Seagrass Bed | Oceana
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Marine Science and Ecosystems

Seagrass Bed

Distribution

Worldwide in tropical to polar latitudes

Physical Ocean Characteristics

Clear, shallow, nutrient-rich, low-energy waters

Keystone Species

Seagrasses, manatees/dugongs, Green Turtles

Ecosystem Services

Juvenile habitat for fisheries species, carbon storage, coastal protection

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Seagrasses are not true grasses but are flowering plants that carry out their entire lifecycles underwater. Like all plants, seagrasses rely on sunlight to convert carbon dioxide into food/energy (via a process called photosynthesis). Therefore, they only succeed in clear, shallow waters. When the conditions are just right, seagrasses can densely cover the sea floor, creating an ecosystem known as the seagrass bed or seagrass meadow.

Several different species of plants, representing at least four distinct families, are collectively known as the seagrasses, so the term does not accurately describe an individual group of plants.  The diversity of species involved in forming seagrass beds leads to the wide geographic distribution of this ecosystem; seagrass beds can be found from the tropics nearly all the way to the north and south poles.

Seagrass beds form an important nursery habitat for several species of fishes and invertebrates that move to coral reefs and other ecosystems as they mature.  They are also important feeding ground for herbivorous grazers, like green turtles, manatees, dugongs, etc., and for foraging omnivores that may feed on invertebrates and other animals that live amongst the plants.  Several species of coral reef fishes forage in seagrass beds during the night and return to the protection of the reefs during the day.  The dense root systems found on most seagrass beds secure the seabed, preventing soft sediments from being washed onto coral reefs and other sensitive ecosystems and providing some protection to coasts and coastal communities from strong ocean storms.  Cold-water seagrass beds provide an important source of shelter for many species.

Local human activities often harm seagrasses.  Pollution, destructive fishing practices, and direct physical disturbance (e.g., dredging, boat strikes) threaten seagrass beds around the world, and scientists estimate that as much as 50% of the total area covered by seagrasses has been lost in the last few decades.  This represents an incredible loss of coastal, marine habitat.

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