Bright and beautiful
12 September 2010
The Octocorallia, or soft corals, are not only diverse in their taxonomy – there are approximately 3000 species known in the oceans worldwide – they are also diverse ecologically.
Sea pens, of the octocoral order Pennatulacea, for example, have a feathery structure, grow up to two metres tall, feed primarily on plankton, and are found in deep tropical or temperate waters, sometimes at depths of 2000 metres. Some species are bioluminescent – when touched they can emit a greenish light.
Octocorals of the order Gorgonacea, however, can be fanlike or bushy, brightly coloured, often red or purple, and are found in tropical waters. Some gorgonian species gain energy through a combination of photosynthesis through creating symbiotic relationships with algae and feeding on plankton.
And blue corals, of the order Helioporacea, produce massive skeletons of aragonite, a carbonate mineral, and the polyps live in tubes within the skeleton. They occur largely on shallow coral reefs in the Indo-Pacific.
Among the great diversity of soft corals, octocoral expert Dr Monika Schlacher-Hoenlinger and Collection Manager Dr Merrick Ekins of the Queensland Museum have some favourites.
"I like the huge fans, candelabras and whips of the gorgonians," Dr Schlacher-Hoenlinger says.
Dr Ekins agrees the gorgonians are "stunning" but adds to the list.
"I like the Sarcophytons: they are mushroom-shaped corals. Xenias are also very pretty: the polyps look like little flowers and you can see them open and close," he says.
Drs Schlacher-Hoenlinger and Ekins are focusing on soft corals during the CReefs expedition. They take small pieces of corals for identification using morphology (the study of the shapes, structure and anatomy), microscopy of the sclerites, and molecular biology (DNA analyses).
This is their second CReefs trip to Lizard Island, and they believe they have now collected examples of many of the shallow-water genera known in Australia.
"Lizard Island is very diverse for soft corals. Last year we sampled widely and collected about 400 specimens. This time we tried to find specimens that we didn't find before," Dr Schlacher-Hoenlinger says.
"We have a piece of Paraminabea, which is uncommon. They usually live deeper than 30 metres, but can be found in shallower waters in caves and under overhangs. They like the dark. We haven't seen one with its polyps out; they may only come out at night," Dr Ekins says.
Drs Schlacher-Hoenlinger and Ekins have also collected pieces of corals of the genus Chondronephthya and the genus Siphonogorgia, which are not commonly found.
While the rare species might be more exciting to find, Drs Schlacher-Hoenlinger and Ekins say there is also still more to be learnt about common genera. They have collected many specimens of the widespread genera Lobophytum and Sinularia around Lizard Island, but say that further laboratory study will be needed to identify some species.
"Often, two specimens of the same species can have different morphology depending on their location on the reef, the turbidity, current and other factors," Dr Schlacher-Hoenlinger explains.
Dr Schlacher-Hoenlinger and Ekins are contributing subsamples of DNA from every specimen they collect to Dr Abigail Fusaro, a representative of the Ocean Genome Legacy on the CReefs Australia project.
"One of the advantages of being in the CReefs project is that the Ocean Genome Legacy is going to sequence our samples, and this will assist us to identify samples of corals in the future," Dr Ekins says.