Meeting Abstract
Zostera marina eelgrass beds in San Francisco Bay fluctuate seasonally in temperature, light availability, nutrients, and invertebrate community composition. A significant invertebrate grazer in this community, the sea hare Phyllaplysia taylori, promotes eelgrass health by clearing blades of epiphytic material. P. taylori has two generations per year that differ in size, lifespan, and thermal performance. One generation matures in the early spring and the other matures in late summer. Thermal performance of the summer generation peaks at lower temperatures than in the spring generation. In this study, parents of the summer generation were acclimated at temperatures representing current winter (13ºC), current summer (17ºC), and future summer (21ºC). Embryos from parents at all three temperatures were reared in a split-brood orthogonal design, raised at all three temperatures with or without an acute heat shock (30ºC) during early embryonic development. Embryo size, density, and survival were assayed. 17ºC had the highest survival across parental and developmental exposures. 21ºC resulted in lower survival for all broods except when this was the parental acclimation temperature. There were no significant effects of the acute heat shock on any treatment group. Conditions that resulted in the lowest embryonic survival experienced the most likely future climate scenario (parental rearing at 21ºC and embryonic development at 13ºC). Therefore, increased habitat temperatures are likely to reduce survival of these sea hares, diminishing their ecological influence on eelgrass.
