Tampa Bay lost about 13 percent of its seagrass in recent years, a survey shows, leaving the ecosystem short of a goal for building upon decades of environmental progress.
Between 2018 and 2020, the bay saw an estimated decline of 5,411 acres of seagrass, according to reviews from the Southwest Florida Water Management District.
“That’s ... less area for manatees to feed on, for fish to hide out and crabs to hide out in their early life stages,” said Maya Burke, assistant director of the Tampa Bay Estuary Program, which announced the news this week. “That’s not just noise.”
Scientists say pollution from runoff and wastewater leaks adds nutrients to the bay, fueling algae growth that hurts seagrass beds.
Tampa Bay contained about 35,240 acres of seagrass, according to an estimate based on aerial pictures. The results, Burke said, track with what Tampa Bay Estuary Program staffers have seen examining tracts of seagrass in the water.
Chris Anastasiou, chief scientist at the Water Management District, said the acreage estimate brings the bay down to a level similar to 2012.
“We’re definitely concerned,” he said. “But 35,000 acres is still quite a lot of grass.”
Seagrass is a keystone of the ecosystem, according to Anastasiou. His agency surveys beds in Tampa Bay and to the south every two years.
“It’s a great way to measure the overall health of an estuary,” he said.
Big algae are replacing seagrasses in some parts of Tampa Bay, according to the local Estuary Program, which works on restoration. The organization recently upped a goal to maintain at least 40,000 acres of seagrass in the bay, compared to a previous target of 38,000 acres. The latest results show the region would be short by either measure.
Seagrass supports clearer water, feeds animals such as turtles and acts as a nursery for fish. Burke said it is a “workhorse” that helps trap carbon, too, forming a natural defense with marshes and wetlands against emissions that worsen climate change.
Seagrass recovery in Tampa Bay is celebrated as an environmental success story. In the 1980s, according to the Estuary Program, mapping showed the bay had less than 22,000 acres, damaged by dredging and people using the water as a dumping ground. Progress came with reductions in pollution.
The biggest area of concern today is Old Tampa Bay, an upper part of the estuary off Largo, where a type of algae known as Pyrodinium has bloomed. It can pass toxins to shellfish, Burke said, and scientists believe the blooms may be connected to the loss of seagrass beds. Old Tampa Bay, she said, is a spot where stormwater outfalls dump nutrients and causeways contribute to sluggish circulation, meaning the water does not flush quickly.
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Researchers are further interested in figuring out whether climate change — namely warmer weather — is worsening the situation by prolonging blooms as conditions stay ripe for the algae to grow, she said.
Seagrasses need sunlight and struggle when algae shade the water.
Declines are not limited to Tampa Bay. Estuaries down Florida’s Gulf Coast saw similar drops. Charlotte Harbor’s total shrunk by 23 percent, Anastasiou said, to the lowest level since the Water Management District began mapping in 1988.
In Sarasota Bay, seagrass dropped by 18 percent, or roughly 2,000 acres, between 2018 and 2020, said David Tomasko, executive director of the Sarasota Bay Estuary Program.
Both Charlotte and Sarasota have experienced bad Red Tide blooms, which Tomasko said could be to blame for losses in a section of his territory typically known for clear water. Though naturally occurring, he said, such harmful outbreaks may grow more rapidly in water tainted by excess nutrients.
“We’re not going to ever prevent Red Tide,” Tomasko said. “But what we are trying to do is to minimize the role that humans have of making it worse.”
Water quality is under a spotlight this spring after the release of more than 200 million gallons of wastewater into Tampa Bay from the old Piney Point fertilizer plant property. Meanwhile, on the state’s East Coast, federal and state experts are investigating a manatee die-off centered on the Indian River Lagoon, which has lost tens of thousands of acres of seagrass amid persistent algal blooms.
Both Tomasko and Burke said they do not want their areas to become like the Lagoon.
Local leaders have plenty of reason to invest in updating wastewater systems, Tomasko said. People want to live by sparkling water, he said, and they pay expensive tax bills to do so. Algae, like slimy sea lettuce that bakes in the sun, turn Florida’s waterways smelly and dark.
“Who wants to live next to a bay where there’s rotting macroalgae?” Tomasko said.