24 May 2010
The fossil record of soft corals dates back millions of years, but pollution of the oceans could significantly reduce the number and diversity of these important animals in a much shorter time frame.
"In the age of the dinosaurs, soft corals such as Sinularia species built the first coral reefs," says Dr Merrick Ekins from the Queensland Museum.
"Some individual reef building soft corals such as Sinularia could be hundreds of years old," he says.
Dr Ekins and his colleague Dr Monika Schlacher-Hoenlinger, also from the Queensland Museum, are focusing on soft corals during the CReefs Ningaloo expedition.
Soft corals are so named because most do not have hard external skeletons; instead many rely on hydrostatic pressure created by actively pumping water into their tissues for structural support. However gorgonians, also known as sea fans, do construct a solid internal axis of gorgonin, a proteinaceous horn-like material. Most soft corals also have hard sclerites, made from calcite, which provide additional structure. These sclerites also provide taxonomists with diagnostic characters that can be studied under a microscope for species identification. The soft corals are also known as octocorals, as they have eight tentacles fringing each polyp, as distinct from the six-tentacle morphology common to hard corals.
While most genera of soft corals are not reef-building, they play other roles, such as filtering water and providing habitat for other creatures.
Drs Ekins and Schlacher-Hoenlinger are collecting specimens of soft corals, looking for new species, and setting a baseline for the abundance and density of species by performing counts on transects: each transect is 5-metres long and the numbers of each species found within half a metre either side of the line are counted. The results allow Drs Ekins and Schlacher-Hoenlinger to determine which species are common or rare, and to compare between reefs.
While they have found less diversity on Ningaloo Reef than on the Great Barrier Reef, there have still been surprises.
"We are excited because we've found a Zignisis," Dr Schlacher-Hoenlinger says.
"This is not a new species – the genus is known from the west coast of Australia – but we haven't found it on any previous CReefs trips. It seems to be rare," she says.
"We won't know until we have identified the samples in the lab, but definitely there will be lots of new species from the CReefs project," she says.
But will these species of soft corals survive for another million years? Drs Ekins and Schlacher-Hoenlinger say that pollution could have a negative effect.
"Pollution and turbidity can affect the health of soft corals," Dr Ekins says.
"If there's construction on land and you get more run-off and sediment, it's likely to change the species makeup in an area. Some soft corals are partially photosynthetic, so if the water becomes dirtier, those species will be affected," he says.