Environmental Engineering Reference
In-Depth Information
A range of chemicals and toxicants have also been trialled for the management
of pest species within natural habitats. h e successful eradication of
C
.
taxifolia
in
Southern California lagoons was achieved by covering colonies of the alga (ranging
in size from 1-500 m
2
) with PVC tarpaulins and applying bleach (in liquid and
solid tablet form; Anderson 2005). Applying copper ions directly to the thalli of
C
.
taxifolia
via
in situ
electrolysis has also proven eff ective in killing the alga (Gavach
et al
. 1996). Herbicides have been employed in the control of estuarine emergent
plant species such as the cryptogenic reed
Phragmites australis
in Chesapeake Bay,
USA (Ruiz
et al
. 1999) and the introduced rice grass
Spartina anglica
in Australia
and New Zealand (Kriwoken and Hedge 2000). Herbicides have proven less eff ect-
ive in the control of algal species, failing to prevent the spread of the introduced
alga
Sargassum muticum
in southern England (Critchley
et al
. 1986), and proving
ineff ective and labour-intensive to administer during
in situ
trials for the control of
U
.
pinnatifi da
(McEnnulty
et al
. 2001). h e broad spectrum insecticide carbaryl
has been used (or considered) for the control of various crustacean pest species,
such as the European green crab
Carcinus maenas
(Carr and Dumbauld 1999) and a
thalassinid burrowing shrimp species in intertidal oyster beds in Washington State,
USA (McEnnulty
et al
. 2001). Advantages of carbaryl are its tendency to be short-
lived in the environment with no bio-accumulation (Dumbauld
et al
. 1997) and
short-term eff ects on non-target populations (Brooks 1993). h e alkaline proper-
ties of lime, and its ability to corrode calcium carbonate, have led to its use as a con-
trol agent of seastars, including
A
.
amurensis
(McEnnulty
et al
. 2001). Following the
broadcast application of lime, seastars are exposed to the corrosive particles as they
settle or crawl over it, dying within 2 weeks. h e spray application of lime solution
has also proven eff ective in controlling pest tunicate species such as
Styela clava
and
Ciona intestinalis
on mussel aquaculture crops in Prince Edward Island, Canada.
Using chemicals to modify the characteristics of a habitat has also been used for
AIS control. Salt (NaCl) has been used successfully for the control of
C
.
taxifolia
at
a variety of spatial scales. A 4ha area of
C
.
taxifolia
in a coastal lagoon in Australia
was controlled by raising the salinity of the entire lagoon through the addition of
1000t of salt (Hilliard 1999). Similarly, salt dispensed from a barge was eff ective
in treating
C
.
taxifolia
in shallow water soft sediment habitats in Australia (Glasby
et al
. 2005). h is method is less successful in deeper waters (
>
6m depth) however
since the salt disperses before reaching the substratum. Small-scale infestations of
C
.
taxifolia
(4 m²) in Sydney Harbour, Australia, were eliminated by scuba divers
spreading salt by hand (4 cm thick, ~50 kg/m²) (Creese
et al
. 2004). h is type of
treatment is usually only applicable to small, relatively enclosed bodies of water
such as lagoons/lakes and again is non-selective, often resulting in the death of
non-target species.
In general, while chemicals have been used with some success in aquatic envir-
onments their utility is compromised by a range of factors. h ese include:
•
A lack of selectivity resulting in mortality of non-target species.
•
The large doses required for effective control.
