Seagrasses in Tampa Bay

Habitat monitoring surveys over the past eight years show a decline in seagrass acreage across the Tampa Bay estuary. A decline of 12% has occurred in the last two years alone. Seagrasses are vitally important to the Tampa Bay estuary because they support thousands of marine species, store carbon, protect coastlines from storm surge and improve air quality. Keep reading to learn more about the benefits of seagrasses and how we can help to protect them in the Tampa Bay estuary.

In marine and estuarine waters, seagrasses are grass-like, blooming vascular plants that are found entirely submerged in marine and estuarine waters. Water clarity, which affects how much light reaches the plant, limits the depth at which seagrass can be found. For these plants to grow through photosynthesis, they must have access to light, therefore seagrasses are limited to shallow areas.

Approximately 52 species of seagrasses exist worldwide. The 2020 Habitat Master Plan Update (Robison et al.) by the Tampa Bay Estuary Program identifies four species dominant in Tampa Bay out of the eight species found in Florida's marine waters.

• Seagrasses are sensitive to changes in water quality, thus they are an important indicator species that signals the bay's health (Sherwood et al., 2017, Greening et al., 2018).

• Seagrasses are a critical habitat and source of nourishment for marine flora and fauna, such as shellfish, finfish, crabs, turtles, manatees, and birds.

• The dense roots and rhizomes of seagrasses stabilize bottom sediments and reduce rates of shoreline erosion.

• Seagrasses provide water filtration services by removing nitrogen. It is estimated that the per acre value for denitrification services is $3,566.94 each year (Todd et al. 2023).

• Seagrasses play an important role in climate regulation by sequestering carbon through photosynthesis. It is estimated that the per acre value of the seagrass carbon sequestration is $83.36 each year (Todd et al. 2023).

Before the 1930s, it is thought that seagrass meadows covered 76,000 acres of Tampa Bay (Johansson, J.O.R et al., 2002). By the 1960s, the bay's water quality had significantly declined as a result of poor sewage treatment methods, an excessive amount of fertilizer loading, and dredging.

In the 1970s, a nationwide campaign to "Save our Bay" spurred coordinated efforts to raise water quality through cooperative bay management. The Clean Water Act and other federal and state laws have aided in the advancement of sewage treatment, industrial waste discharges, and urban stormwater management.

By the early 1980s, up to 70% of the original seagrass cover was disappeared. Cover increased by about 7,550 acres between the early 1980s and 2014 as the size and frequency of physical effects decreased and water quality improved.

In 2014, the seagrass extent reached 40,295.47 acres, exceeding the initial recovery goal of 38,000 acres set in 1996 (Sherwood et al., 2017). This means that the seagrass extent both met and exceeded the recovery objective. Survey results in 2016 revealed an all time high for seagrass acreage, surpassing the 1950 estimates for the first time.

2018 marked a turning point in seagrass coverage and was the first year since 1988 where acreage declined. Since 2018, Tampa Bay has lost more than 30% of seagrass coverage.

According to the 2020 Habitat Master Plan Update for Tampa Bay, two bay segments, Hillsborough Bay and Terra Ceia Bay, saw unusually large seagrass losses between 2016 and 2018. Nearly 30% of seagrass has been lost since 2016 (until 2022). These losses are likely due to direct physical damage from dredging and filling, propeller scars from boats, and indirect damage from light shade associated with deteriorated water quality brought on by algae blooms and suspended particles.

To visualize this trend, the map below compares areas of Seagrass in 2016 (map on left) and areas of Seagrass in 2022 (map on right).  Data  is sourced from the Southwest Florida Water Management District  seagrass mapping program .

The map shows regions of continuous (light green) and patchy (dark green) seagrasses (Definitions adopted from SWFWMD).

Continuous Seagrass - "These areas exhibit a continuous and uniform signature of >25% to 100% seagrass coverage, with less than 25% coverage of any area showing up as unvegetated bottom features."

Patchy Seagrass -"These areas appear as singular, rounded clumps, or elongated strands of isolated seagrass patches mixed with open bottom or sand. As well as areas that exhibit a uniform signature of seagrass and contain a low density of 10% to less than 25% seagrass coverage."

These losses are likely due to direct physical damage from dredging and filling, propeller scars from boats, and indirect damage from light shade associated with deteriorated water quality brought on by algae blooms and suspended particles.

The statistics above show a comparison between 2020 and 2022 seagrass coverage in the bay area. The Tampa Bay estuary lost approximately 4,161 acres, or 12%, of its seagrasses which is double the amount lost by Sarasota Bay. While other estuaries saw a decline in these species, Clearwater Harbor has worked towards bringing a positive change.

To see this trend, the map below compares areas of Seagrass in 2020 (map on left) and areas of Seagrass in 2022 (map on right).  Data  is sourced from the Southwest Florida Water Management District's  seagrass mapping program .

The map shows regions of continuous (light green) and patchy (dark green) seagrasses.

Congress's 1990 designation of Tampa Bay as an "estuary of national significance" laid the groundwork for the 1991 establishment of the Tampa Bay Estuary Program (TBEP). The Tampa Bay Environmental Partnership (TBEP) is a collaboration between the counties of Hillsborough, Manatee, Pasco, and Pinellas; the cities of Tampa, St. Petersburg, and Clearwater; the Southwest Florida Water Management District (SWFWMD); and the Florida Department of Environmental Protection (FDEP). Their goal is to create partnerships that will restore and safeguard Tampa Bay by putting a community-based, scientifically sound management plan into action.

Seagrasses are vital to our estuary's health. Revitalizing seagrass habitats should be an urgent priority for the Tampa Bay region. Community efforts are needed to bring about positive change to seagrass numbers. Small steps from the community can make a big difference.

• To address some of the major nutrient inputs to Tampa Bay, we must reduce fertilizer and pesticide use, maintain septic systems properly, dispose of animal waste responsibly, and reduce fossil fuel emissions.
• You can also support bay restoration efforts by purchasing a TBEP  Tarpon Tag specialty license plate  for just $17 per year, which funds Tampa  Bay Mini- Grants .

Robison, D., T. Ries, J. Saarinen, D. Tomasko, and C. Sciarrino. 2020. Tampa Bay Estuary Program 2020 Habitat Master Plan Update. Technical Report #07-20 of the Tampa Bay Estuary Program. Final report prepared by Environmental Science Associates. 136 pp. + appendix.

Todd, A., Walsh, H., Neville, J. 2023. Economic Valuation of Tampa Bay: Economic Impacts of Ecological Services, Amenities, and Industry Impacts. Final report prepared by the Tampa Bay Regional Planning Council.

Lizcano-Sandoval, L., Anastasiou, C., Montes, E., Raulerson, G., Sherwood, E., Muller-Karger, F.E., 2022. Seagrass distribution, areal cover, and changes (1990–2021) in coastal waters off West-Central Florida, USA. Estuarine, Coastal and Shelf Science 279, 108134.. https://doi.org/10.1016/j.ecss.2022.108134

Johansson, J.O. R., "Historical overview of Tampa Bay water quality and seagrass issues and trends" (2002). Reports. 147.