Flowering plants that live fully submerged in shallow marine waters are seagrasses. They form meadows in coastal zones worldwide, rooted in soft sediments and drawing energy from sunlight that penetrates the clear, shallow water.

Seagrass meadows stabilize sediments, improve water clarity, store carbon in their soils, and provide nursery habitat for commercially important fish and invertebrates. They also feed sea turtles, manatees, dugongs, and a host of smaller grazers. Because they require good water quality and adequate light, seagrasses are sensitive indicators of coastal ecosystem health.

Threats include nutrient pollution that stimulates algae and reduces light, physical disturbance from dredging and anchors, and rising temperatures. Restoration projects transplant seagrass and improve local water quality, with mixed but improving success rates. Protecting existing meadows is generally more effective than trying to restore them after loss.

A single hectare of healthy seagrass can support tens of thousands of fish and bury carbon for centuries.