Reef restoration: Using habitat structure, hydrodynamics, and target species ecology to develop design criteria

Global decline of coral and oyster reefs has led to a growing number of efforts to restore biogenic reef ecosystems. At present, the goal of most reef restoration efforts is to rebuild the physical structure of the reef and success is dependent on natural recruitment processes. Even though providing structure is the primary means of reef restoration, few studies have explicitly examined which aspects of reef topography are most important to enhancing target species recruitment and survival. Successful reef restoration will depend on providing structure that maximizes recruitment and survival of biogenic reef building organisms. This body of work examines the influence of intermediate-scale habitat structure on the recruitment of corals and oysters with the goal of developing design criteria for biogenic reef restoration.;The influence of intermediate-scale habitat structure on recruitment was studied on coral reefs in Belize and oyster reefs in Alabama. Initial observations of coral community structure in spur-and-groove environments of Belize supported the hypothesis that facilitative succession occurs during spur formation. Massive coral species appear to ameliorate physical stress, allowing branching and foliose species to recruit, survive, and eventually overgrow massive species. Research following Hurricane Mitch documented the influence of reef topography on coral recruitment. Substratum topography at the 15-cm scale was the best predictor of recruit density and several coral species displayed nonrandom patterns of recruitment with respect to substratum angle.;Studies of natural oyster reefs and shell plantings in Alabama demonstrated that natural oyster reefs have a significantly higher degree of habitat heterogeneity and complexity than shell plantings, resulting in higher recruitment rates to natural oyster reefs. A model based on detailed studies of the hydrodynamic regime over the two types of reefs predicted similar flux of larvae to both reef types. In contrast, flume experiments with settlement-ready oyster larvae resulted in higher net delivery of larvae to natural reefs than to shell plantings.;Research on both oyster and coral reefs demonstrates the importance of intermediate-scale topography to target species recruitment and suggests design criteria that have the potential to improve existing techniques for reef restoration.