A reproductive and trophic analysis of corals in a degraded environment

Understanding the persistence and resilience of corals in degraded environments can provide insight into the potential persistence of coral communities as coastline urbanization expands. We assessed the reproductive fitness and nutrition of the reef-building coral Siderastrea siderea in Port Everglades (a heavily trafficked manmade seaport) relative to two nearshore coral communities and an ex situ nursery. Fertility and estimated polyp fecundity were quantified using histological analysis. Trophic position and proportion of heterotrophy of a representative subset of male, female, and non-fertile colonies from each site were estimated using amino acid compound-specific isotope analysis of nitrogen. Long-term water quality data were used to compare differences in environmental conditions at ocean-based (in situ) sites. Fecundity did not differ between sites, yet corals in Port Everglades were significantly more fertile than corals at other locations, despite experiencing higher nutrient concentrations (nitrate, nitrite, and orthophosphate) and turbidity than the nearshore coral communities. The trophic position of corals did not significantly differ between sites, but the higher fertility of corals in Port Everglades may be partially driven by greater nutrient assimilation leading to coinciding increases in autotrophy and heterotrophy. Trophic position of fertile colonies ranged from 1.1 to 2.0, indicating that one nutritional source is not exclusively responsible for gamete production. The trophic plasticity of S. siderea and the high fertility of colonies in Port Everglades demonstrate a strong capacity for resilience. Colonies existing in these already degraded environments may be significantly valuable for coral persistence on less-degraded reefs through larval export as urbanization and climate change effects progress.