A widespread necrotizing disease affecting palythoa caribaeorum (Duchassaing and michelotti, 1860) on coastal reefs in Northeastern Brazil

Abstract

A highly aggressive necrotizing disease affecting the zooantharian Palythoa caribaeorum was studied on coastal reefs in northeastern Brazil during March and April of 2008. Approximately 87% of the colonies at each locality showed wounds ranging from 27 cm to 1200 cm long and from 12 to 320 cm wide. This disease initiates with the darkening of the polyps, followed by the appearance of a rapidly enlarging wound that decomposes colony tissues and eventually exposes the substrate. The exposed areas are subsequently colonized by macroalgae, Zoanthus sociatus, and other benthic organisms. The necrotized areas were dark-colored and expelled fetid odors. Although extremely aggressive, complete mortality of the colonies was not observed. Surviving fragments recomposed the colonies within 6 to 9 months. Recurrences of the disease were in the summer of 2008 and from February/2013 to March/2014. During the study period, we found various colonies having black-spots (early stage of necrotizing disease), suggesting stress conditions. Zooxanthellae densities in those black-spots were always lower than in apparently healthy colonies, with reductions of up to 74%. More than one environmental variable seems to influence the zooxanthellae densities significantly, but there is no evidence of any association with abnormally high water temperature, as thermal variations in the study area were within their normal range. Histological analysis showed losses of tissue organization in colonies with black-spots and necrotizing components with hypertrophy and cell apoptosis of the gastrodermal cells; apoptosis of zooxanthellae and damage in completes mesenteries. All these features showed an inflammatory response to necrosis disease.