The importance of soft corals in a coral reef ecosystem, especially in regards to global warming

Original publication mainly cited in this article published here.

Modern coral reefs consists of hard (scleractinian) and soft (alcyonacean) corals, of which the hard corals are believed to be the major reef building corals. Both corals generate strong calcium skeletons, and it is the pile up of these skeletons over generations that builds up a reef. Hard corals tend to build up their skeletons more so than soft corals, which often only has the calcium skeleton as the base.

However, in an archetypical quantity versus quality situation, Renata Ferrari from the University of Sydney, Australia; in a project funded by the Great Barrier Reef Foundation, has identified that individually, soft corals may in fact play a more important role than hard corals as habitation structures.

Images from the publication illustrating the structure of soft coral skeletons, and how reef fish uses them as shelter.

While skeletons of hard corals are inarguably more widespread, it was uncovered by Renata that the structure of soft coral skeletons are intricately made of spiculite and carbonate calcium, which can provide better habitation for fish and hence inhabited by a higher diversity and abundance of fish.

The implications of this is quite profound. The diversity and abundance of fish around soft coral skeletons are found to be similar regardless of whether the actual soft corals themselves are alive or dead. This means that areas of high soft coral density can allow fish to thrive, or at least better survive through coral bleaching events, such as the massive one in 2016 at the Great Barrier Reef. Even when the actual corals themselves have died, what’s left behind can still house the same fish. In contrast, over the same coral bleaching event reef fish associated with soft tissued cnidarians saw a major decline in numbers, such as in the case of the anemonefish Amphiprion melanopus as published here.

However, this finding should only be regarded at arm’s length, as the discovery is still implicative. From the article, it is hard to tell just how many coral skeletons were inspected, nor if it may be specific to any particular taxonomic group of coral. Renata did conclude simply though, that soft corals and hard corals should both be taken into account in future ecological studies, which I am in agreement with.

We often rely too much on simple numbers, and take the majority as indication for importance. However the biological sciences, especially in the field of ecology, as many times proven that there is always more than meets the eye.