Biofouling

ALIEN SPECIES ALERT: Candy-cane colored organism residing on ship hull is an ascidian aka tunicate (Herdmania momus).  Photo by Hawaii DLNR, Division of Aquatic Resources.

How many alien marine algae and invertebrate species reside in Hawaii? Up to 346 alien marine algae and invertebrate species are currently established in Hawaii State waters; they have arrived through various vectors of transfer including, but not limited to, aquaculture intentional/accidental release, unmanaged ballast water, and vessel biofouling.  It is estimated that up to 78% of the alien marine algae and invertebrate species have arrived to the islands by vessel biofouling.

What is vessel biofouling?  Vessel biofouling is the attachment of organisms to wetted areas of a ship or boat, usually below the waterline; this can include the hull, propeller, bilge keel, keel coolers, thruster, inlet gratings, anodes, sea chests etc.  Besides from being a biosecurity risk to the environment, biofouling can drastically reduce fuel efficiency, increase vessel output of carbon emissions, and compromise crew safety during transit.

What methods are used to prevent biofouling on vessels?  Biofouling reduction is primarily achieved through the use of marine coatings, applied in dry dock at regular intervals, which work either through chemical or mechanical means to discourage attachment or accumulation of fouling. 

However, not all organisms are deterred by marine coatings such as the bryozoan Watersipora subtorquata, which settles readily on the copper paint that is toxic to most marine life, facilitating settlement by other organisms that can attach to the bryozoan.

ALIEN SPECIES ALERT: Orange-rust colored biofouling on propeller is a colony-forming organism called a bryozoan (Watersipora subtorquata). Photo by Hawaii DLNR, Division of Aquatic Resources.

Furthermore, all coatings have a limited performance life, and their efficacy diminishes over time.  Periodic removal of biofouling to enhance vessel operation and prolong coating performance is a routine part of ship husbandry. Typically, this is done in-water between dry dockings; in-water cleaning is faster and far less expensive compared to hauling out the vessel and cleaning in a dry dock.

What are the biosecurity risks of in water cleaning operations on a vessel?  While in-water cleaning (hereafter IWC) is an effective way to reduce biofouling extent, and thus reduce the likelihood that a ship will transport species, it also presents a risk of contaminant release if paint particles are removed during cleaning. In addition, if the fouling on the ship is not of local origin, IWC presents a potential biosecurity risk through the release of viable organisms as adults, juveniles, viable fragments, resting stages, and gametes into the water where cleaning is performed. Many species, including sponges, tunicates and algae can survive cleaning and regrow from small fragments after being released from a ship’s hull.

 

For the current update on Hawaii Invasive Species Council in-water Cleaning Resolution, please visit IWC Resolution Update February 9, 2018

For questions related to ballast water or hull fouling (vessel biofouling), please contact Jules Kuo (Hawaii Ballast Water and Hull Fouling Coordinator): [email protected]