Seagrass-Watch Magazine Issue 47 - March 2013 | Page 17

although macroinvertebrates
could recover once the seagrass
meadow recovered, within approx. one year,
there were longer term implications for
larger fauna such as fish, which could
take from 2-10 years
to recover

So impacts to seagrasses from dredging can also affect the fauna
living in seagrass meadows, and those that pass through to feed,
and over longer time scales than the actual dredging event.
Over the past decade, management of dredging has improved
significantly, largely through an improved ability to predict where
and how intense the turbid plumes will be, but also through a
greater understanding on the potential impacts on marine biota.
Generally, dredging projects must go through an environmental
impact assessment and develop an environmental management
plan with the aim of minimising impact to the environment. Yet,
in many cases linking the predictions of changes in the
environment due to dredging i.e. where and how much turbidity
will be generated, and the potential impacts to the seagrass
meadows is difficult to do. While the ability to predict habitat loss
is improving, the capacity to predict the loss of ecological function
associated with less severe dredging impacts remains poor i.e. if
there are reductions in seagrass how does this affect the foodweb.
At present there are a number of research programs around the
globe focusing on improving the capacity to predict the impacts
of dredging. Some of the key questions researchers are
addressing are:
! what levels of stress can different seagrass species tolerate, how
much for how long, and how does this vary at different times of
year?
This type of information can inform managers of the best time
and duration to dredge to minimise impact to the seagrass
meadows
! how do seagrasses respond to dredging-related stressors such
as light reduction or sedimentation, are there any early-warning
signs that they are stressed?
This type of information can help during monitoring of a
dredging event to assess whether the plants are stressed or not,
and can act as a trigger to notify managers of the dredge who
could potentially modify dredging operations to minimize the
stress.
Due to the importance of ports and shipping around the globe,
dredging is likely to continue. However, we can improve our
management of dredging events through increasing our capacity
to predict impacts and effectively manage the associated threats.
Further reading:
EnviCom-Working-Group-108. (2010) Dredging and Port Construction around Coral Reefs. (PIANC).
Erftemeijer, PLA & Robin Lewis III, RR. (2006) Mar. Poll. Bull. 52: 1553-1572.
McMahon et al.. (2011) Mar. Poll. Bull. 62, 270-283.
Gartner et al. (2010) Mar. Ecol.-Prog. Ser. 201, 87-100.
GDP, http://www.dfat.gov.au/aib/trade_investment.html
Ports Australia http://www.portsaustralia.com.au/

MARCH 2013

17