Chemical Contaminant Inhibition of Settlement and Survivorship in Corals: Phase 1

Coral recruitment on Florida’s Coral Reef (FCR) remains critically low, limiting the long-term success of restoration efforts. This project evaluated whether chemical contaminants contribute to recruitment failure by assessing their impacts on coral larval settlement and post-settlement survivorship in two key reef-building species, Montastraea cavernosa and Diploria labyrinthiformis. The study examined environmentally relevant concentrations of metals, hydrocarbons, and organic contaminants through both dissolved exposure pathways and contaminated settlement substrates. Results demonstrate that multiple contaminants can reduce larval settlement and increase mortality, often at concentrations at or below current regulatory thresholds. Contaminants such as fluoranthene, phenanthrene, pyrene, octocrylene, diuron and tributyltin showed consistent negative effects on settlement success. Substrate-associated contamination produced particularly strong impacts, with several contaminants inhibiting settlement or causing mortality at low concentrations, indicating that contamination of reef sediments and hardbottom surfaces can be a significant barrier to coral recruitment. Post-settlement survival was also influenced by exposure type. Coral recruits exposed to dissolved contaminants that survived the initial month generally remained viable and continued to grow. In contrast, those exposed to contaminated substrates exhibited near-zero survival within one month, suggesting persistent or cumulative effects associated with substrate-bound contaminants.
 

Importantly, observed adverse effects frequently occurred at concentrations below existing EPA water quality criteria and Florida sediment threshold effect levels (TELs/PELs), indicating that current regulatory benchmarks may not be sufficiently protective of early coral life stages. These findings highlight the need to incorporate coral-specific toxicity thresholds into water quality and sediment management frameworks. Management applications include prioritizing restoration sites with low contaminant loads, evaluating sediment and substrate quality, and revising regulatory thresholds based on coral early life-stage sensitivity.