What evidence exists on the performance of nature-based solutions interventions for coastal protection in biogenic, shallow ecosystems? A systematic map protocol.

BACKGROUND: Anthropogenic pressures and climate change threaten the capacity of ecosystems to deliver a variety of services, including protecting coastal communities from hazards like flooding and erosion. Human interventions aim to buffer against or overcome these threats by providing physical protection for existing coastal infrastructure and communities, along with added ecological, social, or economic co-benefits. These interventions are a type of nature-based solution (NBS), broadly defined as actions working with nature to address societal challenges while also providing benefits for human well-being, biodiversity, and resilience. Despite the increasing popularity of NBS for coastal protection, sometimes in lieu of traditional hardened shorelines (e.g., oyster reefs instead of bulkheads), gaps remain in our understanding of whether common NBS interventions for coastal protection perform as intended. To help fill these knowledge gaps, we aim to identify, collate, and map the evidence base surrounding the performance of active NBS interventions related to coastal protection across a suite of ecological, physical, social, and economic outcomes in salt marsh, seagrass, kelp, mangrove, shellfish reef, and coral reef systems. The resulting evidence base will highlight the current knowledge on NBS performance and inform future uses of NBS meant for coastal protection. METHODS: Searches for primary literature on performance of NBS for coastal protection in shallow, biogenic ecosystems will be conducted using a predefined list of indexing platforms, bibliographic databases, open discovery citation indexes, and organizational databases and websites, as well as an online search engine and novel literature discovery tool. All searches will be conducted in English and will be restricted to literature published from 1980 to present. Resulting literature will be screened against set inclusion criteria (i.e., population, intervention, outcome, study type) at the level of title and abstract followed by full text. Screening will be facilitated by a web-based active learning tool that incorporates user feedback via machine learning to prioritize articles for review. Metadata will be extracted from articles that meet inclusion criteria and summarized in a narrative report detailing the distribution and abundance of evidence surrounding NBS performance, including evidence clusters, evidence gaps, and the precision and sensitivity of the search strategy.

Dynamic responses and implications to coastal wetlands and the surrounding regions under sea level rise.

Two distinct microtidal estuarine systems were assessed to advance the understanding of the coastal dynamics of sea level rise in salt marshes. A coupled hydrodynamic-marsh model (Hydro-MEM) was applied to both a marine-dominated (Grand Bay, Mississippi) and a mixed fluvial/marine (Weeks Bay, Alabama) system to compute marsh productivity, marsh migration, and potential tidal inundation from the year 2000 to 2100 under four sea level rise scenarios. Characteristics of the estuaries such as geometry, sediment availability, and topography, were compared to understand their role in the dynamic response to sea level rise. The results show that the low sea level rise scenario (20 cm) approximately doubled high-productivity marsh coverage in the marine-dominated estuary by the year 2100 due to an equilibrium between the rates of sea level rise and marsh platform accretion. Under intermediate-low sea level rise (50 cm), high-productivity marsh coverage in the year 2100 increased (doubled in the marine-dominated estuary and a seven-fold increase in the mixed estuary) by expanding into higher lands followed by the creation of interior ponds. The results also indicate that marine-dominated estuaries are vulnerable to collapse as a result of low, relatively uniform topography and lack of sediment sources, whereas mixed estuaries are able to expand due to higher elevations and sediment inputs. The results from the higher sea level rise scenarios (the intermediate-high (120 cm) and high (200 cm)) showed expansion of the bays along with marsh migration to higher land, producing a five-fold increase in wetland coverage for the mixed estuary and virtually no net change for the marine-dominated estuary. Additionally, hurricane storm surge simulations showed that under higher sea level rise scenarios, the marine-dominated estuary demonstrated weaker peak stage attenuation indicating that the marsh's ability to dissipate storm surge is sensitive to productivity changes and bay expansion / marsh loss.

Conventional and technical diving surveys reveal elevated biomass and differing fish community composition from shallow and upper mesophotic zones of a remote United States coral reef.

The world's coral reefs appear to be in a global decline, yet most previous research on coral reefs has taken place at depths shallower than 30 m. Mesophotic coral ecosystem (depths deeper than ~30 m) studies have revealed extensive, productive habitats and rich communities. Despite recent advances, mesophotic coral ecosystems remain understudied due to challenges with sampling at deeper depths. The few previous studies of mesophotic coral ecosystems have shown variation across locations in depth-specific species composition and assemblage shifts, potentially a response to differences in habitat or light availability/water clarity. This study utilized scuba to examine fish and benthic communities from shallow and upper mesophotic (to 45 m) zones of Flower Garden Banks National Marine Sanctuary (FGBNMS, 28°0'N; 93°50'W) from 2010-2012. Dominant planktivores were ubiquitous in shallow and upper mesophotic habitats, and comparisons with previous shallow research suggest this community distribution has persisted for over 30 years. Planktivores were abundant in shallow low-relief habitats on the periphery of the coral reef, and some of these sites that contained habitat transitioning from high to low relief supported high biomass of benthic predators. These peripheral sites at FGBNMS may be important for the trophic transfer of oceanic energy to the benthic coral reef. Distinct differences between upper mesophotic and shallow communities were also observed. These included greater overall fish (as well as apex predator) biomass in the upper mesophotic, differences in apex predator community composition between depth zones, and greater percent cover of algae, rubble, sand, and sponges in the upper mesophotic. Greater fish biomass in the upper mesophotic and similar fish community composition between depth zones provide preliminary support that upper mesophotic habitats at FGBNMS have the capacity to serve as refugia for the shallow-water reefs. Diving surveys of the upper mesophotic and shallow-water coral reef have revealed valuable information concerning the reef fish community in the northern Gulf of Mexico, with implications for the conservation of apex predators, oceanic coral reefs, and the future management of FGBNMS.