Phototoxic effects of two common marine fuels on the settlement success of the coral Acropora tenuis

F Mikaela Nordborg,Susana Agustí,Florita Flores,Diane L Brinkman,Andrew P Negri

doi:10.1038/s41598-018-26972-7

Abstract

Coral reefs are at risk of exposure to petroleum hydrocarbons from shipping spills and uncontrolled discharges during extraction. The toxicity of petroleum hydrocarbons can substantially increase in the presence of ultraviolet radiation (UVR), therefore spills in shallow coral reef environments may be particularly hazardous to reef species. Here we investigated the sensitivity of coral larvae (Acropora tenuis) to dissolved hydrocarbons from heavy fuel oil (HFO) and diesel in the absence and presence of UVR. Larval settlement success decreased with increasing concentrations of dissolved HFO, and co-exposure to UVR doubled the toxicity: 50% effect concentrations (EC50) decreased from 96 (−UVR) to 51 (+UVR) total petroleum aromatic hydrocarbons (TPAH). Toxic thresholds for HFO were similar to concentrations reported during marine spills: EC10s of 24 (−UVR) and 15 (+UVR) µg l−1. While less toxic, diesel also reduced settlement and exhibited phototoxicity: EC10s of 122 (+UVR) and 302 (−UVR) µg l−1. This study demonstrates that the presence of UVR increases the hazard posed by oil pollution to tropical, shallow-water coral reefs. Further research on the effects of oils in the presence of UVR is needed to improve the environmental relevance of risk assessments and ensure appropriate protection for shallow reef environments against oil pollution.

Highlights

Petroleum hydrocarbons are considered among the most prominent pollution threats to marine environments[1]; the risks they pose to coral reef ecosystems remain poorly understood[2,3]
The penetration of ultraviolet radiation (UVR) in marine environments is dependent on a range of physical and biological factors[19], and tropical oligotrophic coral reefs may be at a high risk of polycyclic aromatic hydrocarbons (PAH) phototoxicity as reef organisms are frequently exposed to high solar radiation, including UVR13,18
This phototoxicity was evident under UVR intensities equal to or lower than expected exposures in shallow reef habitats, and the toxic thresholds (EC10) for dissolved aromatics occurred at concentrations below those detected after major accidental spills or releases[7,8,9]

Summary

Introduction

Petroleum hydrocarbons are considered among the most prominent pollution threats to marine environments[1]; the risks they pose to coral reef ecosystems remain poorly understood[2,3]. The penetration of UVR in marine environments is dependent on a range of physical and biological factors[19], and tropical oligotrophic coral reefs may be at a high risk of PAH phototoxicity as reef organisms are frequently exposed to high solar radiation, including UVR13,18. It is increasingly recognised that a considerable proportion of UVR penetrates to ecologically relevant depths in some marine environments, including coral reefs[18,22,23,24] and that exposure to cumulative pressures, such as pollution and UVR, can result in increased environmental impacts[13,18,25]. The larval life stages of aquatic animals may be at higher risk than adults to phototoxic effects due to their small size, often transparent bodies, and time spent in shallow waters[16]

Methods

Results

Conclusion