Shelly Biswell looks at the latest scientific efforts to control pests in our marine environment.
This summer, when you are on a pier or at a marina, take a moment to look just below the water's surface to see what's attached to the posts and other man-made structures around you.
Structures like piers, floats, and ship hulls have a "build it and they will come" effect on barnacles, sea squirts, sponges, seaweeds, and more.
Known collectively as "biofoulers", these pests can cause major problems once established.
"Biofouling compromises the integrity of artificial structures like wharves, piers, floats, and ship hulls through increased erosion and drag," says Cawthron Institute marine ecologist Javier Atalah.
The increased drag biofouling causes can reduce the fuel efficiency of boats and increases the likelihood of fixed structures being damaged or swept away.
Biofouling also spreads non-indigenous pests. When pests become established on ship hulls, for example, they are easily transported from one location to another.
While the economic impacts of biofouling are easily quantified, there are also associated ecological impacts.
In fact, the spread of non-indigenous biofoulers is arguably the biggest problem facing our marine environment.
"It has been shown time and again that non-indigenous biofoulers can reach plague proportions, causing havoc for native species through competition for space and food," says Dr Atalah.
Covering underwater structures with anti-fouling paints containing biocides is one way to deter biofoulers from attaching to a surface.
Releasing a biocide into the sea, however, can be extremely damaging to the environment.
The best known example of a biocide is Tributyltin (TBT) which was banned globally in 2008 because of its wider effects on the marine environment, including changing the sex of some fish and shellfish.
Non-stick paints that prevent foulers attaching to surfaces are available, but they are expensive and require strong currents to dislodge attached organisms, limiting their use to fast-moving vessels.
These paints also have limited lifespans and need to be frequently reapplied.
"Ideally, we would like to develop a formulation based on non-toxic natural ingredients that do not need to be released from the paint to be effective, thus providing long-term and environmentally friendly control of fouling," says Cawthron Institute scientist Patrick Cahill.
Dr Cahill is researching the natural defences of fouling-resistant species to see if some of those defences can be mimicked in a product to reduce biofouling.
"Mother nature may provide a ready-made solution to this complex problem. There are certain marine animals, sponges for example, that are stationary yet don't attract biofoulers.
"If we can figure out whether it's their surface texture, or a chemical they release, or some other quality they possess, we could artificially replicate that property to provide a natural solution to counter biofouling," he says.
Dr Atalah says another approach includes looking at native species that like to eat biofoulers for lunch.
"For the past couple of years we have been involved in research in partnership with Niwa to see if local predators of biofoulers could help in our fight," he says. "We have looked at marine snails, paua, kina, and sea stars with some good results on marina and wharf structures in the region."
To conduct the research, Dr Atalah and his colleagues are using "cages" to house predators on structures. So far a sea snail, the Cook's turban, is the clear winner of this unusual eating competition.
"They not only eat through the biofoulers, but keep them from coming back and they are extremely hardy."
Other species, like paua and sea stars, have voracious appetites but aren't as resilient or they escape. "The highly modified nature of most marinas and ports means that species need to adapt to high levels of pollution and fluctuating salinity levels," Dr Atalah says.
Eventually, the project team's research may influence the way piers and other structures are built.
"Engineers and industrial designers could build structures that can facilitate the establishment of predators or grazers such as sea snails."
While any type of biofouling can be costly, highly invasive biofoulers like the Asian kelp (undaria pinnatifida) and the clubbed sea squirt (styela clava) are of particular concern because they can alter natural biodiversity if they spread to uninfected areas.
That's where some of the same "biocontrol" species that Dr Atalah and other scientists are researching are already making a difference.
Kina, for example, may not stack up against sea snails so far at local marinas, but they have certainly done their part in Breaksea Sound, Fiordland to reduce undaria.
Since 2010, when an undaria plant was found in Sunday Cove, kina have been used as a biocontrol agent for this pesky seaweed.
More than 35,000 kina were transferred to Sunday Cove in an attempt to eradicate undaria. Indications are positive, with the Response Team on the project (Environment Southland, Ministry for Primary Industries, and the Department of Conservation) and the Fiordland Marine Guardians hoping that the highly invasive seaweed can be completely eliminated from the sound.
"It's still early days for some of the marine biocontrol research currently under way," says Dr Atalah.
"Preliminary results, however, suggest biocontrol measures are a good way to reduce or eliminate pests and cause less damage to the environment than other traditional methods."
Marlborough District Council biosecurity co-ordinator Jono Underwood agrees, but says when it comes to invasive species like styela clava, prevention is still the best course of action.
"Maintaining a good cleaning and anti-fouling routine for boats is critical to not only reduce biofouling, but also protect our waters from invasive species," he says.
"For boaties, using anti-fouling paint on your hull and regular cleaning and inspections should be incorporated into your expected maintenance of the boat. The aim is to have your vessel carrying no more than a light slime layer at any time."
- This is from the Science Matters series, contributed by Nelson's Cawthron Institute.