Composition of phytodetrital food resources affects reproductive success in the deposit-feeding sea cucumber, Parastichopus californicus (Stimpson 1857)

Phytoplankton are important sources of dietary fatty acids (FAs) for higher trophic levels, yet FA composition varies among phytoplankton taxa, and under different growth conditions. Changes in the environment that lead to shifts in the composition of phytoplankton communities may thus alter FA supply in marine food chains. Reproductive processes in free-spawning marine invertebrates, which provision eggs with lipid to fuel early embryonic development, are particularly impacted by FA composition of the diet. In order to explore the effects of taxonomic changes in the source of phytodetrital food resources on invertebrate consumers, we conducted captive feeding experiments to examine differences in reproductive fitness of deposit-feeding sea cucumbers (Parastichopus californicus) fed two different algal diets. Body- and egg-condition variables were measured in females that were fed detritus of either the green alga Tetraselmis sp. or the diatom Thalassiosira sp., which differ in nutritional and FA composition. Subsequent timing of development and survival were recorded for pre- and post-feeding larval stages. FA analyses were conducted on feeds, spawned gonads, and eggs to identify specific FAs allocated to reproduction. Females that were fed Tetraselmis sp. had higher fecundity, but showed reduced larval survival relative to females that were fed the diatom Thalassiosira sp. Similar rates of larval development were recorded in both treatments. Significant differences were observed in the abundance of 20:5É·3 (EPA), 20:4É·4 (ARA), 22:3É·6 (DHA), 12:0, 16:0, and 18:0 FAs in eggs and gonads from females fed the two diets. Diet-related variation in fecundity and egg quality could directly affect recruitment success in P. californicus, and suggests that reproductive strategies may be altered under different environmental conditions. If feeding conditions are favorable to planktotrophic larvae, then producing a larger number of eggs with lower energy density (such as under Tetraselmis-fed treatments) may be acceptable, whereas different conditions may favor maternal investment in a smaller number of better-provisioned eggs (such as in Thalassiosira-fed treatments).