Protein Expression in Pisaster ochraceus Eggs and Larvae Exposed to Multiple Salinity Fluctuations

Abstract

Climate Change affects the physical conditions of many environments. Increased temperature causes ice extent to decrease worldwide (IPCC, 2013). Glacier runoff during the spring and summer months increases the amount of freshwater pouring into the ocean creating salinity fluctuations. Surface salinity in the ocean can drop from~30ppt to ~21ppt. These fluctuations affect many marine organisms such as the sea star Pisaster ochraceus that cannot osmoregulate. P. orchraceus produces planktotrophic larvae that will also endure the fluctuations of salinity. The present study investigated whether differences in occurrence and intensity of salinity fluctuations at two locations in the Pacific Northwest cause sea stars to produce eggs and larvae with different protein profiles. Eggs and larvae from Snug Harbor with less influx of fresh water from the Fraser River and Cantilever Point with more, were exposed in the laboratory to two and four salinity fluctuations respectively during their development. Low salinity varied between 20 and 22 ppt and high salinity between 30 and 32 ppt. The length, width, and stomach width were noted and protein profiles obtained for larvae in control and fluctuating salinity treatments. Significant differences were observed between treatments for larvae from Snug Harbor, a site less influenced by the Fraser River. Larvae in the controls were significantly bigger than those reared in fluctuating salinity. No significant differences in larval size were observed for larvae from Cantilever Point, a site that experiences a significant influx of low salinity waters from the Fraser River several times during the summer months. Greater expression of a high molecular weight protein (>300kDa) was observed for eggs produced by females from Cantilever Point than for eggs produced by females from Snug Harbor. Larvae from both locations expressed this high molecular weight protein. Larvae from the two locations differed in mid-range to low molecular weight proteins. The High molecular weight proteins might be a kind of ATPase pump, while the low to intermediate size proteins might be used for cell signaling or heat shock proteins that will help protein folding during stressful events of low salinity