Seagrasses

Seagrass is an angiosperm (flowering plant) that lives in a marine or brackish environment. Seagrasses grow in groups, forming seagrass beds or meadows. These plants provide important habitat for a variety of marine life. 

Seagrass Description

Seagrasses evolved around 100 million years ago from grass on land, thus they look similar to our terrestrial grasses. Seagrasses are submerged flowering plants that have leaves, roots, flowers and seeds.  Since they lack a strong stem or trunk, they are supported by the water. 

Seagrasses attach to the ocean bottom by thick roots and rhizomes, horizontal stems with shoots pointing upward and roots pointing downward. Their blade-leaves contain chloroplasts, which produce energy for the plant through photosynthesis.

Seagrasses Vs. Algae

Seagrasses may be confused with seaweeds (marine algae), but they are not. Seagrasses are vascular plants and reproduce by flowering and producing seeds. Marine algae are classified as protists (which also includes protozoans, prokaryotes, fungi and sponges), are relatively simple and reproduce using spores.

Read More

What Is Seaweed?

By Jennifer Kennedy

Seagrass Classification

There are about 50 species of true seagrasses worldwide. They are organized into the plant families Posidoniaceae, Zosteraceae, Hydrocharitaceae, and Cymodoceaceae.

Where Are Seagrasses Found?

Seagrasses are found in protected coastal waters such as bays, lagoons, and estuaries and in both temperate and tropical regions, on every continent except Antarctica. Seagrasses are sometimes found in patches, and these patches can expand to form huge seagrass beds or meadows. The beds can be made up of one species of seagrass or multiple species.

Seagrasses require lots of light, so the depths at which they occur in the ocean are limited by light availability. 

Why Are Seagrasses Important?

• Seagrasses provide food and habitat for a variety of marine life (more on that below!).
• They can stabilize the ocean bottom with their root systems, which gives greater protection from storms.
• Seagrasses filter runoff and trap sediments and other small particles. This increases water clarity and the health of the marine environment. 
• Seagrasses help boost local economies through supporting vibrant recreation opportunities.

Marine Life Found in Seagrass Beds

Seagrasses provide an important habitat to a number of organisms. Some use seagrass beds as nursery areas, others seek shelter there their whole lives. Larger animals such as manatees and sea turtles feed on animals that live in the seagrass beds.

Organisms that make the seagrass community their home include bacteria, fungi, algae; invertebrates such as conch, sea stars, sea cucumbers, corals, shrimp and lobsters; a variety of fish species including snapper, parrotfish, rays, and sharks; seabirds such as pelicans, cormorants and herons; sea turtles; and marine mammals such as manatees, dugongs and bottlenose dolphins.

Threats to Seagrass Habitats

• Natural threats to seagrasses include storms, climate changes such as floods and droughts affecting water salinity, disruption of seagrasses by small predators as they search for food, and grazing by animals such as sea turtles and manatees.
• Human threats to seagrasses include dredging, boating, water quality degradation due to run-off, and shading of seagrasses by docks and boats.

References and Further Information:

• Florida Museum of Natural History. 2008. ”Seagrasses”. (Online) Florida Museum of Natural History. Accessed November 12, 2008.
• Florida Fish and Wildlife Conservation Commission. 2008. "Learn About Seagrasses." (Online). Florida Fish and Wildlife Conservation Commission Fish & Wildlife Research Institute. Accessed November 12, 2008.
• Florida Fish and Wildlife Conservation Commission.  "Importance of Seagrass." Accessed November 16, 2015.
• Florida Department of Environmental Protection. 2008. ”Seagrasses” (Online). Florida Department of Environmental Protection. Accessed November 12, 2008.
• Seagrass.LI, Long Island’s Seagrass Conservation Website. 2008. ”What is Seagrass?” (Online). Cornell Cooperative Extension Marine Program. Accessed November 12, 2008.
• Smithsonian Marine Station at Fort Pierce. Seagrass Habitats. Accessed November 16, 2015.
• Smithsonian National Museum of Natural History. Seagrass and Seagrass Beds. Ocean Portal. Accessed November 16, 2015.