During the late 1970's, researchers discovered and elucidated deep-sea vent ecosystems. The picture was one of large tube worms, mussels, and other animals that lived on the chemical energy put forth by these vents. Now, researchers are finding that these communities are more diverse than originally believed.
For example, in the vents near Antarctica on the East Scotia Ridge tube worms and mussels are not present. Instead, piles of hairy crabs are found by the thousands. Crabs normally die in polar waters because they cannot expel magnesium from their blood in the cold. But, that problem is minimized as they swarm around vents pouring forth 380 C water. Along with the crabs researchers found barnacles, limpets, snails, and a predatory 7-armed starfish. The researchers speculate that the extreme cold and seasonal swings in Antarctic waters exclude the mussels and shrimp because their larvae need to feed at sea upon hatching.
Along the Southwestern Indian Ridge in the Indian Ocean new seafloor is being created at one of the slowest rates in the world. But, in 2007, researchers found vents at an average density of 2.5 vents every 100 kilometers, which was 2-3 times that which was expected. Here, instead of one species dominating (as is usually seen at vents), there are at least several species in approximately similar densities: shrimp, scaly-footed snails, and yeti crabs, among others.
In the Cayman Trough in the Caribbean Sea volcanic activity has been manifesting for 50 million years. 3.1 million years ago the Isthmus of Panama closed, cutting off direct circulation between the Atlantic and Pacific Oceans. Yet, the Cayman animals resembled not those of the Pacific or the closest cold-water seeps 1,500 kilometers away in the Gulf of Mexico, but those at the hot-water vents along the Mid-Atlantic Ridge, approximately 4,000 kilometers away. The dominant species at a hot-water vent 4,970 meters down was a new type of shrimp.
Prior posts have noted some possible mechanisms for the movement of animals between vents. These new studies show how much is still left to learn about deep-water ecosystems.
The relevant reports can be found at http://www.ncbi.nlm.nih.gov/pubmed/22233630, http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001234, and http://geology.gsapubs.org/content/40/1/47.abstract.