69.5 Friday, Jan. 6 Microscale variation in light intensity and its effects on the growth of juveniles of the temperate coral, Oculina arbuscula> MATTERSON, Kenan O*; GLEASON, Daniel F; University of Alabama at Birmingham; Georgia Southern University email@example.com
Light intensity varies over small spatial scales (e.g. substrate angles) in marine communities and could affect photosynthetic efficiency and growth in juvenile corals. For example, on temperate hard bottom reefs of the South Atlantic Bight off Georgia, U.S.A we have found that light intensities on vertical rock surfaces are 74% lower than those that occur on horizontal surfaces. In this study, we conducted laboratory experiments to investigate the effects that these differences in light regimes may have on chlorophyll concentrations, zooxanthellae density and juvenile growth rates in the temperate scleractinian coral, Oculina arbuscula. The mean light intensity at approximately 18 meters in depth was quantified from multiple hard-bottomed reefs and replicated at three experimental angles (0, 45, 90). A feeding treatment consisting of Artemia nauplii was included to determine if juveniles could compensate for reduced light levels through increased heterotrophy. After 90 days, growth, chlorophyll and algal density were found to vary among treatment angles with significantly lower calcification rates, chlorophyll levels, and symbiont densities in juveniles oriented perpendicularly. The addition of heterotrophic food sources did not enhance growth significantly. Combined, these results suggest that O. arbuscula settling at substrate angles >45° may suffer reduced growth and be at a competitive disadvantage during a critical stage in their life-history.