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Behavior

Too Slick to Stick

Have you ever walked down a dock to look at the boats? How about under the boat? The sides? Chances are you’ve probably seen a few things growing on the boat wherever it is submerged underwater such as barnacles or algae. This is known as biofouling, the unwanted accumulation of plants and animals on a submerged surface.

A boat pulled out f the water and standing on land exposing the propellers and hull which are covered in various fouling organisms.

Biofouling, the unwanted accumulation of plants and animals on a submerged surface, has been problematic for the shipping industry throughout history. Picture credit: Jean-Pierre Bazard

What you may not know though, is that the growth of these unwanted plants and animals can have some negative impacts on the shipping industry. These include an increase in drag, fuel consumption, greenhouse gas emissions, potential invasive species transport, and a decrease in overall vessel efficiency. It has been estimated that there can be about a 40% increase in fuel consumption from the resulting drag associated with vessel hull fouling. In addition, the global shipping industry estimate for the cost associated with biofouling is around 30 billion USD per year. With such negative impacts from small organisms, it’s no wonder there has been so much effort put into finding biofouling prevention methods. One antifouling compound was particularly effective for a long time, but it came with some unintended consequences.

Antifouling Magic…at a Price

Tributyltin (TBT) was once used to combat these fouling problems; however, as effective as it was at preventing biofouling settlement, it had major environmental impacts. TBT had toxic effects on marine ecosystems which resulted in it being banned from antifouling ship hull paints globally in 2008. This resulted in many organizations looking for other more environmentally friendly and effective ways to prevent fouling.

Mussels with their byssal threads attached to the ground and other mussels.

Mussels, a filter feeding animal that is a common fouling organism, use their byssal threads to attach to a surface. Picture credit: Emily Carrington

One concept for a more environmentally friendly antifouling method is Slippery Liquid Infused Porous Surfaces (SLIPS). SLIPS are a result of a strong chemical attraction between the surface and an applied lubricant. Experiments have shown that synthetic oils and lubricants applied to these SLIPS are very effective at not only deterring the settlement of mussels, but also reducing the strength of the attachment threads of the mussels. While these synthetic oils maybe more environmentally friendly than TBT, synthetic oils tend to be fluorinated and the leakage of these chemical compounds over time into the marine environment is still concerning.

Biolubricants

The researchers of this study wanted to see if more non-toxic and eco-friendly fatty acid based biolubricants could be as effective as the synthetic ones. To carry out this research, seventeen Asian green mussels were scattered in a tank onto each checkerboard choice assay (the different SLIPS test surfaces were aligned in a checkerboard fashion) and mussel movement to certain tiles was observed for two weeks. Then the strength of the mussel was measured for each surface attachment.

A bunch of Asian green mussels where some are submerged and water and others are exposed to the air.

Asian green mussels are native to Indo-Pacific waters, but they have been introduced outside of their home range and are now considered an invasive species in many areas. As such, these mussels have become a problematic biofouling organism in the places they have been introduced. Picture credit: Tord Remme

After two weeks in the tank, the mussels formed into two distinct clusters on each of the three checkerboard tiles. This movement of the mussels demonstrates that the mussels were selecting a surface they preferred and were more repelled by the biolubricant SLIPS test surfaces. The adhesion strength of the mussel also decreased for these test surfaces when compared to the control.

Brownie Points for Being Eco-Friendly

These results indicate that the biolubricant SLIPS test surfaces are just as effective as the synthetic oil ones. This is exciting because these environmentally friendly biolubricants can be utilized for the same purpose of antifouling, but without the drawbacks of potential negative environmental impacts.

Paper: Basu, S., Hanh, B. M., Chua, J. I., Daniel, D., Ismail, M. H., Marchioro, M., Amini, S., Rice, S. A., & Miserez, A. (2020). Green biolubricant infused slippery surfaces to combat marine biofouling. Journal of Colloid and Interface Science, 568, 185-197.

 

Hello! I’m a PhD student at the Florida Institute of Technology. The lab I work in focuses on ecological engineering along with marine corrosion and biofouling control. I’ve enjoyed working in the fields of environmental education and outreach. When I’m not working in the lab, I enjoy reading, volleyball, and photography.

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