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all life-history stages: both fertilisation and metamorphosis were inhibited at 1.0 µg l -1 , and polyps became withdrawn and photosynthetic efficiency was slightly reduced at 1.0 µg l -1 .At 10 µg l -1 MEMC, branches bleached and some host tissue died.This high susceptibility of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.