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Thesis - NSU Access Only
M.S. Marine Biology
The Caribbean coral Porites astreoides Lamarck maintains a polymorphism expressed as two different color morphotypes (green and brown). Earlier work has documented the varying abundance of the green and brown populations, with the green morphotype typically more common than the brown in shallower areas of the reef. Prior investigations have also indicated that the green morphotype contains more mycosporine-like amino acids (MAA) (UV-absorbing compounds) and sheds sediment less efficiently than the brown morphotype. Through the use of reciprocal transplants, this investigation focuses on the detection of other differences between the morphotypes, particularly the effects of depth on growth rate (expressed as calcium carbonate accretion). Green (collected from 3 m) and brown (collected from 12 m) colonies were cored, Alizarin Red-S stained and placed on PVC arrays at 3.5 and 11 m at Delta Shoal in the Florida Keys. Each array held 32 cores, providing 16 experimental and 16 control cores for each treatment. After 9 months of treatment, there were no significant differences in buoyant weight between morphotypes on the shallow array, but the brown morphotype grew significantly more than the green on the deep array (two-way ANOVA, p < 0.0001). Linear extension data showed both within- and between-array differences, although the controls of each morphotype accreted skeletal mass at the same rate (two-way ANOVA, P < 0.0001). These results suggest that the transplanted brown morph is not photoinhibited at shallow depths despite lower anticipated MAA concentrations, and the green morph experiences growth attenuation when transplanted to a deeper area of the reef. These results fail to explain the depth distribution of the two morphs, where the green is substantially more abundant than the browns at shallow depths. PhotoaccIimation was also monitored through chlorophyll α and c2 concentrations, zooxanthellae density, and colony height:diameter ratios; skeletal density bands were measured for brown and green morphotypes at the same depth. Height:diameter indices for these morphotypes indicate that the green individuals may be forming colonies with flatter profiles than the brown morphotypes. This study provides additional insight regarding the phenotypic plasticity of P. astreoides and other scleractinians that express polymorphisms.
Susan L. Thornton. 1999. Depth Distribution, Growth Rates, and Photoacclimation of the Green and Brown Color Morphotypes of the Scleractinian Coral Porites astreoides. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, Oceanographic Center. (318)