Longhorn cowfish (Lactoria cornuta) are one of many species that live on seagrass meadows (Image: Bruce Nyden) This emerald leatherjacket also depends on seagrass meadows for its home (Image: Bruce Nyden) Horned sea stars (Protoreaster nodosus) like sheltered habitats, and often live in seagrass meadows (Image: Bruce Nyden)


Seagrass meadows are disappearing at an accelerating pace, according to a new report, which is the first to look at the problem on a global scale.

Seagrass meadows, along with coral reefs, mangrove forests, and salt-marshes, provide valuable ecosystem services like nutrient cycling. They also protect edible crustaceans, like shrimps and crabs, and juvenile fish such as salmon. In addition, seagrass meadows provide habitats for endangered species like dugongs, manatees, and sea turtles.

While marine ecologists have been measuring localized seagrass loss for decades, they had never before pooled their information to get a global perspective. So a team led by Michelle Waycott of James Cook University in Townsville, Queensland, Australia pooled data from 215 regional studies, from 1879 to 2006.

They found that the total area of known seagrass meadow had decreased by 29 per cent over the 127 years. They also found that the rate of loss had accelerated, from less than 1 per cent per year in the 1940s to 7 per cent per year since the 1990s.

Sediment dump

“We put tremendous pressure on sea grass beds, but we get a lot of benefits from them,” says Susan Williams of the Bodega Marine Laboratory, one of the report’s co-authors.

The study points to sediment dumping from coastal development projects, pollution, and agricultural nutrient runoff as major causes of the decline. All three can decrease water quality, starving the plants of the sunlight they need to grow.

Natural disruptions like hurricanes accounted for a small proportion of losses.

According to Williams, the numbers translate to losing a football pitch’s worth of seagrass every thirty minutes.

Shocking loss

Overall, the rate of loss is comparable to that for tropical rainforests and coral reefs.

However, seagrass meadows exist in both tropical and temperate zones, and are more widespread than either rainforests or reefs. Their loss has the potential to affect coastal communities all over the world.

“Those numbers are pretty shocking,” says Ben Halpern, a marine ecologist with the National Center for Ecological Analysis and Synthesis.

Although not involved with this study, Halpern and colleagues released a map last year of human impacts on marine habitats.

“Marine ecosystems have a lot more opportunity to bounce back than ecosystems on land,” he says. “We do need to act quickly, but there is real hope that our actions can be effective.”

Watershed moment

Not all areas of the globe decreased. Of the 51 sites that showed increases, 11 were attributable to improved water quality and restored habitat, showing that human efforts can bring the grasses back.

The report notes that transplantation efforts have generally failed, but watershed management and habitat remediation are effective.

One notable example is Tampa Bay, Florida, US, where efforts to reduce nutrient runoff have resulted in 50 per cent clearer water, and a recovery of 27 square kilometres of seagrass beds in the last 25 years.

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0905620106