Marine species distribution modelling and the effects of genetic isolation under climate change

AIM: Coral reefs are experiencing both an increasing frequency and intensity of anomalously warm ocean temperatures because of climate change. Studies show that the majority of coral populations will likely decline as temperatures continue to increase, although some previous species‐distribution models predict that ubiquitous species, such as the primary reef‐building coral species Porites lobata, will increase their distribution under projected climate change. These predictive models, however, assume that all individuals of a population are able to tolerate the entire range of environmental conditions within the species’ geographic range. The effects of genetic isolation and local adaptation are not considered in species‐distribution models that assume genetically contiguous populations. We aim to determine the effects of genetic isolation and local adaptation in species‐distribution modelling of the ubiquitous species P. lobata under three climate change scenarios by comparing contiguous and isolated subpopulations. LOCATION: Indian and Pacific Oceans. METHODS: We ran a novel species‐distribution model for P. lobata, segregated as five geographically isolated regions across the Indian and Pacific Oceans, and examined the species response to three climate‐change scenarios (i.e., A2, A1B and B1, most recently considered as Representative Concentration Pathways 8.5, 6.0, and 4.5 Wm⁻²) by the year 2100. RESULTS: In contrast with previous homogeneous species‐distribution models that predict a global expansion of P. lobata, (˜5 ± 1%), we predict major losses of suitable habitat for P. lobata in four of the five regions examined, particularly in the central Pacific Ocean (>99% ± <0.1% for all climate scenarios). Indeed, when geographic and genetic isolation were considered, our predictions suggested that P. lobata would lose between 50–52 ± 4% of its habitat, depending on the climate‐change scenario, mainly in the Pacific Ocean. MAIN CONCLUSIONS: Genetic isolation will likely play a major role in the persistence of coral species under climate change, and small isolated populations may be more vulnerable to climate change than populations in large, highly connected regions.