Improved habitat suitability modelling for protected corals in New Zealand waters
Published:
July 2020Download the publication
Summary
Many protected coral species occur as bycatch in commercial fisheries around New Zealand. To estimate the overlap between commercial fishing and corals under present and future climate conditions, and thus the potential vulnerability of these protected species, it is first necessary to predict the present and future spatial extent of corals. This work extends previous coral habitat suitability modelling studies by utilising updated modelling techniques, incorporating additional coral presence records, and by mainly using regional environmental predictor layers for the current and future climate conditions based on the New Zealand Earth System Model (NZESM).
Models were produced for all protected coral taxa considered in initial consultations with stakeholders. These comprised four separate reef-forming scleractinian coral species, Enallopsammia rostrata, Solenosmilia variabilis, Goniocorella dumosa, and Madrepora oculata; the gorgonian octocoral genera Paragorgia (bubblegum corals), Primnoa (primnoid seafans), Corallium (precious corals); and Keratoisis and Lepidisis (bamboo corals) combined; two antipatharian (black) coral genera, Bathypathes and Leiopathes; and two genera of stylasterid hydrocorals, Errina and Stylaster. This selection was based on the need to produce models that cover a range of the protected coral taxa and the requirement for a sufficient number and spread of presence records.
Environmental predictors were derived primarily from outputs of the NZESM, but several fixed predictors, including revised and updated sediment data layers, seafloor slope, and UTF (Underwater Topographical Feature, as a categorical variable) were also considered. Model coefficients were used to produce two sets of prediction grids for each model type; one for present-day environmental conditions (means from the period 1995 to 2014), and one for the predicted environmental conditions at the end of the 21st century (means from the period 2080 to 2099), assuming only moderate mitigation and adaptation to climate change.
Model performance was shown to be acceptable for all taxa, and although predicted taxa distributions largely agreed with previous studies, additional presence records extended the predicted distributions into new areas for some taxa. For the region as a whole, future habitat suitability ranged from somewhat less suitable (e.g. Corallium spp.) to somewhat more suitable overall (e.g. Enallopsammia rostrata), across the 12 taxa examined. For some taxa, especially the hydrocorals, predicted future habitat suitability remained largely unchanged due to the importance of temporally fixed parameters in the models. Use of a less conservative emissions pathway in the NZESM may have also provided more contrast between present and future suitability but was not possible to test due to the constraints of the project.
The risk to corals from interaction with fishing gear was assessed by comparing predicted coral distributions with the aggregated swept area from historical bottom fishing for inshore and deepwater fisheries combined. Overlaying the regions of greatest habitat suitability with the most highly fished regions (using arbitrary habitat suitability and fishing intensity thresholds) revealed considerable variability in vulnerability among taxa, both in degree and location. The greatest overlaps were seen for hydrocorals and the shallower scleractinian species, whereas the deeper scleractinians, gorgonians, and black corals were less vulnerable. Little change in overlap at the end of the century was predicted for many of the modelled taxa. However, a higher future level of overlap off the west coast of the South Island was predicted for the thicket-forming Madrepora oculata, the alcyonaceans Keratoisis and Lepidisis spp., and the black coral Leiopathes spp. A lower level of future overlap was predicted for the hydrocoral genus Stylaster along the east coast of the North Island.
Publication information
Anderson, O., Stephenson, F. Behrens, E. 2020. Improved habitat suitability modelling for protected corals in New Zealand waters. POP2018-01 final report prepared by NIWA for the Conservation Services Programme, Department of Conservation. 108 p.
Contact
Conservation Services Programme
Department of Conservation
PO Box 10-420
Wellington 6143
Email: csp@doc.govt.nz