ABSTRi\CT REPRODUCTION AND GROWTH OF THE CHITON NUTTALL!NA SPP. ALONG THE CENTRAL COAST OF CALIFORNIA Analyses ofreproductive cycles, larval settlement, recmitment, and growth rates of Nuttallina spp. within a coralline algal mat were conducted in Stillwater Cove, Califomia. Nulfallina kata exhibited discrete spawning events in spring and autumn, whereas N. cal!fomica was reproductive throughout the study period. Within the algal mat, increases in mean density of Nuttallina spp. were related to slight decreases in mean size, indicating Nuttallina spp. may have been at or near its saturation level in the algal mat. Significant recruitment occurred in the algal mat, and the majority of Nuttallina spp. in the algal mat were estimated at less than 2 years old. Larval settlement of N. kata occUlTed in the presence of C. vancouveriensis with and without adult mucus, and in the presence of P. neof'arlowii with adult mucus. Grazing activities of Nutta!lina spp. within the algal mat did not signiticantly limit the growth of fleshy macroalgae. Michelle Diane White December 1998 REPRODUCTION AND GROWTH OF THE CHITON NUTTALLJNA SPP. ALONG THE CENTRAL COAST OF CALIFORNIA by Michelle Diane White A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Marine Science in the School ofNatural Sciences Califomia State University, Fresno December 1998 Copyright© 1998 by Michelle Diane White ACKNOWLEDGMENTS 1 would like to thank my committee members Dr. James Nybakken, Dr. Michael Foster, and Dr. Stephen Ervin for their guidance, patience, encouragement, wisdom, and friendship. I have enjoyed working with them and look fmward to continued friendship in the years to come. There are many people at Moss Landing Mmine Laboratories that I would like to acknowledge, but a special thank you goes out to Gail Jolmston, Aldo DeRose, and Joan Parker. It is the combination of students, faculty, and staff that creates a wonderful and unique educational environment. There were many students that helped with my research, including Caren Braby, Jean DeMarignac, Jason Flores, Lori Gant, Satina Giammanco, Michele Jacobi, Korie Johnson, B1ynie Kaplan, Eli Landrau, Mark Pranger, and Kyra Schlining. I was able to convince these students that chitons were cool and that seeing the sunrise can be a ve1y rewarding experience. 1 also need to thank Stephanie Flora for her lmowledge and patience in answering my endless questions. I owe a huge debt of gratitude to the gang at Granite Canyon, including Brian Anderson, John Hunt, Susy Jacobson, Patty Nicely, B1yn Phillips, Witold Piekarski, Max Puckett, and Mickey Singer. Not only did they let me use their lab facilities, they paid me to hang out with them for a couple of years. 1 consider myselffmiunate to have worked with such a wonderful group of people. Financial support was provided in pa1i by the Dr. Earl and Ethyl Myers Oceanographic and Marine Biology Tmst, the Conchologists of America, and the Graduate Studies Depmiment at California State University, Fresno. vi I owe a special thank you to my parents, Everett and Delores White. Throughout my life they have supported me in every endeavor, no matter how long it may have taken me to accomplish my goals. I would not be where I am today had it not been for their physical, emotional, and financial support. Finally, a very special thank you goes out to Tomoharu Eguchi. More than anyone else, he provided daily support and motivation to get the work done and to do it well. He has not only made me a better scientist, but continues to encourage me to grow as a person. His love and support have been inspirational and greatly appreciated. TABLE OF CONTENTS Page LIST OF TABLES. Vlll LIST OF FIGURES 1x INTRODUCTION I MATERIALS AND METHODS 6 Reproductive Cycles. 8 Larval Development and Larval Settlement 9 Density, Size, and Species Composition within the Coralline Algae Mat II Reduction in Density, Algal Assemblages, and Growth Rate 14 RESULTS 19 Reproductive Cycles . 19 Larval Development and Larval Settlement 26 Density, Size, and Species Composition within the Coralline Algae Mat 33 Reduction in Density, Algal Assemblages, and Growth Rate 42 DISCUSSION 44 Reproductive Cycles . 44 Larval Development and Larval Settlement 49 Density, Size, and Species Composition within the Coralline Algae Mat 54 Reduction in Density, Algal Assemblages, and Growth Rate 58 CONCLUSIONS 62 REFERENCES 64 LIST OF TABLES Table Page I. Larval development stages of N. kata and N. cal!fornica and other inteiiidal chitons . 28 2. Two-factor ANOV A of larval settlement rates of N. kata, measured as prop01iion of settled larvae among different substrate types and in the presence or absence of adult mucus 31 3. ANCOVA analysis of the relationships between fomih valve width ( FVW) and total chiton length for large and small size classes of N. ca!ifornica . 37 LIST OF FIGURES Figure Page l. Study area in Stillwater Cove in Cannel Bay, California 7 2. Fomih valve width versus total chiton length for N. cal(fornica I 5 3. Arcsine transfonned gonad indices versus chiton mass (g) and chiton length for all chitons collected prior to natural spawning events 20 4. Mean(+/- SE) monthly gonadal indices of N. cal!fornica and N. kata 21 5. Mean(+/- SE) monthly gonadal indices of N. kata and N. californica. 25 6. Size frequency distributions of male and female chi tons 27 7. Mean proportion of settled larvae ofN. kata among substrate type and in the presence or absence of adult mucus 32 8. Mean density (square root+/- SE) of N. kata, N. califomica, and N. .fluxa from three areas within the C. vancouveriensis algal mat 35 9. Mean size (mm Fomih Valve Widtl1 +/- SE) of N. kata, N. californica, and N. .fluxa from three areas within the C. vancouveriensis algal mat 36 I 0. Estimated age class distributions of N. kata, N. californica, andN. .fluxa in three areas within the C. vancouveriensis algal mat . 39 II. Relationship of foutih valve width versus total chiton length for juvenile N. kata 40 12. Mean density (square root+/- SE) of newly recruited N kat a and unidentified chitons estimated less than 2 months old from three areas within the C. vancouveriensis algal mat 41 13. Mean percent cover (arcsine+/- SE) of coralline algae (a), bare rock (b), sessile invetiebrates (c), and fleshy macroalgae (d) among experimental plots at the initiation (April l 997) and conclusion (October 1997) ofthe experiment 43 INTRODUCTION Distribution and survival of intertidal organisms are affected by many interacting processes, including physical factors such as desiccation and heat stress, and biological factors such as intra- and interspecific competition, larval settlement, and recruitment (Connell 1961, Wolcott 1973, Underwood and Jemakoff 1981 ). Larval settlement can influence the structure of the adult intertidal community (Roughgarden et al. 1985, 1988, Gaines and Roughgarden 1985), whereas inter- and intraspecific competition may negatively influence growth, survivorship, and distribution of individuals after recruitment has occuned (Haven 1972, Underwood 1978, Peterson and Andre 1980). Species migrations also may be induced by interspecific competition (Branch 1975a, 1975b, Underwood 1978, Chow 1989). Studies on reproduction, recruitment, growth, and competition provide important infonnation on the interaction of biological factors influencing community structure in the intertidal. Although many studies have examined factors influencing gastropod assemblages (Underwood 1979, Branch 1981, Underwood and Jernakoff 1981), few have focused on chitons. Approximately II 0 to 125 species of chi tons inhabit the west coast of North America, yet few of these have been studied extensively (Ricketts and Calvin 1968, Strathmann and Eernisse 1987). The majority of information on chi tons pe1iains to reproductive cycles and the timing of spawning events (Pearse 1979, Strathmann and Eernisse 1987). Chitons graze macroalgal spores and gennlings and can significantly reduce the abundance of foliose algae in some areas (Dethier and Duggins 1984, Black et al. 1988, Scheib ling 1994). Grazing activity of chi tons prevents overgrowth of 2 foliose algae and allows the persistence of chi tons and other grazers, such as limpets, which would otherwise be excluded by algae (Dethier and Duggins 1984 and 1985, Bany 1988, Scheibling 1994). Chitons within the genus Nutta//ina are common in the mid to high intertidal along the central coast of Califomia (Ricketts and Calvin 1968, Andrus and Legard 1975). Taxonomists and ecologists have considered Nuttallina to consist of one, possibly two, species along the Pacific Coast ofNmih America based on morphological similarities. Using electrophoretic teclmiques, however, Piper ( 1984) showed the existence of tlu-ee distinct Nuttal /ina species; N calif"omica, N flux a, and N kata. Differences between these three species are apparent in gill morphology, coloration, valve shape, geographical range, abundance, and intertidal distribution (Piper 1984). Nutta//ina cal!f"omica (Reeve 1847) is primarily a cold water species that ranges from the Straits of Juan de Fuca, Washington, to Baja Califomia, Mexico (Burghardt and Burghardt 1969, Smith 1977). This species is typically found noiih of Point Conception, although it is found in cold-water upwelling areas along the Pacific Coast of Baja California, Mexico (Piper 1984). Gills of N ca!ifornica are abanal and holobranchial, and extend from beneath valve vii to beneath valve ii (Piper 1984). The girdle is often dark brown with shoJi brown spines. Incomplete white stripes may extend from the valves to the girdle edge. Uneroded valves tend to be rounded triangular to very triangular in shape. Individuals typically inhabit the high to mid inteiiidal at densities less tl1an 200 m·2 and are often associated with mussels and barnacles (Piper 1984). Larger N cal!f"omica are found higher in the inteiiidal than are smaller chi tons (Itumie 1981 ). Nutta/linafluxa (Carpenter 1864) is considered a warm-water species and occurs primarily in high intertidal areas south of Point Conception (Piper 1984), 3 although it is found from Monterey, Califomia, to the Gulf of Califomia, Mexico (Burghardt and Burghardt I 969).