Predicted changes in marine environmental conditions between the present and 2100 AD derived from global earth system models (ESMs) were used to predict the future distribution of protected deep-sea coral species in the New Zealand region. By incorporating future conditions from ESM models into habitat suitability models, specific areas with high potential for providing suitable conditions for future survival were identified for several protected coral groups.
Present-day and future distributions of protected coral species within the New Zealand region were estimated using Boosted Regression Tree (BRT) models. Key variables included environmental data layers for the 1986 to 2005 reference period and 2090 to 2110 future period as predicted by the best ESM, selected from a suite of candidate models according to the level of agreement between model simulations and observed carbonate parameters in the New Zealand region. The environmental and bathymetric variable layers for the two periods available for the BRT models comprised: bottom temperature, salinity, sea surface height; concentrations of aragonite, calcite, dissolved oxygen, dissolved inorganic carbon, nitrate, and chlorophyll; and two less mutable predictors, slope and seamount.
The modelled taxa comprised four species of reef-building scleractinian corals, four genera of gorgonian octocorals, and four genera of antipatharian black corals. The most important predictors of coral presence varied considerably among these taxa, but nitrate and oxygen levels, sea surface height, and slope had the most influence overall.
For scleractinian corals as a combined group, habitat suitability is predicted to decline markedly over much of the modelled region between the present day and 2100 AD. Notable declines in habitat suitability are also seen for three of the four individually modelled species, although to a more variable degree. The Chatham Rise, especially the extreme north-eastern area, stands out in contrast to the rest of the New Zealand region with generally similar or higher habitat suitability predicted for most of the scleractinian taxa in 2100 AD.
The predicted future distribution of the bamboo corals Keratoisis spp. and Lepidisis spp., the gorgonian coral Primnoa spp., and black corals are less affected by the predicted changes in the modelled environmental conditions. Although for the bamboo corals improved suitability is again indicated for the Chatham Rise, at the expense of other areas. In contrast, conditions for the gorgonian bubblegum corals (Paragorgia spp.) are predicted to improve substantially in almost all parts of the modelled region.
Future directions for research could include; aligning known or estimated species tolerances to environmental conditions with maps of seafloor habitat and predicted future environmental conditions; continuing to improve the accuracy of habitat suitability models by incorporating new, improved, and higher resolution predictor variable data as it becomes available; inclusion of additional presence and absence data from new sampling and new sources such as camera surveys; and further analyses of coral mineralogy and the application of in-aquaria stony coral dissolution experiments with varying temperature and pH regimes, both of which could help to inform the results of future predictions.