Wade out into virtually any stretch of coastal or estuarine water and soon you will find seagrass under your feet. These underwater meadows provide breeding grounds and nurseries for crustacean and shellfish populations and food for fish, waterfowl, green sea turtles and dugongs. What's more, the strong root system stabilises the sea floor, while the plants themselves reduce water currents and protect coastal areas from disturbance. Putting a value on the services that seagrasses provide is hard, but economists estimate they are worth around £2.5 bn per year.

But seagrass has not fared well in recent decades. Fifteen percent of seagrass species are classed as threatened and large areas of seagrass have been damaged or destroyed, with an estimated 110 sq km lost worldwide every year since 1980.

Alana Grech, from James Cook University in Townsville, Australia, and colleagues created a web-based survey to assess seagrass vulnerability. They asked seagrass experts to rank the relative impact of anthropogenic activities and climate-change-related activities in six global seagrass regions.

"There was a global consensus that urban and industrial run-off, coastal development, agricultural run-off and dredging has the greatest impact on seagrasses, though the order of relative impact varied by seagrass region," Grech told environmentalresearchweb.

Meanwhile, sea-level rise and increases in severity of cyclones were considered to be the most pressing climate-change-related activities, but a lesser threat compared with anthropogenic activities. "We were surprised that overall the five climate-change activities were ranked low and experts were uncertain of their effect on seagrasses," said Grech.

The survey, published in Environmental Research Letters, revealed that the greatest threat to seagrasses comes from land-based anthropogenic activities, highlighting the need for seagrass management to be co-ordinated with adjacent watershed planning.

Crucially the new survey will help experts to assess the threats to seagrass in data-poor areas and to overcome some of the problems traditionally associated with expert bias. It also identifies key regional differences that should be taken into account. "Our approach provides a way forward for seagrass managers by informing the strategic deployment of resources at minimal cost," explained Grech.