Lesions in octocorals of the Costa Rican Caribbean During The 2015–2016 El Niño

Emerging infectious diseases affecting marine ecosystems are increasing worldwide. Nevertheless, there are very few histopathological analyses describing the tissue damage associated with a specific disease. This makes it difficult to study the host response and to relate the findings to the isolated agent. Octocoral disease research has focused on the observation of lesions and on the identification of the potential pathogens involved. The aim of this investigation was to identify macroscopic lesions and describe histopathological findings in octocorals to determine potential causes. Fifty-five octocorals were investigated, and 18 of them had visible lesions (32.7%). Samples from the injured tissues of nine individuals of Gorgonia spp., seven individuals of Eunicea spp., one individual of Plexaurella dichotoma and one individual of Pseudopterogorgia acerosa were collected and processed for histopathological analysis. Algal and crustacean abrasions were the main causes of lesions detected in the field. Lesions with a focal distribution were present in most of the colonies, together with changes in tissue coloration. Histopathology revealed that melanization, amoebocytosis and polyp necrosis were the main reactions associated with algae and crustaceans. Histopathology allowed us to confirm the algae and crustacean involvement even when they were not macroscopically evident by the tissue damage and the associated response of these octocorals.