Cold Water Reefs Fuse in a Rare Example of Deep-Sea Cooperation

Tropical coral, the iconic face of coral life everywhere, fuse together with the help of calcareous algae that grow on the crust of the unusual animals' dead branches. However, not every species of coral colonizes in this manner. A new study on cold-water corals has found that even unrelated species can fuse in a unique process that does not require the help of a third party, making for some beautiful combinations of shape and color.

Sebastian Hennige at the Heriot-Watt University Edinburgh recently led a study of stony cold-water corals (Lophelia pertusa) with several international colleagues.

He explained in a recent release how his interest in these unique kinds of corals was initially piqued during an expedition with the German research submersible JAGO.

"Normally it is very hard to see where one coral ends and another begins. But on our dives with JAGO, we were able to find reefs where orange and white types of the coral fused together," he explained. "Coming from a tropical coral research background, seeing coral fusing like this instantly grabbed my attention."

Hennige and his colleagues took samples of these cold-water corals so that they could conduct DNA and structural analysis. They found that surprisingly, these corals were a fusion of different individual colonies, which boast their own colors and structures.

These results were detailed in the journal Scientific Reports.

With these results, the researchers suggest that unlike their tropical counterparts, cold water species actually recognize and join with other members of their own species, even when it is a colony from an utterly different family.

"They seem to have found another way to attain stability," added co-author Armin Form. "Either the corals actually fuse and form a joint stock, or a branch grows over another one without interference."

The researchers add how tropical corals - which dwell much closer to the water's surface - are far more competitive among their own species, releasing chemicals to prevent contact with other colonies. However, this defensive action takes a lot of energy - energy that the researchers suspect corals cannot afford in the deep sea.

So instead these cold-water corals share space and resources, supporting one another even while their tropical cousins squabble over space up above.