Master of Science
Joana Figueiredo, Ph.D.
Hilary G. Close, Ph.D.
David Gilliam, Ph.D.
Stable isotope analysis, coral reproduction, coral nutrition, degradation, nutrients, coral reef, amino acids, fecundity, fertility, energy, Siderastrea siderea
Amid the worldwide decline of corals, the survival of some corals in high nutrient, turbid environments, is intriguing – are they just surviving or are they thriving? This study aimed to determine how these corals acquire energy and whether that energy is sufficient to produce offspring (i.e., develop viable gametes). The nutritional sources and reproductive capacity of Siderastrea siderea in a shipping port (Port Everglades) were compared to two nearshore reefs in Florida, USA and an ex situ coral nursery. Fertility and estimated polyp fecundity were quantified using histological analysis, and water quality parameters were assessed monthly to evaluate differences in site conditions. Amino acid compound-specific stable isotope analysis of nitrogen (δ15N) was used to assess relationships between energy sources (i.e., symbionts, particulate organic matter, and zooplankton), sites, and reproductive capacity. Coral nutrition and reproductive capacity in the Reefs and Port Everglades were then compared to corals maintained in an outdoor land-based nursery to determine ways of optimizing their diet and consequently reproductive capacity for reef restoration efforts. Results demonstrate that corals in Port Everglades are equally fecund but significantly more fertile than corals at nearshore reefs, despite experiencing higher nutrient concentrations (nitrate, nitrite, and orthophosphate) and turbidity. The trophic position of the corals did not significantly differ between sites, nor did it vary with fertility, sex, or fecundity. Trophic position of reproductive corals ranged from 1.1 to 2.0, indicating that one nutritional source is not exclusively responsible for gamete production, and that males and females do not utilize different sources. However, a Bayesian mixing model using phenylalanine-normalized δ15N values of glycine and lysine suggests that corals in Port Everglades and in one of the nearshore reefs relied significantly more on symbionts for energy relative to the other reef. The higher fertility and a heavier reliance on symbionts in the corals from Port Everglades may result from adaptation, acclimation or the fact that their endosymbionts benefit from the higher nutrient environment. Corals maintained ex situ were less fertile, equally fecund, and had higher trophic positions than corals than corals from Port Everglades. Since corals in situ demonstrate utilization of primary producers for energy acquisition, this suggests that land-based nurseries may benefit from the inclusion of phytoplankton in coral diet to maximize fertility. The results of this study indicate that corals from highly degraded environments are thriving, despite the degraded conditions, and that these colonies can be prioritized to be sexually propagated for coral restoration.
Morgan Short. 2021. Are Corals Surviving Or Thriving in Highly Degraded Environments? A Reproductive and Trophic Analysis of Scleractinian Corals. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, . (53)