Investigating the Effects of Chronic Turbidity Exposure to Priority Florida Coral Species

Florida DEP, Coral Protection and Restoration (CPR) Project C1FE5B (MOA- 20210018/12072 amendment 1) was developed in conjunction with resource managers to begin filling priority knowledge gaps related to the effects of turbidity on the Endangered Species Act (ESA)-listed coral, Orbicella faveolata, in relation to anthropogenic activities (e.g., coastal construction, dredging) that can create turbid conditions in exceedance of the Florida water quality criterion (WQC) of 29 NTU above natural background. Because of O. faveolata’s (1) ESA status, (2) Critical Habitat designation for recovery of the species, (3) ecological importance as a major reef-building species, and (4) its population density in areas expected to experience prolonged periods of anthropogenic turbidity from planned dredging operations, \ understanding the tolerance for turbidity is imperative for effectively protecting Florida’s Coral Reef. Our objectives were (1) to identify biological benchmarks for turbidity that are protective for shallow-water corals and (2) to design experiments with assessment endpoints that are able to detect and measure sub-lethal impacts on coral health while also useful to resource managers responsible for minimizing impacts from anthropogenic turbidity affecting reefs. We investigated two aspects of chronic turbidity exposure: dosage effects (turbidity range 0-29 NTU) and effects of combined turbidity (29 NTU) and elevated temperature (30 °C) over a 90-day period. We observed that O. faveolata’s ability to heal wounds (bioindicator of health and fitness) was significantly decreased after prolonged exposure to 20 and 29 NTU at 28 °C, revealing an important impact on coral physiology in response to turbidity lower than the existing WQC. An increase of 2 °C (to 30 °C) combined with 29 NTU reduced wound healing rates, growth rates and total lipid concentrations. Turbidity (29 NTU) alone reduced triglyceride concentrations (energy reserves) and wound healing. Knowing the potential consequences of compounding effects on vital physiological processes with a non-bleaching temperature increase, provides managers key insights for how O. faveolata may be impacted during summer temperatures and potentially more severely with predicted bleaching conditions. This provides an opportunity for managing impacts during turbidity-producing operations, that can occur even within the existing WQC.