Estuaries and Coasts最新文献

Tidal marshes in the Chesapeake Bay are vulnerable to the accelerating rate of sea-level rise (SLR) and subsidence. Restored and created marshes face the same risks as natural marshes, and their resilience to SLR may depend upon appropriate design and implementation. Here, the Coastal Wetland Equilibrium Model (CWEM) was used to assess the resilience of tidal marshes at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island (PI) in mid-Chesapeake Bay, MD, where dredged material from navigation channels is being used to create new tidal marshes planted with Spartina alterniflora in the low marsh and S. patens in the high marsh. The site is microtidal with low inorganic sediment inputs, where the rate of marsh elevation change is dominated by the production of organic matter and, therefore, is proportional to net ecosystem production (NEP). The model demonstrated the importance of marsh development for surface elevation gain. In created marshes, the buildout of belowground biomass adds volume and results in faster growth of marsh elevation, but the gains slow as the marsh matures. Elevation gain is the lessor of the recalcitrant fraction of NEP sequestered in sediment or the rate of increase in accommodation space. Marshes can keep up with and fill accommodation space with sequestered NEP up to a tipping point determined by the rate of SLR. The PI low marsh platform was forecasted to drown in about 43 years after construction at the current rate of SLR. Marsh loss can be mitigated by periodic thin layer placement (TLP) of sediment. CWEM was used to simulate PI marsh responses to different TLP strategies and showed that there is an optimal design that will maximize carbon sequestration and resilience depending on the trajectory of mean sea level.

The Atlantic blue crab Callinectes sapidus (Decapoda, Portunidae) Rathbun, 1896 is native to the east coasts of North and South America and has recently expanded its distribution in the non-native range into the Gulf of Cadiz (SW Iberian Peninsula, Europe). Considering the impacts caused by this invasive species in numerous estuarine ecosystems and its generalist feeding behavior, this study aims to provide the first account of the Atlantic blue crab diet on the East Atlantic coast. We studied the species’ feeding habits using stomach content analyses to predict food web interactions and putative impacts. Samples were obtained in the Guadalquivir estuary (SW Spain, Europe), which was colonized in 2017. The main food items identified on their stomach were, fish (49.9%), mollusks (44.4%) and crabs (32.3%). They also consumed plant material (27.2%), and the sediment (32.3%) in their digestive tract was likely the result of secondary ingestion. The Atlantic blue crab exhibited the same omnivorous behavior as in the native area. There was no sexual variation in diet composition or feeding activity in general, but there was a seasonal variation in the diet composition of females. The decrease of the caramote prawn Penaeus kerathurus (Forskål 1775) observed in the Guadalquivir estuary since 2021 is likely not due to the Atlantic blue crab because they seldomly eat this prey. Overall, our study provides clear baseline information to expand the knowledge about the ecological roles of the Atlantic blue crab in non-native ecosystems.

The Ganges-Brahmaputra Delta (GBD) in Bangladesh exists at a nexus of stability and vulnerability, as the rivers annually carry ~ 800–1000 MT of sediment from the Himalayan Mountains, yet coastal poldering and sediment extraction within the rivers remove elevation capital from the low-lying delta plain. Recent research in the GBD has begun to unravel how the world’s largest fluvio-deltaic mangrove forest—the Sundarbans—is keeping pace with sea level rise (SLR); however, this is contingent on adequate sediment supply delivered to the platform during semi-diurnal tides and the seasonal monsoon. Little is known about the elevation dynamics within human-modified polders by comparison, other than an elevation deficit of 1–1.5 m exists. In this study, seasonal data from Rod Surface Elevation Tables (RSETs) installed within a polder in the southwest region (Polder 32) are compared to the Sundarbans. Over ~ 8 years, results show that surface elevation is gaining within the Sundarbans at a more significant rate (~ 58.4%), and this is due to the higher vertical accretion rates measured in the Sundarbans (~ 67%) from abundant sources of allochthonous material. Elevation gain in the polder, particularly close to the embankment, appears to be attributed to sediment supplied from eroded embankments and local sluice gates, in addition to seasonal subsurface clay swelling during the monsoon. Shallow subsidence within both study areas appears to take place seasonally, but with less delivery of new sediment, the rate of shallow subsidence is lower in the polder compared to the Sundarbans. Despite seasonal shallow subsidence, the elevation change is net positive in both study areas if taken as a whole; however, interior poldered regions exhibit net elevation loss. This comparison in change of elevation, vertical accretion, and shallow subsidence shows how human modification has drastically changed the natural processes. Furthermore, our results are compared to rates of relative and effective SLR, which show that the Sundarbans is keeping pace in this region, while Polder 32 is not. These results are vital to inform embankment mitigation and flood risk in this dynamic delta system.

Coastal mangrove forests are at risk of being submerged due to sea-level rise (SLR). However, mangroves have persisted with changing sea levels due to a variety of biotic and physical feedback mechanisms that allow them to gain and maintain relative soil surface elevation. Therefore, mangrove’s resilience to SLR is dependent upon their ability to build soil elevation at a rate that tracks with SLR, or well-enough to migrate inland. Anthropogenic disturbances, such as altered hydrology and eutrophication, can degrade mangrove forest health and compromise this land building process, placing mangroves at greater risk. Much of Florida’s mangroves are adjacent to highly urbanized areas that produce nutrient-loaded runoff. This study assesses how experimental nutrient inputs in the eutrophic Caloosahatchee Estuary influence the soil surface elevation change (SEC) in two distinct mangrove zones. Annual rates of SEC were reduced by phosphorus additions and differed by mangrove zone, ranging from 0.67 ± 0.59 to 2.13 ± 0.61 and 4.21 ± 0.58 to 6.39 ± 0.59 mm year⁻¹ in the fringe and basin zone, respectively. This suggests that eutrophication can reduce the maximum potential SEC response to SLR and that a mangrove forest’s vulnerability to SLR is not uniform throughout forest but can differ by mangrove zone.

A century ago, measuring elevation in tidal wetlands proved difficult, as survey leveling of soft marsh soils relative to a fixed datum was error prone. For 60 years, vertical accretion measures from marker horizons were used as analogs of elevation change. But without a direct measure of elevation, it was not possible to measure the total influence of surface and subsurface processes on elevation. In the 1990s, the surface elevation table (SET) method, which measures the movement of the wetland surface relative to a fixed point beneath the surface (i.e., the SET benchmark base), was combined with the marker horizon method (SET-MH), providing direct, independent, and simultaneous measures of surface accretion and elevation and quantification of surface and shallow subsurface process influences on elevation. SET-MH measures have revealed several fundamental findings about tidal wetland dynamics. First, accretion [A] is often a poor analog for elevation change [E]. From 50–66% of wetlands experience shallow subsidence (A > E), 7–10% shallow expansion (A < E), 7% shrink-swell, and for 24–36% A is an analog for E (A = E). Second, biological processes within the root zone and physical processes within and below the root zone influence elevation change in addition to surface processes. Third, vegetation plays a key role in wetland vertical dynamics. Plants trap sediment and increase resistance to erosion and compaction. Soil organic matter accumulation can lead to shallow expansion, but reduced plant growth can lead to subsidence, and plant death to soil collapse. Fourth, elevation rates are a better indicator of wetland response to sea-level rise than accretion rates because they incorporate subsurface influences on elevation occurring beneath the marker horizon. Fifth, combining elevation trends with relative sea-level rise (RSLR) trends improves estimates of RSLR at the wetland surface (i.e., RSLR_wet). Lastly, subsurface process influences are fundamental to a wetland’s response to RSLR and plant community dynamics related to wetland transgression, making the SET-MH method an invaluable tool for understanding coastal wetland elevation dynamics.

Invertebrates play a critical role in beach ecosystems, and seasonal variation in their occurrence and abundance likely influences food webs. We examine and characterise seasonal patterns in invertebrate activity on a temperate, southern sandy dune and beach ecosystem at Venus Bay, Victoria, Australia. We index invertebrate abundance, diversity and assemblage composition at fixed-site pitfall traps which were deployed in four transects from the lower dunes to the beach. Seasonal differences occurred in assemblage composition (foredunes only), richness and abundance. Insects dominated assemblages in summer, spring and autumn; crustaceans dominated winter assemblages. Morphospecies richness was lowest in winter (139% higher in summer and 169% higher in autumn). Our results contrast with other studies from temperate beaches in that (1) richness was higher on beaches compared to in foredunes across all seasons and (2) abundance differed significantly such that winter abundance was higher than for all other seasons. Possible explanations include the exposed nature of the study foredunes, marine ecological subsides in the form of beach wrack in winter and/or between-site variations in such factors. Further studies would usefully examine between-beach variation in seasonality in invertebrate activity in foredunes and dunes.

The recognition of the benefits that seagrasses contribute has enhanced the research interest in these marine ecosystems. Seagrasses provide critical goods and services and support the livelihoods of millions of people. Despite this, they are declining around the globe. To conserve these ecosystems, it is necessary to understand their extent and the drivers leading to their loss. However, global seagrass cover estimates are highly uncertain and there are large regional data gaps, especially in the African continent. This work reviewed all available data on the extent of seagrass cover, evidence of changes in cover and drivers of this change in Africa, to inform management and conservation approaches across the continent and identify gaps in knowledge. Using a systematic review and expert consultation, 43 relevant articles were identified. Of the 41 African countries with a coastline, 27% had no data on seagrass cover. For 44%, data were available for some parts of their coastline, while 29% had data for their entire coastline. Quantitative information on trends in seagrass cover change was only available from three countries. The study identified 32 suggested drivers of seagrass cover loss, with impacts from fishing mentioned most frequently. Direct anthropogenic drivers accounted for 66.7% of the mentions, while climate and biologically induced drivers accounted for 22.7% and 10.6%, respectively. This study demonstrates the need for better estimates of seagrass extent, in at least 70% of relevant African nations, and major gaps in our understanding of the drivers of seagrass decline in Africa.

Coastal wetlands have been long recognized for their importance to biodiversity and many biogeochemical processes including carbon sequestration; however, our understanding of plant-microbe interactions that govern many processes in these ecosystems remains elusive. Fungal communities are known to play critical roles in coastal wetlands, particularly due to their close relationships with plants, yet, systematic understanding of their distributional patterns and the factors shaping these patterns in natural coastal wetland environments has been rarely assessed. We synthesized existing published literature from fifty-one studies spanning 60 years to examine global fungal distributional patterns in coastal wetlands, draw linkages between fungi, the plant communities, and their environment, and identify gaps in fungal research and suggest future research directions. We focused on studies that reported root-associated fungi and fungi from the plant rhizosphere (i.e., soil surrounding roots) in coastal dunes, intertidal flats, salt marshes, and tidal wetlands. Our synthesis has revealed that (1) 203 fungal species were reported from salt marshes, 59 fungal species from coastal dunes, 32 from tidal wetlands, and ten from intertidal flats; (2) rhizosphere fungal communities were more species-rich and reported more often for all ecosystems except in salt marshes; and (3) nineteen different fungal guilds, which are predominantly arbuscular mycorrhizal fungi. We conclude that more research is needed to better understand root-associated fungal diversity in less studied ecosystems reviewed here. We have identified knowledge gaps in reported data and outlined suggestions to facilitate future plant-fungal research in these declining, but important, coastal ecosystems.

Estuarine systems that provide valuable ecosystem services to society and important foraging and rearing habitat for fish and wildlife species continue to undergo degradation. In Puget Sound, WA, as much as 70–80% of historic estuarine habitat has been lost to anthropogenic development, and continued losses are expected through the end of the twenty-first century due to rising sea levels. To evaluate whether Puget Sound’s estuarine habitats will keep pace with current and projected sea-level rise (SLR), we assessed vertical rates of elevation change from a regional network of surface elevation tables and marker horizons (SET-MH). Over the past two decades, SET-MH equipment has been installed throughout a variety of habitats in five Puget Sound estuaries: the Nisqually, Snohomish, Stillaguamish, and Skagit River estuaries, and Padilla Bay. These data provide a unique opportunity to assess elevation change and habitat resilience across a spatiotemporal and environmental gradient. We observed different rates of surface elevation change among estuaries and habitats (Nisqually = 4.64 ± 2.81 mm/year, Snohomish = 5.71 ± 5.83 mm/year, Stillaguamish = 12.82 ± 10.29 mm/year, Skagit = 16.13 ± 7.57 mm/year, Padilla = − 1.25 ± 1.58 mm/year). The highest rates were found at restoring sites with regular sediment input in the Stillaguamish and Skagit estuaries, whereas rates were consistently negative at low elevation sites in sediment starved Padilla Bay. Many sites in Puget Sound appear to be keeping pace with current rates of relative SLR, and some areas are on track to exceed projected rates through the end of the century. These findings indicate that Puget Sound’s estuarine habitats can be resilient to rising tidal levels—as long as sediment delivery is maintained.

The Bay of Fundy is a highly productive ecosystem within the Northwest Atlantic where extreme tides and strong currents result in a large gradient of sediment concentrations across and along the bay. We processed daily satellite data from the MODerate resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite from 2003 to 2021 at 300-m resolution to understand and quantify spatial and temporal trends in chlorophyll-a concentration (chl-a, a measure of phytoplankton biomass), and suspended particulate matter concentration (SPM) in the Bay of Fundy surface waters. To account for high sediment loading (up to 100’s g m⁻³) and moderate chl-a (median in situ chl-a of 1.5 mg m⁻³ from 2003 to 2021), coefficients of the OC3M chl-a algorithm were regionally tuned using in situ chl-a data, and satellite-derived SPM was incorporated within the chl-a retrieval algorithm to account for possible bias. The updated new algorithm was denoted as OC_X-SPMCor. Chl-a computed using OC_X-SPMCor showed better performance against in situ chl-a than the generic OC3M with a coefficient of determination that increased from 0.01 to 0.28 and a root mean square logarithmic error that decreased by 35%. Unlike previous remote sensing studies, OC_X-SPMCor correctly predicted the particular chl-a seasonality in the Bay of Fundy, which does not follow the typical occurrence of spring/fall blooms as observed in the adjacent Gulf of Maine and Scotian Shelf. For the first time, satellite-predicted chl-a aligned with the phenology of in situ chl-a, where chl-a continually increased from April to June and remained high all summer, with a small secondary summer peak before decreasing in the fall. SPM seasonality followed an opposite trend where SPM reached a maximum in winter and a minimum in summer. A small number of matchups and high temporal variability on the hourly time scale precluded a robust assessment of the satellite-derived SPM. However, comparisons between time series of remotely sensed and in situ SPM demonstrated the ability of the satellite-derived SPM to capture temporal variations, though the absolute values may be slightly underestimated. Accurate maps of phytoplankton biomass and sediment concentrations are essential variables required for effective management and conservation of marine ecosystems in the Bay of Fundy.