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Seagrasses form an important shallow
water ecosystem that binds the seabed and reduces coastal erosion. They
also provide shelter and nursery grounds for many species. For example
in the Philippines, 20 per cent of the fish caught are associated with
coral reefs and seagrass beds. The global distribution of seagrasses
was plotted for the first time in 2003 (Green and Short 2003). This
atlas used information from a variety of sources and then predicted
distributions through modeling.
In many cases, distribution of seagrass beds overlaps with intensive
commercial fishing operations. This is a problem because certain fishing
techniques drag heavy trawling gear over the seabed, severely damaging
the seagrass. Off Tanzania, in fisheries that use such trawling gear,
80 per cent of the by-catch in the prawn fishery is seagrass (Green
and Short 2003). Studies in Maquoit Bay, Maine, US, have projected that
even small areas (0.3 kmkm2) may take between 10–17 years to recover.
This can have a direct impact on the biodiversity, on local fisheries,
and, ironically, on the livelihoods of the very people who cause the
damage. Tropical and temperate coral reef ecosystems are similarly at
risk from damaging fishing techniques (Box 6).
Box
6: Cold and deep water corals |
Coral reefs do not only occur in warm tropical oceans. Cold
water reefs are built by stony corals such as Lophelia pertusa
which flourish in the cold, nutrient and plankton rich currents
on the seabed of continental shelves and fringes down to several
hundreds of metres below sea level. Cold water reefs rival
their tropical shallow-water counterparts in size, structure,
complexity and biological functions, providing rich habitats
that support and sustain thousands of marine species, including
commercial fish. Environmental threats, such as the physical
impact from trawling operations, have devastated many assemblies
before scientists even know their full distribution and begin
to understand the ecological role of these biodiversity hotspots.
An example of a cold water coral system is the Darwin Mounds.
These are located 180 km off the west coast of Scotland. The
mounds are at a depth of about 1 000 m, and cover an area
of approximately 100 km2. Fishing activities in this area
targeted deep water species (eg blue ling, roundnose grenadier,
black scabbard fish and tusk).
2003 saw an increased recognition of the importance of cold
water coral systems. A European Commission
Regulation (2003/C 161 E/204) came into effect in August 2003,
prohibiting the use of bottom trawls or similar towed nets
within the vicinity of the Darwin Mounds. These emergency
temporary measures were put in place while the commission
develops more permanent measures to protect the area.
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| Source: DEFRA 2003, Freiwald and others (in press) |
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