Meeting Abstract
Benthic marine invertebrates with planktotrophic (feeding) larvae release embryos near the start of the spring phytoplankton bloom, maximizing the feeding period for growth towards metamorphosis. While planktonic, feeding larvae experience numerous stressors, including periods of starvation and encounters with harmful algal blooms. Starvation response by echinoid larvae is well characterized morphologically and more recent molecularly. On the other hand, responses to harmful algae by the same larvae are much less explored. In these respects, what remains unexplored is the gene expression associated with starvation and grazing dynamics on harmful algae. Larvae of the urchin Strongylocentrotus droebachiensis are highly plastic and their distribution and abundance patterns overlap in space and time with toxic dinoflagellate Alexandrium fundyense blooms. Using mRNA-Seq and qRT-PCR, we show that starved S. droebachiensis larvae down-regulate genes involved in growth and metabolic activity while up-regulating genes involved in lipid transport, environmental sensing, defense, and genes known to control aging and longevity in other animals. Furthermore, with respect to number of cells consumed and frequency that a larva consumed at least one A. fundyense cell, S. droebachiensis larvae consume A. fundyense cells in a density-dependent manner, which did not persist in the presence of a non-toxic microalgae. Additional observations reveal a 100% larval survival and that larvae cope with ingested A. fundyense cells in three ways: digestion, regurgitation, and defecation. Based on the adept resistance to phytoplankton-induced stressors, we hypothesize that echinoid larvae are tuned to cope with the biological variation in the patchy abundance and composition of the pelagic environment.
