Abstract
As “ecosystem engineers” framework-forming scleractinian cold-water corals (CWC) build reefs that are unique biodiversity hotspots in the deep sea. Correlating the spatial occurrence of the most common CWC species with modelled environmental conditions, revealed the ecological requirements and tolerances of these species. However, still limited field observations and poorly understood geographical distribution patterns of the CWC restrict the application of the existing knowledge towards assessing their fate (e.g., local extinction, newly established populations) under ongoing global change. Hence, the risk to cross ecological tipping points causing the demise (or establishment) of entire CWC reefs remains unclear. Thus, a major challenge is to identify the key environmental parameters (or stressors) having the potential to control CWC vitality by providing such tipping points. This is largely hampered by the overall lack of present-day observations of such tipping point crossings. However, evidence for such events is frequently preserved in geological records revealing that entire CWC ecosystems vanished or returned at specific moments in the past. Here, a geological approach is presented that by correlating geological CWC records with paleoceanographic data describing past environmental changes allows to identify a set of key environmental drivers that directly or indirectly control CWC vitality. Thus, by combining such a geological approach with common biological techniques (see above) to describe the ecological tolerance of the most important reef-building CWC has a great potential to better assess their future spatial distribution in times of accelerating global change and to improve the sustainable management of the important deep-sea ecosystems formed by CWC.
Highlights
Framework-forming scleractinian cold-water corals (CWC) are ecosystem engineers that form the base for biodiversity hotspots being widely distributed in water depths between 200 and 1,000 m in the Atlantic Ocean (Roberts et al, 2009)
marine protected areas (MPA) provide no protection against threats induced by ongoing global change (Jackson et al, 2014) such as ocean warming, acidification, deoxygenation and decreasing particulate organic matter fluxes to the seabed as these cannot be controlled locally (e.g., Sweetman et al, 2017)
Most of these proxies provide quantitative results describing former conditions, due to rather large error bars the results usually should be seen as semi-quantitative or sometimes only as qualitative estimates. These records provide reliable archives of environmental change through time and linking these records with a pattern of coral presence and absence allows to pinpoint the most dramatic paleoenvironmental changes co-occurring with the on-set/off-set of CWC reefs. With such a multiproxy approach, key environmental drivers pushing the corals across their tipping points can be identified as it is exemplarily demonstrated in the case studies presented below
Summary
Framework-forming scleractinian cold-water corals (CWC) are ecosystem engineers that form the base for biodiversity hotspots being widely distributed in water depths between 200 and 1,000 m in the Atlantic Ocean (Roberts et al, 2009). MPA provide no protection against threats induced by ongoing global change (Jackson et al, 2014) such as ocean warming, acidification, deoxygenation and decreasing particulate organic matter fluxes to the seabed as these cannot be controlled locally (e.g., Sweetman et al, 2017) This range of environmental parameters might be even more critical for the proliferation or survival of CWC considering a combined effect of multiple stressors (e.g., Büscher et al, 2017). It allows identifying CWC tipping points by taking advantage of the long-term development of CWC reefs. This information will allow to develop and to optimize management strategies for the sustainable protection of these important deep-sea ecosystems
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