INDIAN RIVER COUNTY — Indian River County has installed nearly 500 concrete oyster reef balls around Lauren's Island as part of an ongoing effort to restore oyster habitat in the Indian River Lagoon.
County staff selected the site near Riverside Park because environmental conditions make it suitable for oyster restoration and because the area once supported oyster habitat that has since disappeared.
"The site was chosen because there is a freshwater discharge coming through a drainage area just adjacent to Riverside Park there, and oysters, they have a specific salinity ratio that they prefer, but they're also filtering organisms," said Melissa Meisenburg, an environmental specialist with the county's Natural Resources Division. "The project was building basically a ring around the island to create oyster habitat where there had previously been oyster, but it had been lost just from changing ecology of the area."
The reef was designed to encourage oyster growth while maintaining access for fish and other marine life. The layout also takes into account the area's popularity with recreational boaters and kayakers.
"The site has about 350 linear feet of oyster reef balls. There are two rows of oyster reef balls to help build the reef. About every 55 feet, there is a five to six foot opening that allows for marine life to be able to freely move in and out of the area," Meisenburg said. "But we did place signage around it to notify boaters because it's also a popular area where people are coming in and out of Riverside. Whether they're renting boats or kayaking, we obviously don't want anybody to run into it."
The reef balls are made from marine-safe concrete mixed with crushed shell, a combination intended to encourage oysters to settle and grow naturally.
"Oysters are naturally attracted to chemical cues in the water for them to settle, so they look for hard substrates for one, but they're also looking for the calcium carbonate that is naturally released or found with an oyster reef," Meisenburg said. "And concrete, because this concrete actually also has crushed shell in it from other marine organisms, the crushed shell helps to attract oysters to that release of calcium carbonate as well as the concrete itself."
As oysters begin to establish themselves, the structures are also expected to support a variety of other species by providing shelter and surfaces for marine organisms to inhabit.
"They're not a solid object. They're hollow on the inside, and they have openings at the top and in random areas around the sides, which allows smaller organisms to move in and out among the oyster reef balls themselves and use them as sheltering areas," Meisenburg said. "On an oyster reef, we'll get small crabs, shrimp, you'll find tunicates and some macroalgae growing on it. And so those are the types of things that we're currently seeing on the reef balls, as well as the oyster accumulating."
A mature oyster reef can play an important role in the lagoon's ecosystem. Adult oysters can each filter up to 50 gallons of water per day, helping remove excess nutrients, but building a self-sustaining reef takes time.
"It can take time for a reef to become completely established," Meisenburg said. "What we hope is that with the accumulation of oyster on the oyster reef balls, we'll start to see bridging, which is where oysters connect from one reef ball to another by continually growing on top of each other."
County staff plan to monitor the restoration project beyond its first year to track how the reef develops over time.
"We won't just monitor for a year," Meisenburg said. "We'll monitor the site over multiple years to see how it changes and progresses."