Corals under pressure from rising ocean temperatures may also face an additional threat in the form of pesticides running off the land. Collaborative research by AIMS and James Cook University has shown that agricultural chemicals at levels so low as to be practically undetectable can harm corals, especially the more sensitive early life history stages.

The study measured the sensitivity of the eggs, larvae and adults of a common coral, Acropora millepora, to a number of common pollutants including four classes of agricultural insecticides and a fungicide commonly used in GBR catchments. While previous studies had shown little impact of these same insecticides on adult corals, the recruitment of coral larvae was reduced to below half after just 18 hours exposure to very low concentrations of each insecticide. In addition, the study found that all life stages of coral are sensitive to an agricultural fungicide which caused tissue retraction, bleaching and mortality at very low concentrations.  This study revealed some of the most sensitive biological responses yet demonstrated to pesticide contamination in the marine environment and suggest that current water quality guidelines may not adequately protect reef corals. The high susceptibility of coral larvae to pesticides at concentrations close to minimum detection levels highlights the critical need to assess toxicity against all life history stages of keystone organisms, such as reef-building corals, because to focus on mature individuals may underestimate species sensitivity.

Up close image of a coral branch exposed to 1 µg/L of the fungicide MEMC. The brown tissue is normal but the MEMC has caused tissue death, exposing the white skeleton.