What is seagrass?
Seagrasses are flowering plants that live completely submerged in marine and estuarine waters. Seagrasses provide essential habitat for much of Sarasota Bay’s aquatic life. It is generally recognized that the amount of seagrass covering the bay bottom is a function of water clarity and availability of appropriate bottom substrate. The Bay area is home to three common species of seagrasses: shoal grass, turtle grass, and manatee grass, while two more rare species are also found; widgeon grass and star grass.
Seagrasses get their energy from photosynthesis—converting sunlight into energy—and so must live in shallow water where the sun can reach them. They grow into lush meadows not just by reaching their green blades upwards, but also stretching their roots down and sideways. Many stems in a meadow are a single plant, connected underground by their roots in what’s known as a rhizome root system. In some seagrass species, a meadow can spring up from a single plant in less than a year; in slow-growing species, it can take decades for meadows to form.
Why is seagrass important?
Seagrass serves as its own unique habitat. The meadows provide canopy cover that shelters small organisms such as invertebrates and juvenile fish, including commercial fish species. Many species of algae, bacteria and plankton grow directly on the living and dead leaves.
Seagrass meadows are some of the most productive ecosystems in the world. They’re known as the “lungs of the sea” because one square meter of seagrass can generate 10 liters of oxygen every day! Seagrass meadows also improve water quality by absorbing nutrients and attracting particles to their blades. Their roots stabilize the sediment below them and protect coastlines by scattering wave energy.
Vast seagrass meadows also capture and store a huge amount of carbon from the atmosphere. Seagrasses use carbon to build their blades and roots. As their carbon-rich leaves die and decay, they collect on the seafloor and are buried within the sediments. It’s estimated that the world’s seagrass meadows capture 27.4 million tons of carbon each year! The carbon stored in sediments from coastal ecosystems, including seagrass meadows, mangrove forests, and salt marshes, is known as blue carbon.
Seagrass acreage in Sarasota Bay
The Southwest Florida Water Management District began a formal seagrass mapping program in 1988. Every two years, seagrass maps are produced from aerial photographs and then verified for accuracy through ground-truthing field surveys. The results are used to track trends in seagrass coverage and to evaluate ongoing water quality improvement efforts.
Sarasota Bay supports 13,288 acres of seagrass, the largest amount ever recorded for the Bay and an increase of roughly 700 acres from 2012. Historically, seagrass habitat decreased by 30 percent from 1950 to 1988, primarily due to poor water clarity and dredge-and-fill activities. Since then, however, seagrass has steadily increased in the Bay, primarily as a result of increased water clarity. This increased water clarity was achieved primarily through improvements in wastewater and stormwater management by the SBEP’s partners.
Sarasota County manages an annual volunteer-based citizen science project surveying seagrass coverage and species distribution in Sarasota Bay.