The Featured Article for the March 2009 issue of L&O is:
Davies, Andrew J., Gerard Duineveld, Marc Lavaleye, Magda J. Bergman, Hans van Haren, and J. Murray Roberts. 2009. Downwelling and deep-water bottom currents as food supply mechanisms to the cold-water coral Lophelia pertusa (Scleractinia) at the Mingulay Reef Complex. Limnol. Oceanogr. 54(2): 620–629.
This article can be read by clicking here.
Warm-water coral reefs are so eye-catching and visible—the Great Barrier Reef is said to be the only organic structure on the planet that can be seen from outer space—that we tend to forget that there are coral reefs of a very different kind in deeper and colder waters. The featured paper in this issue of L&O draws our attention to these structures and presents vital clues as to how the many mouths of a deep-water coral community in the North Atlantic Ocean, dominated by the colonial scleractinian Lophelia pertusa, are maintained and fed.
Deep water coral reefs are found on continental shelves and slopes at depths below 100m, where there is not enough light to sustain algal symbionts, as is the case in tropical and subtropical coral reefs. Yet deep-water corals thrive: many reefs have been in existence over geological time-scales and have laid down carbonate mounds several hundreds of meters in thickness. An important question has been just how these deep-water corals obtain food. This is not an easy question to answer because their inaccessibility and the exposed nature of such sites has made direct observation for periods long enough to yield answers difficult.
Davies et al. used current meters and sensors on landers and moorings to obtain vital clues that address this question. Over two years, they studied currents, temperature, turbidity, and fluorescence at Mingulay Reef at a depth of 140 m in a relatively shallow strait between the Outer Hebridean Island chain and the Scottish mainland. This enabled them to determine particle supply to the coral community. They found that there are two major mechanisms for supplying organic particles to the hungry coral mouths. The first consists of a tidally-driven process that sucks surface water down to the coral community within an hour at the onset of ebb and flood tides. The second is the upwelling of deeper water, bringing with it a high load of suspended organic matter. These processes combine, usually at peak tides, to deliver particles to the reefs.
Deep-water reefs exist on canyons, slopes, and seamounts and in much deeper waters than this one. This study provides, for the first time, important clues as to how such communities depend strongly on the interplay between water flow and bottom topography to supply the food particles and larvae on which these communities depend.
Beginning with the May 1999 issue of Limnology and Oceanography, selected articles have been made available for reading or download on the L&O Website a few weeks in advance of when the printed issue is mailed. Featured Articles receive no special attention in the printed issue. Each Featured Article is announced to the LO-Feature Mailing List, accompanied by an introduction to the article discussing its significance.