Abstract
Anthropogenic climate change presents a major challenge to coastal ecosystems. Mass population declines or geographic shifts in species ranges are expected to occur, potentially leading to wide-scale ecosystem disruption or collapse. This is particularly important for habitat-forming species such as free-living non-geniculate coralline algae that aggregate to form large, structurally complex reef-life ecosystems with high associated biodiversity and carbon sequestration capability. Coralline algal beds have a worldwide distribution, but have recently experienced global declines due to anthropogenic pressures and changing environmental conditions. However, the environmental factors controlling coralline algal bed distribution remain poorly understood, limiting our ability to make adequate assessments of how populations may change in the future. We constructed the first species distribution model for non-geniculate coralline algae (focusing on maerl-forming species but including crustose coralline algae associated with coralline algal beds) and showed that bathymetry, temperature at the seabed and light availability are the primary environmental drivers of present-day non-geniculate coralline algae distribution. Our model also identifies suitable areas for species presence that currently lack records of occurrence. Large-scale spatial declines in coralline algal distribution were observed under all IPCC Representative Concentration Pathways (ranging from 38% decline under RCP 2.6 up to 84% decline under RCP 8.5), with the most rapid rate of decline up to 2050. Refuge populations that may persist under projected climate change were also identified – informing priority areas for future conservation efforts to maximise the long-term survival of this globally important ecosystem.
Highlights
Rising anthropogenic carbon dioxide (CO2) emissions are causing rapid environmental change and under some scenarios, the mean ocean surface temperature is projected to rise by up to 4.3◦C by 2100 (IPCC, 2014)
Scotland is a European regional stronghold for these coralline algal beds, but here we demonstrate their high sensitivity to projected climate change, and demonstrate the value of SDMs for understanding regional-scale environmental drivers of their distribution
Increased survey activity in order to better establish true presences and absences of beds, and high resolution data on environmental conditions would be appropriate places to start and allow for more detailed and in depth modeling to be carried out
Summary
Rising anthropogenic carbon dioxide (CO2) emissions are causing rapid environmental change and under some scenarios, the mean ocean surface temperature is projected to rise by up to 4.3◦C by 2100 (IPCC, 2014). Aggregations of freeliving, non-geniculate coralline algae (maerl-beds), found globally, are abundant in the NorthEast Atlantic (from the Arctic Ocean to the wider North Atlantic and the Canary Islands) (Pardo et al, 2014a), with Galicia, Brittany, Norway, Ireland, and Scotland being particular strongholds (Hall-Spencer et al, 2010). In this North-East Atlantic region, beds most abundant up to a depth of ∼50 m (Pardo et al, 2014a). P. calcareum is more frequently recorded in shallower waters (above 30 m) (Perry et al, 2017a), but sporadic deep-water observations are known [e.g., 80 m in the Pontian Archipelago, Mediterranean (Basso, 1998)]
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