Artificial reefs offer mangrove-like nursery habitat in dockside settings

SARASOTA – In the mid-1990s, when David Wolff was a student at the University of South Florida, he interned for the Marine Habitat Foundation, a Lee County-based nonprofit that hoped to develop a sustainable way to farm-raise stone crabs and Florida lobsters.

It was part of the rush to find alternative careers for fishermen who would be affected by the state’s ban on gill nets. 

Wolff went on to work at the nonprofit. The plan failed in part because the wood and fiberglass structures were not sturdy enough to survive hurricane season and in part because filter feeders would attach to them.

But out of that failure grew an idea to construct artificial reefs that could encourage the growth of barnacles, tunicates and other filter-feeding organisms that clean seawater, as well as recreate an environment that mimics the safety of mangroves for juvenile fish.

In 2014, Wolff founded the nonprofit Ocean Habitats Inc. that now creates, sells and maintains artificial reef structures that can be attached to docks in canals and waterways.

There are more than 4,000 units installed in Florida and close to 5,000 elsewhere in the United States and other countries.

When most people think of artificial reefs, they think of reef balls that are made of microsilica concrete and are sunk offshore.

Those artificial reefs, Wolff said, are best used offshore as a habitat for adult fish.

“What our unit does is replicate nursery habitat, something more like mangrove trees,” Wolff said. “We’re trying to grow baby shrimp, crabs and fish.”

“Technically, they leave our units and someday may end up on the reef balls,” he added with a laugh.

In their current form, the Ocean Habitat artificial reefs are made of polypropylene sheet layers that are connected by cord and PVC tubes.

Ocean Habitat installs several types of units. One is a 24-inch wide, 36-inch long and 24-inch deep minireef that attaches to docks in canals.

In theory, more than 300 fish and 200 crabs per year can get their start in life at each minireef, which also theoretically filters 30,000 gallons of water per day, once barnacles, tunicates or other filter feeders attach.

A larger unit, 36 inches wide, 48 inches long and 24 inches deep, is also available.

Filter feeders that attach to the units live their whole life there, Wolff said, with the animals improving water quality in about a 10-foot radius.

As the filter feeders and macroalgae flourish, it creates the nursery environment.

“They have protection from the unit because larger fish can’t come in and eat them, and they have better water quality to grow up in,” Wolff said.

The increased presence of fish is what most people who have the minireefs notice first, said Jim McDaniel, the development director of the Center of Anna Maria Island, which is promoting use of the Ocean Habitats-made minireefs as part of a community science initiative.

The center has 145 units either installed or contracted for installation in and around Anna Maria Island – including 28 that will be paid for by an impact grant from the Community Foundation of Sarasota County.

McDaniel saw his first reef under the docks at Mar Vista Dockside Restaurant on Longboat Key. 

“They ride nicely underneath,” McDaniel said.

He noted that The Bridge Tender Inn & Dockside Bar in Bradenton Beach has the artificial reef system as well.

As part of the Go Green Campaign, McDaniel has been getting the word out around Anna Maria Island and getting approval from the island cities to start working with individuals who “want to see their docks become more alive with fish.”

Ocean advocate Philippe Cousteau, grandson of legendary oceanographic explorer Jacques Cousteau, spoke at the Go Green kickoff on Nov. 16, 2019, about the value of the artificial structures replicating the habitat of lost mangroves.

McDaniel is hopeful a partnership with Mote Marine Laboratory & Aquarium that would be funded by a state grant will come to fruition.

That would fund a program that would explore ways to mitigate the impact of red tide that would use everyone from snowbirds to full-time residents as citizen scientists, as well as students from the University of South Florida Patel College of Global Sustainability to monitor the impact of the artificial reefs on water quality.

Part of that calls for a station to be set up in the center, where the citizen scientists could analyze the water quality and file reports.

“I just believe that as we keep growing the reefs and the number of reefs out there and we have, hopefully a really highly developed and growing corps of volunteers, we’re going to be, in my vision, an epicenter of activism and research in Florida,” said McDaniel, who quickly clarified he meant citizen-based science and research.

McDaniel, who was hired as development director in July 2019, sees the water quality research as a way to unify people who use the center for a variety of activities ranging from fitness, sports leagues and senior activities in much the same way as the various Rotary clubs have a common cause of eradicating Polio.

“It was a serious bid to make the center relevant every day to everyone,” said McDaniel, who added that the impact of the 18-month red tide bloom weighed heavily on his choice.

Mote is already involved in citizen-based research using the Ocean Habitats reefs, in the Boca Grande area.

There, too, the interest grew out of the impact of the red tide bloom of 2018, as scientists wanted to see if the artificial structures could clean the water enough to mitigate the respiratory effects of red tide, noted Tracy Fanara, a staff scientist and environmental program manager at Mote Marine Laboratory.

Originally Mote wanted to know how many filter feeders attach to a certain surface area, as well as filtration rates.

Reefs were installed this spring in the Boca Grande area.

“It’s pretty awesome to see how many people in the community in Boca Grande participated and wanted one of these structures for us to conduct this research,” said Fanara, who will soon become the coastal modeling portfolio manager at the National Oceanic and Atmospheric Administration.

“What we are seeing, that the citizens are telling us, it’s bringing over fish, it’s creating an ecosystem that they love, that gets them more connected to our waterways and our environment,” Fanara said. “That’s what community science is all about, getting people involved and inspired, motivated to take actions in their everyday lives to make the world a healthier and more sustainable place.”

The most common species that attach to the minireefs are barnacles and tunicates.

Those aren’t the most efficient filter feeders, which means that while the minireefs can impact water quality, it likely would not be enough to mitigate red tide.

To do that, the scientists are looking into developing oyster-farm structures that could temporarily colonize an area and may have enough of an impact on the water quality to impact the effects of red tide.

While the Ocean Habitat reefs fall short in terms of red tide, they do impact the ecosystem.

“They are increasing habitat and promoting ecological diversity that’s absolutely wonderful,” Fanara said, though she quickly added that there is a concern about putting more plastic – even if it’s polypropylene, which has a reported life of 500 years – into the ocean.

There are thoughts to study the degradation rates of polypropylene structures, though the methodology is still being worked out.

It’s too expensive to monitor the water constantly, especially since degradation is more likely to happen in spurts, as structures break free.

Alternative materials, such as porous activated clay and concrete, are structurally sound but too heavy.

Fanara has hope for a biodegradable material colloquially known as “sustainable plastic,” currently being developed at the University of Florida, though she stresses it’s not plastic.

The filter feeders can still attach to the structures that would eventually degrade and leave the natural calcium carbonate.

Wolff notes that Ocean Habitats looked at several materials for sustainability and durability before going forward with polypropylene. Dating back to his work with Marine Habitat Foundation, he tested hundreds of materials, including wood and fiberglass, and shapes that would resist wave action, before establishing the current model.

His sons, David Wolf II and Alex Wolff, handle installation, as well as maintenance, including replacing any weak lines, to ensure that the reefs stay attached.

“One of the reasons we use polypropylene is because animals are able to attach to it, they’re able to get their hold fast on it and last their whole lives,” Wolff said. “It holds up decently to the sun, it holds up to saltwater and it holds up to thermal ranges without starting to disintegrate and release microplastics.

“All plastics eventually do that,” he added. “Sometime in the future, our units should be recycled – they can actually be recycled.”

Some of the units in place in canals off of Sanibel Island since 1992 were checked and recently moved to canals off of Marco Island and are thriving there.

“They were full of life, sponges, that kind of thing,” Wolff said. “We put them in wet towels and put them in the canal down in Marco and they’re doing their thing down there.

“They are built to last, they’re not built to fall apart the first wave that comes through.”

Interested?

• To learn more about Ocean Habitats, visit oceanhabitatsinc.com.

• To learn more about the Center for Anna Maria Island, visit centerami.org.

• To learn more about Mote Marine Laboratory & Aquarium, visit mote.org.