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.

We report here the occurrence of seasonal changes in the pigmentation of colonies of Siderastrea spp. during bleaching events on coastal reefs in northeastern Brazil. Bleached affected almost 50% of coral colonies analyzed in Cabo Branco reefs (Paraiba state) in the summer of 2005. The same phenomenon was detected along various coastal reefs in northeastern Brazil during the summer of 2007 and 2008. These events were seasonal, and began with the emergence of pale colonies that became pale-pink and then purple during the rainy months. The patterns and intensity of colonies pigmentation changes varied with the studied sites. The decrease in zooxanthellae density and chlorophyll-a content was quantified in the colonies with their pigmentation pattern altered (bleaching). Microbiological analyses revealed higher densities of bacteria in pink colonies (bleached) as compared to brown colonies (normal). Environmental disturbances may lead to the pigmentation changes in Siderastrea spp., but the immediate causes of this phenomenon are not clear and require further investigations.

Se relata aquí la aparición de cambios estacionales en la pigmentación de colonias de Siderastrea spp. durante los eventos de blanqueamiento en arrecifes costeros del noreste de Brasil. En verano de 2005, existían casi 50% de colonias blanqueadas en los corales analizados en Cabo Branco, Estado de Paraíba. El mismo fenómeno se detectó a lo largo de varios arrecifes costeros en el noreste del país durante el verano de 2007 y 2008. Estos eventos son asociados a la variación estacional, que comenzaron con la aparición de colonias pálidas que luego se convirtieron en rosa pálido y después a morado, durante los meses de lluvias. Los patrones e intensidad de los cambios en la pigmentación de las colonias fueron diferentes en los sitios estudiados. La disminución de la densidad de zooxantelas y del contenido de clorofila-a fue cuantificada en las colonias y comparados con el patrón de pigmentación alterada (blanqueo). Los análisis microbiológicos revelaron densidades más altas de bacterias en colonias rosas (blanqueada) en comparación con las colonias marrones (considerados normales). Las alteraciones ambientales pueden conducir a estos cambios de pigmentación en Siderastrea spp., pero las causas inmediatas de este fenómeno no están claras y requieren más investigación.