Cold-water corals and oxygen content

New study on Mediterranean cold-water corals reveals their sensitivity on low oxygen contents

MARUM, Bremen, Germany

fig1A recently published HERMIONE study on continuous sedimentary records from an eastern Mediterranean cold-water coral site revealed a temporary extinction of these deep-sea organisms during the Early to Mid Holocene (11.4–5.9 cal. kyr BP). The timing of the corals' demise coincides with the sapropel S1 event, during which the deep eastern Mediterranean basin (>1,800 m) turned anoxic. The results of this study show that during the sapropel S1 event low oxygen (dysoxic) conditions of 2 ml l-1 even extended to intermediate depths (~600 m), where the cold-water corals formerly thrived. The corals clearly suffered under these extreme conditions, which might have had a negative effect on their growth rate and reproductive processes, and eventually caused their temporary extinction. This very first evidence for the sensitivity of cold-water corals to low oceanic oxygen contents suggests that the projected expansion of tropical oxygen minimum zones resulting from global change will threaten cold-water coral ecosystems in low latitudes in the same way that ocean acidification will do in the higher latitudes.
Above: Schematic NW-SE cross-section across the Apulian margin showing the Santa Maria di Leuca (SML) cold-water coral province in the Ionian Sea. a: Phases of sustained coral growth in the late deglacial and Mid to Late Holocene that were associated with the formation of Adriatic Deep Water (AdDW) resulting in enhanced bottom currents and a well-ventilated water column. b: Temporary demise of cold-water corals during Early Holocene sapropel S1 event in the eastern Mediterranean Sea. Anoxic (>1,800 m water depth) to dysoxic (~500-1,800 m water depth) conditions were caused by enhanced water-mass stratification associated with increased freshwater input, enhanced eutrophication and reduced AdDW formation.

Reference: Fink HG, Wienberg C, Hebbeln D, McGregor HV, Schmiedl G, Taviani M, Freiwald A (2012). Oxygen control on Holocene cold-water coral development in the eastern Mediterranean Sea. Deep Sea Research Part I 62: 89-96.