Date of Award

8-2003

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography

Advisor

Robert S. Steneck

Second Committee Member

Robert L. Vadas

Third Committee Member

Kevin J. Eckelbarger

Abstract

The green sea urchin Strongylocentrotus droebachiensis has been aggressively fished in Maine since 1986 resulting in severe population declines throughout portions of the state. This research used Marine Protected Areas (MPAs) to evaluate the potential for recovery in depleted sea urchin populations. It was necessary to not only look at the direct impacts of the MPAs, but also at larval transport / supply and community interactions to gain a better understanding of the system. We found that MPAs in the Gulf of ~a!ne were of varied utility to restoring depleted sea urchin populations depending on location and community structure. MPAs established in coralline communities appeared to protect sea urchin populations from further declines and may have allowed some slow recovery. However, closures in areas that have undergone a community shift from coralline communities to fleshy macroalgal beds did not provide protection for the remaining sea urchins or appropriate habitat for repopulation. Additionally, this macroalgal state appears stable over time so the potential for sea urchin recovery will probably remain low. This study also determined the point at which sea urchins could no longer control macroalgal production and allowed the growth of fleshy macroalgal beds. This ecologically effective biomass declined exponentially with water depth and was inversely proportional to latitude. These patterns were probably caused by the factors that affect productivity (e.g. light, nutrients) and grazing rates (e.g. temperature, water movement). Mechanisms driving sea urchin settlement were also examined. Competent echinoplutei were found higher in the water and advected onshore when northeast wind events created oceanographic downwelling conditions. Newly metamorphosed sea urchins were also found in the water column, suggesting that contact with the substrate is not needed to initiate metamorphosis. Sea urchin settlement was greatest in coralline communities with high micro-complexity and lowest in macroalgal beds. Survival through the summer, however, only averaged 50% regardless of community type or habitat micro-complexity. Lastly, this study identified adult sea urchins as a potential consumer of juvenile sea urchins, which may account for some of the relatively high mortality seen in sea urchin-dominated coralline communities

Share