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iv ACKNOWLEDGEMENTS vi TABLE OF CONTENTS vii LIST OF FIGURES viii LIST OF TABLES x INTRODUCTION 1 METHODS 4 Field sampling 4 Preparation of host and symbiont fractions 4 Lipid extraction 5 Lipid analysis 7 Statistical analyses 7 RESULTS 9 Fatty acid profiles of Symbiodinium muscatinei and Elliptochloris marina 9 Fatty acid profiles of zooxanthellate, zoochlorellate, and aposymbiotic hosts 15 Fatty acid profiles of hosts and their algal symbiont 20 DISCUSSION 24 Fatty acid profiles of Symbiodinium muscatinei and Elliptochloris marina 24 Fatty acid profiles of zooxanthellate, zoochlorellate, and aposymbiotic hosts 26 Fatty acid profiles of hosts and their algal symbiont 29 Conclusions and future research directions 30 REFERENCES 32

Because planktonic invertebrate larvae may be food-limited, anything that increases feeding and digestive efficiency should increase the chances of larval survival to metamorphosis. As light directly enhances both feeding and digestion in some planktonic heterotrophic protists, we hypothesize that similar processes might occur in the larvae of marine invertebrates. We studied the direct effects of light on feeding and development in sea urchin larvae (Strongylocentrotus droe- bachiensis, S. franciscanus and sand dollar Dendraster excentricus). Larvae were placed in 12:12 h light:dark cycles or in complete darkness and ingestion rates were measured. We monitored larval morphology during the first 2 to 3 wk of development and tested for light-related differences. Short- term changes in light regime had no effect on feeding rates. However, larvae of all 3 species showed longer-term diel feeding patterns with ingestion rates generally higher during daylight hours. These patterns persisted in S. franciscanus larvae even when larvae were held in complete darkness for 3 d. Larvae of D. excentricus exposed to natural light cycles developed longer arms usually associated with food limitation; those held in darkness had significantly shorter arms. The developing juvenile structures (i.e., rudiments) of S. droebachiensis larvae exposed to light were significantly smaller than those of larvae held in continuous darkness, suggesting that light may have negative effects on larval growth and development. Measuring the effects of light on feeding and growth may clarify the behaviors of invertebrate larvae during their critically important planktonic period.