Environmental Engineering Reference
In-Depth Information
benthic pest species such as algae, ascidians, and seastars. When applied correctly,
such approaches prevent light availability for photosynthesis (in the case of plants)
and impede water fl ow, resulting in anoxic conditions and the eventual mortality
of encapsulated biota (McEnnulty
et al
. 2001; Coutts and Forrest 2007).
To date, one of the most successful and cost-eff ective methods available to
treat artifi cial structures
in situ
is to encapsulate them with a physical barrier
such as impermeable plastic (polyethylene). Wrapping wharf piles in imperme-
able plastic has been widely and successfully implemented during eradication
attempts of
D
.
vexillum
(Pannell and Coutts 2007) (Fig. 14.4) and trialled for
the snowfl ake coral
Carijoa riisei
(Montgomery 2007). In both cases, this tech-
nique successfully eliminated all encapsulated biota, except in a few instances
where the wrapping became damaged or failed to completely prevent water
exchange (such as on complex wharf structures). h is technique has also proven
successful for clearing
S
.
clava
and
D
.
vexillum
from fl oating pontoon structures
(Coutts and Forrest 2005, 2007). In areas where wharves and pontoons are in
high demand and require rapid treatment, chemicals such as acetic acid and
bleach (chlorine) can be added to the encapsulated water within the wrapping to
accelerate mortality. For example, the addition of 4% acetic acid within wrapped
pontoons resulted in 100% mortality to the ascidian
S
.
clava
in 10 minutes
(Coutts and Forrest 2005). Similarly, wharf piles infected with the Asian kelp
U
.
pinnatifi da
have been successfully sterilized using bromine compounds
applied inside PVC sleeves (Stuart 2002).
Fig. 14.4
A marina pontoon wrapped in geotextile fabric during efforts to
control an infestation of the pest ascidian
Didemnum vexillum
in Tarakohe
Harbour, New Zealand. Wrapping restricts water exchange to fouling
communities growing on the pontoon, resulting in the development of anoxic
conditions and eventual mortality. Photo: A. Coutts, Cawthron Institute.
