There Goes The Neighborhood

As far as housing markets go, coastal marine ecosystems are far scarier than the worst sub-prime foreclosure ridden neighborhood you could think of. Competition for space is intense. Most of your neighbors are out to get you--or eat you. And just when you think you've got a reinforced, exoskeletal leg up on things, somebody figures out a new way to crack your chitin. (Apologies for the forced metaphors!)

Don't like the rough and tumble coast? There's always the deep cold abyss. And that's pretty much been the direction, from shallows to the deep, that ecologists have thought marine migrations have occurred. Those species less equipped for the fight have often taken refuge in deeper water. But at last week's AAAS meeting in Boston, a biologist presented the first strong evidence that some corals have taken the opposite path, rising from the deep to invade shallow water several times.

Stony, reef-building corals are classified in the Cnidarian class Anthozoa. But another class of corals, the Hydrozoa, are often mistaken for hard corals because they are very similar in appearance. The most commonly recognized species of Hydrocorals are Fire Corals and Lace Corals. Unlike their frame-building Anthozoan relatives, Hydrozoans grow attached to the reef, adding greater niche complexity to the overall reef structure and modifying the flow of water over the reef.

Fire Corals were given their name because they have hairlike structures called dactylozooids which contain nematocysts that produce toxins which can cause painful stings that can feel like mild to severe burns. They use these nematocysts to sting and paralyze prey, as well as for defense against predators such as seastars. Fire corals are commonly found in areas of the reef which have high light intensity and strong currents.

Lace corals also have hard skeletons, but are much more delicately branched than Fire Corals. Their sting is less severe than that of the Fire corals and they are commonly found in shaded areas of tropical reefs, preferring areas that receive strong current flow. But Lace corals--like the specimen of Cyclohelia lamellate in the image at the top of this post--are also known from deep ocean ecosystems as well, as deep as 2800 meters. Alberto Lindner of the Universidade de São Paulo, Brazil, collected samples of Lace corals from around the world, mainly from fishing trawlers that had snagged the corals and from scientific dredging.

After sequencing and compared their DNA, he and colleagues determined that the shallow-water Lace corals evolved from relatives in deeper water. In fact, they have invaded the tropics three times and the temperate waters once. Two lineages gained enough of a foothold to thrive and diversify. Lindner plans to publish his findings soon.

Source: ScienceNOW Daily News
16 February 2008