3.4 HULL FOULING ORGANISMS

The term "fouling organisms" is usually used to describe sessile organisms [or organisms that attach directly to an object without use of a stem or stalk] which attach to suitable substrates and remain fixed for the duration of their adult lives. In this report, the term also includes any non-sessile organism capable of clinging to a submerged part of a ship and being transported from one place to another. For example, sea stars and crabs may "hitch a ride" by nestling amongst encrusted species on heavily fouled vessels or by hiding in small apertures and pipes.
Fouling organisms can be divided into two main groups;
i) micro-organisms such as bacteria, diatoms and algae that form the "primary slime film"; and
ii) macro-fouling species such as molluscs, sea squirts, sponges, sea anemones, bryozoans, tube worms, polychaetes and barnacles.
It has been suggested that the primary slime film is a prerequisite for the subsequent attachment of macro-fouling species²⁸ although individual species vary widely in their responses to these films²⁹.
Most fouling organisms produce eggs or spores which are broadcast into the water column for external fertilisation or released as brooded larvae. Depending on the species, planktonic larvae can remain viable in the water for periods ranging from a few hours to several weeks or months. This means that fouling species may be transferred by ballast water during the larval stage of their life cycle.
The microscopic larvae seek a suitable surface for settlement where they attach and mature into adults. The intensity of fouling can vary with a number of factors including salinity, temperature range, light and water movement. While species vary widely in their settlement seasons³⁰ most fouling organisms spawn in spring and summer due to rises in sea water temperatures³¹ These factors should be taken into account when assessing the risk of transfer of specific fouling organisms, either by ballast water or on hulls.
Wharf pylons are usually heavily fouled and would, at certain times of the year, provide a source of larvae in close proximity to berthed ships. Conversely, larvae emanating from encrustations on a fouled vessel could readily settle onto nearby pylons or other vessel hulls. Larvae with extended periods of viability could disperse long distances from the parental site and settle on other ship hulls and pylons in the port.
Organisms of particular concern because of the possibility of translocation between domestic ports in Australia via hulls (and/or ballast water) are Undaria pinnatifida (Japanese kelp); Sabella spallanzanii, (Sabella worm), Carcinus maenus (European shore crab); Asterias amurensis (northern Pacific sea star); and Musculista senhousia (Asian mussel). [These species are considered in detail in Chapter 4.4 of this report].
The introduction of less visible (or less high profile) organisms could also have important implications for native communities of encrusting species. These impacts are difficult to predict due to the complexity of interactions in marine ecosystems. Any introduced fouling organism poses a risk to the marine ecosystem into which it is introduced.