Coral health and disease assessment in the central republic of Maldives

Currently, it has been estimated that coral reefs, the most diverse of all marine ecosystem, are in severe decline and the most reliable estimates suggest that worldwide 27% have already been lost, with another 16% at serious risk of loss. Coral disease is a significant factor contributing to this decline. However, despite an increasing number of reports of diseases affecting corals and other marine taxa worldwide, and further increases predicted as a consequence of climate change, there has been comparatively little research focused on diseases of Indo-Pacific reef corals. For this reason, given that the Indo-Pacific encompasses 91% of the world’s coral reefs, which are geographically more extensive and specious, knowledge of coral diseases in this region has considerable ecological importance. The Republic of Maldives consists entirely of coral reefs that are significant on a global scale as well, being the 7th largest in terms of area covered, contributing up to 5% of the worlds reef area. Unfortunately the Maldives have been among the most affected areas in the world, with 60 to 100% coral mortality reported due to an unprecedented coral bleaching event in 1997-1998. So, while the coral bleaching phenomenon and the impact on the coral community around the world are well known, the study of the coral diseases is still in his infancy at least in the Indo Ocean region, and especially in the Republic of Maldives. This study aims to fill this gap in knowledge through the identification of the diseases affecting reef-building corals and assessing their distribution, host range and prevalence in the Maldivian Archipelago. Principal findings of this study demonstrate that biotic threats identifiable in corals diseases and algal overgrowth represent a serious risk for the coral community and associated organisms in the Maldivian reefs ecosystem. During the survey period from October 2010 to April 2012 seven islands, belonging to four atolls, were sampled and a total of eight coral diseases were reported for the first time, named: Brown Band Disease (BrBD), Skeleton Eroding Band (SEB), Ulcerative White Spot (UWS), Black Band Disease (BBD),White Syndrome (WS), Black Disease, coral tumors and the not yet described Porites White Patch Syndrome. All coral diseases observed affected in total 17 scleractinian genera belonging to 8 different families, representing about the 25 % of the whole scleractinian genera described in this area. In general, the Siderastreidae, Faviidae and Pocilloporidae families were between the most susceptible. Also the Acroporidae results one of the most affected family, but the greater abundance of this family in the Maldivian reef reduce significant the disease prevalence levels. A specie-specific investigation must be made to identify the real extent of the problem. However, although all diseases are present with very low overall disease prevalence (< 1%), which is in contrast with several other studies on reef, our study reveal as WS, UWS and especially BBD resulted widespread in the surveyed area and relatively diffused in the coral community. Malè North displays the higher overall disease prevalence suggesting a probable influence of human activities on pathogen virulence. Considering the numerous studies that related positively anthropogenic disturbance and increase in disease prevalence we think that this result must be keep in consideration. The overall coral diseases prevalence in the Maldivian Archipelago was estimate around 1.3 %, similar to the level of prevalence reported for the GBR (1.32 %), but the value was lower than the one already reported in the Philippines (4.64 %) for the Indo-Pacific region and Mexican Yucatan (8.3 %) in the Caribbean. Furthermore, even if standardized survey methods and permanent monitoring sites could provide enough information to determine interannual variability in disease prevalence, our level fall approximately in the range of 3 to 5 % estimated for the Indo-Pacific region. In summary, our study have provided for the first time baseline information on the status of coral diseases affecting reefs in the Republic of Maldives. The present study has also revealed that coral diseases are established and can become prevalent on coral reefs of this archipelago. Furthermore, given that levels of coral diseases are an important indicators of coral reef health and that have been correlated with anthropogenic activities and climate warming events, the prevalence values for multiple diseases reported in this study provide a baseline level of diseases prevalence that could be used to monitor the health of Maldivian reef-building corals as gauge for future change.