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Shorebird populations, especially those feeding on shellfish, have strongly declined in recent decades and identifying the drivers of these declines is important for conservation. Changing food stocks are thought to be a key driver of these declines and may also explain why trends have not been uniform across Europe's largest estuary. We therefore investigated how winter population trends of Eurasian oystercatchers (Haematopus ostralegus) were linked to food availability in the Dutch Wadden Sea. Our analysis incorporated two spatial scales, a smaller scale focused on roost counting areas and food available to birds in these areas and a larger spatial scale of tidal basins. A novelty in our study is that we quantify the connectivity between roosting and foraging areas, identified from GPS tracking data. This allowed us to estimate food available to roosting birds and thus how food availability may explain local population trends. At the smaller spatial scale of roost counting areas, there was no clear relationship between available food and the number of roosting oystercatchers, indicating that other factors may drive population fluctuations at finer spatial scales. At the scale of tidal basins, however, there was a significant relationship between population trends and available food, especially cockle Cerastoderma edule,. Mortality and recruitment alone could not account for the large fluctuations in bird counts, suggesting that the site choice of wintering migratory oystercatchers may primarily drive these large fluctuations. Furthermore, the relationship between oystercatcher abundance and benthic food stocks, suggests winter shorebird counts could act as ecological indicators of ecosystem health, informing about the winter status of food stocks at a spatial scale of tidal basins.

We studied nearshore diurnal fish catches and fisheries development in the early stages of mangrove rehabilitation around the village of Timbulsloko on the central north coast of Java, Indonesia. Mangrove rehabilitation was part of a Nature-based Solutions project to re-establish ecological and economic resilience by combining coastal engineering measures with ecological recovery in conjunction with sustainable land and resource use. Creel surveys were conducted during the onset of the monsoon season October–December 2017 to document yields of the three main fishing gears targeting mangrove finfish in a 419 ha mangrove backwater basin. These were accompanied by structured interviews to obtain fisher views on developments in these fisheries. Analysis of satellite images and GIS-mapping were used to follow developments in mangrove coverage and effort in the estuarine lift-net fishery. Mangrove recovery between 2005 and 2018 achieved 8.5% of its maximum possible (historic) cover potential in the basin and followed an exponential growth curve. The increase in lift-net installations targeting finfish lagged in comparison to mangrove increase, remaining virtually zero till 2014, after which it rapidly increased. A baseline study in 2015 found no mangrove-associated finfish fisheries occurring in our study area. The 51 fishers surveyed in 2017, indicated that fishing activity in the area had strongly increased since 2015, with 45% of fishers stating to having started fishing this area a year earlier or even more recently. A significant majority of 87% of respondents with more than one year of experience at this location, stated that their catches had changed in terms of either fish size, quantity or composition since they started fishing, while 86% indicated improvement in terms of either size or quantity. Fishing generated about 1.05 ± 1.11 (SD) USD/hr worth of catch to professional fishers using either of the two net-types studied. As per 2017, fishing had become profitable in our study area, whereas this kind of fishery practically did not exist prior to 2014. We suggest that higher profitability may partially explain the rapid growth seen in fishing activity in the mangrove rehabilitation area. However, for 12 of the 18 larger species caught, the mean size in the catch was lower than mean size of maturation, indicating that these fisheries were principally targeted towards immature nursery fish. The results highlight the need to manage this currently developing fishery, otherwise any benefits to the local community might be nullified by overfishing.

High-resolution surveying techniques of subtidal soft-bottom seafloor habitats show higher small-scale variation in topography and sediment type than previously thought, but the ecological relevance of this variation remains unclear. In addition, high-resolution surveys of benthic fauna show a large spatial variability in community composition, but this has yet poorly been linked to seafloor morphology and sediment composition. For instance, on soft-bottom coastal shelves, hydrodynamic forces from winds and tidal currents can cause nested multiscale morphological features ranging from metre-scale (mega)ripples, to sand waves and kilometre-scale linear sandbanks. This multiscale habitat heterogeneity is generally disregarded in the ecological assessments of benthic habitats. We therefore developed and tested a novel multiscale assessment toolbox that combines standard bathymetry, multibeam backscatter classification, video surveying of epibenthos and box core samples of sediment and macrobenthos. In a study on the Brown Bank, a sandbank in the southern North Sea, we found that these methods are greatly complementary and allow for more detail in the interpretation of benthic surveys. Acoustic and video data characterised the seafloor surface and subsurface, and macrobenthos communities were found to be structured by both sandbank and sand wave topography. We found indications that acoustic techniques can be used to determine the location of epibenthic reefs. The multiscale assessment toolbox furthermore allows formulating recommendations for conservation management related to the impact of sea floor disturbances through dredging and trawling.

Coastal plants have unique adaptability to cope with strong hydrological stresses in tidal wetlands. A fundamental understanding of the establishment and maintenance of coastal plants is needed for conservation and restoration. In the Yangtze Estuary, the plasticity of the morphological and reproductive traits of a pioneer Scirpus species (sedge), in terms of phenotypic growth, biomass allocation, and sexual and asexual reproductive traits, was investigated with increasing flooding intensity (elevation gradient) in a tidal flat. The varying response extents (thresholds) of plant zonation and morphological and reproductive traits to multiscale environmental heterogeneity were also assessed. Our results showed that plant colonization and performance at coastal frontiers are sensitive to the microtopography of elevation and reflect the ecological adaptability at both the landscape and individual scales. Sedge species typically exhibit morphological and reproductive flexibility across the inundation intensity. The plants allocated more biomass to belowground tissues in response to decreasing elevation. The elevation thresholds for the yield of reproductive organs were higher (2.38–2.50 m based on the local Wusong datum) than those for morphology (2.05–2.14 m). The thresholds for the yield of asexual reproductive organs shifted to a lower elevation by approximately 0.15 m relative to that of the sexual reproductive organs. The increasing corm: spike ratios of plants with longer inundation durations also indicated this reproductive plasticity. This study revealed that the combination of morphological and reproductive responses of pioneer sedges contributed to survival and colonization at the foremost coastal flat. Our results are useful for developing restoration strategies for the native Scirpus species on China's coast.

Combined effects of vegetation, tide and sediment on the carbon dynamics in the intertidal creek-marsh systems remain unclear. We investigated the variability of dissolved organic (DOC) and inorganic carbon (DIC), and particulate organic (POC) and inorganic carbon (PIC) in the tidal creeks within the Poaceae and Cyperaceae communities on flood-ebb cycle in a salt marsh of eastern China. In the Poaceae creek with high plant biomass and soil carbon stock, the DOC concentrations were higher by on average 1.00–1.48 times than that in the Cyperaceae creek across all seasons and spring and neap tide stages, while the difference of DIC was not notable. The POC and PIC concentrations were lower in the Poaceae creek compared to the Cyperaceae creek. Spring tides increased the carbon concentrations (except for PIC) in both creeks by on average 7–40%, relative to neap tides. Seasonal variations of sedimentary rate within the communities probably result in the discrepancy of particulate carbon loading between the creeks. The Poaceae creek functioned as a source of DOC and DIC throughout a year but as a sink of POC and PIC in summer and autumn, while it turned to a weak source of PIC in winter and spring. The Cyperaceae creek exhibited as a source of all carbon components throughout a year. We suggest that vegetation type (with soil carbon stocks), tidal regimes and sedimentary dynamics would synergistically determine the fate of carbon in the creeks. Our results are helpful in reliable estimates of carbon transport between the coastal marsh and the adjacent ocean.

Bioturbating benthic organisms have typically been characterised by how they modify the vertical sediment erosion thresholds. By means of several annular flume experiments, we aimed to understand how benthic organisms may affect grain-size sediment properties over time, and how this depends on the sediment type and the sediment loading of the water column. We compared the effect of two bioturbating macroinvertebrate species: a local dominant species, the cockle Cerastoderma edule and a spreading non-indigeneous species, the clam Ruditapes philippinarum. Our results indicate that the effect of benthic organisms on sediment dynamics is strongly dependent on both the prevailing environmental conditions and the benthic species present. If sediment is sandy, the benthos can gradually enhance the silt content of the sediment by mixing in part of the daily tidal sediment deposition. In contrast, if sediment is muddy, benthos can gradually decrease the silt content of the sediment by specifically suspending the fine fraction. Moreover, we observed that the native cockles had a stronger impact than invasive clams. Therefore, bioturbating benthos can have an important effect in determining the local sediment properties, with the outcome depending both on the species in question and the environmental conditions the bioturbator lives in. Our findings show that sediment bioturbation may have strong implications for tidal flat stability undergoing major changes from natural or anthropogenic sources.