ANNA Cold-Water Coral Ecosystems off Angola and Namibia - Cruise No. M122 - December 30, 2015 - January 31, 2016 - Walvis Bay (Namibia) - Walvis Bay (Namibia) (English)

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R/V METEOR expedition M122 focused on the investigation of cold-water coral (CWC) occurrences in the Southeast Atlantic Ocean off the coasts of Namibia and Angola, a region characterised by a distinct oxygen minimum zone. Special emphasis was on the distribution, the appearance, the faunal assemblage and the vitality of these ecosystems under present and past (glacial) conditions. Based on detailed mapping (multibeam echosounder, PARASOUND and multichannel seismic) in the two working areas off Namibia and Angola, a total of 16 dives with the MARUM ROV SQUID were conducted to allow for a detailed characterisation of the existing facies and fauna. These observations were complemented by studies on the structure (CTD and water samples) and variability (lander systems) of the water column and by extensive seabed sampling including long sediment cores that will enable to study the development of CWC ecosystems in the Southeast Atlantic under changing environmental conditions, e.g., over glacial-interglacial cycles. The most remarkable result of the expedition was the observation of living CWC within the oxygen minimum zone off Angola. Thriving CWC under dissolved oxygen concentrations of <1 ml L-1, as found off Angola, have never been observed before, neither in nature nor in laboratory experiments. In contrast, off Namibia, where dissolved oxygen concentrations are even lower with <0.5 ml L-1, only fossil CWC were encountered. However, their presence is a clear indicator for the existence of better living conditions for the CWC in the past. With the framework-building CWC acting as ecosystem engineers, their vitality is decisive for the local biodiversity in the investigated upper continental slope settings.