Walvis Ridge

The Walvis Ridge is an underwater mountain range spanning from the Mid-Atlantic Ridge to the continental shelf of Namibia. The origin of this sea ridge is argued. Some propose it has been formed by the Tristan Hotspot, where lava has been spilling out onto the expanding sea floor. Others suggest that the Walvis Ridge developed as a result of intermittent stress release along the sea floor.

Not many scientific expeditions have studied the biota of the Walvis Ridge. The earliest specimen of Lophelia pertusa was dredged from the Walvis Ridge in 1982 during the Valdivia I scientific cruise. A later cruise in 1984, the Benguela VI, also sampled Lophelia pertusa from Walvis Ridge. Other hard coral species such as Deltocyathus sp. were dredged up on both expeditions. A further cruise in the same year, by Benguela VII, sampled corals such as Deltocyathus sp. and Stephanocyathus sp. but not Lophelia pertusa. All Lophelia specimens were dead skeletons, with no evidence of living polyps. However, living specimens of other hard corals were found, including that of Stephanocyathus campaniformis.

More recently, a scientific research cruise in 2015 has discovered that the Walvis Ridge hosts many living coral colonies but of a patchy distribution. They also confirmed that living specimens of Lophelia pertusa are present on the seamounts. However, it was discovered that the coral species Enallopsammia rostrata is much more common, as are Gorgonian corals, which could not be identified to species level. Diverse coral gardens exist on southern slopes of some Walvis ridge mounds, but they are often small and patchy. One seamount in the ridge, the Ewing Seamount, exhibits high numbers of dead coral. These skeletons are still largely erect and so it is thought that the death is relatively recent.

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