It’s not all bad news for South Florida’s waters, as some experts are casting a hopeful eye toward the future.
At a recent Biscayne Bay Marine Health Summit in Miami Beach, scientists from several South Florida universities, as well local planners and environmental activists detailed some of the positive signs ahead. The news comes from researchers, entrepreneurs, even the Department of Defense.
Consider:
— Broward County seems to have healthier coral than Biscayne Bay.
— Biscayne Bay’s decimated seagrass is showing signs of a comeback.
— Floating flower beds are being created to suck up water pollution.
— Lego-like modules are being installed to help fight storm surge.
Here’s a deeper dive into some of those initiatives.
Broward has less coral bleaching
Florida’s coral reef, the only one in the continental U.S., has been in a steady decline for years. But last summer it suffered some of its worst coral bleaching ever.
Bleaching happens when heat and other stressors cause the host coral to expel the algae that feeds it. When the algae vanishes, the coral turns white. If the water is too hot for too long, coral can die of starvation or become susceptible to disease.
Experts say the marine heat wave was partially to blame. But the University of Miami’s Cailyn Joseph discovered a strange finding: reefs south of Key Biscayne, which includes Biscayne National Park, were much worse off than the more urban areas of Miami and Broward County to the north.
Half of the Biscayne area’s corals were badly bleached last summer, while Broward’s and Miami’s reefs had four times as many healthy corals.
The heat stress on the coral locations was similar, so she looked for another factor.
She found that both areas had nutrient pollution, but the Broward and Miami areas had a higher ratio of phosphorus to nitrogen, and the damaged southern areas had a higher nitrogen-to-phosphorus ratio.
The high nitrogen is known to enhance coral bleaching.
Joseph said this high nitrogen could contribute to the severe bleaching — a key clue as to how to save a reef that is economically and environmentally crucial to the region.
But she said the nutrient ratios were clearly not the only driver. Light availability, water temperatures and historical bleaching could be at play, too.
Shark babies and their estuary need love
Marine biologist Catherine Macdonald, of the University of Miami, said that Biscayne Bay is a crucial juvenile habitat for 10 species of sharks, including the critically endangered great hammerhead.
“Shark nurseries are generally threatened globally,” she said. Here in South Florida they’re damaged by climate change, coastal development, poor water quality and habitat loss.
Some species gravitate to mangrove shorelines while others thrive in seagrass beds, both of which have declined significantly in South Florida. There’s a chain reaction. “We see reductions in prey species that make it harder for small sharks to survive,” she said.
As for climate change, she said, “I think that our juvenile sharks could be resilient to changing temperatures, but not necessarily in the face of the wide range of other stressors they have.”
She said the human world, especially in a place like South Florida, with its surplus of septic, sewer, lawn fertilizer and industrial runoff, can blast the natural world off balance. “We’re talking about mangroves and seagrasses and sharks. … I think people have a hard time drawing the connections between habitats or animals they care about and fertilizing their lawns.”
Seagrass starts a comeback
Pamela Sweeney, chief water scientist of Miami-Dade County, had some relatively good news about seagrass in northern Biscayne Bay, which entire food chains rely on. Between 2010 and 2018, the area north of the Tuttle Causeway lost 80% of its seagrass coverage.
In 2018 there was 5% total seagrass coverage. As of 2023 there was 40% seagrass coverage. Green alga coverage, which replaced seagrass, was at 40% in 2018, and down to 20% in 2023.
The new seagrass is not like the old seagrass. The species is called shoal grass, and it’s more nutrient-tolerant than the lush, billowing turtle grass that once covered nearly the entire area. But it’s a start. Turtle grass may take decades to recover, and only if nutrient loads are properly reduced.
Much of that has to do with leaking septic tanks. Commissioner Raquel Regalado said the county has identified 9,000 vulnerable septic tanks, many of them in the area that flows directly into the northern section of the bay. Sea-level rise makes the problem worse. The county has mandated that any new septic tanks must be fiberglass, which is quite costly, and motivates property owners to connect to sewer. They also have a septic-to-sewer conversion program making some headway.
The Department of Defense vs. storm surge
The U.S. military is fond of their oceanfront properties and wants to protect coastal cities from storm surge. To do so they’ve teamed with the University of Miami to try to design the perfect form of wave protection that will also enhance coral, thus growing as seas rise.
What Brian Haus and his team at the SUSTAIN lab at the University of Miami came up with something called a Seahive, which looks like a giant honeycomb pipe with holes in it.
You can stack them like Legos to create artificial reefs off shore. You can line them up in front of seawalls to snuff wave energy better than traditional rip rap. And you can use them as planters for green infrastructure such as mangroves.
But the Army Corps of Engineers needs proof that these things actually make a difference.
Haus and his team first tinkered with design concepts, such as hole placement and size, and materials that will enhance coral growth. The tinkering was done at the SUSTAIN Lab’s 75-foot-long wave simulator that recreates Category 5 hurricane conditions.
“The key to a lot of this is, how do we take the energy out of the waves without the wave bouncing off and hitting something else, which is what a sea wall does,” Haus said.
“We found certain arrangements of perforated holes in the structures do a surprisingly good job of reducing the wave energy,” he said. As waves travel over the honeycomb, the holes actually pull parts of the wave down, dismantling it into turbulence. “That causes a reduction of the wave energy without breaking or reflecting,” said Haus.
They’ve installed Seahive structures at various locations, including Wahoo Bay in Hillsboro Inlet, where they’re used as prototype mangrove planters, and off Miami Beach, as an artificial reef. The Department of Defense is studying that location to test effectiveness, and how to make them more conducive to coral growth. The Seahives also attract hierarchies of fish, from minnow to lobsters and grouper.
The coral adds an ecosystem benefit, but also ensures the reef will grow over time, adding height to the reef as sea levels rise.
Floating flower beds consume pollution
Nutrients are one of Florida’s and the nation’s largest pollution problems: Sources include agricultural runoff, pig farm effluent and sewer and septic leaks, said Jazmin Locke-Rodriguez, of Florida International University.
Nutrients such as phosphorus and nitrogen fuel harmful algal blooms that can be toxic to humans, pets and sea life, and choke out valuable seagrass beds. Natural wetlands soak up that pollution, but most have been filled in and paved over.
Locke-Rodriguez offered a partial solution: floating wetlands made of platforms that hold plants that suck up the nutrient pollution below. The roots dangle down into the water and absorb nutrients floating by. As a result, the plants are well fed.
She said the floating wetlands need to cover from 10% to 20% of a waterbody’s surface area to make a significant difference in pollution, and can remove up to 40% of phosphorus and 50% of nitrates and nitrites.
Traditional wild wetland plants grow well, but flowers are an excellent option. Thus her business startup, called Phytoflora, which aims to create floating flower farms in South Florida.
Marigolds and sunflowers do particularly well, and she said such operations could be commercially viable, especially since Miami is a global cut flower distribution hub.
Locke-Rodriguez and her team have worked out improvements in design and arrangement, but one thing they have not overcome yet — invasive iguanas love the flowers as much as humans do.
Bill Kearney covers the environment, the outdoors and tropical weather. He can be reached at bkearney@sunsentinel.com. Follow him on Instagram @billkearney or on X @billkearney6.