In the high-salinity seaward portions of estuaries, oysters seek refuge from predation, competition and disease in intertidal areas 1,2 , but this sanctuary will be lost if vertical reef accretion cannot keep pace with sea-level rise (SLR). Oyster-reef abundance has already declined ∼85% globally over the past 100 years, mainly from over harvesting 3,4 , making any additional losses due to SLR cause for concern. Before any assessment of reef response to accelerated SLR can be made, direct measures of reef growth are necessary. Here, we present direct measurements of intertidal oyster-reef growth from cores and terrestrial lidar-derived digital elevation models. On the basis of our measurements collected within a mid-Atlantic estuary over a 15-year period, we developed a globally testable empirical model of intertidal oyster-reef accretion. We show that previous estimates of vertical reef growth, based on radiocarbon dates and bathymetric maps 5,6 , may be greater than one order of magnitude too slow. The intertidal reefs we studied should be able to keep up with any future accelerated rate of SLR (ref. 7) and may even benefit from the additional subaqueous space allowing extended vertical accretion.Oyster-reef communities (Crassostrea virginica) provide numerous ecosystem services, including production of oysters, water filtration 8,9 , provision of habitat for fishes and crustaceans 10 , shoreline stabilization 11,12 , and maintenance of estuarine-water alkalinity 13 . In the face of natural and anthropogenic stressors, such as harvesting, degrading water quality, increasing rates of SLR, warming, disease, ocean acidification, and parasitism, reef habitats and associated services are becoming unsustainable. Loss of these reefs in estuaries that otherwise lack alternative hard substrates is a global problem 4 . SLR, in particular, threatens oyster reefs in the high-salinity seaward portions of estuaries because there, oysters seek refuge from biofouling (space competition), predation and disease in intertidal areas 1,2 . The importance of the intertidal area to individual oyster growth in lower estuaries is apparent from experimental work that has shown intertidal oysters grow 34% faster and exhibit an order of magnitude less fouling (percentage cover) than subtidal oysters 14 . Constructed subtidal reefs in no-harvest sanctuaries (North Carolina, USA) were also found to have few, if any, live oysters (mean density of 0-92 live oysters m −2 ) after six years in euhaline waters, whereas intertidal reefs faired significantly better (200-225 live oysters m −2 ; ref. 15). Restoration is a common mitigation option for historic oyster-reef loss, but project success with accelerating SLR will depend on a reef 's ability to maintain an intertidal position. Model simulations presume that reef-accretion rates cannot exceed the rate of SLR, but parameterizations are not verified with direct measures of reef-scale growth 16,17 . Without direct measures of reef-scale growth, our ability to assess restoration and conservation ...

Carbon burial is increasingly valued as a service provided by threatened vegetated coastal habitats. Similarly, shellfish reefs contain significant pools of carbon and are globally endangered, yet considerable uncertainty remains regarding shellfish reefs' role as sources (+) or sinks (-) of atmospheric CO While CO release is a by-product of carbonate shell production (then burial), shellfish also facilitate atmospheric-CO drawdown via filtration and rapid biodeposition of carbon-fixing primary producers. We provide a framework to account for the dual burial of inorganic and organic carbon, and demonstrate that decade-old experimental reefs on intertidal sandflats were net sources of CO (7.1 ± 1.2 MgC ha yr (µ ± s.e.)) resulting from predominantly carbonate deposition, whereas shallow subtidal reefs (-1.0 ± 0.4 MgC ha yr) and saltmarsh-fringing reefs (-1.3 ± 0.4 MgC ha yr) were dominated by organic-carbon-rich sediments and functioned as net carbon sinks (on par with vegetated coastal habitats). These landscape-level differences reflect gradients in shellfish growth, survivorship and shell bioerosion. Notably, down-core carbon concentrations in 100- to 4000-year-old reefs mirrored experimental-reef data, suggesting our results are relevant over centennial to millennial scales, although we note that these natural reefs appeared to function as slight carbon sources (0.5 ± 0.3 MgC ha yr). Globally, the historical mining of the top metre of shellfish reefs may have reintroduced more than 400 000 000 Mg of organic carbon into estuaries. Importantly, reef formation and destruction do not have reciprocal, counterbalancing impacts on atmospheric CO since excavated organic material may be remineralized while shell may experience continued preservation through reburial. Thus, protection of existing reefs could be considered as one component of climate mitigation programmes focused on the coastal zone.

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.

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Very high-resolution satellite imagery (≤5 m resolution) has become available on a spatial and temporal scale appropriate for dynamic wetland management and conservation across large areas. Estuarine wetlands have the potential to be mapped at a detailed habitat scale with a frequency that allows immediate monitoring after storms, in response to human disturbances, and in the face of sea-level rise. Yet mapping requires significant fieldwork to run modern classification algorithms and estuarine environments can be difficult to access and are environmentally sensitive. Recent advances in unoccupied aircraft systems (UAS, or drones), coupled with their increased availability, present a solution. UAS can cover a study site with ultra-high resolution (<5 cm) imagery allowing visual validation. In this study we used UAS imagery to assist training a Support Vector Machine to classify WorldView-3 and RapidEye satellite imagery of the Rachel Carson Reserve in North Carolina, USA. UAS and field-based accuracy assessments were employed for comparison across validation methods. We created and examined an array of indices and layers including texture, NDVI, and a LiDAR DEM. Our results demonstrate classification accuracy on par with previous extensive fieldwork campaigns (93% UAS and 93% field for WorldView-3; 92% UAS and 87% field for RapidEye). Examining change between 2004 and 2017, we found drastic shoreline change but general stability of emergent wetlands. Both WorldView-3 and RapidEye were found to be valuable sources of imagery for habitat classification with the main tradeoff being WorldView’s fine spatial resolution versus RapidEye’s temporal frequency. We conclude that UAS can be highly effective in training and validating satellite imagery.

Within intertidal communities, aerial exposure (emergence during the tidal cycle) generates strong vertical zonation patterns with distinct growth boundaries regulated by physiological and external stressors. Forecasted accelerations in sea-level rise (SLR) will shift the position of these critical boundaries in ways we cannot yet fully predict, but landward migration will be impaired by coastal development, amplifying the importance of foundation species’ ability to maintain their position relative to rising sea levels via vertical growth. Here we show the effects of emergence on vertical oyster-reef growth by determining the conditions at which intertidal reefs thrive and the sharp boundaries where reefs fail, which shift with changes in sea level. We found that oyster reef growth is unimodal relative to emergence, with greatest growth rates occurring between 20–40% exposure, and zero-growth boundaries at 10% and 55% exposures. Notably, along the lower growth boundary (10%), increased rates of SLR would outpace reef accretion, thereby reducing the depth range of substrate suitable for reef maintenance and formation, and exacerbating habitat loss along developed shorelines. Our results identify where, within intertidal areas, constructed or natural oyster reefs will persist and function best as green infrastructure to enhance coastal resiliency under conditions of accelerating SLR.

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This paper describes a low complexity video codec with high coding efficiency. It was proposed to the high efficiency video coding (HEVC) standardization effort of moving picture experts group and video coding experts group, and has been partially adopted into the initial HEVC test model under consideration design. The proposal utilizes a quadtree-based coding structure with support for macroblocks of size 64 × 64, 32 × 32, and 16 × 16 pixels. Entropy coding is performed using a low complexity variable length coding scheme with improved context adaptation compared to the context adaptive variable length coding design in H.264/AVC. The proposal's interpolation and deblocking filter designs improve coding efficiency, yet have low complexity. Finally, intra-picture coding methods have been improved to provide better subjective quality than H.264/AVC. The subjective quality of the proposed codec has been evaluated extensively within the HEVC project, with results indicating that similar visual quality to H.264/AVC High Profile anchors is achieved, measured by mean opinion score, using significantly fewer bits. Coding efficiency improvements are achieved with lower complexity than the H.264/AVC Baseline Profile, particularly suiting the proposal for high resolution, high quality applications in resource-constrained environments.