Marine matters: the importance of seagrass - Veterinary Practice
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InFocus

Marine matters: the importance of seagrass

Our conservation correspondent looks at some headline issues and highlights some other lesser-known problems

THE oceans of the world are still relatively little understood in terms of their ecology and the effects that human activity is having on them.

Of course we are all familiar with the concept of overfishing and there are well-documented examples of where hugely lucrative fisheries have been destroyed for the medium (perhaps long) term.

So it was good news last autumn when the Marine Conservation Society announced that North Sea cod numbers had increased to the point where they could take it off their list of fish to avoid eating: proof that limiting catches can have the positive effects intended and that fish can be managed sustainably if the best scientific advice is heeded.

Plastic problems

We all know too about the Great Pacific Garbage Patch, a huge collection of plastic garbage in the North Pacific, divided into two major accumulations, west and east.

The long-term effects of such quantities of very slowly degrading plastics remain unknown and the prospects of clearing it up are currently negligible.

Behind these “headline” issues, however, are a myriad of lesser known problems. One of those currently in the headlines is the perilous state of seagrass meadows around the world and around the UK coastline in particular.

The meadows are reported to be declining by 7% globally with 50% of such habitats around the UK already lost.

Seagrasses are a group of flowering plants that live in shallow coastal waters and form dense meadows under the water. The commonest species in British waters is eelgrass, Zostera marina, which is found throughout the oceans of the Northern Hemisphere.

They require sunlight to photosynthesise, which is why they live in shallow water, and because of this they are vulnerable to pollution and increased sediment which blocks the light from reaching them.

Due to where they live they are also vulnerable to human disturbance from trampling and boating activities such as mooring and in particular dredging.

An essential component of the ecosystem

So why is seagrass important? Primarily because it is an essential component of the ecosystem particularly for those creatures at the bottom of the food chain which the rest of marine life relies on.

It is considered to be a prime “nursery” habitat for many species of fish including some that are of economic significance in the fishing industry. Lose seagrass and it has a “knock-on” effect right up the food chain.

Such is its importance that it has sometimes been referred to as the “canary of the sea” as the condition of the meadows can be used as an indicator of the overall health of coastal waters.

Studies of various seagrass sites around the UK using the same techniques as are employed on Australia’s Great Barrier Reef have demonstrated that most of the sites surveyed were at risk from one threat or another (pollution, boating), even those located in relatively remote areas.

One of the most significant findings was high water nitrogen levels caused by “run-off” from agricultural land and to an extent industrial pollution. Tissue nitrogen levels at many sites were found to be 75% higher than the global mean.

As a result of the findings the WWF is calling on the UK government to ensure that seagrass is fully protected from such threats through the establishment of effectively monitored and policed Marine Protected areas: something that would benefit the whole marine ecosystem in the years ahead.

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