Coral Reef Organisms: Differential Sensitivities to an Agricultural Pesticide

Neonicotinoid insecticides are an emerging contaminant of concern in areas with intensive coastal agriculture where they can be introduced into shallow marine ecosystems. The tolerance of four marine species to a selective systemic insecticide (imidacloprid) was determined using dose-response (50 ppm-50 ppb) acute toxicity tests. Species tested were a macroalgae (Ulva sp.), an amphipod (Elasmopus levis), green sea urchin embryos (Lytechinus variegatus), and cauliflower coral (Pocillopora damicornis), representing different trophic levels in a coral reef ecosystem. Macroalgae, Ulva, showed increased growth that was positively correlated with imidacloprid concentrations with maximum growth at 10 ppm. Elasmopus levis exhibited immobility at a LOEC of ≥ 10 ppb and mortality at 1 ppm. Lytechinus variegatus embryo development was not affected in the concentration range tested. Pocillopora damicornis showed a LOEC at ≥ 10 ppm for two endpoints: wound healing and health physioscores. The persistent polyp retraction is indicative of stressful conditions and inability to feed. Reduced wound healing ability may impact a coral’s ability to regenerate tissue increasing its vulnerability to other threats such as algal overgrowth and disease. The mechanism of effect on corals is not yet fully understood, as cnidarians do not have nicotinoid acetylcholine receptors, its primary mode of effect in terrestrial arthropods. This study demonstrated differential species sensitivities to a systemic insecticide with macroalgae < sea urchin embryos < amphipods < coral. These data suggest that toxic effects of imidacloprid are seen when water concentrations reach ppm levels, but further work should be done considering the effects brought on by bioaccumulation and subsequent ingestion of imidacloprid.