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The blue crab (Callinectes sapidus) is ecologically and economically important in Chesapeake Bay. Nursery habitats, such as seagrass beds, disproportionately contribute individuals to the adult segment of populations. Salt marshes dominated by smooth cordgrassSpartina alternifloraare intertidal nursery habitats which may serve as a refuge from predation for juvenile blue crabs. However, the effects of various characteristics of salt marshes on nursery metrics, such as survival, have not been quantified. Comparisons of juvenile survival between salt marshes and other habitats often employ tethering to assess survival. Although experimental bias when tethering juvenile prey is well recognized, the potential for habitat-specific bias in salt marshes has not been experimentally tested. Using short-term mesocosm predation experiments, we tested if tethering in simulated salt marsh habitats produces a habitat-specific bias. Juvenile crabs were tethered or un-tethered and randomly allocated to mesocosms at varying simulated shoot densities and unstructured sand. Tethering reduced survival, and its effect was not habitat specific, irrespective of shoot density, as evidenced by a non-significant interaction effect between tethering treatment and habitat. Thus, tethering juvenile blue crabs in salt marsh habitat did not produce treatment-specific bias relative to unvegetated habitat across a range of shoot densities; survival of tethered and un-tethered crabs was positively related to shoot density. These findings indicate that tethering is a useful method for assessing survival in salt marshes, as with other nursery habitats including seagrass beds, algae and unstructured sand. 

Restoration of native oyster ( Crassostrea virginica ) populations in Chesapeake Bay shows great promise after three decades of failed attempts. Population models used to inform oyster restoration had integrated reef habitat quality, demonstrating that reef height determines oyster population persistence and resilience. Larval recruitment drives population dynamics of marine species, yet its impact with reef height and sediment deposition upon reef restoration is unknown. To assess the influence of reef height, sediment deposition and larval supply, we adapted a single-stage population model to incorporate stage structure using a system of four differential equations modeling change in juvenile density (J), and changes in volume of adults (A), oyster shell reef (R), and sediment (S) on an oyster reef. The JARS model was parameterized with empirical data from field experiments. Larval supply included larvae from the natal population and from outside populations. The stage-structured model possessed multiple non-negative equilibria (i.e., alternative stable states). Different initial conditions (e.g., oyster shell reef height) resulted in different final states. The main novel findings were that the critical reef height for population persistence and resilience was jointly dependent on sediment input and larval supply. A critical minimum larval supply was necessary for a reef to persist, even when initial sediment deposition was zero. As larval supply increased, the initial reef height needed for reef persistence was lowered, and oyster reef resilience was enhanced. A restoration oyster reef with higher larval influx could recover from more severe disturbances than a reef with lower larval influx. To prevent local extinction and assure a positive population state, higher levels of larval supply were required at greater sediment concentrations to overcome the negative effects of sediment accumulation on the reef. In addition, reef persistence was negatively related to sediment deposited on a reef prior to larval settlement and recruitment, implying that restoration reefs should be constructed immediately before settlement and recruitment to minimize sediment accumulation on a reef before settlement. These findings are valuable in oyster reef restoration because they can guide reef construction relative to larval supply and sediment deposition on a reef to yield effective and cost-efficient restoration strategies.