Environmental Engineering Reference
In-Depth Information
continued incursion, establishment, and spread of marine invasive species is inev-
itable (Wotton and Hewitt 2004). Ongoing surveillance and monitoring is there-
fore vital to detect new species arrivals, and to allow the management response to
commence immediately. If the opportunity to rapidly respond is missed and the
invasive species becomes widely distributed, it will be di cult, if not in most cases
impossible, to eradicate. In the few documented examples of successful marine
pest eradications, the target pest was always detected at an early stage and its dis-
tribution was restricted to a localized area or habitat (Culver and Kuris 2000; Bax
et al
. 2002; Kuris 2003; Miller
et al
. 2004; Wotton
et al
. 2004; Anderson 2005).
In instances where exclusion and eradication of new invaders fails, and contain-
ment at the point of incursion is no longer an option, prompt and clear decisions
must be made on the best management end point for a given situation. A key con-
sideration is whether or not spread can be prevented and, if not, whether incursion
response is desirable (Forrest
et al
. 2006). For example, in the case of aquaculture it
may be more desirable and cost-eff ective to simply manage pest densities to a level
that avoids adverse aff ects to stock and equipment, even when repeated incursions
are inevitable and eradication is unfeasible. Additionally, it may be worthwhile
characterizing the 'manageability potential' of the target pest to estimate the degree
of management success that can be expected. For example, introduced organisms
that are large and conspicuous, and have highly specifi c habitat and environmen-
tal requirements and short dispersal ranges, are inherently more manageable than
small or cryptic organisms that are habitat generalists with long planktonic life-
stages (Forrest
et al
. 2006). Using a similar approach, key attributes of the receiving
environment can be assessed to determine the feasibility of surveillance and/or
incursion response. For example, it is much easier to manage a sheltered, access-
ible environment with clear water and a relatively two-dimensional bathymetry,
compared to an exposed remote environment with turbid water and a complex
heterogeneous bathymetry.
Once a marine pest has become established in a new location, one important
approach to managing spread is the identifi cation of 'internal borders' (Forrest
and Gardner, in review). Internal borders defi ne post-border management inter-
vention points around which relatively localized management approaches may be
feasible, and involve applying a similar set of criteria and tools used for preventing
and managing pest incursions at a national scale to protect key values at smaller
geographic scales (e.g. vector management, pest surveillance, incursion response,
containment, etc.). Critical to this is an understanding of the natural habitat bar-
riers or broad-scale oceanographic features that may prevent or restrict the natural
dispersal of pest organisms (Forrest
et al
. 2009). Knowledge of the natural dispersal
potential of a pest organism may be used to identify instances where even the most
robust management of human transport pathways and activities would be futile in
preventing its spread.
For some marine pest species, current management strategies appear inef-
fective and ongoing introductions are almost inevitable. In order to manage
new incursions of the more intractable pest species the development of novel
