Term of Award

Fall 2012

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Department

Department of Biology

Committee Chair

Daniel Gleason

Committee Member 1

Risa Cohen

Committee Member 2

Kelly McLain

Committee Member 3

Kelly McLain

Abstract

Light intensity varies with slight changes in substrate angles in marine communities and could affect photosynthetic efficiency and growth in juvenile corals. The goal of this study was to examine the effects of substrate angle on chlorophyll concentrations, algal densities and juvenile growth of the temperate scleractinian coral, Oculina arbuscula. Light intensity was quantified at different substrate slopes on live-bottom reefs at ~18 m depth in and around Grays Reef National Marine Sanctuary approximately 20 NM off the Georgia coast. The settlement angles for juvenile O. arbuscula occupying these reefs were also quantified and principle component analysis was used to correlate red, green and blue (RGB) color data quantified from in situ field images to chlorophyll concentrations determined through acetone extractions. Light intensities on vertical rock surfaces were ~74% lower than those occurring on horizontal surfaces. Concomitant with these differences in light intensity, settlement angles for juvenile corals were negatively correlated with chlorophyll concentrations. Results obtained from the field were incorporated into an 84-day laboratory experiment investigating the consequences of settlement at substrate angles of 0, 45, and 90 degrees from the horizontal on O. arbuscula juveniles. The mean light intensity from the live-bottomed reefs was replicated at the three experimental angles and a feeding treatment consisting of Artemia nauplii was included to determine if juvenile corals can compensate for reduced light levels through heterotrophy. Growth rates were found to be highest for juveniles oriented at 0° and were independent of the presence or absence of a food source. Chlorophyll concentrations and algal densities on the other hand, were higher at all angles of orientation when Artemia were provided, suggesting that zooxanthellae utilize heterotrophically acquired nutrients in order to maintain stable densities in juveniles while contributing low amounts of photosynthetically fixed nutrients towards the host. Combined, these results indicate that the symbiosis between temperate corals and zooxanthellae may shift between mutualism and parasitism depending on light and food availability in the natural environment.

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