Meeting Abstract
P2.149 Saturday, Jan. 5 Is the upward migration of Pisaster ochraceus larvae motivated by the presence of food at the halocline or the salinity they are acclimated to? BASHEVKIN, S*; DRIVER, P; GEORGE, S; Tufts University, Medford, Massachusetts; Georgia Southern University, Statesboro; Georgia Southern University, Statesboro georges@georgiasouthern.edu
Salinity fluctuations are expected to become increasingly frequent in the Salish Sea in the Pacific Northwest due to glacial melting caused by global warming. The Salish Sea is characterized by a distinct stratified upper layer between 5 and 20 m depth with salinities of 20 to 30ppt at the surface. Thin phytoplankton layers are common in these stratified regions of the water column and have the potential to induce predator aggregation and increase trophic transfer. The present study addressed how brachiolaria larvae of Pisaster ochraceus respond to low salinity and the presence of a thin phytoplankton layer at the halocline. Four treatments with 2 replicates were set up: larvae reared in 20 and 30ppt were introduced into control columns and haloclines with and without the alga Isochrysis galbana. Brachiolariae reared in 30ppt aggregated in the halocline when food was present but those in 20ppt swam through the food patch to the top of the column. Brachiolariae from both salinity treatments remained lower in control water columns when food was present than when absent. These results indicate that the upward migration of P. ochraceus larvae may be primarily motivated by the search for food. The presence of algae in the water column can affect the vertical distribution of P. ochraceus larvae and therefore their horizontal displacement by currents. However, low salinity larvae swam through the food patch to reach their preferred salinity. These larvae might not benefit from thin phytoplankton layers situated in regions of high salinity. They might spend a longer time in the plankton, less time feeding, with a greater possibility of either being eaten or carried away from favorable sites to settle.
