Insecticides and a fungicide affect multiple coral life stages

Coral reefs are under threat from land-based agricultural pollutants on a global scale. The vulnerability of early life stages of corals is of particular concern. Here, we compared the sensitivity of gametes, larvae and adult branches of the broadcast-spawning coral Acropora millepora (Ehrenberg) to a number of common pollutants, including 4 classes of insecticides—2 organophosphates (chlorpyrifos, profenofos), an organochlorine (endosulfan), a carbamate (carbaryl) and a pyrethroid (permethrin)—and a fungicide (2-methoxyethylmercuric chloride, MEMC). Fertilisation of gametes was not affected by any of the insecticides at concentrations up to 30 µg l–1. In contrast, settlement and metamorphosis were reduced by between 50 and 100% following 18 h exposure to very low concentrations (0.3 to 1.0 µg l–1) of each insecticide class. The insecticides had few visible effects on adult branches following 96 h exposure to a concentration of 10 µg l–1, with the exception of profenofos, which caused polyp retraction, bleaching (i.e. algal symbiont densities were reduced) and a slight reduction in photosynthetic efficiency of the algal symbionts. The fungicide MEMC affected all life-history stages: both fertilisation and metamorphosis were inhibited at 1.0 µg l–1, and polyps became withdrawn and photosynthetic efficiency was slightly reduced at 1.0 µg l–1. At 10 µg l–1 MEMC, branches bleached and some host tissue died. This high susceptibility of coral larvae to pesticides at concentrations around their detection limit highlights the critical need to assess toxicity against all life-history stages of keystone organisms: to focus on mature individuals may underestimate species sensitivity