P3.107 Friday, Jan. 6 Vertical distribution of Pisaster ochraceus larvae in haloclines after prior exposure to low salinity LEE, D.; GEORGE, S.B.*; Georgia Southern University; Georgia Southern University firstname.lastname@example.org
An increase in the frequency and intensity of fresh water incursions into the Puget Sound could change the dynamics of rocky shore communities in the Pacific North West due to the potential negative effects on the larval stage of the keystone species Pisaster ochraceus. The present study investigated the effect of prior exposure of embryos and bipinnariae to low salinity on the vertical distribution of brachiolariae 1, 11, and 24 hours after introduction in haloclines. Four treatments were setup; controls (31‰), larvae exposed to 20‰ throughout development (CL), gastrulae exposed to 20‰for 3 days (SF3), bipinnaria exposed to 20‰ for 7 days followed by a gradual increase to 31‰ by the 14th day (SF14). Five day-old larvae from the SF3 and CL treatments were significantly wider and shorter than those from the SF14 and control treatments. Those from the CL treatment remained wider and shorter up to 26 days. Differences in larval morphology and other salinity-induced stresses influenced the vertical distribution of brachiolariae in haloclines. One hour after introduction a significantly higher proportion of brachiolariae from the control treatment hovered around the halocline compared to brachiolariae from the SF14, SF3, and CL treatments. Eleven hours later, a significantly higher proportion from the controls and the SF14 treatment had moved above the halocline and by 24 hours a majority of the brachiolariae had moved to the surface. These results suggest that fresh water incursions into the rocky intertidal during the reproductive season could affect the morphology, feeding and swimming of Pisaster brachiolariae.