OYSTER REEFS AND DRAWDOWNS

Increasing water quality in nearshore habitats continues to be of great benefit to improving fish habitats in the Indian River Lagoon (IRL) and St. Lucie County. The IRL continues to be a source of fish recruits for St. Lucie County’s artificial reefs with oyster reefs and muck removal projects being used to increase water quality in the IRL and improve fish habitat.

The ability of oysters to filter the water column of nutrients is well documented. Oysters are filter feeders, consuming microalgae floating in the water column, and incorporating nutrients in the algae into their tissues and waste products. Besides acting as biological filters, oysters can improve water quality by their effect on wave energy. Oysters can grow in intertidal areas. When waves hit exposed oyster reefs, the wave energy decreases and sediments suspended in the water fall out of solution. This settlement means that there are less sediments in the water column, which results in clearer water and greater seagrass growth.

Oyster reefs can also improve water quality by deflecting stormwater effluents. If oyster reefs are placed in front of stormwater outfalls, the reef will deflect stormwater flow. In some instances, flow from a two-foot outfall may originate from a drainage basin of hundreds of acres. Compressing all of the stormwater into a small diameter outfall can increase the velocity of the stormwater effluents, scouring any seagrasses which may be growing near the outfall.

On March 5, Boy Scout Troop 58 out of Oviedo, led by local SeaGrant Extension Agent Vincent Encomio, deployed two oyster reefs at the Old Fort Park stormwater outfall in the City of Fort Pierce. The deployment was notable in that it was a combination of the Boy Scouts, Florida SeaGrant, the University of Florida, and the St. Lucie County Artificial Reef Program. The modules used were a new plastic-free, prism-shaped design, formulated at the University of Florida, and constructed and filled by the Boy Scouts and Florida SeaGrant. The modules were filled with oyster shells donated by the Indian River Lagoon Aquatic Preserve and are hoped to become the basis for a living shoreline demonstration project at Old Fort Park.

The St. Lucie County Artificial Reef Program has become involved with a project in Moore’s Creek that will also affect water quality in the Indian River Lagoon. Moore’s Creek is an urban tributary running through the heart of the City of Fort Pierce. Its headwaters were cut off by the construction of Interstate 95 and flow of water into the Indian River Lagoon was reduced by a salinity control structure in the 1960s. Clean headwaters have been replaced by stormwater effluents.

In an effort to aid volunteers with the Marine Cleanup Initiative in removing trash, the City of Fort Pierce has started to lower water levels in the creek. After the second and third drawdown, it was noticed that muck levels in the creek bottom had started to decline. Lowering water levels to oxidize muck sediments in natural water bodies is a common practice but is usually accomplished when levels can be lowered for months, not days. The Florida Fish and Wildlife Conservation Commission and the St. Lucie County Artificial Reef Program are studying this drawdown technique to see if it might be used in larger tributaries. Irrespective of the mechanism, reductions in muck in the tributaries to the Indian River Lagoon will have a beneficial effect on the lagoon’s water quality, sending more fish to artificial reefs offshore.

For more information on the St. Lucie County Artificial Reef Program or to get involved with water quality restoration efforts, contact Jim Oppenborn, St. Lucie County Coastal Resources Coordinator, at oppenbornj@stlucieco.org or (772) 462-1713.