Monitoring in the Western Pacific region shows evidence of seagrass decline in line with global trends.

Seagrass systems of the Western Pacific region are biodiverse habitats, providing vital services to ecosystems and humans over a vast geographic range. SeagrassNet is a worldwide monitoring program that collects data on seagrass habitats, including the ten locations across the Western Pacific reported here where change at various scales was rapidly detected. Three sites remote from human influence were stable. Seagrasses declined largely due to increased nutrient loading (4 sites) and increased sedimentation (3 sites), the two most common stressors of seagrass worldwide. Two sites experienced near-total loss from of excess sedimentation, followed by partial recovery once sedimentation was reduced. Species shifts were observed at every site with recovering sites colonized by pioneer species. Regulation of watersheds is essential if marine protected areas are to preserve seagrass meadows. Seagrasses in the Western Pacific experience stress due to human impacts despite the vastness of the ocean area and low development pressures.

Accelerating loss of seagrasses across the globe threatens coastal ecosystems.

Coastal ecosystems and the services they provide are adversely affected by a wide variety of human activities. In particular, seagrass meadows are negatively affected by impacts accruing from the billion or more people who live within 50 km of them. Seagrass meadows provide important ecosystem services, including an estimated $1.9 trillion per year in the form of nutrient cycling; an order of magnitude enhancement of coral reef fish productivity; a habitat for thousands of fish, bird, and invertebrate species; and a major food source for endangered dugong, manatee, and green turtle. Although individual impacts from coastal development, degraded water quality, and climate change have been documented, there has been no quantitative global assessment of seagrass loss until now. Our comprehensive global assessment of 215 studies found that seagrasses have been disappearing at a rate of 110 km(2) yr(-1) since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879. Furthermore, rates of decline have accelerated from a median of 0.9% yr(-1) before 1940 to 7% yr(-1) 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.

EELGRASS WASTING DISEASE: CAUSE AND RECURRENCE OF A MARINE EPIDEMIC.

Eelgrass populations are currently infected with a disease that produces symptoms and epidemiology reminiscent of the famous eelgrass wasting disease of the 1930s. This disease virtually eliminated eelgrass (Zostera marina L.) in the North Atlantic for three decades. For 50 years scientists have speculated about the cause of the 1930s eelgrass decline. We have now proven that the causal organism of the present epidemic is a pathogenic strain of Labyrinthula, which was suspected, but never conclusively shown to cause the 1930s wasting disease. We have isolated the infectious form of Labyrinthula from eelgrass from Maine to North Carolina on the Atlantic coast, and from Puget Sound on the Pacific coast; disease-related dieoffs of eelgrass beds are confirmed in Maine, New Hampshire, and Massachusetts.