Summary1. Gradients in competition and predation that regulate communities should guide biogenic habitat restoration, while restoration ecology provides opportunities to address fundamental questions regarding food web dynamics via large-scale field manipulations. 2. We restored oyster reefs across an aerial exposure gradient (shallow-subtidal-tomid-intertidal) to explore how vertical gradients in natural settlement, growth and interspecific interactions affected the trajectory of man-made shellfish reefs. 3. We recorded nearly an order-of-magnitude higher oyster settlement on the deepest (subtidal) reefs, but within a year abundance patterns reversed, and oyster densities were ultimately highest on the shallowest (intertidal) reefs by over an order-of-magnitude. 4. This reversal was due to (i) significantly elevated survivorship on intertidal reefs and (ii) larger surviving oysters on intertidal reefs. These patterns are likely to have developed from greater levels of biofouling and predator abundance (e.g. stone crabs, gastropods) on deeper reefs where aerial exposure was <5% of the monthly tidal cycle. 5. Synthesis and applications. The success of restoration initiatives involving habitat-forming species can be enhanced by accounting for the biotic interactions that regulate population fitness. In littoral systems, vertical gradients in predation, competition and disturbance can be exploited to guide restoration of vegetated (e.g. mangrove, seagrass) or biogenic reef habitats. In particular, our results demonstrate that paradigms of vertical zonation learned from the rocky intertidal and saltmarshes also describe the fate of restored shellfish reefs. As with rocky shores, the lower vertical limit of adult oyster distribution in our study system was most likely driven by predatory and competitive (i.e. smothering) interactions, with a threshold depth at c. 5% daily aerial exposure. Below this depth, experimentally restored reefs failed completely. As with Spartina saltmarsh, accumulation of oyster biomass was greatest at an intermediate vertical position relative to mean sea level (i.e. mid-to-low intertidal). Our developing model proscribes a vertical 'hot spot' for restoration efforts to maximize biogenic reef fitness and production.

No abstract

No abstract

The early life history of many marine organisms includes a dispersive planktonic larval phase which allows for the exchange of individuals among subpopulations. Knowledge of the degree of exchange, or connectivity, is critical to understanding the abundance and distribution of marine populations. Here, we applied geochemical tagging to assess estuarine‐scale larval connectivity among subpopulations of the commercially and ecologically important eastern oyster, Crassostrea virginica. To generate an “atlas” of geochemical signatures associated with spawning sites and potential dispersal pathways from spawning sites, we outplanted recently spawned oyster larvae to stationary moorings and surface drifters, respectively. Using the atlases generated from both outplant methods, we predicted natal origin, and thus larval connectivity, for newly settled oysters (spat) during three field trials over two summers (June 2013, June 2014, and August 2014), within three regions (∼ 35 km × 15 km quadrants) of Pamlico Sound, North Carolina, U.S.A. Patterns of larval connectivity varied both between months and annually but were predominately directed south to north following wind patterns. Predicted self‐recruitment was variable, as up to 100% of spat in a given region displayed signatures consistent with natal origin within that same region. Predicted connectivity patterns varied significantly based on atlases generated from outplanting on stationary moorings vs. surface drifters. For example, drifter‐predicted connectivity followed biophysical larval dispersal models more closely than mooring‐predicted connectivity, while mooring‐predicted connectivity displayed a higher diversity in larval sources. Both connectivity models highlight the need for resource management strategies such as reserve networks to incorporate designs that account for inherent variability in dispersal pathways.

Shoreline hardening is a major driver of biodiversity and habitat loss in coastal ecosystems yet remains a common approach to coastal management globally. Using surveys of waterfront residents in North Carolina, USA, we sought to identify factors influencing individual shore-protection decisions and ultimately impacting coastal ecosystems, particularly coastal wetlands. We found that neighboring shore condition was the best predictor of respondent shore condition. Respondents with hardened shorelines were more likely to have neighbors with hardened shorelines, and to report that neighbors influenced their shore-protection choices than respondents with natural shorelines. Further, respondents who expressed climate-change skepticism and preference for shoreline hardening were opposed to shoreline-hardening restrictions. Despite preferring hardening, respondents ranked wetlands as highly valuable for storm protection and other ecosystem services, suggesting a disconnect between the ecological knowledge of individuals and social norms of shore-protection decisions.However, our results also suggest that efforts to increase the installation of living shorelines have the potential to conserve and restore important coastal habitats and support biodiversity along shorelines that may otherwise be degraded by hardening. Further, encouraging waterfront-property owners who have adopted living shorelines to recommend them to neighbors may be an effective strategy to initiate and reinforce pro-conservation social norms.