Concerns arise about amount of ‘gumbo’ algae found in upper Sarasota Bay

Sarasota Bay Estuary Program volunteers visit 10 sites to ascertain extent of problem

These are four sites that the Sarasota Bay Estuary Program volunteers visited, which show the presence of Lyngbya. Image from the SBEP website

On May 2, trained volunteers with the Sarasota Bay Estuary Program (SBEP) visited 10 sites in upper Sarasota Bay to investigate recent reports from fishing guides and long-term residents about “very substantial amounts of macroalgae on the bottom of the bay,” SBEP Executive Director David Tomasko reported on the nonprofit’s website.

In all of the locations, he wrote, divers found mostly a type of algae known as “Lyngbya,” whose scientific name is Dapis pleousa. Commonly called “gumbo,” he added, “it is the algae that you (and we) see floating around on the surface, and collecting wherever the wind blows it.”

A few other types of algae were discovered, but he believes, he noted, that “the Lyngbya algae is easily 90 to 95% of what we encountered out there.”

“[T]he ‘good news,’” Tomasko continued, “is that in areas where we still have seagrass, the Lyngbya did not appear to be overly problematic — the seagrass was still there …”

Moreover, he noted, “[I]f you cleared out the algae, the bottom was white sand, not black mucky organic-rich stuff.”

Conversely, Tomasko wrote, “[M]uch of that portion of the upper bay deeper than 4 to 5 feet that used to have seagrass no longer has seagrass. And in the absence of seagrass, it looks like this Lyngbya algae is growing in its place. And Lyngbya mats do not appear to have much habitat value — at all. We all noted the relative lack of fish in the area with mostly macroalgae.”

Then, on the other hand, Tomasko wrote, “[T]he water clarity “is really good, so how much of this is ‘new’ and how much of this is being able to see the bottom in 10 feet of water? I think it’s not entirely new, but I also remember lots of areas behind Jewfish and Sister Keys where there were beautiful grassbeds that are now sand, or sand and Lyngbya.”

This aerial map shows Jewfish Key and the Sister Keys. Image from Google Maps

The algae needs sunlight, he explained, “which is helped by the clear water. … And it needs nutrients,” which can come from humans, lost seagrass meadows, nutrients from the dead fish from the 2021 red tide event, and “nutrients from fertilized lawns and sewage spills and such.”

If local leaders can get the nutrients under control, Tomasko continued, that should foster new seagrass growth. Nonetheless, he suggested the potential of transplanting seagrass, a project on which he and others are working with state officials.

Given the water clarity, Tomasko pointed out, “I think what we might have is the old adage that ‘nature abhors a vacuum’ — or, if no seagrass meadows [are] around something will take advantage of that opening in the bay bottom and start growing.”

At least in Little Sarasota and Roberts bays, Tomasko noted, the “water quality is good, macroalgae is low, and it looks like we might be seeing some seagrass recovery in those areas — at least no further decline.”

A graphic shows Little Sarasota Bay, outlined in red. Image from the Sarasota County Water Atlas

Details about the macroalgae and the sites visited

In regard to the Lyngbya, Tomasko explained that it “starts out its growth by attaching to something on the bay bottom — seagrass blades or clam shells or sponges. It then grows upwards, and breaks off and floats on the surface. When you see it on the surface,” he continued, “it is typically not growing, but decomposing. Thus the smell …”

The sites the group visited, he noted, included areas north and south of Longbar Point, “on both the east and west sides of the bay.” The farthest southeast they went, he added, was to the seagrass beds on the shoals west of the Sarasota-Bradenton International Airport, “about a mile offshore of the runways.”

This aerial map shows the bay offshore of Sarasota-Bradenton International Airport. Image from Google Maps

He added, “The northernmost site … was about halfway between the northern tip of Jewfish Key and the western tip of Tidy Island.”
At each site, Tomasko explained, divers measured the amount of bay bottom covered with the macroalgae at three different locations, using a quadrant device measuring 50 centimeters by 50 centimeters.

This is a photo of the quadrant device that the volunteers used to measure the macroalgae. Image from the SBEP website

He also noted, “We focused our efforts mostly on the deeper areas of the upper bay where we lost about 2,000 acres of seagrass between 2018 and 2020. At those sites, the Lyngbya can cover 100% of the bottom, or be completely absent.”

Tomasko further added that the SBEP volunteers focused on waters deeper than 6 feet.

Although he did not have figures as of May 2 showing the percent of macroalgae coverage on the bottom or the biomass estimates, he wrote that he believes “they are going to come in somewhere about 50% or so, and with a biomass that doesn’t come close to what we picked up after Piney Point.”

The latter reference was to the April 2021, state-approved release of about 215 million gallons of contaminated water from the former site of a fertilizer plant. A leak was discovered in the plastic liner of one of stacks holding millions of gallons of wastewater left from the production of the fertilizer, which was between 1966 and 2001, the Tampa Bay Estuary Program explains.

The leak prompted state leaders’ worry that the collapse of that stack would lead to the destruction of hundreds of nearby homes and businesses.

In June 2021, Tomasko told the Sarasota City Commission that the effluent dumped into Tampa Bay “had a nutrient concentration 10 times higher than the worst performing wastewater treatment plant in Florida.”

An ensuing red tide event potentially was linked to the release of the effluent.

Since the beginning of the year, the Florida Fish and Wildlife Conservation Commission (FWC) has reported little evidence of the red tide algae, Karenia brevis, in Southwest Florida. The agency’s Jan. 14 update said the algae was observed at background concentrations in Manatee County, while the March 25 report noted background concentrations offshore of Collier and Monroe counties.

Then, again, on April 1 and April 22, FWC noted that Karenia brevis had been observed at background concentrations from Manatee County samples.

The prior report

In an earlier report — dated April 27 — Tomasko had noted that staff and supporters of the SBEP “have recently been quite excited about a potential turnaround in the health of Sarasota Bay.” The organization’s latest “report card” provided “evidence of the continued ‘good’ health of Palma Sola Bay in 2021, along with a recovery of water quality in the Upper Bay from conditions that existed in 2017 and 2018. The report card also indicates a recovery of ecosystem health in the three lower bays.”

Tomasko pointed out that those results were for 2021.

This chart shows the 2021 ‘report card’ for the bay. A score of 4 is the best. A score of 3.5 or higher indicates apparently healthy conditions; 2.5 to 3.49 indicates potential concerns; a score of 1.5 to 2.49 means conditions are problematic; and any score under 1.5 is a sign of multiple factors leading to degradation of the ecosystem, David Tomasko explained to the Sarasota City Commission last year. Image courtesy SBEP

Then he referred to the reports that the SBEP staff had received about the macroalgae, “from the shoreline adjacent to El Conquistador Parkway north of Bowlees Creek up to Longbar Point and areas offshore to the west.” He added that “it has been described as being highly unusual by people who have worked or recreated on the water for decades.”

A few potential sources for the macroalgae bloom, he noted were as follows:

  • 1) Lingering impacts of the 2,000-acre seagrass loss between 2018 and 2020, “which not only released a pulse of nutrients into the water column, but represents lost assimilative capacity.
  • 2) “[L]ingering impacts of the fish killed by 2021’s red tide, which was particularly bad in that part of the bay …
  • 3) “[I]mpacts associated with the massive cyanobacteria blooms we documented in Anna Maria Sound, which arose in the weeks to months after 2021’s Piney Point discharges.
  • 4) “[P]otential nutrient leaks from wastewater collection and treatment and disposal practices.
  • 5) “[R]esponse to substantial mangrove trimming along the bay, which can both increase local nutrient loads and also increase susceptibility of a water body to nutrient loads.
  • 6) “[O]ther sources.”

Nitrogen has been identified as the major food for the red tide algae. The Sarasota County Commission has allocated about half-a-billion dollars to converting its three major wastewater treatment plants to Advanced Wastewater Treatment (AWT) status, which, staff has pointed out, will result in a dramatic decrease in the nitrogen loads going into Sarasota Bay.

This May 8, 2019 graphic provided to the Sarasota County Commission shows details about the nitrogen loads from wastewater treatment plants in the county. Image courtesy Sarasota County

If the macroalgae persists, Tomasko continued in that report, “[I]t might also cause a loss of seagrass, which we believe was at least partly responsible for seagrass losses in the lower bay between 2013 and 2016.”

During a June 2021 presentation to the Sarasota City Commission on the 2020 bay “report card,” Tomasko pointed out that, 10 years earlier, Sarasota Bay was much healthier. The Upper Bay, he noted during that appearance, seemed to be most affected by the April discharge from Piney Point.