Notes from the field: A vet’s eye view of coral disease and pathologyThu 21 Dec, 2017
Pull on a mask, snorkel and fins and slip into the cyan blue waters of the Caribbean Sea. Instantly a new world comes alive, one bursting with life in a framework of soft and stony corals building a stunning underwater landscape. To see coral is wonderful, but to know how old it is, how it feeds, how it plays a crucial role in this spectacular ecosystem, gives one a new perspective.
Unfortunately, those coral reefs are a shadow of their former selves. This is most likely a combined result of global warming, eutrophication, overfishing and a myriad of diseases for which most causative agents remain yet unknown and consistency in their gross lesions description is lacking.
Veterinary pathologists from Ross University School of Veterinary Medicine (RUSVM) on the island St Kitts have been snorkeling the island’s shallow reefs in an effort to systematically monitor, describe and categorize macroscopic coral lesions.
To this end, their recent study (between september 2016-May 2017) monitored the lesion progression (active versus quiescent) in major reef building species Orbicella annularis (Boulder Star Coral) and Orbicella faveolata (Mountainous Star Coral). The mean prevalence of a diseased state in both species was around 40% and different types of macroscopic lesions and lesion progression could be identified. Pathologists spotted pigmentary changes such as bands of yellow or brown tissue surrounding areas of tissue loss, many fitting with current case definitions for Caribbean yellow band disease. Shown in the picture is another spectacular lesion characterized by annular bands of black film overlying the coral tissue and leaving a central area of bare, white skeleton, typical of black band disease. Alarming is the progression rate of those lesions which were associated with tissue loss. Likewise, bleaching lesions, where pigmented symbiotic zooxanthellae have been lost apparently due to seawater temperature, significantly impair coral health. Those lesions are of widespread global occurrence and St Kitts’ reefs are unfortunately no exception to that, especially at the shallower reefs on the West side of the island.
Overall, the study could categorize seven different types of macroscopic lesions and progression and is currently being followed up at RUSVM by detailed histopathologic examination and collaboration between different veterinary disciplines to unveil etiologic agents of Orbicella coral diseases on St Kitts’ reefs. We must take care to protect what we have and restore what we can. To this end, filling information gaps in coral disease is invaluable in assessing the causes of coral reef decline and actions for coral reef conservation.
Elize Dorrestein, DVM
Anne A.M.J. Becker, DVM, Msc, PhD
Ross University School of Veterinary Medecine (RUSVM)
Master of Research student: Elize Dorrestein, DVM
Michelle Dennis, DVM, PhD, DACVP
Associate Professor of Anatomic Pathology
Saundra Sample, DVM, DACVP
Assistant Professor Clinical Pathology