Environmental Engineering Reference
In-Depth Information
the use of plastic encapsulation and smothering methods, although these are not
insurmountable (Table 14.1).
14.3.2.3 Physical treatment
A variety of heat-based methods have been developed for the treatment of nat-
ural habitats and artifi cial structures. Eradication of the sabellid polychaete
Terebrasabella heterouncinata
at a Californian aquaculture facility involved immers-
ing abalone shells in warm seawater to kill the polychaetes (Culver and Kuris
2000). Heated water was successfully used to eradicate gametophytes of the Asian
kelp
U
.
pinnatifi da
fouling the hull of a sunken vessel in the Chatham Islands, New
Zealand (Wotton
et al
. 2004). This work comprised sterilizing sections of the ves-
sel hull by attaching a plywood box lined with industrial electrical elements to the
side of the hull and heating the encapsulated water to 70°C. In addition, a fl ame
torch was used for inaccessible areas (e.g. near the seafl oor) and for areas with heavy
fouling. A similar
in situ
heat treatment method based on surface generated steam
supply has been applied to marina pontoons and natural rocky reef habitats, albeit
with limited success (Blakemore and Forrest 2007). Laboratory-based studies have
also suggested heat treatment as a feasibility method for disinfecting ballast water
(Mountfort
et al
. 1999).
Heat treatment, freshwater baths, and air-drying have all demonstrated poten-
tial for managing the transfer of marine pest species via human-mediated path-
ways such as aquaculture. Exposure of mussel seed-stock to hot water at 55°C
for approximately 5 seconds was eff ective in achieving complete mortality of
U
.
pinnatifi da
gametophytes, whilst having little eff ect on mussel survival (Forrest
and Blakemore 2006). Similarly, fresh water immersion resulted in 100% mortal-
ity of
U
.
pinnatifi da
on infected seed mussel ropes, without aff ecting mussel health
(Forrest and Blakemore 2006). As mussels and oysters can survive for extended
periods out of water, desiccation has been found to be a cost eff ective and envir-
onmentally friendly method to control fouling species. Mussel infrastructure (i.e.
moorings, warps, fl oats, and backbones) can be removed from the water, desic-
cated, and later returned to the same location (Forrest and Blakemore 2006).
Heat treatment is generally di cult to implement in open marine conditions,
unless fouled habitats can be isolated and have uniform surfaces (e.g. vessel hulls,
wharf pylons). It is also unlikely to be eff ective in controlling organisms with thick
coverings or shells (e.g. oysters; Nel
et al
. 1996). Heat treatment has the added
disadvantages of being impractical over large areas and damaging to non-targeted
species, although adverse impacts on the natural environment are likely to be
short-term (see Table 14.1). Logistic constraints in the procurement and use of
large volumes of freshwater in some marine environments (e.g. aquaculture farms,
isolated locations) may also limit its e cacy as a pest control solution.
14.3.2.4 Chemicals
Chemicals have been trialled with varying success for the control and eradication
of a range of AIS. In aquaculture, solutions of saturated salts (brine) and hydrated
