Is hot water hurting seagrass recovery in Tampa Bay? A new study aims to find out.

OLD TAMPA BAY — Sheila Scolaro took a long, deep breath.

The salty air whistled first into her snorkel, and then her lungs, before she leaned forward and plunged into the murky depths of Tampa Bay.

Cloudy green water hid the seafloor below. Looking through a diving mask, she could see a foot, maybe 2, in front of her.

Scolaro, a seagrass scientist, dove down with a question: How much seagrass is here?

After floating on the bottom for a few seconds, she surfaced with an answer.

“There’s no grass here,” she said. “Nothing.”

The observation didn’t come as a surprise to Scolaro, the community programs scientist for the Tampa Bay Estuary Program. After all, she was diving in Old Tampa Bay, the northwestern section of Florida’s largest open-water estuary, where more than 4,000 acres of seagrass, or 38%, disappeared between 2018 and 2020.

That’s why there’s another, broader question on Scolaro’s mind. It’s one of the main reasons she’s out here on a sizzling late-summer afternoon:

Are hot water temperatures hurting seagrasses’ chance to recover?

To answer that question, the estuary program has launched a five-year study to track water temperature in the shallow seagrass beds of Old Tampa Bay.

On this particular day at the end of August, Scolaro was placing underwater temperature monitors in six pre-selected parts of the bay. In three areas, seagrass has bounced back. In the other three, seagrass continues to struggle.

The process is repetitive but necessary: Scolaro uses zip ties to attach temperature monitors, which run about $100 each, to a metal anchor. On each dive to the seafloor, she screws them into the sand and muck on the seafloor. The coin-sized devices are programmed to record water temperatures for three seconds, every 10 minutes, for up to four days at a time.

Each year, researchers will monitor water temperatures from July through October — historically the hottest time of year. Data collected from this study will offer scientists a clue about how temperature might be thwarting restoration of one of Florida’s finest ecological jewels.

Tampa Bay faces a number of threats to its health, with human-caused pollution chief among them. But at a time when climate change is exacerbating warmer summers and hotter waters, sparking more seagrass-harming algae to thrive for longer, every piece of data counts in the fight to save the bay.

“Old Tampa Bay needs help,” Scolaro said from the stern of a turquoise boat owned by the nonprofit Tampa Bay Waterkeeper. It was just days before Hurricane Idalia skirted the Pinellas coastline, and the air was sticky and tropical.

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“There’s a lot of questions that we still don’t understand,” Scolaro said. “Things are changing in Tampa Bay and we’ve seen a lot of seagrass loss over the past couple of years. We’re trying to figure out what might be contributing to not only the loss but the lack of recovery.”

Old Tampa Bay at historic low seagrass coverage

In February, the long-anticipated results of a seagrass survey revealed the entire estuary lost 12% of its seagrass in just two years.

By far, the losses in Old Tampa Bay were the worst.

Here, an algae species known as Pyrodinium blooms and smothers the blades of aquatic vegetation on the bottom. The unique hydrology of this part of the bay — the way water moves — doesn’t help: It can take weeks for water to flush out of the system, bringing newer, cleaner gulf water along with it.

For these reasons and more, seagrass coverage in Old Tampa Bay is now at a historic low, according to the survey results from the Southwest Florida Water Management District. That can have serious implications: Not only is seagrass a crucial habitat for fish and other marine life, it stabilizes the sand and sediment on the seafloor, reduces shoreline erosion and produces oxygen.

Seagrass, in short, is a necessity for a healthy bay.

“The story of Old Tampa Bay is a really complicated one,” said Maya Burke, the Tampa Bay Estuary Program’s assistant director. “We know that this bay segment sees more harmful algae blooms than any other. And there’s a couple of ways that temperature might matter.”

For instance, temperature can determine how phytoplankton, a tiny marine algae, can grow or stay dormant in the water, Burke said. Or it can cause seagrass to conserve energy, causing the plant to shut down its reproductive system.

“Is there a temperature difference in the areas where we’re continuing to see seagrass and the areas where we’ve lost seagrass — but we know have supported seagrass in the past?” Burke said. “That’s what we’re trying to find out.”

Burke’s job on this late-August trip was to jump into the waist-high bay water and log Scolaro’s observations as she read them aloud, moving her snorkel to communicate each new data point. This was the team’s fifth research deployment into Old Tampa Bay this year, and it’s clear the duo has their tasks memorized and streamlined.

After the pair records the exact coordinates where the temperature monitors are left behind, the team motors away to the next spot in the bay. In the face of ecological decline, the team tries to keep their spirits up: Famed ska groups like Toots and the Maytals blast on the portable speaker between each destination.

Once the monitors have successfully logged data for four days, the research team heads back into the bay to retrieve them from the silty waters.

“An adult Easter egg hunt,” Burke calls it.

“Troubling signs of stress”

Old Tampa Bay continues to puzzle scientists. In many areas, nutrient pollution has been slashed and water quality targets are met.

So why is the seagrass still dying?

“We’re facing a new frontier in terms of understanding what’s going on in Old Tampa Bay,” Burke said. “We’ve seen troubling signs of stress where we’ve done all the right things. We’re not seeing the results we’d expect.”

This new temperature study should get researchers one step closer to determining what percentage of seagrass loss can be tied to temperature changes. Across the entire estuary between 2007 and 2021, average water temperatures have increased by about 1 degree Celsius, Burke said.

The study is beginning just as hot water temperatures have spurred national headlines, especially in Florida. This summer, an unprecedented marine heat wave, fueled by an El Niño weather pattern and supercharged by effects of climate change, has caused widespread coral bleaching off the Florida Keys. Shallow-water temperatures in South Florida have reached over triple digits.

Justin Tramble, executive director of Tampa Bay Waterkeeper, joined the research team as the research boat’s captain. He also took water quality measurements such as salinity while Scolaro and Burke were in the water collecting seagrass coverage data.

For Tramble, protecting Tampa Bay is protecting a lifestyle that includes recreating, angling and immersing in the natural wonder of the estuary. Many members of Tramble’s organization are fishing captains and speak regularly about the bay’s declining health they witness while out on the water.

“Something that we lean heavy into is the economic impact of having clean water,” Tramble said. “It supports our economy here.”

A new report led by the Tampa Bay Regional Planning Council, released this month, shows just how important a healthy Tampa Bay is for the region’s economy: The bay supports more than $32 billion in output each year. Restoring seagrass means keeping jobs alive in Tampa Bay, Tramble said.

“Tampa Bay supports our way of life, and having a better understanding of the bay will allow us, as a community, to protect it.”