Estuaries and Coasts最新文献

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.

Species invasion in salt marsh wetlands is known to disturb the balance of biotic and abiotic ecosystems (e.g., changing material exchange cycles and community structure). However, its influence on the morphological evolution of salt marshes is not yet understood in depth. This study investigates the long-term temporal and spatial distributions of an invasive plant (Spartina alterniflora) and its morphological characteristics in the Yangtze Estuary by remote sensing imagery interpretation, tidal creek extraction, regional statistical analysis, and proximity analysis. The invaded site shows an area of Spartina alterniflora with a 35-fold increase from the start to the end of its initiation phase; it is the second biggest species in the study area. It is found that species invasion not only limited the expansion of native pioneer vegetation but also changed bio-geomorphic feedback loops. With the influence of plant invasion, median tidal creek lengths decreased and the median tidal creek sinuosity ratio remained stable, between 1.06 and 1.07 in the subarea. The method used here is adaptable to other salt marshes. The findings from this study can provide practical guidance for the restoration of native salt marshes in the estuary and thus control the spread of invasive species.

Portunid crabs are an iconic, high value species in NSW, but catches are highly variable in space and time. Substantial variation in biomass is observed in both exploited and unfished populations, and environmental effects on distribution and abundance are an important factor contributing to this variability. Predicting and responding to this variability is a challenge for management and sustainability of exploited populations. We examine spatial and temporal variation in Blue Swimmer Crab (Portunus armatus) populations, over a 2.5 year trapping survey in two temperate estuaries that differ in tidal flow and riverine input. Specifically, monthly catch rates and distribution throughout the estuary are examined alongside variation in temperature and conductivity. In Wallis Lake, the shallower estuary with a restricted entrance, both water temperature and conductivity impacted abundance and distribution of crabs but there was no evidence that pulses of freshwater flow had a major impact. For a 10 °C increase in temperature the population on average shifted ~ 700 m closer to the ocean. Males were consistently located slightly further into the estuary compared to females, but there was no convincing evidence of estuarine egression in response to lower salinity. In Port Stephens, the deeper, tidal estuary, water temperature and conductivity also impacted abundance, but while males were more dispersed than females, the distribution of crabs within the estuary did not appear to be influenced by temperature, conductivity or flow. These results highlight the links between nuanced environmental relationships and estuarine geomorphology for Blue Swimmer Crab.

Abstract

Low-lying islands are vulnerable to coastal erosion, and mangroves, which can mitigate erosion, have suffered enormous losses in recent decades owing to human impacts. Previous studies have little investigated mangrove shores on atolls, which may face combined multiple threats. We analysed the large Marshall Islands atoll of Jaluit, at a higher resolution than previous spatial change studies, finding that mangrove shorelines prograded seawards over the last seven decades. Biogeomorphic colonisation processes were characterised from transects along ~ 14.6 km of shorelines. Mangrove progradation occurred in patterns of arc-shapes evident of long-shore drift deposition, patch expansion of offshore mangrove colonisers, and linear shoreline advance. Significant differences in the rates of expansion were identified, with arc-shaped colonisation showing the fastest rates of expansion. However, linear shoreline advance was the most frequent expansion pattern showing greater than three-fold more classified transects than arc-shaped colonisation and patch expansion. These results have implications for low island mangrove restoration. Applying mangrove planting patterns mimicking these different natural colonisation processes may enhance restoration success in ecosystem-based adaptation projects to mitigate sea level rise vulnerability. Results from this study show that atoll mangrove shorelines demonstrate resilience during past sea level rise rates, and that rates of expansion vary according to patterns of biogeomorphic colonisation.

The COVID-19 lockdown opened an opportunity to assess the response of animal populations to diminished human activities. As coastal dunes face many disturbances caused by increasing human activities, we assessed the effect of reduced human mobility on coastal bird diversity and abundance and on the Least Tern nest failure rate on an island in the southern Gulf of Mexico before, during, and after the lockdown to test the hypothesis that diminished tourism and recreational activities can contribute to the conservation of coastal ecosystems by increasing species richness and abundance and decreasing the nest failure rate. We used data from 2016 to 2021 to estimate nesting failure probabilities using Bernard’s cumulative distribution function, Kaplan‒Meier tests, and Cox regression for hazard rates. Bird species richness and abundance were compared using Kruskal‒Wallis rank tests. Factors related to breeding site preference were assessed using the BIOENV method. The lockdown did not affect species richness, but bird abundance was inversely related to pedestrian traffic (rho = − 0.908, p < 0.0001, n = 48). Nest failure decreased during the lockdown in 2020 (p < 0.0001) due to reduced presence of people, which allowed occupancy of sites never used before. During the lockdown, the proportion of nest failure was lower than that in the other sampling years (p < 0.0001, φ range = − 0.445 to − 0.278). Accordingly, diminished pedestrian traffic can increase nest survival (log-rank p < 0.0001). Policies to reduce beach pedestrian traffic will help strengthen wildlife conservation and building coastal resilience.

The Terminos Lagoon Flora and Fauna Protection Area is the largest coastal lagoon in the southern Gulf of Mexico and has the largest population of bottlenose dolphins, Tursiops truncatus, reported in the region. Photo identification studies have reported permanent and seasonal residence of dolphins; however, how dolphins coexist ecologically is unknown. In the present study, from 17 dead specimens stranded on the coast of Isla del Carmen (barrier island) between 2014 and 2016, stable isotopes in the liver, heart, and muscle, which represent different time scales, were analyzed to determine residence through δ¹³C values and niche width and trophic coexistence through δ¹⁵N values. Differences between sexes (δ¹³C liver: p = 0.009; heart: p = 0.01) and age classes (δ¹⁵N muscle: p = 0.02) were found, which indicated trophic sexual segregation and changes in resource use during growth, respectively. The lack of significant differences in δ¹³C values indicated isotopic equilibrium between the tissues, indicating the possible permanent residence of 12 dolphins in Terminos Lagoon as a coastal ecotype (− 16‰) and a second group (five dolphins) as an oceanic ecotype (− 18‰). In conclusion, most dolphins stranded in the Terminos Lagoon are potential permanent residents of this habitat, with evidence of resource partitioning as a coexistence strategy.