Responses to salinity of color polymorphs in two populations of the sea star, Pisaster achraceus

Pisaster ochraceus was analyzed to determine if varying salinities, animal color, or location affect the physiology of these sea stars. The three responses analyzed were aerobic respiration, ammonia excretion, and self-righting. The tested variables included two different color morphs (orange and purple) of P. ochraceus, two different locations (open coast and inland straits) in Washington State, and three salinities (22, 30, and 40 psu). Wet mass-specific oxygen consumption rates were not significantly affected by color, location, or salinity, and Dry mass-specific oxygen consumption rates showed no significant differences for main effects, but a three-way interaction was identified. Similarly, ammonia excretion rates were unrelated to color, location, or salinity. Self-righting times were significantly different with color, location, and salinity. Although measurements from the three experiments carried out in this study do not all point to differences in responses of the two color morphs, they nonetheless provide some evidence that color and location both have a significant effect on self-righting times at the three salinities tested. The results of my study suggest that, within a certain range (± 8 psu), P. ochraceus appears to be able to maintain normal aerobic respiration and ammonia excretion. However, when stressed to greater extremes outside of the range they are able to cope with, such as salinities of ± 10 psu or greater, their basic functions of mobility, such as self-righting responses, may be impaired