"SENTINELS OF CHANGE" WHISPER DANGER

       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 percent per year before 1940 to 7 percent 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 was published in the Proceedings of the National Academy of Sciences ."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 stabilise sediment and provide coastal protection, as well as trapping carbon and helping in nutrient transportation.
       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in the extent of seagrass cover spanning at least two years.They included published studies, online databases and unpublished but audited research.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 110km2 per year. While 25 percent of sites increased in size and 17 percent showed no detectable change,58 percent declined.
       Overall, the measured area of loss between 1879 and 2006 was 3,370km2 from the total of 11,592km2 for which suitable records were available - a loss of 29 percent. Extrapolating this to a global scale suggests 51,000km2 of seagrass meadows have been lost since records began.
       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 it is more widely distributed.
       "The seagrass ecosystem in general is quite unacknowledged," says Short.
       Giuseppe DiCarlo, marine climate change manager at Conservation International and a member of the steering committee of the World Seagrass Association, says that even where sea-grass meadows have been lost there is the opportunity for recovery if protection via the designation of Marine Protected Areas can be brought in.
       "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 Global Marine Species Assessment, says experts wouldn't be surprised to hear a 30 percent 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."