Published online 29 June 2009 | Nature | doi:10.1038/news.2009.608

News

Vital marine habitat under threat

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

DugongA dugong grazes on seagrass.Jurgen Freund / naturepl.com

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.

A synthesis of quantitative data from 215 sites suggests that 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, which is published this week in the Proceedings of the National Academy of Sciences1. "Our report of mounting seagrass losses reveals a major global environmental crisis in coastal ecosystems, for which seagrasses are sentinels of change."

As well as supporting unique wildlife such as green turtles (Chelonia mydas) and dugong (Dugong dugon), seagrass meadows also 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, as well as trapping carbon and helping in nutrient transportation.

Suffering sentinels

For the global survey, the researchers compiled a database of all data on changes in the extent of seagrass cover spanning at least two years. They included published studies, online databases and unpublished but audited research.

Their synthesis shows that since 1980 seagrasses have been destroyed at the rate of 110 square kilometres per year. While 25% of sites increased in size and 17% showed no detectable change, 58% declined.

Overall, the measured area of loss between 1879 and 2006 was 3,370 square kilometres from the total of 11,592 for which suitable records were available — a loss of 29%. Extrapolating this to a global scale suggests 51,000 square kilometres of seagrass meadows have been lost since records began.

“We are abusing our coastal systems.”

Frederick Short
University of New Hampshire

Study author Frederick Short, a researcher at the University of New Hampshire, Durham, admits that there is "not that much data" available on seagrass, so the total loss is difficult to pin down exactly.

Still, he says, "It is looking quite bleak for many parts … we are abusing our coastal systems."

The vast majority of this decline, say Short and other experts, is attributable to human activity. Nutrient and sediment pollution from nearby human activities and the introduction of invasive species are both contributing to their decline.

Seagrasses — flowering plants that evolved from terrestrial plants — are also likely to be affected by climate change, the authors note. And while the world focuses on photogenic coral, seagrass loss is just as worrying, perhaps more so as they are more widely distributed.

"The seagrass ecosystem in general is quite unacknowledged," says Short.

Uncertain fate

Giuseppe DiCarlo, marine climate change manager at Conservation International and a member of the steering committee of the World Seagrass Association, told Nature News that even where seagrass meadows have been lost there is the opportunity for recovery if protection via the designation of Marine Protected Areas can be brought in.

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"It's nice to finally have some global numbers that can be used when advocating for the protection of seagrass," he says. "If you look at a regional scale, like in the Caribbean, we're going to lose the seagrass beds altogether [if something isn't done]."

Susanne Livingstone, programme officer on the International Union for Conservation of Nature (IUCN) Global Marine Species Assessment, says experts wouldn't be surprised to hear a 30% figure for losses, but despite these losses seagrass rarely makes it into the public consciousness. "It's probably because they're not as sexy [as corals], they're not as attractive," she says. "They're just as ecologically important if not more so."

Livingstone has been working on the forthcoming assessment of seagrass from the IUCN's Red List of the world's most threatened species. While the results of this are not yet available, she confirms that it will take the newly published research into account. 

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  • #60581

    I'm amazed the government is allowing this to go on. Clearly, they are more interested in 'saving face', coming up with poor excuses and biased statistics instead of addressing the problem directly. Shame on you, this is our global heritage being destroyed. JustinI @webs.com

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