Petroleum oil remains a pollutant of significant concern in shallow-water, tropical reef environments due to its continued use, extraction and transport through or close to coral reefs. While efforts are underway to characterise the sensitivity of coral reef taxa to oil pollution, tropical systems remain understudied compared to subtropical and temperate counterparts. Substantial efforts have been made towards developing a framework for unbiased comparison of species sensitivity and to model potential oil spill impacts to inform risk assessment, response planning and injury assessments. This framework is based on the target lipid model of toxicity for narcotic chemicals (TLM), which accounts for the individual toxicity and water solubility of compounds as well as species-specific sensitivities to exposure. However, the use of the TLM requires a species-specific sensitivity constant (critical target lipid body burden; CTLBB) for each species and endpoint to be compared. To date, no definitive CTLBBs have been published for highly sensitive coral reef taxa, including coral larvae.
To estimate the first definitive CTLBB for a coral reef species, we exposed larvae of the coral Acropora millepora to seawater solutions containing dissolved toluene, naphthalene, 1-methylnaphthalene, phenanthrene, anthracene or pyrene for 48 h. Following exposure, the health of larvae was assessed and the no effect- and 50% effect concentrations (NEC and EC50) derived using Bayesian generalized nonlinear models. Metamorphosis success was negatively affected for all compounds tested while larval survival was only affected for some of the tested compounds. The CTLBB derived for metamorphosis success EC50 indicate that coral larval metamorphosis is one of the most sensitive endpoints assessed using the TLM to date. These results can be used to apply oil toxicity and spill modelling tools in tropical reef environments and highlight the need for further research on the sensitivity of reef taxa to petroleum exposure.