Corals are under global threat from anthropogenic pressure and climate change, making them susceptible to disease. The Western Indian Ocean (WIO) has been particularly affected by El Niño Southern Oscillation (ENSO) events, leading to coral bleaching and a concomitant increase in disease. Coral diseases are enigmatically designated by rather loose terms such as ‘black band disease’, describing signs of recognisable disease usually associated with a suite of mostly secondary pathogens. Identification of the original causative organism is essential to elucidate the nature of such diseases and options for their prevention and treatment. This is rarely achievable due to difficulties in culturing marine microbes. In the case of the WIO, we surveyed the incidence of coral diseases in localities of varied perturbation, viz. Reunion, Mayotte and South Africa, and found a decreasing level of both in the order listed.1 These trends reflected the levels of human development in the respective reef areas. Six coral diseases were prevalent at the study sites and two previously unreported coral diseases were described and characterised, viz. Porites white patch syndrome (PWPS)2 and Porites black patch syndrome (PBPS)3. The former was more prevalent and 16S rRNA sequence analysis revealed a high variability between bacterial communities associated with PWPS-infected tissues in Porites lutea. Several bacterial ribotypes affiliated to potential putative pathogens were consistently found, notably Shimia marina and Vibrio hepatarius. Isolates from PWPS-diseased tissue yielded 14 pure cultures, one of which satisfied Henle-Koch’s postulates in reproducing PWPS and proved to be Vibrio tubiashii, the closest known sister taxon to Vibrio hepatarius.4 PBPS was less frequently encountered and appears to be a multi-stage disease triggered by cyanobacterial invasion, rapidly followed by secondary bacterial infections that grow in decomposing tissue. Bacterial 16S rRNA sequences yielded a broader diversity of bacterial taxa in PBPS-infected tissues than in healthy tissue, represented by the genus Vibrio (24.9%), followed by sulphate-reducing or sulfide-oxidizing genera such as Desulfovibrio (20%), Clostridium (12.9%) and Arcobacter (9.9%).
This work was co-funded by the European Union (EU, FEDER), the Regional Council of Reunion, the French Ministry of Higher Education and Research (DRRT), the French Department of Ecology, Sustainable Development, Transportation and Housing (DEAL), the French Ministry of Overseas (MOM), the Applied Centre for Climate and Earth System Science (ACCESS), Western Indian Ocean Marine Science Association (WIOMSA) and the South African Association for Marine Biological Research (SAAMBR). A number of colleagues collaborated in the work, provided assistance in the laboratory or support in the field, particularly the late Stephanie Bollard, Pascale Chabanet, Stuart Laing, Phanor Montoya-Maya, Jean-Pascal Quod, Michael Sweet, Pedro Tortosa and David Wilkinson.
1. Séré MG, Tortosa P, Chabanet P, Turquet J, Quod J-P, Schleyer MH. 2015. Identification and prevalence of coral diseases on three Western Indian Ocean coral reefs. Diseases of Aquatic Organisms 114: 249–261
2. Séré MG, Tortosa P, Chabanet P, Turquet J, Quod J-P, Schleyer MH. 2013. Bacterial communities associated with Porites White Patch Syndrome (PWPS) on three Western Indian Ocean (WIO) coral reefs. Plos One DOI: 10.1371/journal.pone.0083746
3. Séré MG, Wilkinson DA, Schleyer MH, Chabanet P, Quod J-P, Tortosa P. 2016. Characterisation of an atypical manifestation of black band disease on Porites lutea in the Western Indian Ocean. Peer J 4, e2073. DOI 10.7717/peerj.2073
4. Séré MG, Tortosa P, Chabanet P, Quod J-P, Sweet MJ, Schleyer MH. 2015. Identification of a bacterial pathogen associated with Porites white patch syndrome in the Western Indian Ocean. Molecular Ecology 24: 4570–4581. doi: 10.1111/mec.13326