PS 8-76 - Identification of climate-change refugia for the bubblegum coral Paragorgia arborea off Nova Scotia, Canada

Background/Question/Methods

The large, fan-shaped octocorals of the antitropical genus Paragorgia Milne Edwards, 1857, known as ‘bubblegum corals’, form ecologically significant habitats on hard substrates along the continental margins of eastern North America. Paragorgia species are long-lived and slow-growing, attaining colony heights of 240 cm. They are considered to be indicators of vulnerable marine ecosystems, and are thereby linked to international conservation efforts advanced by the United Nations. Dense aggregations have been protected from bottom-contact fishing in the Scotian Shelf bioregion off Nova Scotia, Canada. Predictive models of species distributions enable managers to make informed decisions in marine spatial planning, while insight into the impacts of climate change on the size and configuration of suitable habitat, can improve conservation. We modeled the predicted distribution of this species in the Scotian Shelf bioregion, using both machine learning (random forest) and generalized additive model (GAM) frameworks, including projection to 2046−2065. We applied diagnostics tools to determine the degree to which all models projected into novel environmental space both in single variables and in combinations of variables. 3-D Lagrangian particle tracking simulations were used to evaluate the potential for connectivity among existing protected areas, and for colonization of unsurveyed areas predicted to have suitable habitat.

Results/Conclusions

The best predictors of the species’ distribution were a suite of temporally-invariant terrain variables that identified suitable habitat along the upper continental slope in steep and rugged areas, reflecting variability in seafloor elevation, and on steep slopes at scales of kilometres and tens of square kilometers, as well as where vertical relief was of hundreds of metres. 3-D Particle tracking models showed potential for biophysical connectivity along that strip of predicted P. arborea habitat on the upper slope, mediated by the Shelf-Break Current, the principal water flow on the Scotian Shelf, at all times of year and independent of larval vertical behaviour. Extrapolation uncertainties to novel environments showed our predicted distributions under climate projections for 2046–2065 are only reliable for the upper continental slope and portions of the eastern Scotian Shelf. There environmental conditions in some areas are expected to stay within suitable ranges for the species at least through to the mid-century. The Gully MPA, the Lophelia Coral Conservation Area and other areas along the Scotian Slope east of Sable Island have potential as climate refugia, where environmental conditions important to the species are projected to remain stable through to 2046-2065 at least.