An investigation into the effects of rearing salinity on blastocoel development in pre-pluteus Dendraster excentricus larvae

Abstract

In this study, I aimed to test whether raising Dendraster excentricus larvae developing in different salinities differ in blastocoel volume. I used two salinity Timm (2011) 3 treatments: salinity approximately 3‰ higher than that of sea water from Friday Harbor, WA, and salinity approximately 3‰ lower than that of sea water from Friday Harbor, WA. Prior to direct observations, I modeled a suite of larval shapes, blastocoel volumes, and densities, predicting the effects of these features on larval swimming. Results of the models indicated that water density affected swimming, and that altering blastocoel density compensated for these effects. Using this information, I was able to narrow down physically feasible blastocoel volumes and fluid densities, which helped shape my hypotheses. My hypotheses were further shaped by the natural history of D. excentricus larvae: In the earliest stages of the larva, the blastocoel is anteriorly located. This means that the fluid within the blastocoel should be less dense than the larval body in order to ensure correct orientation. Based on the models, I hypothesized that there would exist a direct correlation between the rearing salinity and the larvae’s internal density. Based on the developmental process, I further postulated that larval blastocoel volume would increase as rearing salinity decreased.