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The Chagos Archipelago is the most isolated and biologically diverse group of atolls in the central Indian Ocean. It contains 5 islanded atolls, including the world’s largest atoll, the Great Chagos Bank. Following the abandonment of the copra plantations, in 1973, most islands are uninhabited and have rarely been visited. The only exception is Diego Garcia, part of which is a strategic military base with appropriate infrastructure to support long range aircraft and ships which visit and reside for extended periods in the lagoon which provides anchorage. In 1996, a research programme was undertaken in Chagos (Sheppard and Seaward, 1999) to assess the atolls biodiversity, biogeographic role with respect to fisheries, and the degree of their pristine condition. Analyses of sediment samples from throughout the Archipelago revealed that hydrocarbons present were predominantly of biogenic origin (Readman et al., 1999). However, these studies also revealed some petrogenic and pyrogenic polycyclic aromatic hydrocarbons (PAHs) at sub to low ng g 1 dry sediment. Organochlorine analyses revealed that only some polychlorinated biphenyl (PCB) congeners and the pesticide lindane were above limits of detection. It was concluded that atmospheric transport (from industrial parts of the world) was the major route for the introduction of organochlorines to the region. A parallel study (Everaarts et al., 1999), based upon analysis of anthropogenic organic contaminants and toxic metals in sediments and biota, confirmed that, at least in 1996, Chagos belonged to the category of least impacted coastal areas. During recent years, antifouling products used in boat paints have tended to incorporate organic ‘‘booster’’ biocides to enhance performance and to move away from tributyltin compounds (which were restricted in most countries due to their demonstrated toxicity to non-target organisms at very low concentrations). The booster biocide products are primarily herbicidal and contain active ingredients including: Irgarol 1051 (2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine), Sea-Nine 211 /kathon 5287 (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one), chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile), dichlofluanid (1,1-dichloro-N-[(dimethylamino)sulfonyl]-1-fluoro-Nphenylmethanesulfenamide), diuron (DCMU, [3-(3,4-dichlorophenyl)-1,1-dimethylurea]), TCMS pyridine, TCMTB, zinc pyrithione and zineb. Irgarol 1051 has recently been shown to be a potent inhibitor of coral photosynthesis in both isolated endosymbiotic coral zooxanthellae (i.e. isolated algal symbionts in vitro) and in the intact coral symbionts (i.e. in vivo) for a number of Atlantic and Pacific coral species (Owen et al., 2002, 2003; Jones and Kerswell, 2003; reviewed by Jones (2005)). In in vitro experiments, Owen et al. (2002) report no CðHCO 3 Þ incorporation in zooxanthellae isolated from the common branching coral Madracis mirabilis after a 6 h exposure to 63 ng l 1 Irgarol 1051 . In vivo, the The objective of BASELINE is to publish short communications on different aspects of pollution of the marine environment. Only those papers which clearly identify the quality of the data will be considered for publication. Contributors to Baseline should refer to ‘Baseline—The New Format and Content’ (Mar. Pollut. Bull. 42, 703–704).

Irgarol 1051 ® is a s -triazine herbicide used in popular slime–resistant antifouling paints. It has been shown to be acutely toxic to corals, mangroves and sea grasses, inhibiting photosynthesis at low concentrations (>50 ng l −1 ). We present the first data describing the occurrence of Irgarol 1051 ® in coastal waters of the Northeastern Caribbean (Puerto Rico (PR) and the US Virgin Islands (USVI)). Low level contamination of coastal waters by Irgarol 1051 ® is reported, the herbicide being present in 85% of the 31 sites sampled. It was not detected in water from two oceanic reference sites. In general, Irgarol 1051 ® was present at concentrations below 100 ng l −1 , although far higher concentrations were reported at three locations within Benner Bay, USVI (223–1300 ng l −1 ). The known toxicity of Irgarol 1051 ® to corals and sea grasses and our findings of significant contamination of the Northeastern Caribbean marine environment by this herbicide underscore the importance of understanding, more fully, local and regional exposure of reef and sea grass habitats to Irgarol 1051 ® and, where necessary, implementing actions to ensure adequate protection of these important ecosystems.