Use of Bioengineered Artificial Reefs for Ecological Restoration in Estuarine Environments

Abstract

Bioengineered reefs have been developed that enhance natural spatset of oysters Crassostrea virginica and other sessile organisms, and can be emplaced in appropriate coastal waters. These reefs encourage growth of desired organisms and, in areas where regeneration of oyster populations are needed, can in themselves constitute ecological restoration. However, in addition to hosting sessile organisms, these reefs, which have high porosities (material use is less than 20% of usual rock breakwaters), also allow juvenile fish to find shelter and may enhance sedimentation or reduce erosion. Engineering design has focused on optimizing growth of organisms, allowing potential harvest, reducing wave erosion, sequestering carbon for long periods (millennia), and assisting in coastal wetlands restoration. Growth of organisms is enhanced by providing larger amounts of surface area (more than twice the surface area compared to rock) and including attractants (agricultural byproducts which release nitrogen compounds), as well as by the geometry. Harvest could be made from such reefs, and, since they are engineered, they can be made more harvestable. Wave energy is reduced more as growth occurs, so this is a potential negative when first emplaced, but allows enhanced sustainability over time, while carbon is sequestered in shells long term. The current coastal settlement rate of ~1-2 cm/yr allows carbon sequestration that could offset millions of tons annually in large emplacements. Finally, coastal wetlands are enhanced both by reduction of erosion and by enhanced habitat for juvenile fish and plant species. The potential for ecological restoration has only begun to be explored.