|entioning corals conjures
up the warm, shallow, turquoise waters of the tropics. But some species inhabit dark, cold, nutrient-rich waters in virtually every ocean on Earth. But as these cold-water corals are more remote than their warm-water cousins, and usually live in relatively inaccessible areas like the edges of the continental shelf and water sometimes hundreds of metres deep, it is only recently that scientists have been able to examine them more closely.
These corals form habitats just as large and complex as the more familiar warm-water corals, including reefs and forest-like gardens in otherwise rather featureless and murky surroundings. In the darker, colder waters, they cannot rely on algae for their nutrients, but live on organic matter floating by on the currents. It is the absence of algae in their tissues that makes these coral communities less colourful than the reefs of warmer environments; nevertheless they provide habitats for thousands of other species, including commercial fish.
Indeed, commercial fishing poses the greatest threat to them. Take the common practice of bottom-trawling, when a fishing boat drags along the seabed a net held open by metal trawl doors to catch bottom-dwellers such as flatfish and crustaceans. The doors, which can weigh several tonnes, smash into corals and stir up sediment, often destroying or severely disrupting the reef ecosystem.
Exploring for and producing oil and gas, laying cables and pipelines and the dumping of wastes also pose threats. And because the corals - some up to 8,000 years old - are slow growing and fragile, it may take centuries for these treasure troves of biodiversity and economic worth to recover.
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