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Ecosystem effects

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.

Source: DEFRA 2003, Freiwald and others (in press)

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