We present a quantitative food-web analysis of the cold-water coral community, i.e., the assembly of living corals, dead coral branches and sediment beneath, associated with the reef-building Lophelia pertusa on the giant carbonate mounds at ,800-m depth at Rockall Bank. Carbon flows, 140 flows among 20 biotic and abiotic compartments, were reconstructed using linear inverse modeling by merging data on biomass, on-board respiration, d 15 N values, and literature constraints on assimilation and growth efficiencies. The carbon flux to the coral community was 75.1 mmol C m 22 d 21 and was partitioned among (phyto)detritus (81%) and zooplankton (19%). Carbon ingestion by the living coral was only 9% of the carbon ingestion by the whole community and was portioned among (phyto)detritus (72%) and zooplankton (28%). Carbon cycling in the community was dominated by suspension-and filter-feeding macrofauna associated with dead coral branches. Sediment traps mounted on a bottom lander trapped 0.77 mmol C m 22 d 21 (annual average), which is almost two orders of magnitude lower than total carbon ingestion (75.1) and respiration (57.3 mmol C m 22 d 21 ) by the coral community. This discrepancy is explained in two ways: the coral community intercepts organic matter that would otherwise not settle on the seafloor, and through their action as ecosystem engineers, the increased turbulence generated by the coral framework and organic-matter depletion in the boundary layer augment the influx to the coral community. A comparison of macrofaunal biomass and respiration data with soft sediments reveals that coral communities are hot spots of biomass and carbon cycling along continental margins.Oceans and seas cover almost 75% of Earth's surface and are underlain with predominantly soft sediments. In recent decades, however, increased use of underwater videos, video-guided sampling gear, and remotely operated vehicles (ROVs) has contributed to the discovery of other deep-sea ecosystems.
A set of 40 Uranium-series datings obtained on the reef-forming scleractinian cold-water corals Lophelia pertusa and Madrepora oculata revealed that during the past 400 kyr their occurrence in the Gulf of Cádiz (GoC) was almost exclusively restricted to glacial periods. This result strengthens the outcomes of former studies that coral growth in the temperate NE Atlantic encompassing the French, Iberian and Moroccan margins dominated during glacial periods, whereas in the higher latitudes (Irish and Norwegian margins) extended coral growth prevailed during interglacial periods. Thus it appears that the biogeographical limits for sustained cold-water coral growth along the NE Atlantic margin are strongly related to climate change. By focussing on the last glacial-interglacial cycle, this study shows that palaeo-productivity was increased during the last glacial. This was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling.After the Younger Dryas cold event, the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the GoC. This primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems. Moreover, these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern NE Atlantic where more suitable environmental conditions established with the onset of the Holocene.
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