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August, 1979 the Thesis of John Grenfell Is Approved California State University, Northridge Ecological Aspects of Feeding Behavior of Some Tellinaceans \l (Mollusca: Bivalvia) A thesis submitted in partial satisfaction of the requirements for the degree of ~~ster of Science in Biology by John Kemp Grenfell August, 1979 The Thesis of John Grenfell is approved: Earl Segal committee chairman California State University, Northridge ii ACKNOWLEDGEMENTS I would like to thank Ross Pohlo, the chairman of my oommi ttee, for his help and valuable criticisms of the ini tlal thesis drafts. I am also indebted to Earl Segal and Tony Gaudin for their helpful criticism and advice. I would also like to thank my wife, Carol, without whose help tr~s project would not have been completed. iii TABLE OF CONTENTS Page ACKNOWLEDGEHENTS • • • • • • • • • • • • • • • • • • • • • • • iii LIST OF TA.BLJ<jS • • • • • • • • • • • • • • • • • • • • • • • vi LIST OF FIGURES • • • • • • • • • • • • • • • • • • • • • • • vii LIST OF PLATES • • • • • • • • • • • • • • • • • • • • • • •Viii ABS'ffiACT • • • • • • • • • • • • • • • • • • • • • • • iJc INTRODUCTION • • • • • • • • • • • • • • • • • • • • • • • 1 JifA. T.ERIALS AND METHODS • • • • • • • • • • • • • • • • • • • • • 4 Areas of Study • • • • • • • • • • • • • • • • • • • o • 4 Sampling Technique • • • • • • • • • • • • • • • • • • • • 16 Substrate Analyses • • • • • • • • • • • • • • • • • • • • 16 Shell Measurement • • • • • • • • • • • • • • • • • • • • • 19 Mantle Cavity and Stomach Contents • • • • • • • • • • • • 19 Feeding Behavior • • • • • • • • • • • • • • • • • • • • • 19 Statistical Analyses • • • • • • • • • • • • • • • • • • • 19 RESULTS • • • • • • • • • • • • • • • • • • • • • • • 21 Mantle Cavity and Stomach Contents •••••••••••• 21 Behavior of the Inhalent Siphon • • • • • • • • • • • • • • 21 Population Density •••••••••••••••••••• 25 Shell Size • • • • • • • • • • • • • • • • • • • • • • • 29 Substrate Analyses • • • • • • • • • • • • • • • • • • • • 31 DISCUSSION • • • • • • • • • • • • • • • • • • • • • • • 34 Feeding Behavi.or • • • • • • • • • • • • • • • • • • • • • 34 Population Density • • • • • • • • • • • • • • • • • • • • 37 Substrate Analyses • • • • • • • . -· • • • • • • • • • • • 38 Shell Size • • • • • • • • • • • • • • • • • • • • • • • 38 LITERA1URE CITED • • • • • • • • • • • • • • • • • • • • • • • 40 APPENDICES Appendix 1 Dimensions for ~~coma nasuta collected from Mugu Lagoon • • • • • • • • • • • • • • 42 Appendix 2 Dimensions for ~anguinolaria nuttallii collected from Mugu Lagoon • • • • • • • • • 42 iv TABLE OF CONTEN'lli cont. Page Appendix 3 Dimensions for Tagelus californianus and Macoma nasuta collected from Edison Canal • • 43 Appendix 4 Dimensions for Tagelus californianus collected at Back-Bay Newport • • • • • • • • 44 Appendix 5 Dimensions for Macoma secta and Sanguinolaria nuttallii collected from Lower Newport Bay • • • • • • • • • • • 0 • • 45 Appendix 6 Dimensions for ~~coma nasuta, Macoma secta and Florimetis obes~ollected at NewPort Bay-:-. • • • • • • • • • • • • • • • 46 Appendix 7 Regression analyses for Tagelu~ californianus • • • • • • • • • • • • • • • • 47 Appendix 8 Regression analyses for Sa~nol~~ nuttallii • • • • • • • • • • • • • • • • • • 48 Appendix 9 Regression analyses for Macoma nasuta • • • • 49 Appendix 10 Regression analyses for Florimetis obesa • • 50 Appendix 11 Regression analyses for Macoma ~ • • • • 51 v LIST OF TABLES Table Page 1 Stomach contents, siphonal behavior, and feeding type • • • • • • • • • • • • • • 0 • • • • • • • • 22 2 Mean number and t-values for species collected allopatrically and sympatrically per 0.5 m2 ••••••• 26 3 Mean number and t-values for allopatric populations and total number of tellinaceans in sympatric communities per 0.5 m2 •••••••••••••••••• 28 4 Mean length and height and t-values for allopatric and sympatric species •••• • • • • • • ••• 30 5 Slopes of regression lines and t-values comparing the slopes of those lines • • • • • • • • • • • • • • •• 32 6 Sediment size distribution and organic carbon content from the areas of study, percent by weight •••••••• 33 vi LIST OF FIGURES Figures Page 1 Locations of tellinaceans and nature of occurrence • • • 7 2 Morro Bay • • • • • • • • • • • • • • • • • • • • • • • 9 3 Edison Canal • • • • • • • • • • • • •••••••••• 11 4 Mugu Lagoon • • • • • • • • • • • • • • • • • • • • • • 13 5 Newport Bay . ~ . ·- . • • • • • • • • • • 15 6 Types of inhalent siphonal behavior • • • • • • • • • • 24 ~ vii LIST OF PLATES Plate Page 1 Species studied. • • • • • • • • • • • • • • • • • • • • 6 A. Macoma nasuta B. Tagelus californianus c. Macoma secta D. Flarimetis obesa E. Sanguinolari~ nuttallii 2 The quadrat sampler and sieve • • • • • • • • • • • • • 18 viii ABS'ffiACT Ecological Aspects of Feeding Behavior of Some Tellinaceans (Mollusca: Bivalvia) by John Kemp Grenfell Master of Science in Biology August, 1979 The feeding behavior of five species of tellinaceans was studied in four locations in California, USA. The organisms were studied in areas where they occurred sympatrically with other tellinaceans and in other areas where no other tellinaceans ¥tere present., Random samples v1ere taken to determine population densities. Shell sizes were measured to determine if there was any difference due to competition. Each population was examined to ascertain the type of feeding behavior. Feeding behavior was determined from the stomach contents and from the behavior of the inhalent siphon. It was observed that when closely related species occur in the same location they exploit different microhabitats. Some organisms use suspended material as their primary food source, while others ingest deposits. Macoma nasuta is a deposit feeder when not in competition with other tellinaceans, but fed on both deposits and ix - ~ - --------------- suspended material when coexisting with other deposit feeding Tellinacea. There is not any significant change in the population denslty or shell size which can be attributed to differences in feeding behavior. Growth of tellinacean species was the same in different geographical locations. X INTRODUC'llJ:ON The superfamily Tellinacea is a gToup of burrowing bivalves found on the Pacific Coast of North America from Alaska to Panama. Five species within this superfamily were studied. Macoma nasuta (Conrad, 1837) is usually found in quiet waters with muddy substratum about 15 em below the surface, rangi-ng from Alaska to Baja California, Mexico (Abbott, 1954). Macoma secta (Conrad, 1837) is found in bays 15 to 20 em below the surface from Vancouver Island to the Gulf of California (Abbott, 1954). Sanguinolaria nuttallii Conrad, 1837 can be located in estuaries 15 to 25 em oelow the surface from Monterey, California to Baja California (Abbott, 1954). Tagelus californianus (Conrad, 1837) is found on muddy sand flats 15 to 30 em below the surface, from Humboldt Bay, California to Panama (Abbott, 1954). Floriroetis obesa (Deshayes, 1855) is found in clean sand about 15 to 25 em below the surface, from Point Conception, California to Magdalena Bay, Baja California (McLean, 1969). According to Yonge (1949) all Tellinacea are deposit feeders. More recently Bradfield and Newell (1961), Holme (1961), Purchon (1963), Wade (1965), Pohlo (1966, 1967, 1969, 1972, 1973), Mauer (1967), .and Reid and Reid (1969) showed some members of the Tellinacea are suspension feeders. Both Macoma nasuta and Macoma secta are considered to be deposit feeders, while Taeelus califorruanus and Sanguinolaria nuttallii are considered to be suspension feeders (Pohlo, 1969, 1972, 1973). However Florimetis obesa may function as both a suspension and deposit feeder (Pohlo, 1973). 1 ,.., .::. In suspension feeders, the animal holds the inhalent siphon at or near the surface often in a conical depression and at times extends it several centimeters above the substratum. At no time, however, is the siphon seen actively inhaling the deposits. The stomach contents reflect the siphonal behavior. Sand grains and nutrient particles in the stomach are small, averaging 50 fl• Nutrients are composed of bacteria, flagellates, small dinoflagellates, diatoms and debris (Reid and Reid, 1969). In deposit feeders, the inhalent siphon rests on the substratum, moving aro1tnd continuously, periodically pressing its aperture down on the sand inhaling small amounts of the surface matter (Yonge, 1949, and Reid and Reid, 1969). Stomach contents consist of surface diatoms, debris, and bacterial colonies living on large sand grains (Reid and Reid, 1969). In this study allopatric refers to the presence of only one tellinacean species, while sympatric refers to the coexistence of two or more tellinaceans. 'l'ellinacean species have been observed coexisting (Pohle, personal communication). If the sympatric species are all deposit or all suspension feeders, does this constitute niche overlap? Pianka (1978) maintains that, "niche overlap occurs when two organismic units use the same resources or other environmental variables.". If resources are not in short supply it is possible that two species may coexist, using the same resource. Hutchinson (1957) proposed that a species population could be described or characterized by its position along several dimensions, such as temperature, prey size and food source. He treated niche overlap in a simple way: he 3 made the assumption that the environment was saturated and that competition and exclusion must occur. The Gause (1934) principle states that species cannot coexist for long if they use the same resources.
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