One of the SEAHIVE units is lowered into the ocean off northern Miami Beach. Credit: Photos: Joshua Prezant/University of Miami

FL - Unique hybrid reefs deployed off Miami Beach

The first piece of a series of concrete structures was lowered into the water off the coast of Miami Beach on Wednesday morning, a massive crane on the deck of a floating barge hoisting the unit into the air and sinking it to the seabed.

During the next six hours, crewmembers aboard the barge would repeat that process until the structures, some stacked on top of each other, were settled on the seafloor, 14 feet below the surface.

To casual observers onshore, the daylong operation might have seemed routine. But this maritime activity was hardly run-of-the-mill.

In a project that could pave the way for greater efforts to protect coastlines from sea level rise and storm surge and serve as an innovative base structure to develop thriving coral reefs, a team of researchers and scientists from the University of Miami sunk 27 interlocking concrete structures that will form two hybrid reef units 1,000 feet offshore of North Beach Oceanside Park, at the northern edge of Miami Beach.

The units are the centerpiece of a project called Engineering Coastal Resilience Through Hybrid Reef Restoration, or ECoREEF, which combines cement- and nature-based strategies to foster coastal resilience. Supported by the University's Laboratory for Integrative Knowledge (U-LINK) and the City of Miami Beach, the project was developed at a time when coral reefs are struggling to survive. A recent study indicates that half of the world's living coral reefs have died since the 1950s. Meanwhile, other research has shown that healthy and complex coral reefs are able to buffer up to 97 percent of the energy from waves and can also reduce flooding frequency.

"Coral reefs are disappearing at alarming rates throughout the world as a result of disease and warming oceans, so our reefs have lost a lot of the structure they need to reduce wave energy," said ECoREEF lead investigator, Diego Lirman, an associate professor of marine biology and ecology at the University's Rosenstiel School of Marine, Atmospheric, and Earth Science.

"By placing these [hybrid] reefs near the shoreline and planting stress-tolerant corals on them, we hope to recover some of the lost services provided by healthy reefs, such as coastal protection, and to build a habitat for organisms like fish and lobsters."

One of the hollow structures submerged this week was shaped like a trapezoid, with rocks on its outer surface to mimic the texture of coral reefs and to attract marine life. The other unit is a series of hexagons, the iconic honeycomb-like shape that is being incorporated into more and more projects, including the powerful Webb Telescope.

Perforated to allow seawater to flow through them, the hollow, hexagonal SEAHIVE structures—tubes that look like honeycomb and each weighing 2,500 pounds—are stacked in a pyramid-like shape and attached to a few solid concrete SEAHIVEs to enhance the stability of the structure.

To build the hybrid structures, researchers also used an eco-friendly concrete mixture, with composite reinforcements instead of steel, both for durability and to attract marine life.

Haus and Rhode-Barbarigos peer through a six-foot-tall perforated SEAHIVE unit, which they designed with other faculty members, on the barge that lowered dozens of the units into the ocean.

"Designing structures to dissipate wave energy while providing a hospitable environment for corals has been a challenge," said Landolf Rhode-Barbarigos, an assistant professor in the College of Engineering, and one of the project's lead investigators. "There are no design guidelines for nature, but hopefully this can be translated into something bigger and provide novel solutions for coastal protection."

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