Seagrass Disappearing From Florida's Tampa Bay, New Survey Shows

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F​lorida's Tampa Bay has been considered a model of water quality restoration for decades.

B​ut a recent mapping survey showed the amount of seagrass in the bay has dropped by nearly 30% since 2016, according to a report by the University of South Florida Water Institute.

Scientists say a number of factors are at play, including pollution, algae blooms and climate change.

W​hat's Been Lost

The Southwest Florida Water Management District surveys seagrass in Tampa Bay and other waterways in the region every two years. The most recent map, for 2022, was released in February.

It was the third consecutive survey to show a decline in seagrasses in the bay, according to the USF Water Institute.

Surveys in 2014 and 2016 showed more than 40,000 acres, or about 62 square miles, of seagrass in Tampa Bay. That was the most since monitoring began in the 1980s.

That number dropped slightly in 2018 and more in 2020. By the 2022 survey, it declined to about 30,000 acres, or roughly 47 square miles.

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“Seagrasses are a foundational habitat of a healthy Tampa Bay — and this is a bellwether of things to come if we don’t maintain those persistent seagrass coverages in Tampa Bay,” Ed Sherwood, executive director of the Tampa Bay Estuary Program, told the Tampa Bay Times.

Some other waterways also saw losses, including Sarasota Bay, which is adjacent to the southwest corner of Tampa Bay.

What’s At Stake

Seagrass is vital to the health of Florida’s brackish and saltwater bays, rivers and estuaries. It helps filter sediment to keep water clear, prevents erosion and provides critical habitat and food for marine life. Seagrasses also serve as a carbon sink, helping to absorb world-warming carbon dioxide from the atmosphere.

Seagrasses in Tampa Bay reached a low point in the late 1970s and early 1980s. Local, state and federal agencies, as well as nonprofits and other groups, came together to work on ways to improve and monitor water quality. That included modernizing and replacing some wastewater treatment plants and reducing industrial pollution.

In the years after, the bay’s water became clearer. Manatees, once nearly extinct, rebounded. So did other wildlife. The U.S. Environmental Protection Agency called the Tampa Bay Estuary Program, started in 1991, a model for other communities to follow.

A massive loss of seagrass over several years in the Indian River Lagoon, on Florida’s Atlantic coast, is blamed for an ongoing manatee die-off that has killed hundreds of the iconic marine mammals since 2020.

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The waters of T​ampa Bay cover more than 400 square miles and are bordered by three counties – Pinellas, Hillsborough and Manatee. Besides environmental impacts, the bay plays an economic role through its three commercial ports and the 5 million tourists that visit the area each year, according to the estuary program.

W​hat’s Happening Now

R​ecent years have seen an increase in fish kills from red tide, including an outbreak that washed hundreds of tons of dead fish onto the shores of Tampa Bay in the summer of 2021. Scientists say nutrients such as fertilizer from stormwater runoff and other sources can fuel red tide growth. Hurricanes might also play a role by churning up deep water that brings red tide to the surface.

In the spring of that same year, millions of gallons of wastewater from a former fertilizer plant at Piney Point, on the bay's south side, were released into the bay when a holding pond sprung a leak.

Rainfall and power outages from h​urricanes and tropical storms can overwhelm water treatment systems across Florida. T​ens of millions of gallons of partially treated or raw sewage were dumped into Tampa Bay when Hurricane Hermine brought heavy rains to the area in 2016, according to the Tampa Bay Times. Before Hermine, a hurricane hadn't made landfall in Florida in 11 years.

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A​ series of storms since then, including Irma in 2017 and Ian in 2022, resulted in millions more gallons of wastewater discharges.

Nutrient pollution feeds algae blooms that, among other things, block out the sunlight seagrasses need to grow.

T​he Role Of Climate Change

Warmer temperatures can boost algae growth and extend the amount of time it may be present.

And because they need sunlight, seagrasses typically grow in water less than 6 feet deep. Sea levels in Tampa Bay have risen about 7.8 inches since 1946, according to a 2019 report from the Tampa Bay Climate Science Advisory Panel.

The National Oceanic and Atmospheric Administration projects additional sea level rise of about 1 to 1.5 feet by 2050, based on data from a monitoring station along the bay in St. Petersburg, Florida.

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E​ven with the decline in seagrass, numbers are still higher than at the peak of the bay's problems 40 years ago.

And Anastasiou said it's not too late for things to take a more positive turn.

“We have many groups that are working on tackling these issues on the technical level all the way up to the policy level,” he said.

“It absolutely can be turned around."

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