Heavy issue: Biodiversity of fouling organisms

They have names like Blue Sponge and Yellow Ball sponge. They are often colourful and have interesting shapes such as that of a flower vase. And of course, some of us are probably familiar with the natural sponge we use for our bath. Beautiful and innocuous they may be, they are fouling our marine structures such as ship hulls, anchors and undersea pipelines. Often, they attach themselves to navigation buoys and weigh them down. In Singapore, as much as 50 per cent of the surface of marine structures underwater may be covered by sponges, besides other organisms such as barnacles, tubeworms, mussels and algae.






This is indeed, a heavyweight issue -- fighting fouling is important but so is conservation of biodiversity. An ideal anti-fouling agent is yet to be found -- one which can repel fouling organisms without harming them and the environment. One of the most effective anti-fouling systems, a paint containing an organotin compound known as tributyltin (TBT), is also one of the most toxic compounds synthesised by man, and a worldwide ban is being implemented. It is known to cause deformation in oysters and sex changes in whelks, amongst other deleterious effects.

EXPLORING THE WORLD OF ALIEN BIVALVES: Dr Tan Koh Siang examining Mytilopsis sallei. Taking the problem by the horns, researchers at the Tropical Marine Science Institute (TMSI) in collaboration with National Parks' Biodiversity Centre are, for a start, looking at the local phenomena. It is essential to know exactly what comprises the fouling community in Singapore to understand how to prevent fouling in tropical waters, said Dr Tan Koh Siang, Research Fellow at TMSI, one of the collaborators in this research project.

He and his team have started some four years ago, on a pioneer study on sponges with the aim to characterise the various species found in Singapore waters. So far, they have found about 70 species of sponges that can contribute towards fouling.

"Sponge larvae, like most babies of marine organisms, travel quite a bit, swimming and drifting with the currents until they eventually anchor themselves onto marine structures to grow into adults," Dr Tan explained. Sponges secrete their skeleton, a matrix of glass spicules and proteins, as they grow and these contribute to fouling. Currently, the best way to fight such fouling is still to scrape them off, a tedious and time-consuming job -- often costly as well. Navigation buoys, for example, have to be scraped and every two to three years because of such fouling.

"Many sponges are just known by their colours and shapes in Singapore. They are quite diverse but we really don't know that much about them even today. For example, we are not sure at this point in time whether they encourage corrosion of marine structures -- or actually slow down the process. Besides secreting their skeletons, they also secrete some unique chemicals and scientists now are trying to extract some of these chemicals for study. Some are already known to have anti-cancer properties," said Dr Tan.

"We need to identify them first of all before we can devise ways to stop them from fouling. Each species has its own ecological preferences. So, we are not only researching those responsible for fouling, but we are also looking at them in their natural environment," he added. The study has taken him and his team to various coastal habitats including rocky shores, seagrass meadows, mudflats, mangrove swamps and estuarine reefs.

Besides sponges, Dr Tan and other researchers at TMSI are looking at the biodiversity of other organisms which contribute to fouling in our local waters. These include molluscs such as snails, oysters, clams and mussels. One of the more intrepid clingers, the true oyster, cements one half of its shells firmly to the substratum," said Dr Tan.

Snails too, contribute to fouling. A particular group known as vermetids, attach their shells firmly to surfaces too, causing fouling. They secrete a mucus net to catch passing plankton for food.

Given the "global-ness" of Singapore, what we have in local waters may also be imports from elsewhere. Said Dr Tan: "We are also studying a certain group of clams known as Mytilopsis sallei. They come from the Gulf of Mexico. This Caribbean species look like a small mussel and can be seen today in the thousands on the walls of our monsoon drains. They are very resilient and proliferate rapidly, possibly finding their way into pipes and waterways too.

ALIEN MUSSELS: Mytilopsis sallei, which comes from the Caribbean region and now well-established in Singapore, are close relatives of zebra mussels (Dreissena polymorpha) from Central Asia. The latter species causes serious fouling of waterways and industrial cooling stations in the US and Canada. "In the United States and Canada, freshwater zebra mussels (called Dreissena polymorpha), which originated in Central Asia and are close relatives of the Caribbean species already established in Singapore, cause serious fouling of waterways and industrial cooling stations. So we must be alert now. We have started collecting data from monsoon drains to determine the population structure of Mytilopsis in Singapore, and we are also working with countries like India, Taiwan and Hong Kong in our study of the problem, looking at their invasion route."

Conservation however, remains the big picture for researchers. In the overall conservation of Singapore's biodiversity, the nation can only proceed if it knows what it has. TMSI researchers' findings on these lesser-studied organisms will certainly contribute to Singapore's conservation programme.

"Southeast Asia is the centre of biodiversity in the tropics. In collaboration with National Parks' Biodiversity Centre, we hope to have a better understanding of our marine heritage so that we can begin to tackle marine conservation in a scientific way," Dr Tan added.