Trace element proxies and stable isotopes used to identify water quality threats to elkhorn coral (Acropora palmata) at two national parks in St. Croix, USVI

Biological impairments have been documented on reefs at two national parks in St. Croix, USVI. Although several water quality parameters have been out of compliance with USVI criteria, whether these parameters or other pollutants are responsible for coral health impacts is unknown. Trace elements quantified in sediment showed four sites at SARI, which is closer than BUIS to settlements and land-derived anthropogenic outflows, had Cu mass fractions above sediment quality guidelines for invertebrate toxicity. Trace elements were also analyzed in the skeleton of threatened elkhorn coral, Acropora palmata, to evaluate potential exposure. Heavy metals (Pb, Zn) were significantly greater in coral skeleton at SARI than BUIS. Cu, Pb, and Zn may be impacting coral health in these parks. Potential anthropogenic sources of these metals were revealed by the coral tissue stable isotope levels (δ13C and δ15N). These findings provide a framework for determining heavy metal impacts on these invaluable reefs. •Cu and Ni were above invertebrate effects ranges in SARI estuary sediment.•Coral skeleton had greater Zn and Pb at SARI reefs compared to BUIS reefs.•Coral tissue had lower δ13C and δ15N at SARI reefs compared to BUIS reefs.