Environmental Engineering Reference
In-Depth Information
human health, property or resources, impair biological diversity or interfere with
other legitimate uses of such areas (IMO 2004 ). As a result this term HAOP includes
all potentially harmful non-indigenous, cryptogenic and impacting native aquatic
species including pathogens.
Natural Species Movements
Many species have the potential to spread by their own means, for example, the
migrations over long distances known for, e.g., birds that may carry associates with
them that may either attach to them or otherwise infect them. Cladocerans, which
are free swimming crustaceans that for part of their life cycle have a relatively
smaller resting stage, have been found encrusted on birds feet and so explains how
they can be spread between different separated water bodies. Otherwise their spread
would not have been possible, as a result birds have been implicated in the spread of
many species. Similarly, turtles have been found to spread several species found
either entangled or attached to the turtle shell (e.g., Oliverio et al. 1992 ), such as
macroalgae, bryozoans, barnacles, sea squirts, molluscs which were moved over
long distances in this way (Pfaller et al. 2008 ).
Further, ocean currents can move species and under certain rare hydrodynamic con-
ditions, with perturbations in the strength and direction of fl ow, species can be moved
beyond their normal geographic range, perhaps also as a result of climate alterations,
for example the increased spread of the sardine, a pilchard, which is occasionally found
in the southern North Sea and western Baltic as a result of a rare northeast Atlantic
Ocean water infl ow and warmer water temperatures (Weber and Frieß 2003 ).
These natural phenomena result in changes to local species richness and may
only appear on a temporary basis within a region, being known as rare guests, or
vagrants. Such natural appearances, especially on the fringing ranges of a species
where their ability to survive is just possible are a normal part of nature's biodiver-
sity and is often seen as an advantage. In contrast are the human-assisted species
movements which can cause irreversible negative impacts.
Human-Assisted Species Movements
In contrast to natural spread, species have been transported since humans started to
explore the world. Early movements will have been with solid ballast (and the damp
ballast conditions will have allowed for several attaching, sediment dwelling, or
otherwise associated, near-shore and intertidal species to survive and become carried)
used to stabilise wooden vessels, as attached hull fouling, with boring organisms in
hulls, and what might have been carried as cargo (Eldredge and Carlton 2002 ;
Minchin et al. 2005 ). Many of the movements will have been unintentional and there
is little historic record of what might have been transferred several centuries ago.
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