 6 1 9 4 7 8 y Wave i m p a c t D i a g r a m s h o w i n g c a g e removed f r o m cement s l a b w i t h p o s i t i o n s marked. 120 Table 6. L o c a l D i s t r i b u t i o n of L i t t o r i n e s . Lowest Record. Wave Sa- S a l i n i t y Presence Expos- l i n - Sept.* 68 of Place Substrate ure i t y to Jun. '70 s i t . scut.' Lonesome Cove, rough shale M H yes yes SJ Marvista Resort ,rough shale H ' H yes yes SJ C a n t i l e v e r Pier,rough shale M H yes yes SJ boulders & M H yes yes g r a v e l P i l e Pt., SJ rough shale H H yes yes boulders & H H yes yes gr a v e l Deception Pass rough shale M H yes yes State Park, boulders M H rare yes near Anacor-tes Anacortes Fer- g r a v e l M H yes rare r y landing p i l i n g s M H rare yes Saxe Pt. Park rough shale M H yes yes near V i c t o r i a s h e l f smooth w a l l M H no yes A l b e r t Head rough shale M? H yes yes Lig h t s h e l f F a l s e Bay,SJ mud f l a t w/rocks & g r a v e l L H yes yes Montague Har- mud f l a t w/grav- L H yes yes bor, on Gal- e l & oyster eano Is . s h e l l s shore-gravel & M H rare yes oyster s h e l l s • Jekel's La- mud f l a t w/ grav- L H yes no goon, SJ e l & rocks Fanny Basin mud f l a t L 1 yes rare near Nanaimo p i l i n g s 1 no yes Chesterman's wave exposed VH H no yes Is. near shore Tofino high splash p o o l L ? yes no V i c t o r i a g r a n i t e cubes w/ H H no yes Breakwater barnacles Port Renfrew sand.shore f l a t H H yes yes June, 1969 Nov., 1969 VH H rare yes high t i d e pools H H yes rare 121 Table6.? continued Lowest Record. Wave Sa- Salin. Presence Expos- l i n - 9/68 - of Place Substrate ure i t y 6/70 s i t . scut. Edward King shore-rough H H yes yes Is. near' shale Bamfield high tide pools L yes no L i l l y Pt., compressed t i n M M 21.2#. No yes Pt. Roberts cans, rock & boulders Brockton Pt. seawall L M 16.9%« rare yes boulders & gravel L M yes yes Second Beach boulders L M yes yes Eng. Bay by boulders L L no yes Sylvia Hotel Under Burrard boulders L L no yes St. Bridge Maritime boulders & L L yes yes Museum seawall Jericho barnacled pier L L no yes Beach Spanish Banks by: 1. oceano- Barnacled boulders L VL no yes graphy plat-form 2. guntowers i t L VL 3.0/O0 no no Gales Park boulders L L? no yes Light House sandstone M M? no yes Park shelves Sunset Marina boulders L M? yes yes Wave Exposure Estimates VH = very exposed H = exposed M = medium exposure L = sheltered Salinity Estimates (for values around Vancouver, courtesy of Ora Johannsson) H = high s a l i n i t y , around 31ppt. most of the year. M = s a l i n i t y may drop as low as 15 ppt. i n the summer L = sa l i n i t y may drop as low as 7 ppt. i n the summer VL = s a l i n i t y may drop below 7 PPt. in the summer SJ = San Juan Island TABLE 7 Number o f a n i m a l s o f b o t h s p e c i e s f o u n d on t h e s u r f a c e a n d i n c r e v i c e s o f a q u a d r a t ( 5 0 cm by 5 0 cm ) t a k e n a t M a r v i s t a R e s o r t ( F i g . 1 1 ) . A n i m a l s i n s u r f a c e s a m p l e were b r u s h e d o f f a n d a n i m a l s i n c r e v i c e sample were p i c k e d o u t w i t h f o r c e p t s . S m a l l A n i m a l s ( s i z e 1 t o 4 ) c r e v i c e s a m p le s u r f a c e s a m p l e L . s i t k a n a Obs. E x p . 59 1 2 48.33 22.66 L . s c u t u l a t a Obs. 118 7 1 E x p . 128.66 6 0 . 3 3 X 2 = 1 0 . * * L a r g e A n i m a l s ( s i z e 5 and. 6 ) L . s i t k a n a Obs. E x p . L . s c u t u l a t a Obs. E x p . C r e v i c e s a m p l e 1 5 4 . 2 5 1 2 2 2 . 7 5 S u r f a c e s a m p l e 1 0 2 0 . 7 5 1 2 2 1 1 1 . 2 5 X = 3 8 . 9 5 * * * TABLE 8. A b i l i t y of the two s p e c i e s of l i t t o r i n e s t o r e s i s t wave exposure i n the f i e l d . 124 WAVE EXPOSURE P r o p o r t i o n of animals D i f f e r e n c e remaining betw«n»r«*s P l a c e Date S u b s t r a t e L . s i t k a n a L. s c u t u l a t a X 2 L i l l y p o i n t Oct. 20-22 1968 b a r n a c l e d t i n can rock, h o r i z o n t a l 7/10 7/10 b a r n a c l e d t i n can rock, v e r t i c a l 2/10 8/10 ' 1.979 b a r n a c l e d p i l i n g , v e r t i c a l 4/20 6/20 A p r i l 15-16 1969 v e r t i c a l t i n can rock h o r i z o n t a l t i n can rock 11/20 14/20 16/20 16/20 2 . 9 9 0 Brockton P o i n t Oct. 2-4 1968 March 13-14 sea w a l l sea w a l l 11/20 2 1 / 5 0 13/20 3 5 / 5 0 7.466 Saxe P o i n t Feb. 8-11 1969 v e r t i c a l smooth w a l l 4/38 15/38 7.017 Chesterman 1s I s l a n d May 1-2 1969 exposed shore, b a r n a c l e s 37/49 47/49 6.740 P o r t Renfrew June 5-6 1969 low l e v e l , f l a t sandstone s h e l f 26/ 5 0 4 6 / 5 0 8.734 h i g h l e v e l , on Fucus sp. 33/ 5 0 47 / 5 0 10.562 High l e v e l , sandstone s h e l f 3 1 / 5 0 47 / 5 0 13.119 Nov. 21-22 1969 Low l e v e l , sandstone s h e l f s m a l l animals 34/50 35/ 5 0 0.047 low l e v e l , sandstone s h e l f , l a r g e animals 1 9 / 5 0 34/ 5 0 9 . 0 3 2 5 POOLED DATA 254/487 366/487 55.657 ( Y ) * Yates c o r r e c t i o n f o r smal l c e l l frequency was used. 125 TABLE 9 . WAVE EXPOSURE L a b o r a t o r y Experiments Number of animals remaining on s u b s t r a t e a f t e r s q u i r t i n g them wi t h a j e t of sea water Number used 18 18 18 L. s i t k a n a 1 1 1 L. s c u t u l a t a 5 1 0 4 T o t a l 5 4 1 9 12.842 ( Y ) * P r o p o r i o n of animals remaining on s u b s t r a t e a f t e r s q u i r t i n g them with a j e t of sea water. Large Small L. s i t k a n a L, s i t k a n a 4 / 2 7 10/24 4/24 10 / 2 2 2 / 2 3 5/24 0/12 1/12 3/20 5 / 1 9 2/20 6/20 T o t a l 15/126 37/121 1 2 . 9 4 7 Yates c o r r e c t i o n f o r smal l c e l l f r e q u e n c i e s was used. 126 TABLE 1 0 . T o l e r a n c e of two s p e c i e s o f l i t t o r i n e s t o 3 and 4 days d e s i c c a t i o n a t room temperature. Time of Exposure L. s c u t u l a t a L. s i t k a n a (days) Number a l i v e 2 0 1 ? Number Dead 0 3 Number a l i v e 4 4 3 5 Number dead 1 6 2 5 3 . 0 0 N.S. 127 TABLE 1 1 HIGH WATER TEMPERATURES T h r e e m i n u t e e x p o s u r e t o P r o p o r t i o n o f a n i m a l s r e c o v e r i n g a f t e r 2 m i n u t e s 24 h o u r s L . s i t k a n a L . s c u t u l a t a L . s i t k a n a L . s c u t u l t a t a 4 4 ° w a t e r 4 5 ° w a t e r 3 0 ° w a t e r 3 0 ° w a t e r 1 / 2 5 0 / 2 5 2 5 / 2 5 2 5 / 2 5 2 / 2 5 0 / 2 5 2 5 / 2 5 2 5 / 2 5 1 / 2 5 0 / 2 5 1 1 / 2 5 5 / 2 5 E x p o s u r e t o fr a d u a l h e a t i n g 1 5 ° C i n 3 h o u r s ) D i s h b , h e a t e d up t o 4 5 ° C D i s h a , h e a t e d u p t o 4 2 ° C P r o p o r t i o n o f a n i m a l s r e c o v e r i n a f t e r 2 m i n u t e s 219 H o u r s L . s i t k a n a L . s c u t . L , s i t k a n a L . s c u t , o / 2 5 1 / 2 5 0 / 2 5 4 / 2 5 1 7 / 2 5 1 1 / 2 5 2 5 / 2 5 1 7 / 2 5 T o t a l Number o f a n i m a l s A l i v e D e ad L . s i t k a n a L . s c u t u l a t a 2 9 IB 7 1 42 x2 = 1 7 . 1 0 9 * * * D.f.= 1 P C . 0 0 1 128 TABLE 12. T o l e r a n c e of l i t t o r i n e s to s a l i n i t y extremes. Groups of 5 0 ( s i z e 4 ) animals of each s p e c i e s were s u b j e c t e d t o 16°C sea water a t v a r i o u s s a l i n i t i e s . A f t e r 28 hours the number of dead animals was noted. SALINITY NUMBER OF ANIMALS COUNTED DEAD AFTER 28 HOURS. ( p a r t s p e r thou thousand) L. s i t k a n a L, s c u t u l a t a 7 . 5 1 2 2 2 1 5 2 3 3 0 0 1 5 0 2 1 3 D i f f e r e n c e s between s p e c i e s 7.5 p a r t s per thousand X 2 = 4.455 * 5 0 p a r t s per thousand X 2= 7.843 ** X 2 1 D.f. (K . 0 5 = 3.84 ^ . 0 0 5 = 7 . 7 9 129 Table 1 3 . E l e c t i v i t y Coefficients for Searlesia dira (proportion of prey organisms of one species i n diet divided by the proportion of that prey species i n the environment). An el e c t i v i t y value greater than 1 indicates prey selection, one less than 1 indicates prey avoidance. Total Feeding Number i n E l e c t i v i t y Prey Species Observations Environment Coefficient Littorina sitkana 57 357 3.3^ L. scutulata 30 1+95 1.28 Acmea d i g i t a l i s & A. paradigitalis 21 1399 0.315 A. scutum 13 37b 0.73 A. pelta 7 211 0.70 Total prey organisms observed being eaten = 138 Total prey organisms i n environment = 2920 Data courtesy of Margaret Lloyd Colin's Cove study area October, 1968 to July, 1969 130 Table 14 . E l e c t i v i t y Coefficients for Leptasterias hexactis (pro-portion of prey organisms of one species i n diet divided by the proportion of that prey species i n the environment). An ele c t i v i t y value greater than 1 indicates prey selection, one less than 1 indicates prey avoidance. Lonesome Cove Lonesome Cove Dead Man's Cattle Species Resort Area Far Point Bay Point Balanus glan-dula 0.61 2.14 0.88 0.23 B. cariosus 1.04 0.24 2.78 0.35 Acmaea scutum 5.25 0.51 0.84 1.82 L i t t o r i n a scutulata 2.91 1.54 _ 6.53 Lacuna spp. 5.3^  0.15 0.71 1.54 Acmaea pelta 2.69 1.95 4.47 4.99 A. paradigitalis 1.72 3-59 0.43 2.38 L. sitkana 14.53 - - 5.86 Tonicella lineata 8.45 _ Margarites spp. - 1.42 0.23 0.28 Ishnochiton sp. - 5.89 - -Chthamalus d a l l i 0.22 - O.69 0.16 Katherina tun-icata 0.25 0.09 0.4i Data courtesy of Bruce Menge 131 Table 1 5 . Food choice by Lep t a s t e r i a s hexatis as determined by contact c prey. R e l a t i v e Escape # Obs. Feedings Preference Coef. Responses o f Prey Species # Contacts (%" success, encounters) Prey Species Lacuna sp. 6/25 24.00 + L i t t o r i n a s c u t u l a t a 9/40 22.50 + L. sitkana 9/hh 20.40 + Acmaea d i g i t a l i s 2/15 13.30 + A. p a r a d i g i t a l i s V 7 9 5.10 -Mytilus e d u l i s 1/42 2.38 s e s s i l e A. p e l t a 2/74 2.70 . ++ Calliostoma ligatum 1/58 1.72 +++ Balanus glandula 2/121 1.65 s e s s i l e A. scutum 0/124 0.00 +++ Katherina t u n i c a t a 0/35 0.00 -T o n i c e l l a l i n e a t a 0/25 0.00 -Balanus cariosus 0/12 0.00 s e s s i l e Thais c a n a l i c u l a t a 0/17 0.00 -Thais lamellosa 0/17 0.00 -Thais emarginata 0/16 0.00 + Data courtesy of Bruce Menge T a b l e 16. S u r v i v a l of L. s c u t u l a t a caged i n h i g h i n t e r t i d a l and s p l a s h zone a t L i l l y P o i n t , P o i n t R o b e r t s . Height of cage P r o p o r t i o n of animals a l i v e a f t e r 38 days 1 f t . above h i g h e s t observed L. s c u t u l a t a 3/7 l£ f t . above h i g h e s t observed L. s c u t u l a t a , sun and wave s h e l t e r e d s i d e of p i l i n g , i n y e l l o w l i c h e n zone. 5/6 i f t above h i g h e s t observed L. s c u t u l a t a , i n b l a c k l i c h e n zone 10/10 133 TABLE 1 7 . Mean Growth Increments of L i t t o r i n a sitkana and Acmaea scutum from single and mixed species cages. Species Treatment Mean Length N standard T Increment deviation value Acmaea scutum single species 0 . 1 2 6 3 1 9 0 . 2 7 9 5 mixed species 0 . 2 2 2 2 9 0 . 3 5 8 9 L i t t o r i n a sitkana s i n g l e species 2.644 17 1.889 mixed species 1.977 9 1.104 0 . 7 7 3 N.S. 0 . 7 9 4 N.S. TABLE 18. 134 S t a r f i s h predation on l i t t o r i n e s and limpets at two tide l e v e l s . T i d a l Level ( feet) - 0 . 5 T o t a l L. scutulata A. p a r a d i g i t a l i s # empty, # attached, # empty, # attacked 4 0 4 0 1 1 2 0 5 0 5 0 4 0 0 0 "~14 1 11 o + 2 1 0 0 1 0 0 0 0 0 t 0 2 1 0 0 0 0 Total 0 The number of L i t t o r i n a scutulata and Acmaea p a r a d i g i t a l i s eaten by Leptasterias  hexactis at two t i d a l l e v e l s . Difference between number of Acmaea p a r a d i g i t a l i s and number of L. scutulata eaten X2= 0.164 N.S. Difference between number of animals eaten at low and mid t i d a l l e v e l 2 X =16.397 *** 135 TABLE 19, D i s p e r s a l b e h aviour of L. s i t k a n a under two d e n s i t i e s , Number of animals r e a c h i n g the edge of the s l a b a f t e r 5 minute t r i a l s . Number of 12 12 36 an j. max o per s l a b /slab number t A 2 3 T o t a l 4 1 3 8 6 16 1 3 7 36 24 9 8 11 28 20 8 6 14 28 26 12 1 7 10 39 21 7 14 10 3 1 20 T o t a l 56 59 55 1 7 0 1 1 7 Observed Expected 143 143 X 2 c a l c u l a t e d = 1 1 . 0 * * * 136 TABLE 20. Number of l i t t o r i n e s of both species found on cement slabs with and without algae. Diatom covered slabs Clean slabs Number of Number of Number of Number of L. sitkana L. scutulata L. sitkana L. scutulata 6 0 0 0 10 2 0 2 10 1 2 0 11 1 1 0 6 2 3 2 4 3 2 1 47 9 8 5 Total Observed 28 7 28 7 Expected Difference between diatom and clean slabs. L. sitkana X 2 = 13. 0 * * * L. scutulata X 2 = 1.2 N.S. 137 TABLE 2 1 T o t a l number o f l i t t o r i n e s o f b o t h s p e c i e s l e a v i n g d i a t o m c o v e r e d a n d c l e a n s l a b s . d i a t o m c o v e r e d s l a b c l e a n s l a b L . s i t k a n a L . s c u t u l a t a L . s i t k a n a L . s c u t u l a t a T o t a l O b s e r v e d 24 9 5 1 20 E x p e c t e d 3 7 . 5 1 4 . 5 3 7 . 5 1 ^ . 5 D i f f e r e n c e b e t w e e n c l e a n s l a b . L . s i t k a n a X 2 = o L . s c u t u l a t a X = d i a t o m c o v e r e d a n d 9 . 7 2 0 * * 4 . 1 7 2 * TABLE 22. P o s i t i o n of L. sitkana 14 hours a f t e r introduction into modified sea water table ( F i g . 16 ). Number of Animals No Food Slab 4 Food Slab 4 Bottom of water Table 5 Around Drain 14 Side of water Table 23 TABLE 2 3 . 139 B e h a v i o r a l response of l i t t o r i n e s t o c r e v i c e s . F i v e l i t t o r i n e s o f each s p e c i e s were a l l o w e d t o a t t a c h t o o y s t e r s h e l l s w i t h b a r n a c l e s ( c r e v i c e d s u b s t r a t e ) and t o o y s t e r s h e l l s without b a r n a c l e s ( smooth s u b s t r a t e ) . A f t e r 1 0 minute i n t e r v a l s the number of l i t t o r i n e s r e m a i n i n g on each .type o f s h e l l was noted. L i t t o r i n a s i t k a n a Smooth s h e l l s b a r n a c l e d s h e l l s 0 3 1 0 3 0 5 5 4 8 4 7 T o t a l 9 4 7 X 2 1 d . f . 2 7 . 5 5 7 * * * L i t t o r i n a s c u t u l a t a Smooth s h e l l s b a r n a c l e d s h e l l s 0 4 0 1 2 2 1 0 3 7 4 6 1 1 6 7 7 T o t a l 1 0 5 1 X 2 1 D.F. = 2 5 . 7 8 6 * * * 140 TABLE 24. Comparison between abundance of food i n L. sitkana and h* scutulata cages through out the year. ( Data was taken from tables 3 2 to 40 ). The Wilcoxan Matched-Pairs Signed-T Ranks tests were used ( S i e g e l , ( 1 9 5 6 ) pp. 7 5 - 8 3 ). Low numbered or high numbered cages of L. sitkana and L. scutu-l a t a comprised a matched p a i r . . Density Number of paired values Number of ranked differences Rank with less f r e -quent sign T tabled <* = . 0 5 Low Medium High 1 6 1 6 1 6 1 3 1 0 6 3 5 . 5 N.S. 2 1 N.S. 6 . 5 N.S. 14 or less 8 or less 0 141 TABLE 25 Biomass and l e n g t h increment r e l a t i o n s h i p s f o r L. s i t k a n a and L. s c u t u l a t a i n August from s i n g l e s p e c i e s low d e n s i t y t r e atments. S p e c i e s O r i g i n a l a d j u s t e d mean l e n g t h ( mm ) O r i g i n a l Weight dry weight increment ( grams ) ( grams ) Percent i n c r e a s e i n weight L. s c u t u l a t a 9.750 L. s i t k a n a 8.244 0.01275 0o01225 0.00095 0.01005 7 82 S p e c i e s O r i g i n a l a d j u s t e d l e n g t h (mm) Length increment ( mm ) Perce n t i n c r e a s e i n l e n g t h L. s c u t u l a t a L. s i t k a n a 8.997 8.997 o.2462 2.14075 3 24 142 TABLE 26 F a l l T h e e f f e c t o f d e n s i t y on n a t a l i t y . C h i - s q u a r e d t e s t s were u s e d t o t e s t t h e h y p o t h e s i s t h a t a n e q u a l p r o p o r t i o n o f e g g masses were l a i d u n d e r t h e t h r e e d e n s i t y t r e a t m e n t s . S i n g l e s p e c i e s O b s e r v e d E x p e c t e d Number o f e g g masses p r o d u c e d Low Medium H i g h d e n s i t y d e n s i t y d e n s i t y 3 1 1 9 5 ^ 3 8 48 7 6 XX 2 2 7 . 0 3 * * * M i x e d s p e c i e s O b s e r v e d E x p e c t e d 10 12.6 2 6 2 5 . 1 5 2 5 0 . 3 0 . 6 1 N.S, S p r i n g S i n g l e s p e c i e s O b s e r v e d 1 5 H 8 E x p e c t e d 4 . 9 9 . 7 1 9 . 4 3 M i x e d s p e c i e s O b s e r v e d 14 1 1 E x p e c t e d 2 . 3 4 . 6 9.1 3 5.81 * * * s a m p l e s i z e t o o s m a l l 143 TABLE 2 7 . T e s t s on t h e E f f e c t o f S p e c i e s C o m p o s i t i o n o n t h e N a t a l i t y B a t e o f L . s i t k a n a . Range t e s t s ( S o k a l , R o h l f , 1 ° 6 9 ) were u s e d t o t e s t t h e h y p o t h e s i s t h a t t h e r e was no d i f f e r e n c e b e t w e e n t h e number o f e g g masses l a i d i n s i n g l e a n d m i x e d s p e c i e s c a g e s . DENSITY MEAN NUMBER OF EGG MASSES RANGE RANGE OF TEST DENSITY S i n g l e s p . M i x e d s p . VALUES VALUE N a t a l i t y a s a F u n c t i o n o f L . s i t k a n a d e n s i t y u n -c o r r e c t e d f o r e q u a l d e n s i t y 20 F A L L 40 N a t a l i t y , s i n g l e s p e c i e s c o r r e c t e d f o r e q u a l number o f a n i m a l s p e r c a g e . 10 F A L L 20 40 1 5 . 5 2 7 6 . 5 1 3 2 3 28 .41 * . 5 0 * 7 . 2 5 1 3 . 5 1 2 2 . 2 5 6 . 5 1 3 1 2 . 5 .40 * 1 3 . 5 0 * 2 3 .04 N.S. N a t a l i t y a s a F u n c t i o n o f L . s i t k a n a d e n s i t y u n -c o r r e c t e d f o r e q u a l d e n s i t y 20 7 . 5 . 2 5 1 5 .48 * SPRING 40 5 . 5 . 2 5 8 . 3 8 * N a t a l i t y , s i n g l e s p e c i e s c o r r e c t e d f o r e q u a l number o f a n i m a l s p e r c a g e 10 3 . 7 5 3 . 5 0 7 . 5 . 0 3 N.S, SPRING 20 2 . 7 5 . 2 5 4. . 5 0 * 40 2.00 . 2 5 3 . 5 8 * Range T e s t = D i f f e r e n c e o f 2 Means/ Range c x = . 0 5 , N= 6 , Range T e s t V a l u e = . 3 1 2 144 TABLE 28. Comparisons between the n a t a l i t y of L. s i t k a n a i n s i n g l e and mixed s p e c i e s cages and between l e f t and r i g h t cages ( p o o l e d d a t a ). Number o f Egg masses produced S i n g l e s p e c i e s Mixed s p e c i e s D i f f e r e n c e X 2 P a l l Observed Expected S p r i n g Observed Expected 1 3 3 1 1 0 . 5 3 4 2 5 8 8 1 1 0 . 5 1 6 2 5 4 . 5 8 6.48 * R i g h t cages L e f t cages D i f f e r e n c e X 2 P a l l Observed Expected S p r i n g Observed Expected 1 1 6 1 1 0 . 5 4 4 25 1 0 5 1 1 0 . 5 6 2 5 0 . 5 4 N.S, 28.88 * * * 145 TABLE 2 9 . Comparison of survivorship curves of l i t t o r i n e s i n 24 cages f o r species and density e f f e c t s . L. sitkana Analysis of Variance D.F. S.S. M.S. F Densities 2 7.3390 3.6695 0.2415 N.S, Species 1 6.1479 6.1479 0.4046 N.S, Interaction 2 4 . 6 8 8 8 2.3444 Remainder 12 182.3126 15.1927 L. scutulata Analysis of Variance D.f. S.S. M.S. F Densities 2 2.3632 1.1916 3.0956 N.S, Species 1 0.0313 0.0313 0.0820 N.S, Interaction 2 0.9741 0.4871 Remainder 12 4 .5807 0.3817 F, F, d.f. 2,12 ( ^ = . 0 5 )= 3.8853 d.f. 1.12 (©\=.o5 )= 4.7472 TABLES 3 0 , 3 1 . S u r v i v o r s h i p , and M o r t a l i t y Data f o r L. s i t k a n a and L. s c u t u l a t a . C h i - s q u a r e d t e s t s were performed t o t e s t the f o l l o w i n g hypotheses. 1 ) There i s no d i f f e r e n c e i n the s u r v i v o r s h i p , m o r t a l i t y and number of n o n - s h e l t e r e d animals i n s i n g l e and i n mixed s p e c i e s cages. 2) There i s no d i f f e r e n c e i n the p r o p o r t i o n o f animals s u r v i v i n g , d y i n g , and b e i n g non-s h e l t e r e d i n the th r e e d e n s i t y treatments. 3 ) There i s no d i f f e r e n c e i n the m o r t a l i t y , s u r v i v o r s h i p and number of n o n - s h e l t e r e d animals i n l e f t ( more s h e l t e r e d ) and r i g h t ( l e s s s h e l t e r e d ) cages. Data f o r these t e s t s were taken from f i g u r e s 3 ^ t CHI-SQUARED D.F. SURVIVORSHIP June 69-June 70 Total Overal good-ness of f i t 2 Species Low Density 1 Med.Density; 1 High Density 1 Total 3 Species pooled density 2 Heterogeneity 1 Density Single Species 2 Mixed Species 2 Total 4 Density pooled-species 2 Heterogeneity 2 Fig. 34 23.396*** .642 1.066 14.087*** 15.795*** 15.076*** .719 2.2189 sample size too small 7.328* Left vs right cagew 1 27.769*** EMPTY SHELL MORTALITY CRUSHED-SHELL • NON-SHELTERED SUMMER WINTER MORTALITY ANIMALS March 3&6,1970 Fig.35 ,37 Fig.35,38 Fig. 39 Fig. 40 5.703* 17.333*** 7.781* 13.7173* 1.195 0.000 2.400 ' 3.200 1.067 1.841 .016 1.636 .203 15.138*** .116 .006 2.464 16.979 2.531 4.842 .446 13.586** .953 .008 2.018 * 3.392 1.578 4.834* .994 1.250 3.447 9.553** 4.128 2.606 4.197 3.952* 5.117 3.856 7.644 13.505** 2.976 .398 - 4.397 9.929** 2.140 3.458 3.247 3.576 .018 40.533*** 1.613 19.854* TABLE 30 L. sitkana CHI-SQUARED D.F. SURVIVORSHIP • June 69-June 70 Total Overal good-ness of f i t 2 Species Low Density 1 Med^ Density . 1 High Density 1 Total 3 St>ecies pooled density 2 Heterogeneity 1 Density Single Species 2 Mixed Species 2 Total .4 Density pooled snecies > 2 Heterogeneity 2 Left vs right cages 1 Fi?. 34 [ 9 . 5 0 0 * .421 .071 3.613 4.095 1.008 3.087 7.530** ,580 8.110 4.390 3.720 5.27* EMPTY SHELL MORTALITY CRUSHED SHELL SUMMER WINTER MORTALITY Fig. 36 Fig. 3 6 , 3 7 Fiej. 39 NON SHELTERED ANIMALS March 3&6,1970 Fig. 40 2.07 18.304* 8.327* 19.555* .643 .044 .037 .056 .011 21.631*** .691 2 1 . 7 3 0 * * * .287 8.563 .404 '13.167*** sample too small 1.066 .642 1.778 0.000 .190 2.919 3.109 .478 2.631 .659 .938 1.597 .518 1.079 10.459* 2.248 12.707* 4.725 7.982* 1 .229 sample too small 4.772 3.855 12.725** 16.580** 15.755*** .825 1,391 15 .223* 1.111 3 2 . 5 0 7 * * * TABLE 31. L. scutulata CO.. 149 TABLE 32. Incidence of cercariae shedding i n experimental animals. Number of animals examined Echinostome Number % Mic r o p h a l l i d Number % L. sitkana L. scutulata 56 60 0 0 4 6.7 6 6 10.7 10.o Number of animals ( lumped species ) shedding Microp h a l l i d cercariae at two d e s n i t i e s . Number shedding Microphallids Number not shedding Microphallids Low and Medium .' Densities 3 51 High Density 9 51 Chi-squared 1.946 N.S. Friday Harbor Density-Species Interaction Experiment, June 17 to July 15, I969 # Empty OD at 665 Estimated # Survivors Shells millimicrons Amount Density Species Cage #f s i t , scut, s i t , scut, sam. a sam. b of Algae Control Flyscreen con-0 Littor- trol .236 .019 ++ ines uncaged control 25 .001 . 0 0 1 0 • control next to #5 .004 0 control next to wall .004 0 Low L. sitkana 1 19 2 .452 .507 +++ 20 L. sitkana . 13 19 1 .026 .019 ++ L. scutulata 2 21 0 .066 .066 + L. scutulata Ik 17 2 .085 .032 Mixed spp. 3 7 8 k 1 .025 .037 ++ Mixed spp. 10 9 . 11 1 . 0 1.250 .630 Mixed spp. 15 8 8 1 0 .014 .090 + Mixed spp. 22 12 10 0 2 .062 .028 ++ Medium L. sitkana 6 39 2 .002 .0035 0 4o L. sitkana 17 36 k .003 .002 0 L. scutulata k ko 2 .082 .0125 ++ L. scutulata 16 39 1 .005 .005 0 Mixed spp. 5 22 20 1 0 .001 .0025 0 Mixed spp. 11 19 19 1 0 .005 .008 0 Mixed spp. 18 17 19 k 2 . 0 0 3 .004 0 Mixed spp. 23 15 19 0 0 .002 . 0 0 3 0 High L. sitkana 7 70 7 .002 . 0 0 3 0 80 L. sitkana 19 75 7 .0025 .0025 0 L. scutulata 8 77 1 .002 .005 0 L. scutulata 20 78 0 .006 .0025 0 Mixed spp. 9 29 38 7 0 .002 .002 0 Mixed spp. 12 37 38 1 . 0 .004 . 0 0 2 0 Mixed spp. 21 3k 38 6 0 .002 .004 0 Mixed spp. 2k 39 38 1 1 .003 .003 0 Friday Harbor Density-Species Interaction Experiment, August 11 Density Species Cage # # Surviv-ors sit. scut. # Empty Shells sit. scut. OD at 665 millimicrons sam.a sam.b Controls Caged control uncaged control? 25 Control next Vcage effect to #5 no cage ;ef. Control next "7 cage effect to rock wallj no cage ef. .113 .018 .010 .012 .OOU .277 .012 .016 .008 .004 # Unaccounted For sit, scut. Low L. sitkana 02 19 0 . 0 9 0 .165 N = 20 11 13 5 .obQ .040 L. scutulata 01 21 0 .353 .!+59 n 14 16 1 .Obk .031 Mixed spp. 03 7 8 . 212 .171 11 10 9 8 .221+ .357 11 15 6 7 2 1 .025 .027 11 22 8 11 1 0 .025 .O69 Medium • L. sitkana 6 . 3 6 3 .005 .029 N = bO 11 17 3b l 0 .006 2 L. scutulata 04 36 3 .015 .015 1 11 16 39 .007 .005 Mixed spp. 5 21 20 0 0 .005 .005 11 11 17 17 1 1 .012 .007 1 1 ti 18 16 18 1 1 tube.broken.Oil 11 23 13 19 2 0 .008 .007 High L. sitkana 7 57 5 .0025 .003 N = 80 11 19 6 9 , 5 .002 .002 1 L. scutulata 8 76 1 .005 .003 11 20 77 1 . 002 .005 Mixed spp. 9 29 39 0 1 .001+ .003 II 12 32 3b 3 0 .001+ .003 1 1 11 21 3b 38 •h 2 .001+ .001+ +1+ 11 24 36 39 b 0 0 .002 i-3 CD Friday Harbor Density-Species Interaction Experiment, Sept. 17 Density Species Cage # # Survivors s i t . scut. # Empty Shells s i t . :scut. # Original Animals Left s i t . scut. Controls Caged control uncaged cage effect uncaged cage effect 25 25 Next to ' #5 Low L. sitkana 01 L. sitkana 13 L. scutulata 02 L. scutulata Ik Mixed spp. 03 Mixed spp. 15 Mixed spp. 10 Mixed spp. 22 Medium L. sitkana 06 L. sitkana 17 L. scutulata Ok L. scutulata 16 Mixed spp. 05 • Mixed spp. 11 Mixed spp. 18 Mixed spp. ".. 23 High L. sitkana L. sitkana L. scutulata L. scutulata Mixed spp. Mixed spp. Mixed spp. Mixed spp. 07 19 08 20 09 21 12 2k 18 15 9 6 8 6 20 20 9 11 10 2 2 1 k 2 3 0 1 0 2 0 0 17 10 6 k 6 5 20 16 7 8 8 9 32 32 18 19 Ik 15 38 39 19 17 19 18 8 2 3 1 6 5 2 2 1 1 1 1 29 27 18 11 8 33 38 19 17 70 50 35 26 35 32 81 78 38 35 39 36 15 17 6 9 5 0 o 2 3 3 3 2 ~W 1+9 23. 21 29 81 75 37 33 36 # Unaccounted For s i t . scut. 0 3 0 k +1 0 0 0 +5 - 3 +1 -k o 0 +1 1 +3 0 +1 0 - 2 0 -1 +1 0 +1 - 2 +2 - 2 t-3 a* M CD VJ1 Friday Harbor Density-Species Interaction Experiment, Sept. 17 (con'td) Number of OD at 665 Estimated egg masses Cage # millimicrons Abundance Microscopic in cages Density Species sam. a sam. b of Algae Algae red pink yellow Total Controls caged control 1 .041 .090 +++ uncaged 25 i .020 .020 ++ cage effect .025 .013 ++ uncaged Next to .030 .010 ++ cage effect #5 .010 .042 Low L. sitkana 01 .040 .060 ++ b Ulva L. sitkana 13 .100 .140 ++ L. scutulata 02 .240 .270 +++ L. scutulata 14 .070 .192 .++ 3 Ulva Mixed spp. 03 .080 .040 ++ co a1 Mixed spp. 15 .020 .045 ++ M ro Mixed spp. 10 .180 .202 +++ heavy Ulva cover/diatoms Mixed spp. 22 .070 .095 +++ 9 Ulva Medium L. sitkana 06 .100 .130 +++ L. sitkana 17 .090 .060 ++ 12 12 L. scutulata Ok .060 .110 +++ 2 Ulva • L. scutulata 16 .090 .145 +++ Mixed spp. 05 .040 • 305 +++ ' 9 9 Mixed spp. 11 • 060 .110 ++ Mixed spp. 18 .220 .360 ++++ Ulva: Mixed spp. 23 .080 .065 ++ 1 2 3 High L. sitkana 07 .030 .032 ++ greenish L. sitkana 19 .060 .010 ++ L. scutulata 08 .030 .042 ++ greenish L. scutulata 20 .110 .062 ++ Mixed spp. 09 .030 .040 ++ greenish 1 1 Mixed spp. 21 .070 .050 ++ Mixed spp. 12 .040 .045 ++ greenish Mixed spp. 2k • 055 .075 ++ k k Friday Harbor Density-Species Interaction Experiment, October 2 2 , 1969 Density Species j //Survivors Cage # s i t , scut. # Empty # Original Shells Animals Left s i t . scut. s i t . scut. # Unaccounted For s i t . scut.. Controls caged uncaged 25 cage effect Next to uncaged #5 cage effect Low L. sitkana 01 Ik 1 13 0 L. sitkana 13 5 10 6 0 L. scutulata 02 16 2 16 0 L. scutulata : 11+ 18 1 17 0 Mixed spp. • 03 5 7 2 1+ - 6 0 0 Mixed spp. 10 8 9 7 6 0 -1 Mixed spp. 15 6 11 ' 1+ 8 0 0 Mixed spp. 22 1+ 8 1 1 k 8 0 0 Medium L. sitkana Ok 19 13 16 0 L. sitkana • 17 2l+ 12 21 0 .L. scutulata 06 36 1 33 -1 L. scutulata 16 35 1+ 3k 0 Mixed spp. 05 11 16 5 11 16 -1 - 3 Mixed spp. 11 13 15 12 13 0 - 2 Mixed spp. 18 9 17 k 1 7 13 -1 -1 Mixed spp. 23 ll+ 17 2 0 7 16 +1 -1 High L. sitkana 07 59 7 k5 -4 L. sitkana 19 1+7 1+ 1+6 +1 L. scutulata 08 75 0 73 -5 - L. scutulata 20 69 8 67 -1 Mixed spp. 12 30 35 k 3 25 32 -*8 +3 Mixed spp. 09 19 35 5 0 17 33 -10 - 2 Mixed spp. 21 31 36 3 l 27 36 -1 - 2 Mixed spp. 2k 30 36 1 1 28 36 -1 +1 H3 p> C I- 1 CD CTl Friday Harbor Density-Species Interaction Density Species Cage if | O.D. at 665 millimicrons samp, a samp, b Controls caged i .102 .093 uncaged *) . 25 .104 .086) cage effect J" next to .092 .119J uncaged "I #5 .205 .177? cage effect \ .064 .095J Low L. sitkana 01 .187 • .159 L. sitkana 13 .147 .321 L. scutulata; 02 .103 .020 L. scutulata 14 .084 .202 Mixed spp. 03 , .320 .194 Mixed spp. 10 .244 .470 Mixed spp.• 15 .500 .272 Mixed spp. 22 .058 .069 Medium L. sitkana 04 .570 .232 L. sitkana 17 .280 .108 L. scutulata 06 .280 .106 L. scutulata ' 16 . Mixed spp. 05 .114 .087 Mixed spp. 11 .110 .068 Mixed spp. 18 .157 .195 Mixed spp. 23 .382 .500 High L. sitkana 07 .175 .210 L..sitkana 19 .800 .214 L. scutulata 08 .073 .086 L. scutulata 20 .598 .398 Mixed spp. 12 .105 .035 Mixed spp. 09 .275 .195 Mixed spp. [ 21 .580 .213 Mixed spp. ! 24 .200 .330 Experiment, October 22, I969 Estimated m a c r o s c 0 p i c Number of Egg masses abundance ^ c o l o r of Egg masses of algae _ red pjnk yellow ++ ++++ +++ ++H-+ ++ ++++ ! ++++ ,. a l l Ulva ++++ +-H-+ +++++ ++++ ++++ ++++•)-++++ ++ +++ +++++ ++++ +++++ ++ +++++ +++ ++++ +++++ +++++ 4 Ulva Enteromorp* 3 brown 2 brown 2 brown 3 6 4 3 9 1 1 3 7 1 11 15 12 8 8 20 t-3 P3 a" V>1 ui VJl Friday Harbor Density-Species Interaction Experiment, December 9? 19^9 Density Species # Alive C a g e s i t . scut. # Empty # Original Est. Abun. #Egg Shells Animals # Missing of Masses sit, scut, sit, scut. sit..scat. Diatoms red pink yel. Controls Caged uncaged cage effect 25 i next to #5 Low L. sitkana 02 15 5 12 0 ++++ 1 3 10 L. sitkana • 13 5 3" k -12 ++ L. scutulata 01 17 3 14 0 +++ L. scutulata 14 18 0 15 0 +++ Mixed 03 8 10 1 0 k 8 • 0 0 0 U t , r d - 0 1 0 Mixed 10 6 9 1 0 5 0 -1 +++ Kttf* 1 3 0 Mixed 15 0 10 7 0 0 . io 0 0 Mixed 22 4 7 k 0 2 1 -1 0 +++ i-3 P a 1 M CD Medium L. sitkana 04 19 5 15 - 6 bit c- 0 k L. s itkana 17 31 6 19 - 3 ++++ o 2 6 L. scutulata 06 20 2 20 -18 ++++ L. scutulata 16 35 2 31 0 4-f 1 brow* Mixed 05 14 17 5 3 8 14 ' 0 0 ++++ o 0 1 . Mixed 11 5 12 3 3 2 11 - 7 - 1 ++ . Mixed 18 10 18 . 9 1 k 17 -1 -1 ' 0 0 Mixed 23 6 15 6 4 6 13 - 7 0 ++ High L. sitkana 07 57 13 39 - 5 + k 0 3 L. sitkana 19 56 15 32 - 1 +++ 3 1 3 L. scutulata 08 73 2 69 - 3 +++ L. scutulata 20 79 0 70 -1 ++ Mixed 09 o). 36 3 23 32 0 0 + 0 0 1 Mixed 12 17 36 . 21 4 13 32 +3 0 + Mixed 21 10 2k 10 4 11 21 -13 - 8 ' ++ . 0 0 1 h Mixed 24 Ik 3'+ 24 5 13 29 0 0 ++++ c Friday Harbor Density-Species Interaction Experiment, February 2 , 1970 Density Species # Empty # Original Est. Abun-I # Alive Shells Animals # Missing dance of Cage # sit. scut. sit. scut. sit. scut. sit. scut. Diatoms Caged Control Cage effect uncaged ++++ +++ ++ Low L. sitkana 02 18 1 10 1 +++++ L. sitkana 13 10 9 2 I ++++ L. scutulata 01 20 0 Ik 0 +++++ L. scutulata 14 17 2 12 1 +++ Mixed 03 6 9 3 0 3 0 1 ++++ Mixed 10 n O 9 2 0 k - 0 1 Small Mixed 15 7 10 3 0 0 8 0 0 +++-<-Mixed 22 9 8 1 0 +1 - 2 +++ Medium L. sitkana Ok 28 k 2 +++ L. sitkana 17 26 9 12 5 ++++ L. scutulata 06 31 7 0 ++++ L. scutulata 16 32 7 23 1 +++ • Mixed 05 Ik 19 k 1 2 0 +++ Mixed 11 8 18 8 2 0 k 0 • +++ Mixed 18 12 12 6 7 2 9 0 0 ++++ Mixed 23 12 Ik 9 6 5 9 +1 0 ++++ High L. sitkana 07 . 57 12 7 ? L. sitkana 19 35 31 13 14 +++ L. scutulata 08 Ik 3 1 ++ L. scutulata 20 71 10 62 +1 ++ Mixed 09 27 3k 10 6 2 0 + Mixed 12 19 36 16 0 5 4 + Mixed 21 19 32 14 7 k 14 7 1 +++ Mixed 2k 6 28 28 8 0 2k 6 4 ++ 3^ P> CD 00 Friday Harbor Density-Species Interaction Experiment,-April 17, 1970 Density Species Cage |# # Alive sit. scut. # Empty Shells sit. scut. # Unac-counted For sit. scut. # Egg Masses red pink yellow Est. Abun-dance of Diatoms Caged control cage effect uncaged control ++ 0 0 Low L. sitkana L. sitkana L. scutulata L. scutulata 2 13 1 Ik 17 11 18 16 2 9 0 3 1 0 - 2 - 1 12 3 ++ u w * ++++ br«,-*Uw",v,Vo^4 Mixed 3 9 9 1 1 0 0 2 + + + + + Mixed 10 6- 5 2 5 2 . k 3 3 6 +++ kuw«. Mixed 15 2 7 7 4 1 +1 + + + Mixed 22 k 10 5 1 • 1 +1 + + + + Medium L. sitkana k 32 7 - i 2 6 + + + + L. sitkana 17 23 14 - 3 3 ++++ b«W4ul^  L. scutulata 6 36 4 0 + + + L. scutulata 16 31 8 - 1 + - H - + + £3 CO ++ cr-j j Mixed 5 17 19 3 1 0 0 1 Mixed 11 19 19 3 1 +2 0 + + + CD Mixed 18 8 17 10 3 - 2 0 + + + VJJ + + + + Mixed 23 9 15 10 k -1 -1 High L. sitkana 7 68 12 - 0 6 0 L. sitkana 19 30 37 -13 1 1 + + + + L. scutulata 8 73 7 0 + L. scutulata 20 74 6 0 + Mixed 9 22 33 18 8 0 +1 + . . . ... . -Mixed 12 2k 36 5 3 -11 -1 0 « + + + CO Mixed 21 13 31 25 10 - 2 - 8 1 Mixed 2k 26 27 13 12 -1 - 1 + + + Friday Harbor Density-Species Interaction Experiment, June 22, 1970 Density Species i # Survivors Cage //; sit, scut. # Empty # Orig. Anim-Shells als Alive sit. scut. sit. scut. # Unaccount, for sit. scut. Est. # Egg Jbun. Masses 8ia-red pink yel. toms. Control caged control cage effect uncaged control +++ ++ L. s itkana 2 19 2 9 +1 L. s itkana 13 17 3 0 0 l ++ L. scutulata l 17 1 10 2 ++++++ UlUA. L. scutulata l4 20 7 0 +++ U\l>*. Mixed spp. 3 7 10 2 0 0 6 •1 0 2 ++++ Mixed spp. 10 9 7 1 3 5 •k 0 0 dry +++++ Mixed spp. 15 7 10 2 0 0 5 1 ++ Mixed spp. 22 10 10 0 . 0 6 ++ Ii. s itkana 4 36 4 k 0 + L. sitkana. 17 39 2 6 +1 + fD L. scutulata 6 36 1 11 3 L. scutulata 16 37 3 18 + <° .Mixed spp. 5 18 19 2 2 5 10 0 +1 Mixed spp. 11 19 19 2 1 0 10 +1 0 + Mixed spp. 18 18 18 2 2 0 8 + Mixed spp. 23 16 20 3 0 0 6 1 ++ L. sitkana, 7 72 6 20 2 0 L. sitkana 19 67 12 1 -1 0 L. scutulata 8 75 5 58 0 L. scutulata 20 66 12 41 2 0 Mixed spp. 9 38 37 1 2 2 24 1 1 0 Mixed spp. 12 38 39 6 1 0 23 1 0 0 H Mixed spp. 21 37 35 2 k 0 17 1 1 0 ^ Mixed spp. 2k 36 32 k 2 0 10 0 6 0 TABLES 41 t o 5 6 G r o w t h D a t a f o r L . s i t k a n a a n d L . s c u t u l a t a f o r t h e p e r i o d J u l y 1 9 6 9 t o J u n e 1 9 7 0 . T a b l e s 41 t o 5 5 f o l l o w t h e f o l l o w i n g p a t t e r n : T r e a t m e n t D e n s i t y S p e c i e s Number C o m p o s i t i o n 1 l o w s i n g l e 2 l o w m i x e d 3 medium s i n g l e 4 medium m i x e d 5 h i g h - s i n g l e 6 h i g h m i x e d T a b l e 5 6 f o l l o w s • t h e r e v e r s e p a t t e r n . ( REGRESSION RESIDUAL N SSX SPXY SSY B SS DF SS DF 38 12 2.51 8. 56 9. 31 0.070 0.60 1. 8.71 36 34 131 .06. 2.70 6 . 41 0.021 0.06 1 6.35 3? 75 319.62 - 8 . SO 9. 8 6 -0.023 0.24 1 9.61 73 73 3 9 l i 9 2 - 2 1 . 7 9 10. 49 - 0 . 05 6 1.21 1 9.28 71 136 3 74.98 -12.32 9 . 0 8 - 0 . 0 3 3 0.40 1 8.67 134 .133 .45.8, .06 - 1 2 . 45 10. 9 6.... -0.02 7 0.34 1 10.62 131 POOLED REGRESSION CX E F F I C I E N T I S -0 . 025 SOURCE SS OF MS F REGRESSION (BB AR ) 1.08 1 1 . 0 3 .,- 9.69 AMONG SAMPLE RS POOL ED RES I DUAL WITHIN SAMPLE 1,180 L o v J i 'single 0 . 752 Hect s i ^ e 1.77 5 53.25 477 5 6 . 10 433 0.35-0.11 3 . 17 £ • Co I—' cr 1 <<! B H H - CD 0.671 Med-, 0.614 HigVi , si'wejl-e-0 .579. Hv^ W . ir^ixec* Y ADJUSTED 9.15 1 .83 1 6 . 3 9 CO M CO o " "2* c+ THE X VALUE TO WHICH YS ARE ADJUSTED I S X= 8 . 2 1 8 pi CO c+ CO o REGRESSION N SSX SPXY SSY 3 SS D 1 31 105.87 ' 4.7C 36.17 0.044 0.21 2 29 132.00 -12.26 23.55 -0.093 1.14 3 67 263. 37 -39.23 27.62 -0. 146 5. 73 RES IOUAL SS DF 35. 96 29 22 41 27 21.89 65 62 125 118 2 85.£2 353. J55 349.30 -50 .65 -41. 73 •36.39 34 .0 7 21. 56 20. 2 4 -0.177 -0.118 •0.104 8.99 4.92 3. 79 2 5.03 60 16.64 123 16.45 116 POOLED REGRESSION COEFFICIENT IS -0.117 SOURCE SS DF MS F REGRESSION (BBAR) 20.62 1 20.62 i 62.57 AMONG SAMPLE BS POOLED RFSI DUAL WITHIN SAMPLE 2.107 1.8 74 1.281 K.,S. 4.16 5 0.8 3 138 .43 420 0 .3 3 163. 21 426 2. 53 1.354 M..H, 0.883 U.S. 0.841 H-'H, Y ADJUSTED 54. 21 10.8 4 32.89 rr fD THE X VALUE TO WHICH YS ARE ADJUSTED I S X-= 8.244 a-fO • U 1 U 5>tfk C. 5,*/" REGRESSION RESIDUAL N _ s s x SPXY SSY B SS DF SS DF 1 31 6 3 . 15 - 9 . 57 17. 1 6 -0.152 1.45 1 .15.71 29 2 28 131.03 -8 .09 9 .12 - 0 . 0 6 2 0 . 50 1 8.62 26 < 3 64 194. 85- -36.69 24 .24 -C. 18 8 6.91 1 17.33 62 ? 4 66 , . 234.J95 -30.81 ?0 . 56 - 0 . 131 4.04 1 16.52 64 5 119 Z69.0H -38.84 17 . 79 -0.144 5.61 1 12.18 117 . 6_ 119 385.29 - 2 8 . 34 _ 13 • 6 9_._ -Q.._074 2_.08 1 16.61 117 POOLEO' REGRE SSIQN COEFFICIENT IS - 0 . 1 1 9 . SO URCE SS DF MS F REGRESSION (BRAR) 18.16 1 18 . 16 > 8 6 . 65 AMONG SAMPLE BS 2.44 5 J.49 - 2.33 POOLED RESIDUAL 86.97 4 15 0.21 WITHIN SAMPLE _ 107.56 421 • 1.431 k,*., wit-" H9 1 .2.03 U, M.. _ :. <§ • g. 1.02 0 N • ) s. CD W M H - CD 0. 837 K.( 0.484' C.477 H . n-s. & CD H ci-s ^ Y ADJUSTED ~~ " 4 0 . 0 2" ' 5 8.00 38.19 —. O d -V THE X VALUE TO WHICH YS ARE ADJUSTED I S X = 9.334 A< P> c+ Co ON ro y N SSX SP XY SSY 1 19 48 .66 1. 39 6.80 2 21 8 8. 70 0. 36 1. 79 3 42 59.80 -7.72 7.76 4 45 8 7> 22 -A . 53 6.22 5 105 197!. 33 - 2 0 . 10 14.56 ft ... 107 256.24 . - 1 7 . M 4 11.13 REGRESS ION B SS DF 0.029 0.04 1 0.004 0.00 1 •0. 129 1.00 1 RES I DUAL SS DF c.76 17 1.79 19 6.76 40 -0.052 -0. 102 •0.070 0 . 24 1 2.05 1 1. 24 1 5.99 43 12.52 103 9.89 105 POOLED REGRESSION COEFFICIENT IS -0 . 066 SOURCE SS DF MS F REGRESSION ( B B A R ) 3.18 1 3 . 1 8 . 2 3 . 78 AMONG SAMPLE BS POOLED RESIDUAL WITHIN S AMPL E _ 0.729 C. 544 1.38, 5 43.70 3 27 48.27 333 0.2 3-0 .' 1 3 2.07 Oltr^ o • c+ 1-3 to 0.654 0 to M H - CD 0.432 0.419 0. 399 <H-s a » CD Y ADJUSTED 2. 56 5' " 0 . 51 3. 82 q c+ THE X VALUE TO WHICH YS ARE ADJUSTED IS X= 9.914 data ON i 2 3 N 18 18 39 _ s s x 142.13 7 9 . 32 166 . 18 REGRESSION SPXY SSY B SS D •2.33 0.34 -0.016 0.04 •3. 46 0.38 -0.044 0.15 -4. 16 0.61 - 0 . 0 2 5 0 . 10 RES I DUAL SS DF 0.30 16 0.23 16 0. 50 37 POOLED REGRESSION COEFFICIENT. IS -0 .0 2 5 SOURCE SS DF MS F REGRESSION (BBAR) 0.51 1 0.51 \ 45.66 4^  5 .6. 27 75 54 72.j76 196. ;i6 172.32 -1 .12 •4. 5 8 •4.85 0.05 0.55 1.06 -0.015 •0.023 -0.028 0.02 0 . 11 0 . 14 0.03 25 0.44 73 0. 92 52. AMONG SAMPLE BS POOLED RESIDUAL WITHIN SAMPLE. _ 0.27 5 0. 219 0 . 209 0.05 5 2.43 219 2.98 225 0 .01 0 .01 0.85 Wit* H3 CD • fD O & CD B CD H H - CD CD VJ1 0 . 153 0 . 145 _ 0.182 Y ADJUSTED 0.31 0 . 06 5. 66 o —« 13' THE X VALUE TO WHICH YS ARE ADJUSTED I S X= 10.198 p-f» c+ P ON II >0 (C H O f\J t\i ITi ZD G 00 LU a: to <o OO <$• •o o o cc ,00 00 UJ o LU a: l/) rH f\J CM oo CM CM rn O o O >- co s t\j oo so cc 00 . . . O o —1 >• in L' x - * J a. • • • o t»- r- o I I i x C J m >-H oo o r- r-oo • • . sT vC <M in fT: cc. CM r\ CM cc o rn CM m m vl- CO -4" (X) rH vO m. in o in CM vT CM CM O : O O Oj cr o m r- a OS (M ro. re CM o o O O o Oj • • • • • o 1 o 1 o 1 o 1 o 1 oi 1 ! »C CO «Cf. r- f- O rH o rH o <i- <r. CM cc rn. r*~ i—* CM x- r- 4-rr-. m r—i O O O1" -4" cr ^ IA >0 -A. CM CM UJ o u. IC UJ o o oo oo LL! CL O G UJ _J O o a 00 00 < CD CD UJ U cx 2: r) a c — O0 O0 00 LU cc O LU iTable !L. s i February o ro CM v ? o • • • t—I o .—i IT. o o r-i-O cr m! rH CM • • • r-H c < : LU O _ J «— a. oo «c LU <T ar. oo C-o z ifi ^ m Cj) UJ r-i CM CM f\J z: - i i • • • o o t- O O o s: a ~ < O 2 _ f 2: < 00 46. ' kana growth i CM I G i UJ t— l<! sO H 1/1 in « n o CM rH CM ""J • • • G o o o < data CO M X 00 C LLJ t— OO ZD ~> G < a' < oo > I o X c I— UJ > LU X auaxns mi SNMI sswsna KOIUH IX. CO r-l CM sJ- in o (XI rH in in O- oo < c 00 r~ <- in vO >!• —' oo r- cn O r—1 o oo • » • a « o m o CM a ct: r-l CM m rn u_ r—1 r-l —i r-l r-l r-l o 1 o i » oo r- r-l <o CM in! 00 OO CM CM CM ON oO • • • • • • l UJ tn in m IT: CV| a: 1 O 1 UJ i a. I 1 CO sO m o r-l tn CM o •c o M r-l r—i r-l O! • • • • « o I o 1 o 1 o 1 o 1 o: i : > m co m CO a> on c c a- -o cn C T ' 00 in o cn in r- «—l i > CM o cn o t—i' X r-l m CO' a. • • • • oo cn m (V m i—' cn 1 r\! 1 m l m 1 in 1 m 1 j X m m r- i CM: 00 cn in CC r—; OO • • • • • CM in r-l r-l c CM CM i—1 •—' CM r-l cn c-o in LTV CO o cn <c 1 CM CM IT in c- CO i l-< CM cn in 1 -A. UJ o UJ o o oo OO LU oc o UJ <x o UJ _J o c CL I Table i L. s i i •April r-- -o r-l CM 00 • • r-CM o 00 tx <x EC CC U J O0 O0 oo a o UJ a: o 1—1 in CV CM <n. m CI l r- r-l CV CM m • • • • m in CM m r-l r-l: 00 —I CO <x u-1 o _i >-i a : 00 z. U J < cc oo < oo 47. kana growth o -z r-<r m CM r~ O U J • cn CM cv _ J X • . • O O t— r-J —« r-l J n i-t < o. 3: CO CM m CM Q UJ CO vT if"-. CM CO CM in ov- o-<-. o o <r data -4-r-rn . co H x O0 I—I c U J I— OO —> c, <r a : < oO > I X c IU < > LU X •WKOhM Oil u_ m r-< Q i/l >T O >— 1/1 & >? 1/1 • » UJ o c «a- ,H m 2 O a to o m sT co to to IT. f\i to • t • • • t UJ o •c CO in cc (NJ —1 m cn o 1—1 at 1 j CO o <o r-l m 00 fM o «r m CM m CM • • • • • « O 1 l O 1 o 1 o l O 1 > o —I C T o> m to in co CM m CM (/> • • t • t • in CM in cc «o m r» CM o o i— i r-i. >• ffj CO m CO so CO o a. • • t t fl • to o o —1 o r~ j - r- •4-o CM 1 1 1 1 CM 1 —< 1 X I—< CM oo r- vO to o r- o m to « • « • • a cn CM o in a-(NJ -o CO o CM cn m •d- • i " in 0> o> cr o m <M r-1 —< r-1 r-4 in N - CO CM >0 O —I m co r-•r in 5> t » • •T m N -A. >3-m o i IT) UJ U. LL UJ D O o to to u o UJ cc Q UJ - J o a a. CO m m to • £ CM CM U-O 0> * CNi tO O tO CM or < CO CO UJ o oc I D o to to to UJ cc 71 aTable L. _ June 48. s i Itkana growth o NO SO rn r» < • m o m o «~i CM CM ON CO co m en • • » *G O <0 CM «—< O 00 _ J co < UJ o UJ o. to jr UJ < or to o m < z: -» o> o uj •—i o co m Z - J X • * • h- CO CM CM O 3 X c < a ; in 1° « i CO o CO cn in CM o «i" CM m to m ^ —t ;D I - I O N " ) cn CM CM <t 157 data CO r» 00 CO II X to to -5 o < UJ cc < to >-X o ^4 X o UJ _J < > UJ X REGRESSION RESIDUAL N ssx SPXY SSY B SS DF SS DF 1 38 160.33 -3.91 0.56 -0.0 24 0.10 1 0.46 36 2 34 185. 53 -2 . 89 0.41 -0.016 0.05 1 0.37 32 3 69 280.01 -6.74 1.03 -0.024 0. 16 1 0. 87 67 4 55 208. 73 -3 . 65 0.58 -0.017 0.06 1 0.51 53 5 137 389.05 - 3 . 76 2.39 -0.010 0.04 1 2.35 135 6 140v 361.79 -6 .06 0.72 -0.017 0. 10 1 0.62 138 POOLED REGRESSION COEFFICIENT IS -0 .017 SOURCE SS DF MS F REGRESSION (BBAR) 0. 46 1 0.46 40.92 AMONG SAMPLE 3S • 0. 04 5 0 .01 0.78 POOLED RESIDUAL 5. 18 4 61 0 .01 WITHIN SAMPLE 5. 69 467 -0.006 H3 -0.009 c • CO a" -0.00 3 cao M <D -0.051 s-: «+ j> -0.046 0 H • -0.055 P' c-t-Y ADJUSTED 0. 20 5 0 .04 3.65 ,' CO U°. H o t3* THE X VALUE TO WHICH YS ARE ADJUSTED IS X= 9.881 y 1 2 3 REGRESSIGN N SSX SPXY SSY B SS DF 37- 208.09 -10 .64 3.34 -0.051 0. 54 30 172.19 -14.27 3.94 -0.083 1.18 50 194.06 -18.86 7.41 -0.097 1.83 4 5 8 5 87 6 10 2 244.29 239.55 257.32 •15 .79 - 4 . 41 13. 77 7.91 1. 77 5.0 4 •0.06 5 •0.018 •0. 054 1.02 0.08 0. 74 RF SI DUAL SS DF 2. 79 35 2.76 28 5.58 48 6.88 56 1.68 85 4.30 100 POOLED REGRESSION COEFFICIENT IS -0.059 SOURCE REGRESSION (BBAR) SS DF • MS F 4.59 1 4.59 67.36 AMONG SAMPLE BS POOLED RESIDUAL WITHIN SAMPLE 0.20 8 0.231 0. 239 0.80 24.0 1 29. 40 5 3 52 358 0.. 16 0 .07 2. 36 0. 180 0 .00 4 C.03 6 Y ADJUSTED 3.35 0.67 9.81 £ O M » Co <rr CO THE X VALUE TO WHICH YS ARE ADJUSTED IS X= 9.750 a. CO CO U3 u_ in cr CM o ro (\j «o c LU fx oo m ro o 1/1 s m n O -H <\J U_ rH r-i -H 2 C O i-t oo •-«(*_ ro y i y> H in o> 00 • • • LU O O O o UJ on CO O >4- (NJ OJ. ro O r- ro o O O o o o O • • • • • • o l o 1 o 1 o 1 o 1 o 1 > o v0 o o 00 co o vl- rH 00 O r—1 ro LC. ro ST > co CO in <r r-X CO 0 0 vt 4- <*• Q-00 ro U3 <M IA o ro I 1 r-4 1 rsj f—1 0=^ X O O CO 00 CM O I S -00 • • • CO r--rvi ro r-•—< rH r-l Z r- r-( ro ro vo f\j ro r- 4- oc in m oj CT1 «fr ro f\J CO LO I A rH ro r- vD ro H N >0 O. I I r\i <t- <f <r co >f H O CC ro co rH-H-O <\1 O1 -c o in in rf, .4- in vo -A Table L . s 5 1 . ciitulata September in >t in u. . . in r-H o t-H ro on' l-H in ro o o o . 00 . . o 1 s: ro o o OO •—. LL —J in in rH h- o o z LU X?" <r •—•4 i—" -O rH cc m c • 0 . . U- ro O in X LL O0 rH rH LU O0 CO z < l/> oo co CQ < oO CO LU LU LU _ LU O : o; _J »-H C-o a: a. 00 '.JJ r> o LU < (X o < en 00 00 OO oo o o in Q oo ~Z CSJ ro UJ LU UJ M rH rH rH —1 CC s: _i I o o o •— O o c LU »—> c. a: < a. 3 grow;h data ! O c LU I— O- ro O oo (M O D rH O • • . Q o a o <t L70 O1 in II X 00 o LU 00 _3 < < oo V x X o < > X LU X 3 0 0 REGRESSION N SSX SPXY SSY B SS OF 1 28 87.05 -2.94 0.38 -0.034 0.10 2 28 113.31 -3.52 0.51 -0.031 0.11 3 69 161.69 -5.02 1.39 -0.031 0.16 RESIDUAL SS DF 0.28 26 0.40 26 1.23 67 4 55 5 133 6 133 15 3. 13 26 5.82 224. 14 -2.99 •13.02 - 6 . 22 0. 76 2.68 2. 54 •0. 019 •0.049 -0.02 8 0. 06 0.64 0.17 0.70 53 2.04 131 2.36 131 POOLED REGRESSION COEFFICIENT IS -0.034 SOURCE REGRESSION (BBAR) SS DF MS F 1.13 1 1.13 69.81 AMONG SAMPLE BS POOLED RESIDUAL WITHIN SAMPLE 0.095 C .049 0.044 0.-021 0.045 G .08 1 Y ADJUSTED 0.10 5 7.02 434 8 .26 4 40 0.2 2 0.02 0.02 0 .04 1.27 2.72 O • CD M CD T= £ ro fo 0*3 O THE X VALUE TO WHICH YS ARE ADJUSTED I S X= 9.967 to <rt-h • 5 cuJc c — i REGRESSION RES I DUAL ' N SSX SPXY SSY B SS DF SS DF I 24 ~ 7 4 . 10 -1.54 0.27 -0.021 0.03 1 0.24 22 2 26 118.73 - 3 . 45 0 . 72 -0.029 0.10 1 0.62 24 \ 3 35 108.87 -1.91 0.27 - 0 . 0 1 8 0 . 03 1 0.23 33 r 4 42 113.01 -2 . 64 0 .30 -0.02 3 0 .06 1 0.24 40 5 125 263.71 - 7 . 58 1.45 : - 0 . 029 0 . 22 1 1.23 123 6 102 16 3.90 -2 .80 0 .70 -O.C17 ._ C O 5 1 0.66 100 POOLED REGRESSION COEFFICIENT IS -0.024 SOURCE SS OF MS F REGRESSION < BBAR ) 0.47 1 0 . 47 50.07 AMONG SAMPLE BS POOLED RESIDUAL WITHIN SAMPLE -0.011 0 . 02 5 -0.041 O.C 2 5 3.22 342 3.71 348 0 .00 0.01 0.47 -0.039 -0.018 -0.037 Y ADJUSTED wltr» i-3 o a 1 ( B O H -J3- " m 0 . 10 0.02 2.21 M • SO CO o THE X VALUE TO WHICH YS ARE ADJUSTED IS X= 10.081 p. c+ . REGRESSION RESIDUAL N SSX SPXY SSY B SS OF SS DF 1 35 76.45 -1.26 0.27 - 0 . 0 1 6 0.02 1 0.25 33 2 35 133.14 -3.93 0.54 -0.03G 0.12 1 0.43 33 3 61 168.98 -5.92 0.48 - 0 . 0 3 5 0.21 1 0. 27 59 4 61 171.01 - 4 . 95 0.53 -0.C29 0 . 14 1 0 . 39 59 5 143 2 9 5 . 23 - 6 . 18 0.68 -0.021 0 . 13 1 0.55 141 6 130 267.43 -3.91 0 .42 . .-0.015 0.06 .1 0. 37 128 POOLED REGRESSION COEFFICIENT IS -0.024 SOURCE SS DF MS F REGRESSION (BBAR) 0.61 1 0.61 123.27 AMONG SAMPLE BS 0.06 5 0.0 1 2.37 POOLED RESIDUAL' 2.26 453 0.00 WITHIN SAMPLE 2.93 459 -0.02 6 hrjhr. ^  ,-. .-, „ CO • CO 0. Ou 3 a- a--0.022 : 2 a -0.029 ; : -0.041 -0.055 . ... ... 5-* Y ADJUSTED 0.12 5 0 .0 2 4.84 p 3 THE X VALUE TO WHICH YS ARE ADJUSTED IS X= 9.619 p. co <rt-CO REGRESSION RESIDUAL N ssx SPXY SSY B SS DF SS DF l ~ 30""" 7 0 . 11 - 8 . 75 3 .68 -0.125 1 .09 1 2.59 28 2 30 142.82 -11.30 3 .92 - 0 . 0 7 9 0 . 89 1 3. 03 28 \ 3 65 177. 67 -31.35 11 .83 - 0 . 176 5.53 1 6.30 63 4 71 270.80 - 1 6 . 1 3 8 .28 - 0 . 060 0.96 1 7.32 69 5 149 735.66 -10 7.90 50 .60 - 0 . 1 4 7 1 5 . 82 1 34. 77 147 6 112 230.39 -11.77 6 .66 -O.C51 0.60 1 6.0 6 110 POOLED REGRESSION COEFFICIENT IS - 0.115 SOURCE SS DF MS F REGRESSION ( BB AR ) 21.53 1 21 . 53 159.50 AMONG SAMPLE BS POOLED RESIDUAL WITHIN SAMPLE 0.554 Ue<*t, si'iglt. 0.53 5 L o w i T'*e<* 0. 636 MecXiiA,^, SI »v>) I-t. 3.37 5 60.0 7 4 4 5 8 4 . 9 8 4 5 1 0.67 0 . 1 3 5. 00 0 . 5 4 6 iM eciiV^v, ^i\e<A 0 . 4 2 6 i-W^W, S , * 5 I < L 0 . 4 1 7 W i ^ K , * V M ' > C « M Y ADJUSTED 2 . 94 0.59 4.36 tr" • i» a" co M o CD n— I—1 • f» <r+-C» OJ 4 O -rt— P . fa <+ P THE X VALUE TO WHICH YS ARE ADJUSTED I S X= 9.2 94 N. r\^ W,Wvi\«< 1 111 U f ^ u s . ^ l e 2 H 7 ssx 218.28 225.19 145.76 REGRESSION SPXY SSY B SS D •52.79 29.23 -0.242 12.77 •57.85 36.80 -0.257 14.86 •25.02 22. 17 - 0 . 172 4. 30 RES I DUAL SS DF 16.46 109 21.94 115 17.88 54 ^Med-^i^le 4 57 121.01 Lou^vV.^M 5 29 100. 55 L O W J , s.'r^l-e. 6 25 61.07 -39.11 -IS.14 -13.49 39.65 -0.323 13.80 -0.180 11.48 - 0 . 221.. 12.64 1 3.27 1 2. 98 ...1 27. 01 10.53 8. 50 55 27 23 POOLED REGRESS ION COEFFIC IENT IS -0.237 SOURCE SS DF MS F REGRESSION (BBAR) 48.86 1 48.86 182.92 AMONG SAMPLE BS POOLED RESIDUAL WITHIN SAMPLE 0.782 'r^Mifd 0. 762 W S 1.158 M M 1.95 5 0.39 102.31 383 0.27 153.12 389 1. 46 C • Co CD 1.301 ~TTJ~ 0.978 M 1.124 Lowe Y ADJUSTED ca r-1 • co <-)-co 16. 94 3.39 12.68 3 o -rr-P-co <+ co THE X VALUE TO WHICH YS ARE ADJUSTED IS X= 9.834 VJ1 

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