Environmental drivers of ecosystem spatial patterns in the Atlantic

To increase our knowledge of ecosystem distributions, and their causes, outputs from iAtlantic work package 2 ‘Mapping deep Atlantic Ecosystems’ were collectively analysed to determine environmental drivers of ecosystem spatial patterns across scales. In this deliverable, important environmental characteristics identified from basin (iAtlantic deliverable D2.2) and regional (iAtlantic deliverable D2.5) habitat suitability models (HSM) were compared, and the potential mechanisms by which they influence ecosystem spatial distributions were discussed. We also evaluated how habitat mapping based solely on environmental parameters, as carried out within iAtlantic (Deliverable 2.1), can be used as a broad-scale interpretation of ecosystem distribution, both at basin-wide and regional scale, when direct biological observations are scarce.

Across the range of HSMs developed within iAtlantic, cold-water corals (CWCs) were the predominant modelled species, followed by commercially important fish, shark and crustaceans. This was due to a mixture of species biogeography, regional conservation and management relevance, and data availability. As a result, our interpretation here is largely focused on drivers of CWC-related vulnerable marine ecosystems (VMEs).

Our analysis concluded that the relative importance of environmental variables is in part influenced by the native resolution from which they were interpolated to be input into HSMs, with those variables observed or modelled at ecologically relevant spatial scales (resolution & extent close to spatial scale and extent of key biological processes and ecological interactions for the species under consideration) often identified as the most important.

The combined review of the iAtlantic mapping studies found that CWC habitats are principally dictated at broad spatial scales by large geomorphological features (e.g. oceanic islands, mid-Atlantic ridges, seamounts, canyons), water mass properties and latitudinal or regional gradients in productivity associated with circulation regimes and mixing zones. At finer, regional scales CWC habitats are dictated by finer-scale terrain complexity occurring on top of the large-scale geomorphological features (e.g. steep slopes, ridges, gullies), which in turn influence substrate and local hydrodynamics, or can generate local gradients in food provision to the corals.

The multiple-scale influence of these key environmental characteristics is reflected in the overlap of predicted CWC habitats, with the regional-scale predictions of species occurrence fitting within, and refining, the areas identified through basin-scale seabed classification or HSMs. This highlights the potential use of seabed classifications, purely based on environmental variables, to identify potential VMEs where biological data are not available.