Quantifying the role of heterotrophic feeding in Port of Miami “urban corals”: implications for persistence in marginal environments

Throughout Florida and the Caribbean, coral reefs have undergone unprecedented declines in both cover and diversity due to a myriad of climatic and anthropogenic stress events. In particular, Florida’s coral reefs have undergone significant degradation due to disease outbreaks, nutrification, and thermal bleaching. However, resilient corals have been found on artificial substrates in Florida’s urbanized ports, such as the Port of Miami. Urban corals are abundant and appear resilient to environmental stressors, while their conspecifics on natural reefs continue to decline in abundance. Understanding the mechanisms of resilience in urban corals is critical to identifying strategies to increase the resilience of corals used in restoration. One such mechanism is a shift from reliance on photoautotrophic symbionts to heterotrophic feeding on plankton, which has been linked to thermal and ocean acidification resilience previously. In this study, stable isotope analyses, lipid quantification, and molecular identification of symbionts were used to assess the nutritional strategy in Pseudodiploria strigosa specimens from urban and natural reef environments. A shift towards heterotrophy was observed in urban corals relative to natural reef conspecifics. Additionally, while the dominant symbiont genera were different between urban and reef sites, symbiont identity did not impact trophic strategy based on stable isotope analyses. This indicates that a shift in trophic strategy or increased abundance of particulate food sources may be a factor in the increased resilience of Port of Miami urban corals.