Acute toxicity of arsenate and arsenite in two scleractinian coral species: Acropora cervicornis and Orbicella faveolata

Inorganic arsenic, specifically arsenate [As(V)] and arsenite [As(III)], disrupts physiological and biochemical processes in marine organisms, yet their specific impacts on coral reef species remain largely unstudied. This study is the first to assess the acute and subacute toxicity of arsenate [As(V)] and arsenite [As(III)] on two threatened scleractinian coral species, <i>Acropora cervicornis</i> and <i>Orbicella faveolata</i>. Using four 96-h static-renewal assays, corals were exposed to six treatments: five concentrations and a negative control with all concentrations being analytically verified. Toxicity was evaluated through three endpoints: mortality (LC50), coral condition (EC50), and photosynthetic efficiency (IC50). The LC50s were found to be 0.0365 mg L^-1 As(V) and 0.111 mg L^-1 As(III) for <i>A. cervicornis</i> and 0.315 mg L^-1 As(V) and 0.235 mg L^-1 As(III) for <i>O. faveolata</i>. Both species showed significant adverse effects across all subacute endpoints, with <i>Orbicella faveolata</i> significantly more sensitive to As(III), whereas <i>A. cervicornis</i> showed greater sensitivity to As(V). This challenges the prevailing assumption that As(III) is universally more toxic to marine taxa. Species sensitivity distributions found that the LC50 values for these corals were lower than previously reported marine organism's LC50s, highlighting the heightened vulnerability of coral. These findings provide critical data for refining sediment quality guidelines and improving ecological risk assessments in arsenic-impacted reef environments.