Biological invasions are widespread throughout the world’s oceans, with many of these invasions occurring as a result of human-mediated mechanisms.
Marine vessels are largely responsible for facilitating the movement of aquatic pest species across bioregions, as small marine animals and plants easily attach to the submerged surfaces of a vessel, as it moves through the water.
The build-up of of microorganisms, plants, algae, or animals on artificial surfaces (also known as biofouling), has long been recognised as a mechanism for the introduction of non-indigenous marine organisms. Biofouling presents a major biosecurity risk to Australia. It has potential to, not only, contaminate marine waters, and increase invasion of non-indigenous taxa that compete with native species, but it also places an economic burden on the country. It is estimated that 75% of introduced marine species have established in Australian waters, as a result of biofouling on marine vessels.
Biofouling is especially problematic for underwater structures, such as seawater intake pipes, cables, fishing nets, and jetties.
It can also greatly impact on boating performance and durability, and create significant drag to a boat’s movement as a result of the heavier weight from the accumulated microorganisms. In addition, biofouling can increase the risk of mechanical failure, as the buildup of growth can move its way into hull openings and affect moving parts like propellers and rudders. The presence of biofouling increases vessel maintenance costs, as cleaning operations required to combat the build-up of scum need to be more frequent and over more prolonged periods of time. These cleaning processes also generate high volumes of poisonous substances that are released into the ocean.
The degree of biofouling which occurs on a vessel depends on numerous factors such as, the level of biofouling already evident, the vessel’s maintenance history, the presence of an anti-fouling coating on the vessel, whether the settlement onto the boat surface coincides with active reproduction of organisms, and the amount of time available for a species to settle onto a spot. Biofouling also tends to be more predominant in areas with high water temperatures, as warmer conditions are favourable for breeding and increasing rates of growth.
Biofouling management is a difficult issue to address, as marine organisms can settle onto a submerged vessel almost immediately after it has been cleaned, with it taking only a few weeks for these organisms to evolve into a complex biological community.
This fast rate of development can be delayed through adequate cleaning and maintenance and the adoption of antifouling methods (either chemical, biological or physical). Modern anti fouling methods primarily use antifouling paint, a commercially available underwater paint that is applied to the outer layer of the hull of a ship or boat. This coating acts as a barrier against corrosion, slows down the growth of organisms, and encourages their detachment to the surface they have become affixed to. The correct application and maintenance of antifouling paint is highly recommended to prevent the build-up of biofouling, however, this action must also be followed up with appropriate removal and disposal of the coatings which may contain harmful substances, which can deleterious effects on the environment.
Vessel operators are reminded to apply the principles of the National Biofouling Management Guidelines for Recreational Vessels, in order to establish best-practice methods to minimize the impact of biofouling on Australian waters.
Vessels that have been in contact with seawater at their last port of call or within one week prior to arriving in Australia, must ensure that they clean their vessel’s hull, and internal seawater systems, to remove any accumulation of marine growth.
Ideally, biofouling removal should occur prior to departure in the location where it was acquired. Where practical, vessels should be removed from the water for cleaning and maintenance, as opposed to cleaning in-water, which can damage anti-fouling coatings, reduce the service life of the coating, and contaminate the water due to accidental release of potentially toxic substances and invasive aquatic pests.
It should also be conducted at a registered haul-out facility utilising a high-pressure water cleaning system.
The hull should be sprayed with an effective anti-fouling coating that is no more than 12 months old, and particular attention should be focused on cleaning the following areas:
- Ancillary gear – During extended port stays, biofouling can build up and attach to ancillary gear. Routine maintenance is recommended any ancillary gear that has in in contact with seawater.
- Internal Water System– Port environments provide ample opportunities for aquatic life to enter internal seawater systems, such as engine cooling, toilet flushing and galley sinks.
- Underwater hull areas– These areas are at increased risk of biofouling, particularly when exposed to prolonged periods of submersion in seawater.
While anti-fouling is a laborious and expensive process, it is a wise investment. A regular maintenance program for antifouling your vessel will also reduce inspection time, if you have been travelling across multiple bioregions and intend on returning to Australia.
Inspection and maintenance should be carried out regularly, and the cleaning program should be accompanied by a voyage history and biofouling maintenance log, which will permit the operator to keep up to date with hull cleaning and anti-fouling renewal.