Seagrass-Watch Magazine Issue 47 - March 2013 | Page 5

Cumulative impact mapping framework

Cooktown

Cairns

Map of risks to seagrasses in the Great Barrier Reef
World Heritage Area:
Coastal areas that are dark blue have a high likelihood
of seagrass presence and are areas where the risk of
impacts from human activities is low.
Coastal areas that are red have a high likelihood of
seagrass presence and are areas where the risk of
impacts from human activities is high.

An alternative approach we used was Geographic Information
Systems (GIS) which allowed us to map spatially the threats to
seagrass which have been identified as important. The only
restriction of this approach is that we can only complete this
where we have good spatial data sets. So, as we have worked
many decades within the Great Barrier Reef province, we used it
to focus our assessment.
Rarely do threats occur by themselves. They accumulate as
composite risk in what is best termed as "hot spots". It is possible
that seagrass meadows will survive the impact of one threat, but
what if a meadow is subject to multiple threats. For the Great
Barrier Reef we found nine good spatial data sets we could use
and these were overlaid on a model of likely seagrass presence in
coastal waters (<15m). Summarising the result, the urban coast
in the south of the Great Barrier Reef has the most threats, with
few threats in the north, roughly Cooktown and above. The
highest accumulation of threats (as many as eight) was in the
urban ports: Cairns, Townsville, Mackay and Gladstone.
So in summary, the processes most likely to damage seagrass are
associated with urban and port development and agriculture and
the risk accumulate most around key cities and ports along our
coast and are likely to do so in other parts of the world. For the
Great Barrier Reef province, the key problem is ports, cities and
farms which cluster around sheltered bays and estuaries which
also support major seagrass meadows providing for a true
“hotspot” for likely seagrass damage and loss.

Mackay

High

High

Low

Low

Townsville

Cumulative risk score

Likelihood of
seagrass presence

Townsville Port
HT

Gladstone

[a] comprehensive global
assessment...found that
seagrasses have been
disappearing at a rate of
110 square kilometres
per year since 1980 (3)

MARCH 2013

5