The Effect of Freshwater Influxes on Pisaster ochraceus Larvae in the Salish Sea

Abstract

Global temperatures have been steadily increasing annually, causing increases in artic ice melting. The resulting freshwater from this artic ice retreat enters local river systems, which flow down to the Pacific Northwest and add freshwater to the Salish Sea. With significant melting occurring in the summer months from May to June, the Salish Sea receives multiple influxes of low-salinity water every summer that can persist for a couple of days. These freshwater events can lower surface water salinity from normal 31‰ to as low as 21‰. Understanding the impact of these low-salinity events is particularly important for the larvae of seastar Pisaster ochraceus, which are limited in their ability to swim out of low-salinity surface waters. Since P. ochraceus can take over 200 days to develop and metamorphose, larvae are bound to experience at least one lowsalinity event during their development. This study looked at the effect of a constant lowsalinity environment verses a fluctuating salinity environment on P. ochraceus survival, morphology, development, and protein expression. No significant differences in survival and body size were found between treatments. However, low-salinity reared larvae had significantly shorter posterolateral arms, which has implications for feeding and swimming behaviors. Osmoregulatory and mechanosensory protein expression was upregulated in fluctuating salinity treated larvae, while low-salinity reared larvae were not significantly different from the controls. This upregulation indicates that P. ochraceus larvae are changing their protein expression in response to the lower salinity environment.