Healthy Seagrass Forms Underwater Meadows That Harbor Diverse Marine Life

Overview

Seagrass meadows are home to an astounding array of ocean life. Manatees and turtles nourish themselves on the swaying blades. Young fish begin life there, and shrimp and crabs find shelter.  

These marine grasslands are among the most important and valuable ecosystems on Earth. They capture the sun’s energy to generate food and oxygen for animals; provide habitat for fish and shellfish that feed people and form the backbone of coastal businesses; stabilize sediments; and absorb the power of waves, helping to stave off erosion and protect coastlines from storms. They also soak up climate-changing carbon and polluting runoff.

But these essential underwater grasslands are disappearing around the globe at the rate of two football fields an hour, pushed beyond their limits by a range of chronic and acute threats.¹ Some are battered by storms, floods, droughts, disease, invasive species, and warming waters while others are ripped from the sand by trawls, dredges, propeller blades, and anchors. Still others are stressed by shifting water levels from runoff and other discharges from land, or they wither under the shade of suspended sediment and smothering algae fueled by pollutants flowing from cities and farms, particularly nitrogen-rich fertilizers.

Protecting seagrass is vital to the health of the oceans as well as businesses and coastal economies.

What is seagrass? 

Seagrasses, which resemble prairies on land, are mostly found in the clear shallow waters of bays, lagoons, and estuaries, where they can receive the sunlight they depend on. Worldwide, there are more than 70 species of seagrass, with at least one found on every continent except Antarctica.

Seagrasses are flowering plants with blades, roots, and rhizome networks that spread and anchor to the seafloor or sediment, forming dense beds that can extend for miles. They are not seaweed or algae, and although they are similar in many ways to plants found in marshes and wetlands, they differ significantly from those terrestrial plants because they live fully submerged in salty water.

Like corals, seagrasses form structures where animals find homes, food, and nursery areas.² These undersea communities are filled with a variety of species, such as bay scallops, crabs, seahorses, corals and sponges, snappers and groupers, salmon, sharks, dolphins, and birds ranging from pelicans to herons. Some animals eat the grass, and others feast on small organisms that grow on the blades and roots. Still others, such as small schooling fish like pinfish, anchovies, and smelts, hide from predators among the blades.

Healthy seagrasses also sustain activities that boost coastal economies, such as duck hunting, wildlife watching, and fishing for tarpon, stripers, salmon, and crabs.

Romona Robbins

Seagrass Statistics

Seagrass is a valuable ecosystem that provides varied services in the water and on land.

• Humans have used seagrasses for more than 10,000 years to fertilize fields, insulate houses,  weave furniture, thatch roofs, make bandages, and fill mattresses and car seats.³
• More than a billion people live within 31 miles of a seagrass meadow.⁴
• Seagrass meadows are believed to be the third-most valuable ecosystem in the world after estuaries and wetlands.⁵ About 2½ acres of seagrass (roughly the size of two football fields) provides habitat, erosion control, and other benefits with an estimated value of nearly $29,000 a year.⁶
• A single acre of seagrass can support nearly 40,000 fish and 50 million small invertebrates, such  as lobsters and shrimp.⁷
• More than 100 times as many animals gain shelter and nourishment in seagrass beds as on  adjacent bare sand.⁸
• Seagrasses stabilize sediments and reduce wave action by 20 percent, slowing beach erosion and lessening storm damage to coastlines.⁹
• Seagrass mitigates the effects of climate change by absorbing about 10 percent of the total estimated organic carbon sequestered in the world’s oceans each year.¹⁰
• In some places, 1 acre of dense seagrass can sequester more than 1,200 pounds of carbon per year— equivalent to the amount emitted by a car traveling about 6,259 miles, more than twice the distance across the U.S.¹¹
• Global seagrass coverage is diminishing at a rate of 1.5 percent a year, or about two football fields  each hour. Estimates suggest that 29 percent of seagrass meadows have died in the past century.¹²

Charlie Shoemaker The Pew Charitable Trusts

Seagrass shores up Florida’s economy

Along the Florida coastline, seagrass meadows bolster economic activity by nurturing commercially important fish, stone crabs, and shrimp and by drawing tourists from around the world for manatee watching, scalloping, fishing, snorkeling, and paddle sports. The state’s seven species of seagrass span more than 2.5 million acres¹³ and give Florida the nation’s most diverse seagrasses and two of its largest contiguous seagrass beds: Florida Bay at the southern tip of the state and the Big Bend, between the mouths of the Suwannee and Apalachicola rivers along the Gulf Coast.

Florida is also home to the first and only marine plant listed under the Endangered Species Act: Johnson’s seagrass.¹⁴

The approximately 400,000-acre habitat along the Nature Coast—which encompasses the shorelines of Citrus, Hernando, and Pasco counties bordering the Gulf of Mexico north of Tampa—is one of the healthiest seagrass habitats in the state.¹⁵ Here, seagrass mingles with mangrove islands, salt marsh, naturally occurring algae, sponges, and corals to provide habitat for recreationally and commercially important marine species that are the lifeblood of the region’s economy. The area is home to the “Manatee Capital of the World” and hosts world-class fishing and recreational opportunities that draw hundreds of thousands of tourists, support thousands of jobs, and generate millions of dollars annually.

Romona Robbins Getty Images

Florida Seagrass Delivers Economic Bounty

• Florida seagrass beds contribute more than $20 billion a year to the state’s economic health by providing habitat for commercially and recreationally important finfish and shellfish, stabilizing the seafloor, and filtering pollution, which keeps the water clear and healthy for marine species and human enjoyment.¹⁶
• Coastal tourism and recreational activities in the Nature Coast counties generate more than $250 million for the region’s economy, provide about 8,000 jobs, and support nearly 500 businesses.¹⁷
• Approximately 70 percent of the species that fishermen target in Florida, including redfish, grouper, and tarpon, spend at least part of their life cycle within seagrass communities.¹⁸
• Commercially fished seagrass-dependent species generate more than $12 million in average annual revenue in the Nature Coast counties.¹⁹
• Since 2003, Citrus and Hernando counties each reaped nearly $2 million a year in economic impact from recreational scallop harvesting in seagrass areas, and in Pasco County, seagrass provided essential habitat that helped the diminished scallop population recover sufficiently to support 10-day mini-seasons in 2018 and 2019.²⁰

Charlie Shoemaker The Pew Charitable Trusts

Carol Grant

Charlie Shoemaker The Pew Charitable Trusts

Seagrass damage threatens Florida’s economy  

Florida’s seagrasses are threatened by stormwater runoff, failing septic tanks, agricultural nitrogen pollution, coastal development, disease, warming waters, and a host of other problems.

During the 20th century, Florida’s seagrass experienced large acreage declines as well as changes in species, density, and size of beds. Recent efforts to improve water quality and clarity have increased seagrasses in a few Florida estuaries, but total seagrass coverage in coastal waters continues to decline along most of the state’s shoreline.

Although excellent water quality along the Nature Coast has generally kept the region’s seagrass habitats healthy and stable, the lush beds are showing increasing signs of thinning.²¹ Many of the threats to Nature Coast seagrass are shared by meadows in other locations around the state and country, but two issues stand out along the Nature Coast:

• Physical damage from boats. Hulls and propellers slice through grasses or rip their roots from the bottom, leaving barren channels known as prop scars. Historical surveys indicate that as much as 40,000 acres of Nature Coast seagrass has experienced some level of prop scarring from careless boaters,²² and heavy localized scarring continues around several nearshore keys and spring-fed river mouths.²³ Once this scarring occurs, tides, storms, and algal growth can quickly deepen and widen the cuts, leading to further loss of seagrass that can last for decades.²⁴
• Increasing tourist and retirement activity. As more people visit and move to the area, and as roads, housing, and other developments are built, additional polluted runoff may reach seagrass and block the sunlight these plants need. The total population of all Florida coastal counties is expected to double from 2010 to 2060, magnifying these stressors.²⁵

The Pew Charitable Trusts

Some of the worst damage to the state’s seagrass has occurred in the Indian River Lagoon on the east coast and in Florida Bay to the south. Polluted sediments and nitrogen-laden runoff have fueled repeated toxic algae blooms that have received national attention, and water quality has become so poor that sometimes just being close to the water has made people feel sick.²⁶ Under these harsh conditions, seagrass coverage in the lagoon has decreased more than 80 percent during the past decade, a loss of more than 42,000 acres.²⁷ 

As the lagoon’s health has deteriorated, so have the economic benefits of tourism, fishing, and recreational activities, which support local businesses supplying everything from bait to gas. Commercial fisheries in the area have declined precipitously, including a 72 percent reduction in shellfish landings and a 54 percent drop for finfish since 1996.²⁸ Despite a 12 percent increase in the local population during that time, boater registrations, primarily for small inshore and coastal vessels, fell 11 percent, indicating a decrease in overall fishing and recreational boating, which could jeopardize the $1.2 billion in annual consumer spending generated by these and other water-related activities.²⁹

Florida Bay, the marine gem of the world-famous Everglades National Park, also has experienced significant seagrass die-offs. A prolonged drought and high temperatures in the summer of 2015 damaged more than 40,000 acres of seagrass, followed two years later by Hurricane Irma, which swept through the region, further damaging the seagrasses and delaying recovery of beleaguered meadows.³⁰

Understanding the causes and consequences of seagrass loss is vital, because the most successful conservation efforts have been those that prevent, lessen, or remove threats and allow seagrasses—and the vital coastal economies they support—to recover and thrive.

Charlie Shoemaker The Pew Charitable Trusts

Efforts to protect seagrass in Florida  

Using funds from the Deepwater Horizon oil spill legal settlements, Gulf Coast leaders, including state and federal officials, university faculty members, and local citizens, are focusing on seagrass restoration, especially in Panhandle estuaries. In other parts of Florida, networks of federal, state, and county officials, nongovernmental organizations, and local communities are working together to find long-term solutions that can stem further declines of seagrass and set the stage for recovery.

Conclusion  

Seagrasses play a vital role in coastal ecosystems and support activities and businesses that power economies. But as chronic and acute threats increase in duration and frequency, these productive and diverse habitats are at growing risk. Given the right environmental conditions, seagrasses can recover from damage resulting from pollution, boat propellers, storms, warming ocean waters, and other stressors. Urgent action on the part of state marine resource managers, elected officials, and others can help protect, conserve, and restore these special habitats.

Endnotes

1. P.L. Reynolds, “Seagrass and Seagrass Beds,” Smithsonian Institution, https://ocean.si.edu/ocean-life/plants-algae/seagrass-andseagrass-beds.
2. K.L. Heck et al., “Trophic Transfers From Seagrass Meadows Subsidize Diverse Marine and Terrestrial Consumers,” Ecosystems 11 (2008): 1198-210, doi:10.1007/s10021-008-9155-y.
3. T. Carruthers, W. Dennison, and G. DiCarlo, “Seagrasses: Prairies of the Sea,” Integration & Application Network (University of Maryland Center for Environmental Science), Conservation International, 2010, http://www.seagrasswatch.org/publications.html; Reynolds, “Seagrass and Seagrass Beds.”
4. Carruthers, Dennison, and DiCarlo, “Seagrasses: Prairies of the Sea.”
5. Reynolds, “Seagrass and Seagrass Beds.”
6. Ibid.; R. Costanza et al., “Changes in the Global Value of Ecosystem Services,” Global Environmental Change 26 (2014): 152-58, http://dx.doi.org/10.1016/j.gloenvcha.2014.04.002.
7. Reynolds, “Seagrass and Seagrass Beds.”
8. Carruthers, Dennison, and DiCarlo, “Seagrasses: Prairies of the Sea”; D.A. Smale et al., “Spatiotemporal Variability in the Structure of Seagrass Meadows and Associated Macrofaunal Assemblages in Southwest England (U.K.): Using Citizen Science to Benchmark Ecological Pattern,” Ecology and Evolution 9 (2019): 3958-72, doi:10.1002/ece3.5025.
9. M.D. Spalding, R.D. Brumbaugh, and E. Landis, “Atlas of Ocean Wealth” (The Nature Conservancy, 2016), https://oceanwealth.org/wpcontent/uploads/2016/07/Atlas_of_Ocean_Wealth.pdf.
10. J.W. Fourqurean et al., “Seagrass Ecosystems as a Globally Significant Carbon Stock,” Nature Geoscience 5, no. 7 (2012): 505-09, doi:10.1038/ngeo1477.
11. E. Mcleod et al., “A Blueprint for Blue Carbon: Toward an Improved Understanding of the Role of Vegetated Coastal Habitats in Sequestering CO2,” Frontiers in Ecology and the Environment(2011), doi:10.1890/110004.
12. Reynolds, “Seagrass and Seagrass Beds.”
13. L.A. Yarbro and P.R. Carlson, “Seagrass Integrated Mapping and Monitoring Program: Mapping and Monitoring Report No. 2” (Fish and Wildlife Research Institute, 2016).
14. Carruthers, Dennison, and DiCarlo, “Seagrasses: Prairies of the Sea.”
15. L.A. Yarbro and P.R. Carlson, “Seagrass Integrated Mapping and Monitoring Program Report No. 3—Springs Coast Update” (Fish and Wildlife Research Institute, 2018), doi:10.13140/RG.2.2.12366.05445.
16. Yarbro and Carlson, “Seagrass Integrated Mapping and Monitoring Program Report No. 2”; R.J. Orth et al., “A Global Crisis for Seagrass Ecosystems,” BioScience 56, no. 12 (2006): 987-96, https://academic.oup.com/bioscience/article/56/12/987/221654.
17. Office for Coastal Management: Digital Coast, “Enow Explorer,” National Oceanic and Atmospheric Administration, https://coast.noaa.gov/enowexplorer/#/.
18. Florida Fish and Wildlife Conservation Commission, “Importance of Seagrass,” https://myfwc.com/research/habitat/seagrasses/information/importance/.
19. Florida Fish and Wildlife Conservation Commission, “Commercial Fisheries Landings Summaries,” https://public.myfwc.com/FWRI/PFDM/ReportCreator.aspx.
20. N. Blassy, “First Scallop Season Opens in Pasco County After More Than 20 Years,” WGCU News, July 23, 2018, https://news.wgcu.org/post/first-scallop-season-opens-pasco-county-after-more-20-years; B. Hall-Scharf et al., “Assessment of the Economic Impact Associated With the Recreational Scallop Season in Hernando County, Florida” (Florida Sea Grant College Program and the Food and Resource Economics Department, UF/IFAS Extension, 2018), https://edis.ifas.ufl.edu/pdffiles/SG/SG16100.pdf; T. Stevens et al., “Economic Impact on the Reopened Scalloping Area for Citrus County, Florida—2003” (Food and Resource Economics Department, UF/ IFAS Extension, 2004), http://edis.ifas.ufl.edu.
21. Yarbro and Carlson, “Springs Coast Update.”
22. F.J. Sargent et al., “Scarring of Florida’s Seagrasses: Assessment and Management Options” (Florida Marine Research Institute, 1995), http://aquaticcommons.org/114/.
23. Yarbro and Carlson, “Springs Coast Update.”
24. South Florida Natural Resources Center, “Patterns of Propeller Scarring of Seagrass in Florida Bay: Associations With Physical and Visitor Use Factors and Implications for Natural Resource Management” (Everglades National Park, National Park Service, 2008), https://www.nps.gov/ever/learn/nature/upload/Final%20PropScar%20Report%20Secure%20Low%20Res.pdf.
25. S. Cerulean, “Wildlife 2060: What’s at Stake for Florida?” (Florida Fish & Wildlife Conservation Commission, 2008), https://myfwc.com/conservation/special-initiatives/wildlife-2060/. 
26. L.E. Fleming et al., “Review of Florida Red Tide and Human Health Effects,” Harmful Algae 10, no. 2 (2011): 224-33, doi:10.1016/j.hal.2010.08.006. 
27. L.A. Yarbro and P.R. Carlson, “Seagrass Integrated Mapping and Monitoring Program Technical Report No. 3—Southern I.R.L. Update” (Fish and Wildlife Research Institute, 2018); L.A. Yarbro and P.R. Carlson, “Seagrass Integrated Mapping and Monitoring Program Technical Report No. 3—Northern I.R.L. Update” (Fish and Wildlife Research Institute, 2018).
28. East Central Florida Regional Planning Council and Treasure Coast Regional Planning Council, “Indian River Lagoon Economic Valuation Update” (Florida Department of Economic Opportunity, 2016), http://tcrpc.org/special_projects/IRL_Econ_Valu/ FinalReportIRL08_26_2016.pdf.
29. Ibid.
30. South Florida Natural Resources Center, “2015 Florida Bay Seagrass Die-Off” (Everglades National Park: National Park Service, May 2016), https://www.nps.gov/ever/learn/nature/upload/seagrass-Dieoff_final_web_hi_res.pdf.