Coral tissue microstructure and necrosis: relation to catastrophic coral mortality in Panama

Abstract

During 1983, patchy but extensive mortality of several stony coral species occurred off the Pacific coast of Panama, associated with loss of their symbiotic zooxanthellae. This disturbance was coincident with the prolonged 1983 El Nino warming event. Normally colored colonies receiving bleached colony portions in iso-, allo- and exografts remained in a healthy state during a 7 mo period. Neither these transplantation experiments, nor histopathological examinations, revealed the presence of an infectious agent which might be responsible for the widespread bleaching, although suspected bacteria were found in electron microscopy preparations of 2 species of bleached corals. The condition of affected coral tissues ranged from slight to severe atrophy and necrosis, but normal-appearing zooxanthellae remained in all but the most necrotic specimens, although reduced in numbers. These observations suggest that environmental (particularly high thermal) stress may have been responsible for the coral deaths.