Environmental Engineering Reference
In-Depth Information
the surrounding environment may survive and establish, increasing the risk of an
introduction occurring (Hopkins and Forrest 2008). As a result, in-water clean-
ing has been restricted or banned in some countries. An improved mechanical
brush system that simultaneously removes and collects biofouling from vessel hulls
is currently in development, with trials indicating its effectiveness at removing
and collecting up to 90% of biofouling from treated vessels (Hopkins and Forrest
2008). A prototype underwater vacuum device and cutting system was also devel-
oped and trialled for the removal of the invasive ascidian Didemnum vexillum from
vessel hulls, however this proved ineffective except as a means of biomass reduction
(Coutts 2002).
High pressure (>2000psi) spraying is another available technique for the phys-
ical removal of unwanted fouling species. h is was found to be eff ective at dislodg-
ing microscopic gametophytes of the Asian kelp Undaria pinnatifi da from marine
farming equipment and associated mussel shells (Forrest and Blakemore 2006).
In contrast, Canadian aquaculture farmers had less success in trialling water blast-
ing to remove the invasive sea squirts Ciona intestinalis and S . clava from mussel
lines, with damage incurred by both the mussels stocks and farming equipment
(Heasman pers. comm.). Although the use of high-pressure water jets is generally
considered an acceptable (environmentally friendly) and successful management
option under the right circumstances, it can be expensive and time consuming to
implement, and appropriate procedures are needed to prevent the re-release of AIS
back into the marine environment.
Physical removal may be a cost-eff ective eradication tool within natural habi-
tats, particularly in small discrete areas where a species distribution is limited. Over
larger areas however, these methods become expensive and time-consuming, and
may need to be repeated to ensure complete removal. Consideration must also
be given to any potential eff ects that mechanical and physical removal methods
may have on the habitats in question and associated fl ora and fauna. Manual and
mechanical removal of numerous algal pest species has been attempted with vary-
ing degrees of success. For example, small outbreaks of C . taxifolia (up to 200m 2 )
have been eradicated by divers manually removing the plants (Cottalorda et al .
1996; Meinesz 1999; Meinesz et al . 2001; Creese et al . 2004). Diver-operated suc-
tion devices have also been trialled for the control C . taxifolia in Australia (Creese
et al . 2004), Croatia (Zuljevic and Antolic 1999a,b) and the Spanish Mediterranean
(Meinesz et al . 2001). Removal by hand was successful in eradicating the seaweed
Ascophyllum nodosum from San Francisco Bay, primarily due to its early detection
and the relatively small area of infected shoreline (Miller et al . 2004). In contrast,
monthly removal of U . pinnatifi da by divers across an 800m 2 area in Tasmania
(Australia) was ultimately unsuccessful in eradicating the alga due to the persistence
of 'hot spots' of growth (Hewitt et al . 2005). Mechanical harvesting proved a viable
control measure for the alga Sargassum muticum in England, however this method
was costly, time consuming, labour intensive, and caused considerable physical
and ecological damage to the shoreline (Critchley et al . 1986). Containment and
disposal of collected materials also proved problematic. h e early detection of
 
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