Natural variability in size and condition at settlement of 3 species of marine invertebrates

Experimental studies have demonstrated that for many marine invertebrate species, variability in larval condition or quality at settlement may have important effects on post-settlement, early juvenile performance. Relatively few studies, however, explicitly examine natural variability in larval condition at settlement. This study examines natural variability in larval attributes (size and lipid index) at settlement for terminal-stage larvae of intertidal mussels (Mytilus sp.) and barnacles (Pollicipes polymerus and Chthamalus dalli) from southern California. Despite significant differences among cohorts in larval attributes, for all 3 species a greater percentage of the variance in larval length (80-100%) and lipids (58-83%) occurred among individuals within a cohort, rather than among cohorts. For all 3 species, coefficients of variation within a cohort for length were much smaller (3-8%) than those for lipid index (30-93%), suggesting that lipid storage is a much more plastic attribute than size for larvae. For mussels, settlement intensity and larval attributes were decoupled, such that average larval condition of a cohort was not related to the number of larvae that settled. At the cohort level, Mytilus and Pollicipes settling together across 3 dates showed similar trends of decreasing lipid index over time, suggesting that environmental conditions may influence co-occurring planktonic larvae similarly across species. This work highlights the need for further experiments in the field on the effects of larval history on recruitment success in natural populations, and further studies to determine what factors influence larval attributes for planktonic larvae in the field.