Disturbance of epifauna in seagrass-seaweed mixed beds by pesticides discharged into the coastal area: Asymmetric effect on crustaceans and molluscs

Although pesticides are a cornerstone of modern agriculture, they are also known to be a major factor in the decline of biodiversity. Even pesticides applied in inland agricultural areas can be transported via rivers and have often been detected in marine environments. Pesticides would disturb not only the ecosystems around agricultural areas but also marine ecosystems, and there is a growing need for research on how pesticides affect marine environments. Recently, several pesticides have been detected at high concentrations in the coastal areas of Ishigaki Island, Japan, where seagrasses and seaweeds form important macrophyte bed ecosystems. To elucidate the effects of pesticides on the macrophyte bed epifauna, a field survey was conducted in the intertidal seaweed-seagrass mixed beds in Ishigaki Island. As a result of the survey, several pesticides were detected, including the highly toxic insecticide fipronil. The epifaunal abundance, taxon richness and Shannon's diversity index (H') were all negatively and significantly correlated with fipronil concentration. Crustaceans were found to be more affected by fipronil than molluscs. Abundance, taxon richness and H' of crustaceans were negatively correlated with fipronil concentration, whereas those of molluscs were not. The alteration and decline of epifaunal assemblages by pesticides may lead to a loss of the ecological functions and resilience of macrophyte bed ecosystems. This study demonstrates the disturbance of epifauna by discharged pesticides in in situ coastal macrophyte bed ecosystems. Pesticides appear to disturb a much wider range of ecosystems than previously considered, and accordingly may require a reconsideration of pesticide use and discharge in the future.