BATON ROUGE, La. – Louisiana’s issues with coastal land loss are well-documented. Scientists estimate that since 1930 as much as 25 square miles of land per year have been lost in the Mississippi River delta area. Much of these losses can be traced to land subsidence – land simply sinking and being covered by water – and erosion from wave energy.
Megan Lapeyre, an estuarine ecologist with the LSU AgCenter’s School of Renewable Natural Resources and the U.S. Geological Survey, is studying engineered reefs and examining how these reefs perform in stabilizing land primarily in areas of high wave energy.
“We are studying these reefs in three different areas. One in the Vermilion Bay area, one in Grand Isle and another in the Biloxi marsh area,” she said.
Lapeyre said one goal of the studies is to answer just how effective reefs are for shoreline stabilization. “Ideally, they would assist in creating marsh,” she said. “At this point, it is too early to tell.”
Both public and private entities have provided financial support, with funding coming from the Louisiana Department of Wildlife and Fisheries and The Nature Conservancy.
Lapeyre said the engineered reefs may not only provide shoreline stabilization but also create habitat for marine organisms. “The reefs are designed to encourage oyster recruitment and offer a place for fish to spawn or be a refuge from predators,” she said.
Two designs are being used for the construction of the reefs.
One is a concrete-rebar model that is triangular-shaped and is placed in an interlocking fashion. The rebar is designed to degrade in approximately 15 years, leaving behind a reef consisting of recruited organisms.
The second reef is a concrete mixture shaped in a circular form resembling a tire. Researchers hope it, too, will become covered with living organisms.
Lapeyre reported that preliminary data had shown the reefs have provided habitat for a number of fish and crustaceans, including blue crab, bay anchovies and gulf menhaden (pogy). Researchers used a variety of nets to sample the organisms that were using the reefs.
Another facet of the research is examining the role of the reefs in filtering water. The successful recruitment of a viable oyster population is essential for water filtration to occur, Lapeyre said.
“The filtration abilities of the oysters would be a primary contributor to enhancing water quality and clarity, but the reefs’ ability to absorb wave energy would also be a factor,” she said.
Lapeyre noted that not all sites experiencing coastal land loss are suitable for the reefs. She said land that is subsiding would not be an ideal location. Areas that experience high boat traffic and are exposed to wave energy created by localized storms would be better suited.
Another factor in site selection involves choosing locations that are conducive to oyster survival. In order for the reefs to be successful, oysters will play a crucial role. Issues such as water salinity and the firmness of the water bottom should also be considered, Lapeyre said.
“Many of the questions can’t be answered within a short time. Additional monitoring time will be needed to determine whether this is a viable solution to shoreline stabilization,” she said.