Detoxification of sulphidic African shelf waters by blooming chemolithotrophs

Algae that bloom unnoticed Data obtained by RV Alexander von Humboldt in waters off the Namibian coast reveal that an area of about 7,000 km2 of African coastal shelf, covered by sulphidic water, was detoxified by the action of bacteria: the biologically harmful sulphide was oxidized to non-toxic colloidal sulphur and sulphate. Eutrophication of coastal waters, often due to human activity, can lead algal blooms causing severe oxygen depletion and the episodic occurrence of hydrogen sulphide with disastrous consequences for the ecosystem. The discovery that sulphide can be completely consumed by bacteria in subsurface waters, and can thus be overlooked by remote sensing or monitoring of shallow coastal waters, suggests that sulphidic bottom waters on continental shelves may be more common than was thought, so could have an important but previously neglected effect on benthic communities.