The effects of temperature on energy utilization by marine invertebrate larvae

Most ectothermic organisms are larger when reared at lower temperatures and temperature can greatly affect an organism's physiological state, so understanding how temperature affects larval size and quality can provide insight into how the larval thermal environment affects post-metamorphic success. Because quality is often defined in terms of size and energy content, I focused on how temperature affects energy utilization by larvae and how differences in energy accumulation and utilization may carry over into the juvenile stage. Marine invertebrate larvae are often classified into two groups: larvae from smaller eggs that must obtain food from the environment in order to gain energy for development (planktotrophy), or larvae from larger eggs that utilize maternal energy stores to obtain energy needed for development (lecithotrophy). Any differences in how energy utilization by feeding or nonfeeding larvae is affected by temperature may provide insight into why species with feeding larvae tend to be more abundant in warmer waters and species with nonfeeding larvae tend to be more abundant in colder waters. When reared within their optimal thermal range for development, both feeding and nonfeeding larvae utilized more energy over the course of development when reared at higher temperatures. Feeding larvae also consumed less energy from algae over development when reared at warmer temperatures. Juveniles from feeding larvae were larger at lower rearing temperatures due to a combination of increased energy intake and decreased energy expenditure, and juveniles from nonfeeding larvae were larger due to decreased energy expenditure alone, and smaller juveniles experienced higher mortality rates. However, outside of the optimal thermal range for development, the duration of development was greatly extended, resulting in increased energy expenditure and smaller juvenile size. In addition, rearing temperature may interact with the size of the egg from which larva develops, and larvae from species with larger eggs may be more strongly affected by increases in temperature than larvae from species with smaller eggs. Together these data suggest that larval rearing temperature can have an effect on juvenile quality and survival, which in turn can affect recruitment of new individuals into populations.