Abstract
White coral communities consist of scleractinian corals that thrive in the ocean’s bathyal depths (~ 200–4000 m). In the Atlantic Ocean, white corals are known to form complex, three-dimensional structures on the seabed that attract vast amounts of other organisms, accumulate suspended detritus, and influence the local hydrodynamic flow field. These attributes coincide with what we generally describe as a coral reef. With time, environmental change causes decline of the framework-constructing corals; this is followed by erosion of the reef sequence or its draping with noncoral-related deposits. After several such sequences, the structures are known as coral carbonate mounds, which can grow as high as 350 m. Both bathyal white coral reefs and mounds are widely distributed in the Atlantic Ocean and adjacent marginal seas, such as the Gulf of Mexico. The Mediterranean Sea, however, known for its richness of fossil white coral communities exposed in land outcrops, harbors very few extant coral communities. The HERMES project extended its study sites deep into the Mediterranean with state-of-the-art mapping and visualization technology. By doing so, many previously unknown coral sites were discovered during inspections of Mediterranean narrow shelves, canyon walls, escarpments, and seamounts by remotely operated vehicles. Such shelf and continental margin settings are characteristic of the dynamic margins of the Mediterranean Sea and contrast significantly with the much broader shelves of the Atlantic Ocean. This paper reports on a HERMES cruise that was dedicated to exploring these rough submarine topographies in search of white coral communities in the central Mediterranean, and re-evaluates the general perception of the assumed paucity of white corals in this sea.
Highlights
The White Cor al C o mm unity The term “white coral” community is local jargon first used by high-seas fishermen to distinguish the “white” Lophelia pertusa and Madrepora oculata from the “yellow” Dendrophyllia cornigera and D. ramea in the Atlantic Ocean
The North Adriatic Dense Water (NAdDW) flows south and cascades into the sub-basin along the southwestern margin of the Adriatic sub-basin, where it mixes with the Adriatic Dense Water (ADW), which is formed through winter deep convection here
The remotely operated vehicles (ROVs) dives performed during R/V Meteor cruise M70-1 yielded evidence of far more living white coral occurrences than previously thought for the central Mediterranean Sea
Summary
By André Freiwald, Lydia Beuck, Andres Rüggeberg, Marco Tav i an i , DierkHe bb e l n , an d R / VMeteorCruiseM 7 0 - 1 Pa rtici pant s. The major source of information on the distribution of Mediterranean deep-water corals is based on scientific and fishing dredge and trawl hauls—a method notorious for its biases in terms of precise positioning, catch selectivity, and destructive effect on benthic communities Knowledge of these communities has steadily grown in recent years due to dedicated, cooperative geological and biological deep-sea projects, including much needed visual inspection of Mediterranean deep-water coral habitats using manned submersibles and remotely operated vehicles (ROVs). The White Cor al C o mm unity The term “white coral” community is local jargon first used by high-seas fishermen to distinguish the “white” Lophelia pertusa and Madrepora oculata from the “yellow” Dendrophyllia cornigera and D. ramea in the Atlantic Ocean This deep-water coral assemblage was frequently encountered in trawl hauls conducted in the canyon-rich Bay of Biscay continental margin (see review by Reveillaud et al, 2008). Living White Cor al Communitie s in the Mediterr ane an Se a The true extent of the white coral community in the Mediterranean Sea is poorly known and the relatively few verified records of live L. pertusa and M. oculata exhibit a scattered distribution pattern rather than a belt
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