Graduation Date

Spring 2019

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Paul Bourdeau

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Edward Metz

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

John Reiss

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Brian Tissot

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories



Rocky intertidal zones are highly dynamic environments that exhibit substantial spatial and temporal variation in abiotic conditions, which can drive body form variation and energy allocation within calcifying species. Wave exposure, specifically, has been shown to be a significant driver of skeletal and structural morphology in organisms including gastropods, bivalves, and sponges. Many of such organisms, from sponges to echinoderms, rely on calcium carbonate for structural support and protection.

In the phylum Echinodermata (named for possessing a ‘spiny skin’), research on the form and function of calcium carbonate spines is largely relegated to Class Echinodea (e.g., urchins and sand dollars) and superorders Spinulosacea and Valvatacea within Class Asteroidea (sea stars). Few studies have provided morphological descriptions and functional hypotheses for spines in the Superorder Forcipulatida within Asteroidea. Here, I examine aboral spine morphology and variation in the forcipulate seastar, Pisaster ochraceus, a habitat generalist in rocky intertidal zones of the eastern North Pacific. I found that aboral spine density was significantly higher in sea stars in more physically-harsh bench and boulder field habitats compared to more physically-benign habitats like protected embayments. I also found specific aboral spine morphotypes that were associated with specific habitats; sea stars in protected embayments had spines that were upright and columnar, whereas bench and boulder field sea stars had shorter, convex spines. I hypothesize that dense, convex aboral spines have the potential to function as protection for the aboral surface of sea stars in habitats exposed to the combined stresses of high wave action and sediment load, but future studies are necessary to fully elucidate function.

Citation Style



Thesis/Project Location