LIFE HISTORY PATTERNS OF THREE ESTUARINE BRITTLESTARS (OPHIUROIDEA) AT CEDAR KEY, FLORIDA by STEPHEN EDWARD STANCYK A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1974 UNIVERSITY OF FLORIDA 3 1262 08552 5847 ^ ACKNOWLEDGMENTS I owe a great" deal to all the people who made the completion of this dissertation possible. The members of my committee deserve special tnanks, particularly Drs. Frank Maturo and Thomas Emmel , who were always ready with encouragement and advice. I thank Drs. John Erookbank and Ariel Lugo for their careful reading of the manuscript, and Dr. John Ewel for his timely services. Dr. John Anderson was generous with both equipment and time. Of the many fellow students and friends who assisted me, William Ingram deserves special thanks for his indispensable aid in fostering an agreeable relationship between myself and the computer. John Caldwell, John Paige, Christine Simon and Michael Oesterling were of particular help in the field, and I would like to thank Dave David, Renee Lindsay,- Kent Murphey, Dave Godman and Steve Salzman for their assistance in the. laboratory. Marine biologists are often in need of a sa c e haven in a storm, and V.am therefore very grateful to Lee and Esta Belcher and thei wonderful family for their hospitality, and for making my work at Cedar Key such a pleasurable experience. Ms-:. Lib by Coker typed the final manuscript, and Mr. Paul Laessle provided. materia Is and advice for completion of the figures. The facilities of the University of Florida Marine Laboratory at Seahorse Key were used extensively during this study. Part of this research was supported by University of Florida Division of Sponsored Research Grant No. 297F36, through the Division of Biological Sciences to F. J, 5. Mature Computer funds were obtained from the Northeast Regional Data Center at the University of Florida. in TABLE OF CONTENTS Page ACKNOWLEDGMENTS i 1 ABSTRACT v INTRODUCTION 1 DESCRIPTION OF SPECIES 3 DESCRIPTION OF AREA AND STATIONS 13 MATERIALS AND METHODS 23 RESULTS 31 DISCUSSION AND CONCLUSIONS 58 SUMMARY 70 LITERATURE CITED 73 BIOGRAPHICAL SKETCH 78 IV Abstract, of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy LIFE HISTORY PATTERNS OF THREE ESTUARINE BRITTLESTARS (OPHIUROIDEA) AT CEDAR KEY, FLORIDA by Stephen Edward Stancyk August, 1974 Chairman: Frank J. S. Maturo, Jr. Major Department: Zoology The polyhaline estuary at Cedar Key, Florida, has a high diversity of echinoderms, most of which possess reproductive modifications that appear to adapt them to unpredictable environmental variability. To gain clearer insight into this problem, populations of three ophiuroids with different modes of development were studied. Collection of monthly population samples and analysis of growth, mortality, reproduction and respiration showed that the three populations exhibit different life history patterns, each providing them with high fitness in an unpredictably variable environment. The disappearance of the Ophiothrix a ngulata population at the end of the first year of study (July, 1973) was correlated with a poor spring recruitment due to low salinities and with high summer mortality of adults during periods of warm water temperatures. 0. angulata has a short life and low tolerance of environmental fluctuations. It has a short-lived planktotrophic larva and spawns year-around. Individuals have only one spawning season. It is a fugitive species selected for high dispersal and the ability to colonize and recolonize disturbed habitats after local extinction. Ophiophragmus filograneus is a short-lived species, probably has direct development, and breeds year-round. Individuals have but one spawning season. Its tolerance of environmental variability is broad and it appears to be selected for low disperal and high survival of both adults and young through most environmental fluctuations. Ophioderma brevispinum is long-lived, has a short-lived vitellaria larva and broad environmental tolerance range as an adult. The spawning season is short, but individuals spawn each season for several years. 0. brevispi num seems to be selected for high adult survival, with adapta- tions in the larval stage to help avoid environmental fluctuations while retaining some dispersal abilities. The life history patterns of these three ophiuroids provide empirical evidence which supports theoretical predictions for life history and reproductive strategies in disturbed or variable environments. ChalChairman / INTRODUCTION Echinoderms are usually considered to be relatively stenohaline organisms, although there are numerous examples of species which occur in low or variable salinity regimes (Binyon, 1966). The occurrence of at least 25 species of echinoderms in the euryhaline estuary at Cedar Key, Florida, suggested that this might be an interesting area in which to examine echinoderm adaptations to variable estuarine conditions. Since the youngest stages or larvae of many benthic populations are most sensitive to variable conditions (Kinne, 1964), reproductive and larval biology were studied first. Stancyk (1973) found that up to 75% of the echinoids and ophiuroids at Cedar Key had some sort of developmental modification which helped to reduce larval exposure to the capricious pelagic environment. These were of three basic types: short-lived planktotrophic development, in which feeding plutei remain in the plankton for a week to ten days; planktonic lecithotrophi c development, in which non-feeding motile vitellariae metamorphose in three days; and direct development, in which a juvenile emerges directly from the egg, with no intermediate larval stage. Concerning older stages, Turner (1974) found distinct adaptations for avoiding variable surface conditions in juvenile Ophiophragmus filograneus , a common brittlestar of the area. He stated (p. 276) that "0. filograneus has probably developed physiological, morphological, and behavioral mechanisms at all stages of its life cycle for avoiding or reducing contact with extreme conditions in the water column." The 1 idea that organisms have such adaptations is in agreement with the views of numerous population biologists, such as Gadgil and Bossert (1970, p. 21), who wrote that "the tremendous variation in life history patterns of organisms is best explained as adaptive." Since Cole (1954) published his classic paper on life history phenomena, a great deal has been written about life history patterns and their adaptive nature (e.g., Murdoch, 1966; Holgate, 1967; Murphy, 1968; Calow, 1973; Schaffer, 1974). Most of this work involved models or was based on scant empirical evidence, and all of it dealing with marine or unpredictably variable environments was theoretical. However, there have been some excellent qualitative reviews of the reproductive and larval strategies of marine invertebrates (Thorson, 1950, 1964, 1966; Mileikovsky, 1971), and these have helped to generate some intriguing theoretical papers concerning the life history patterns of marine benthic invertebrates (Strathmann, 1974; Vance, 1973, 1974). The purpose of the research reported here was to study the biology of three estuarine ophiuroids with different developmental patterns ( Ophioderma brevispinum (Say), Ophiothrix angulata (Say), Ophiophragmus fiiograneus (Lyman)) in order to elucidate their adapations to an unpredictably variable environment, and to see the effects of these adaptations on their life history patterns. The information derived from this study may lend support to certain of the theoretical arguments in the literature, and help to shed light on life history strategies of benthic invertebrates in unpredictably variable environments. DESCRIPTION OF SPECIES Qphiodenr.a brevispinum (Say) is a large (adult disk diameter about 15 mm) and motile green or brown brittlestar with a leathery disk covered by fine granules (Figure la). It has four bursal openings in each interbrachium (Figure lb), a characteristic of the family Ophiodermatidae. The arms are sturdy, of medium length (4-5 times disk diameter), and have closely appressed short spines. It is a common species, occurring in littoral areas from Massachusetts to Florida, the Gulf of Mexico and the Caribbean (Ziesenhenne, 1955). Q Stancyk (1 70) found that 0. brevispinum was capable of feeding on detritus, as well as being an active scavenger-predator, which inhabits the substrate surface of the extensive grass flats of the Cedar Key area of western Florida. The adults have a high tolerance of salinity fluctuation, surviving prolonged exposures to 15 parts per thousand (o/oo) with no apparent ill effects. The embryology of 0. brevispinum was described by Grave (1S99, 1916), who also made several observations on its ecology, parasitology and physiology. The larva is a lecithotrophic, short-lived planktonic form called a vitellaria which metamorphoses in 4-5 days. This type of development has since been described in only four other species (Mortenson, 1921, 1938; Fenaux, 1969; Stancyk, 1973) and its adapti veness to an unstable environment has been discussed by Stancyk (1973). Figure la. Aboral view of Ophioderma breyispinum (Say, 1825) Figure lb. Oral view of same. Qphi othri x angulata (Say) is a member of the widespread and diverse family Ophiotrichidae. At Cedar Key it is most abundantly found clinging to sponges