M.S. Marine Biology
Coral reefs are essential to coastal economies, protecting coastlines from storms, and harboring high biodiversity. However, reefs are declining due to local anthropogenic stressors and ocean warming. Sedimentation, a local stressor, aggravates the impacts of warming on corals and hinders their survival and growth. Therefore, it is important to investigate whether sedimentation and temperature have a synergistic effect on vulnerable coral species, especially during earlier stages of development. To quantify these effects, survival and growth of newly settled Acropora cervicornis corals were measured at two temperatures (29 and 31°C, representing current and predicted for 2050 Summer temperatures) and three sediment concentrations (30, 60 and 120 mg.cm-2, representing a range from natural sedimentation to dredging conditions). The intent of this study was to mix multiple genotypes to test temperature and sedimentation among genotypic unique individuals. However, only 20% of colonies spawned, and spawning was asynchronous by genotype. Therefore, individuals were produced from self-fertilization. The overall high mortality seen in this study suggests that self-fertilization in A. cervicornis does not produce viable juveniles. Although temperature did not have a significant effect on the survival of self-fertilized juveniles, sediment concentration did. The lowest sediment concentration led to the highest juvenile survival in both ambient and heated conditions. The growth of A. cervicornis selfed individuals was not significantly affected by temperature or sedimentation. These results suggest that reducing sedimentation in dredging and coastal construction areas around coral reefs facilitates the survival of Acropora cervicornis juveniles and may help to ensure their persistence in the future. Because self-fertilized larvae were used, these results need to be interpreted with caution, and this research needs to be repeated with outcrossed A. cervicornis. What is clear is that genotypic diversity is needed for A. cervicornis population growth and resilience.
Chimeras occur when two or more genetically unique individuals of the same species fuse together. The presence of chimerism can aid in the survival and evolution of organisms. This study investigated whether the prevalence of chimerism differs between coral species of different reproduction modes and growth rates. To fulfill this goal, the surface area of egg and/or larvae of three coral species, Montastraea cavernosa, Acropora cervicornis, and Porites astreoides, were measured and compared with the respective surface areas of the newly settled juveniles. This comparison suggested that M. cavernosa displayed a greater tendency to form chimeras than A. cervicornis and P. astreoides. Observations during embryogenesis confirmed this prediction. Montastraea cavernosa is a slow grower and has the smallest eggs of all three study species. Chimerism during embryogenesis may increase this species’ tendency to start the sessile stage at a slightly bigger size and thus increases its competitive abilities for reef space. In contrast, A. cervicornis is a broadcast spawner, fast grower and has a relatively larger egg size, possibly explaining the reduced chimeric tendency during embryogenesis. It is possible that P. astreoides formed chimeras during embryogenesis within the polyp, but they did not form them in the swimming planulae stage. The lack of chimerism during P. astreoides planulae development may be attributed to its brooding reproductive mode, directly releasing large competent larvae that have large initial sizes at settlement. Therefore, the ability to form chimeras in an early developmental stage might provide an ecological advantage to M. cavernosa that contributes to its abundance in Broward County: the greater size at settlement caused by chimerism during embryogenesis may provide this species a competitive advantage for reef space.
Hayley De Marchis. 2017. "The Effects of Ocean Warming and Sedimentation on the Survival and Growth of Acropora cervicornis" and "Differential Prevalence of Chimerism during Embryogenesis in Corals". Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, . (463)