Estuaries and Coasts最新文献

Coastal salt marshes of the eastern United States are particularly vulnerable to accelerated sea level rise, and urban marshes are at greater risk of erosion, inundation, and conversion to mudflat if left unmanaged. To guide New York City (NYC) salt marsh restoration strategies, NYC Parks collected up to 10 years of salt marsh elevation change data through 2020 at six salt marsh sites using the Surface Elevation Table-Marker Horizon (SET-MH) method, conducted a salt marsh trends analysis to determine shoreline change from 1974 to 2012, and conducted a salt marsh conditions assessment. We found that the citywide average surface elevation trend of 3.31 mm yr⁻¹ was not significantly different from the 30-year (1990–2020) Relative Sea Level Rise of 4.23 mm yr⁻¹ at The Battery, NY, tide station, probably due to high variability across and within sites. We also found that accretion rates differed across sites and watersheds, and sites situated lower in the tidal zone had higher accretion rates. Notably, Jamaica Bay’s Idlewild salt marsh, long suspected of being sediment-starved and ranking lowest in our conditions assessment, had the highest accretion rate at 9.5 mm yr⁻¹. Our salt marsh trends analysis also showed marsh loss at the shoreline edge, bare ground cover, and other indicators of marsh degradation. In mitigating marsh loss, the design grades for our recent wetland restoration projects enlarge the upper elevation ranges of the low- and high-marsh zones and incorporate wider and more gradual slopes in upland transition zones to enable inland marsh migration.

Coastal ecosystems with karstic geology have a unique characteristic where the dissolution of carbonate rocks can increase total alkalinity (TA) and dissolved inorganic carbon (DIC). This results in higher inorganic carbon budgets in coastal areas. One such ecosystem is the Terminos Lagoon, the most extensive tropical estuarine lagoon system in Mexico, located in the karstic aquifer of the Yucatan Peninsula and connected to the southern Gulf of Mexico (sGoM). We measured TA and DIC to evaluate the variability in Terminos Lagoon’s of the carbonate system. We also estimated pH, partial CO₂ pressure (pCO₂), and aragonite saturation (Ω_Ar) along two transects from the main lagoon tributaries (Palizada and Candelaria rivers) to the coastal zone during the dry and rainy seasons. During the dry season, TA and DIC concentrations were significantly higher (3092 ± 452 µmol kg^-1 TA, 2943 ± 522 µmol kg^-1 DIC) than during the rainy season (2533 ± 228 µmol kg⁻¹ TA, 2492 ± 259 DIC µmol kg⁻¹). Our calculations indicate that the rainy season pCO₂ (2532 ± 2371 µatm) seems higher than in the dry season (1534 ± 1192 µatm). This leads to a reduction in pH (7.9 ± 0.3 to 7.8 ± 0.3). These significant changes indicate that rain increases the flow of unsaturated river water into the lagoon. The results of this work contribute toward a dissolved inorganic carbon variability baseline in the sGoM and can be helpful to Terminos Lagoon decision-makers.

Sea-level rise (SLR) will produce unprecedented changes in tidal marsh systems that already cope with daily tidal fluctuation, disturbances from storms, and salinity changes from droughts and runoff events. Additionally, negative impacts from non-native invasive species may alter marsh plants’ ability to respond to SLR stressors like increased inundation and salinity. Increasingly, tidal marsh communities must tolerate both changes in the physical environment from SLR and increased risk of invasion by non-native species. To assess the response of a threatened tidal marsh cordgrass (Spartina foliosa) to both stressors, we implemented a field experiment in San Francisco Bay, CA, USA, exposing cordgrass to a treatment that extended tidal inundation projected with SLR using a recently developed in situ method. At one of two field sites, we also enclosed the cordgrass with or without the invasive European green crab, Carcinus maenas. We found that cordgrass responded negatively to longer inundation, although these effects varied by site and year. In higher inundation treatments, cordgrass survival increased with increasing surface elevation of the plot. Cordgrass survival was lower in the presence of invasive green crabs relative to controls. We did not find interacting effects of responses to increased inundation and invasive species presence, which highlights the need to consider how latent or sequential effects of multiple stressors may affect ecosystems. This study demonstrates significant biological responses to invasive species presence and increased inundation. Evaluating relative effects and timing of multiple stressors, especially those induced by climate change and invasive species, will help us to manage threatened ecological communities in a changing world.

Seagrasses have long been a focal point for management efforts aimed at restoring ecosystem health in estuaries worldwide. In Tampa Bay, Florida (USA), seagrass coverage has declined since 2016 by nearly a third (11,518 acres), despite sustained reductions of nitrogen loads supportive of light environments for growth. Changing physical water quality conditions related to climate change may be stressing seagrasses beyond their optimal growth ranges, requiring an assessment to determine if this decline can be linked to climate stress. Three ambient water quality datasets of varying sampling designs and coverage were evaluated to characterize physicochemical environments in Tampa Bay and the potential relationships with seagrass change. Tampa Bay has become hotter and fresher with water temperature increasing by 0.03–0.04 °C per year and salinity decreasing by 0.04–0.06 ppt per year, translating to an increase of 1.3 to 1.7 °C and a decrease of 1.6 to 2.6 ppt over the last 50 years. Additionally, the number of days when temperature was above 30 °C or salinity was below 25 ppt has increased on average across all bay segments by 48 and 37 days, respectively, since 1975. These changes varied spatially and seasonally, with the most dramatic changes observed in the upper bay. Generalized Additive Models provided a weight-of-evidence that recent seagrass declines are somewhat associated with hotter and fresher conditions. Trends in warming and increased precipitation in the region are likely to continue, further creating suboptimal conditions for seagrasses in Tampa Bay. These results should compel resource managers to consider the likelihood that reduced resilience of estuarine resources due to shifting ecological baselines driven by additional climate change drivers will complicate long-standing management paradigms. While conventional management approaches that focus on limiting nutrient loads should be continued, their future effectiveness may be confounded by climate change drivers and warrant additional, complementary interventions and continuous monitoring data to support ecosystem health into the future.

Long-term declines in coastal water quality and sedimentation can affect the restoration success of ecosystems such as seagrass and shellfish reefs. Resnagging coastal seascapes offers a potential alternative restoration method that is not reliant on abiotic conditions and which may enhance degraded landscapes for fish and fisheries. While common in freshwater ecosystems, such interventions are unusual for coastal seascapes despite log snags supporting significant benefits for coastal fish. In this study, we identify the spatial (e.g. seascape connectivity), habitat condition (e.g. log snag complexity and food availability) and water quality variables that best explain variation in fish assemblages on log snags to help prioritise the placement and design of resnagging efforts in estuaries. We surveyed fish assemblages on log snags using underwater videography at 363 sites across 13 estuaries in southeast Queensland, Australia, over 3 years. Sites less than 10,000 m from the estuary mouth, more than 2500 m from urban structures and located in water depths of < 3 m harboured more diverse fish assemblages. Sites less than 10,000 m from the estuary mouth with lower (< 25%) algae cover harboured greater total fish abundance and harvested fish abundance. Similar trends were found for the abundance of individuals from key functional groups, although these trends were mediated by other seascape contexts (e.g. the area of natural habitat) and water quality variables (e.g. chlorophyll-a concentration and dissolved oxygen saturation). Our results indicate that log snag placement in estuaries for benefits to fish and fisheries can be maximised if sites are planned strategically.

Erosion poses a significant threat to coastal and estuarine environments worldwide and is further exacerbated by anthropogenic activities and increasing coastal hazards. While conventional engineered structures, such as seawalls and revetments, are commonly employed to protect shorelines from wave impact and erosion, they can also cause detrimental environmental effects. By creating/restoring coastal habitats with engineered structures, hybrid living shorelines offer coastal protection and other co-benefits. Using aerial imagery, we studied the rates of shoreline change before and after living shoreline installation, and between living shorelines and adjacent bare shorelines in three estuaries in New South Wales, Australia. Mangroves had established behind most rock fillets and displayed a trend of increasing canopy cover with fillet age. In the first 3 years since installation, the rates of lateral shoreline change reduced from − 0.20, − 0.16, and − 0.10 m/year to − 0.03, − 0.01, and 0.06 m/year in living shorelines in Hunter, Manning, and Richmond Rivers, respectively. However, when compared to control shorelines, the effectiveness in reducing erosion varied among living shorelines with mean effect sizes of 0.04, − 0.28, and 1.74 across the three estuaries. A more positive rate of shoreline change was associated with an increasing percentage of mangrove canopy area and an increasing length of protected shoreline at wide channels. While hybrid mangrove living shorelines are a promising solution for mitigating erosion and creating habitats at an estuary-wide scale, they may also contribute to downdrift erosion, emphasising the importance of considering site-specific hydrogeomorphology and sediment movement when installing living shorelines.

Foundation species support highly productive and valuable ecosystems, but anthropogenic disturbances and environmental changes are increasingly causing foundation species shifts, where one foundation species replaces another. The consequences of foundation shifts are not well understood, as there is limited research on the equivalency of different foundation species and the functions they support. Here, we provide insight into community-level consequences of foundation shifts in the Gulf of Mexico, where the typical marsh foundation species (Spartina alterniflora) is being replaced with a mangrove foundation species (Avicennia germinans), forcing marsh fauna to rely on Avicennia for foundational support. We evaluated the interactions of two common and ecologically valuable basal consumers, fiddler crabs (Uca spp.) and marsh periwinkle snails (Littoraria irrorata), with both foundation species across sites with different levels of mangrove encroachment. By investigating both physical support, measured as habitat association and co-occurrence, and trophic support, as basal resource diet contributions, we found that Avicennia can physically replace Spartina for some consumers, but is not providing equivalent trophic support. Uca and Littoraria commonly occupy encroached sites and associate with mangroves but incorporate almost no mangrove plant matter into their diets. The ultimate consequences of a foundation shift in the case of mangrove encroachment may include shifting energy flows and resource use and decreased populations of basal consumers. Looking at interactions with foundation species from multiple perspectives is necessary to obtain a complete picture of the effects that foundational shifts are having, especially as such shifts are becoming increasingly common.

Macroalgae and phytoplankton support the base of highly productive nearshore ecosystems in cold-temperate regions. To better understand their relative importance to nearshore food webs, this study considered four regions in the northern Gulf of Alaska where three indicator consumers were collected, filter-feeding mussels (Mytilus trossulus), pelagic-feeding Black Rockfish (Sebastes melanops), and benthic-feeding Kelp Greenling (Hexagrammos decagrammus). The study objectives were to (1) estimate the proportional contributions of macroalgal and phytoplankton organic matter using carbon and nitrogen stable isotopes, (2) determine if macroalgal use affected consumer growth using annual growth rings in shells or otoliths, and (3) describe changes in organic matter use and growth during the Pacific Marine Heatwave (PMH; 2014–2016) in one consumer, mussels. Macroalgae were the major organic matter source (> 60%) to the diet for all three consumers. The relationships between macroalgal contribution and growth were neutral for both fish species and significantly positive for mussels. During the PMH, mussels had a drop (> 10%) in macroalgal contributions and grew 45% less than in other time periods. Simultaneously, the relationship between macroalgal contribution and mussel growth was strongest during the PMH, explaining 48% variation compared to 3–12% before or after the PMH. Collectively, the results suggest that macroalgae is likely more important to cold-temperate nearshore food webs than phytoplankton. Management actions aimed at conserving and expanding macroalgae are likely to benefit nearshore food webs under all climate scenarios and especially during marine heatwaves.

Living shorelines (LS) stabilize eroding banks while providing more natural habitats and creating a gentler slope for enhanced migration of flora and fauna migration as sea levels rise. Typical LS practices include using several different materials, including oyster shell bags, to stabilize shorelines and planting marsh grasses. However, incorporating other important species interactions among marsh organisms can improve LS function and stability. For example, ribbed mussels, Guekensia demissa, benefit marsh plants by adding nutrients and stabilizing sediments. Unfortunately, mussels are not typically included in management and restoration practices. In this study, the objective was to investigate whether ribbed mussels facilitate marsh grass growth at a LS site in the southeastern US. We conducted field surveys for mussel abundance and recruitment, and a manipulative in situ experiment at an established LS site in Georgia to explore the impacts of adding mussels. Although mussel treatment did not have a significant effect on Spartina alterniflora metrics (i.e., density, height, biomass), Spartina plots with high mussel density exhibited ~300% increase in biomass relative to the start of the experiment, while plots without mussels only increased by ~100%. Some of the variability within treatments can be explained by high and sustained mussel mortality throughout the experimental period, likely due to predation, that impacted the actual mussel densities in our plots. We found that Spartina height, density, and biomass exhibited significant positive relationships with mussel biomass. Thus, ribbed mussels may be useful in living shorelines restoration projects if they are planted in sufficient densities, in aggregations, and/or with protective devices.

Hypoxia in coastal waters is a pressing ecological problem caused by continued eutrophication and climatic change that has widespread consequences for metazoan life and biogeochemical cycles. Numerous studies have investigated the controls on seasonal hypoxia formation and persistence in many of the world’s large estuaries and coastal hypoxic zones, but far fewer studies have examined the controls on short-term oxygen variability that leads to diel-cycling hypoxia in shallow-water environments. We utilized a unique, comprehensive (181 stations) record of dissolved oxygen concentrations collected at shallow water sites (primarily < 2 m) at high frequency (15 min) throughout the estuarine complex of the Chesapeake Bay and its tributaries to quantify how internal and external variables co-varied with dissolved oxygen. We used a combination of time-series analysis, harmonic analysis, and machine learning (e.g., classification and regression trees (CART)) approaches to identify spatial patterns in major controls on oxygen variability and the duration of moderate hypoxia. We found that key controls on oxygen variability varied substantially over space. For example, photosynthetically active radiation (PAR) was a strong predictor of oxygen dynamics in the majority of mesohaline waters. In more fetch-exposed stations, wind strongly controlled hypoxic duration, but in eutrophic, inshore locations, chlorophyll a, or turbidity were often better predictors. Specifically, diel oxygen variability was muted in upstream regions characterized by high turbidity. The duration of low oxygen conditions, which we defined conservatively as less than 4.8 mg O₂ L⁻¹ (156 µM), was strongly controlled by temperature, and simple projections of regional warming and CART-derived oxygen thresholds suggest that the Bay could experience a 10% increase in this type of hypoxia duration by mid-to-late twenty-first century. The ratio of tidal to biological variability in oxygen was found to increase under conditions of higher turbidity, stronger wind, and lower salinity, but biological variability was typically a factor of two higher than tidal variability. Although chlorophyll-a generated high oxygen concentrations at some locations, those stations with exceptionally high chlorophyll a (> 30 µg L⁻¹) were the most vulnerable to hypoxia. Because conventional water quality modeling frameworks are designed to capture hypoxia on relatively long time scales, these new insights can help inform updated oxygen models to support the management of shallow-water estuaries in the face of managed nutrient reductions and climate change.