30 June 2009

Destruction of seagrass on a par with loss of rainforests and coral reefs

Globally, seagrass meadows the size of a soccer field is lost every thirty minutes.
It's amazing that lush seagrass meadows can still be found on Cyrene Reef, surrounded by industrial installations and a world class port.

The decline is caused by direct impacts from coastal development (growing urban centers, artificially hardened shorelines) and dredging activities, and indirect impacts of declining water quality. Nutrient and sediment pollution from nearby human activities and the introduction of invasive species are also contributors. As more and more people move to coastal areas, conditions only get tougher for seagrass meadows that remain.

While the world has focused on the destruction mankind has brought to coral reefs, the massive loss of an equally important ecosystem has been widely ignored.

Now the first comprehensive assessment of the state of seagrass meadows around the world has revealed the damage that human activities have wrought on these economically and biologically essential areas.

The world has lost more than a quarter of its meadows in the past 130 years, since records began, and that the rate of that decline has grown from less than 1% per year before 1940 to 7% per year since 1990

"Seagrass loss rates are comparable to those reported for mangroves, coral reefs and tropical rainforests, and place seagrass meadows among the most threatened ecosystems on earth," write the authors of the synthesis.

The consequences of continuing losses also extend far beyond the areas where seagrasses grow. There's a very close connection between reef systems and seagrass systems in the tropics.

According to one of the authors, studies have found that seagrass fixes as much carbon dioxide as tropical forests, and is also a crucial part of the ocean food chain. About 75% of seagrass feeds bacteria, which are the bottom of the ocean food chain. They actually feed the whole food web. The other 25% of seagrass is eaten directly by animals such as dugongs, green turtles, fish, snails and crustaceans, as well as birds like geese and swans.

Seagrass meadows are also crucial to the survival of fish that live in coral reefs. They serve as a vital nursery for fish, supporting populations for coral reefs and commercial fisheries.

They also serve to stabilize sediment and provide coastal protection. Seagrass buffers coastal areas from damaging waves, expected to increase with rising seas, and also acts as a filter for toxic materials released into the ocean from industry. Seagrass also traps carbon and helps in nutrient transportation.

Despite the bleak findings, even where seagrass meadows have been lost there is the opportunity for recovery if protection via the designation of Marine Protected Areas.

What about Singapore's seagrasses?
The volunteers of TeamSeagrass monitor six seagrass meadow locations in Singapore. Seagrasses are also found on many of our shores, in varying states of health.

Here's factsheets about our seagrasses.

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