The effects of antifoulant-paint-contaminated sediments on coral recruits and branchlets

Abstract

The 184-m cargo ship "Bunga Teratai Satu" ran aground on Sudbury Reef, within the Great Barrier Reef Marine Park, on 2 November 2000. Although no cargo or fuel was lost, the ship remained aground for 12 days and a large quantity of antifoulant paint containing tributyltin (TBT), zinc, and copper was scraped from the hull during the grounding and subsequent refloating operation. This resulted in extensive contamination of the reef sediments for up to 250 m surrounding the grounding site. Two laboratory-based experiments assessed the impact of contaminated sediments on the survival of both newly settled corals of Acropora microphthalma and branchlets of A. formosa. Newly settled corals exposed to sediments containing 8.0 mg kg⁻¹ TBT, 72 mg kg⁻¹ Cu, and 92 mg kg⁻¹ Zn or greater suffered significantly higher mortality after 72 h, compared to control or low-concentration treatments. Coral recruits exposed to 40 mg kg⁻¹ TBT (Sn), 306 mg kg⁻¹ Cu, and 403 mg kg⁻¹ Zn were all killed within 38 h. Branchlets from adult corals exposed to sediments with a high concentration of contaminants (TBT 160 mg kg⁻¹, Cu 1,180 mg kg⁻¹, and Zn 1,570 mg kg⁻¹) suffered significant mortality (38%), whereas branchlets placed in treatments with lower levels of contaminants suffered no mortality. Visual bleaching of the branchlets was observed at high contaminant levels, but an overall reduction in the symbiotic zooxanthellae populations was not observed in surviving corals. The photosynthetic yields of light-adapted zooxanthellae remained constant in live branchlets, indicating that the TBT-contaminated sediment may be more toxic to the host than the symbiont. Our results show that antifoulant contamination at ship-grounding sites has the potential to cause major mortality of resident coral communities and can have a negative impact on the recovery of adult populations.