Comparative physiological studies of marine invertebrate larvae from Antarctic and temperate environments

Life histories of many marine invertebrates include a pelagic, larval stage. The larval stages of these marine invertebrates are considered the most vulnerable as they are subjected to highly variable environmental conditions (i.e. temperature, salinity). Larvae that are planktotrophic during their pelagic life history stage are also subjected to fluctuating nutrient levels as they disperse. All of these factors make the study of larval physiology and biochemistry important in understanding how larvae cope with a highly variable environment to successfully metamorphose.;In this thesis, the larvae of a number of marine invertebrate species are studied with respect to respiration and biochemical aspects of metabolism. The central question answered is how changes in one or more environmental parameters affect the overall metabolism of a larva. The studies encompass a variety of comparative approaches to this question, including multi-species comparisons and comparisons of larval families of the same species with different genotypes. The effects of different endogenous nutrient conditions on growth, metabolism and an enzyme involved in aerobic respiration are studied in three echinoderm species in Chapter One. These results show that relationships between whole-animal metabolism and the amount of a mitochondrial enzyme exist in the larval species studied. Chapter Two looks at larvae of the Pacific oyster produced from factoral crosses of inbred adult oysters. Hybrid larvae grow faster than inbred larvae, despite similar metabolic rates between each group. This indicates that hybrid oyster larvae are metabolically more efficient than inbred larvae. Chapters Three and Four explore the effects of temperature on larval physiology by comparing the metabolism, gross protein growth efficiencies and nitrogen excretion between larvae of temperate and Antarctic echinoderms. Antarctic echinoderms have high gross protein growth efficiencies relative to temperate larvae. The high retention of protein in Antarctic echinoderm larvae is also indicated by the amount of nitrogen excreted.;This body of work contributes to the body of knowledge in the field of larval biology and physiology. The studies presented here employ robust comparative approaches that are unique in this research field.