Florida's Red Tide Is Decimating Marine Plants

Seagrass growing in the waters off Florida's Gulf Coast has been dying off at a rapid rate over the past few years as a result of toxic red tides and other environmental stresses, and that's having a damaging effect on marine wildlife.

The Southwest Florida Water Management District has found that since 2016, Tampa Bay has lost 30 percent of its seagrass, with nearby Sarasota Bay losing 26 percent.

Between 2020 and 2022 alone, Tampa Bay's seagrass declined by over 4,000 acres, totaling around 12 percent of its coverage.

"It's a mixed bag," David Tomasko, executive director of the Sarasota Bay Estuary Program, told the Miami Herald. "In 2020-22, we lost 5 percent of our seagrass meadows. The two years before that, we lost 18 percent."

These declines are thought to be the result of water pollution and the resulting so-called red tides.

Red tides are harmful algal blooms, often caused by an algae called Karenia brevis.

"It occurs naturally in the Gulf of Mexico at low concentrations, but occasionally develops into dense blooms. The hot spot for these blooms is along the coastline from around Tampa Bay to Naples," Larry Brand, a professor of marine biology and ecology at the University of Miami's Rosenstiel School of Marine and Atmospheric Science, previously told Newsweek.

Seagrasses are plants that grow on the seafloor, usually in the shallows, as their growth is limited by the amount of light that they can receive.

Red tides can result in massive reductions in seagrass coverage. During large blooms, the algae of the red tides can grow to form large mats, blocking the sunlight from reaching the plants growing on the seabed, causing them to die and eventually rot, further feeding the algal bloom.

In the Indian River Lagoon on the east coast of Florida, over 32,000 acres of seagrass were lost between 2009 and 2012 as a result of red tides, resulting in a local reduction of seagrass cover of around 60 percent.

These meadows of seagrass, which cover around 2.7 million acres along Florida's coastline, are hugely important to the marine ecosystem, sheltering and feeding marine life like the manatee and hundreds of other species, preventing coastal erosion and storing carbon.

Red tides, and therefore their effect on the seagrasses, are worsened by environmental pollution containing nitrogen and phosphorous. These chemical fertilizers cause the algae to grow at accelerated rates.

"Blooms result from a complex sequence of events starting with conditions that favor their growth more than 80 miles offshore in the Gulf, currents that move them toward shore, and pollution that intensifies and prolongs the blooms," Don Boesch, a professor of marine science at University of Maryland Center for Environmental Science, previously told Newsweek.

"A particularly important contributor to this land-based pollution is runoff flowing down Florida rivers of excessive nitrogen, a nutrient which stimulates the blooms."

It is thought that the seagrass declines on the Florida Gulf Coast may be related to pollution released from an industrial site on Piney Point. Some 215 million gallons of contaminated water were released from the site, authorized on March 30, 2021 by the Florida Department of Environmental Protection.

"Piney Point was probably the worst thing that happened to Tampa Bay for 50 years," said Tomasko. "It was like 200 million gallons of liquid fertilizer. It's going to take awhile for us to get through this. It's going to have manifestations."

"We believe that a certain amount of this loss of seagrass is attributed to Piney Point," Tomasko said. "We also believe that it created some of the worst macroalgal blooms in upper Sarasota Bay in people's memory."

Nitrogen pollution feeds algae, causing blooms to grow larger and faster, therefore killing more and more seagrass and as a result many marine animals that are dependent on it.

According to the Florida Fish and Wildlife Conservation Commission (FWC), there have been 59 manatee deaths recorded in Lee County alone in 2023, which is a 126 percent increase from the first three months of 2022. Across the state, 215 deaths have been recorded in 2023 so far.

"Their food is sea grasses and we have seen sea grasses decline in Lee County," James Douglass, a professor at the Florida Gulf Coast University Water School, told local news FOX4 regarding the recent manatee deaths. "We might also be seeing some pure starvation happening."

This is not just due to the loss of seagrass, which the manatees eat, but due to the toxins produced by red tides called brevetoxins, which can be breathed in by the marine mammals, or eaten if the algae coats the blades of seagrass. These toxins can also result in the deaths of dolphins, sea turtles, sea birds and fish, sometimes causing thousands of fish carcasses to wash up on beaches.

"It's further evidence that we really need to get our act together quickly," Tomasko said.

"If you lose too much seagrass, there's a concern that you'll be [seeing] a different system moving forward. You won't have seagrass; you'll have a system dominated by algae."

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