Climate envelope modelling of hard corals

Abstract

The global climate change is pushing marine ecosystems towards extinction. The sensitive ecosystems like coral reefs will be the first few to take the imminent impacts of an increase in temperature. Unlike any other oceans, Northern Indian Ocean(NIO) is thought to be highly vulnerable due to its typical topography with the massive Eurasian Continent in the north. The Indian Ocean is the warmest among all tropical oceans and more vulnerable in the era of climate change. The ecosystems of this landlocked sea will not permit the migration of the organisms to cooler waters as the years' progress. Scleractinians, the Hard Corals, are sessile and are very sensitive to the shifts in biogeochemical variables. The hard corals in the northern Indian Ocean are increasingly susceptible to elevated anthropogenic stressors, including impacts from climate change, overfishing, runoff, and ocean acidification. In order to study the precise impact of such stressors, the knowledge about the existing extent of hard coral distribution is necessary. The wider distribution and their growth in the oceanic remote islands and ridges makes their complete distribution unknown to science. With the emergence of new powerful statistical techniques and GIS tools, the development of predictive habitat distribution models has become easier. In this study, climate envelope modeling is carried out using maximum entropy principle (MaxEnt) to predict the occurrence of five hard coral species viz., Acropora mitricaUi. Favia pallida. Plaiygyra ckieckilea, Pocillopora damicorms and Porites Itttea by correlating their point observations of data with gridded environmental variables. The statistical model that expresses the correlation and the species threshold to different independent variables is thus employed to create maps of predicted occurrence by applying the model to maps of the environmental parameters. The future distribution of each species was delineated using the IPCC emission scenarios, RCP 4.5, RCP 6.0, and RCP 8.5 for the period of 2040-50 and 2090-2100. The study unveils possible distribution areas of these hard-coral species' in the northern Indian Ocean and their vulnerability towards elevated greenhouse gas emissions in the future decades. Much of future estimates of occurrences, all these corals are noted in new areas that are now devoid of coral reefs mainly the entire Indian coast and the east African coast. A. muricuta is found to be most vulnerable species under all the three RCPs. It is also found that the Red Sea, Persian Gulf and Indian coasts are found to be more exposed to the vagaries of climate change regarding coral distribution. Tlie nature of the relationship of coral distribution with the climatic parameters as predicted by this study can also help conservators and marine protected tnea managers well prepared for expected but sudden environmental changes. Prediction of future shifts in the hard-coral occurrence will provide a guideline to the management actions either to decrease the impact or prevent possible extinction events.