The Sylt Roads pelagic time series covers physical and hydrochemical parameters at five neighboring stations in the Sylt–Rømø bight, Wadden Sea, North Sea. Since the beginning of the time series in 1973, sea surface temperature (SST), salinity, ammonium, nitrite, nitrate, and soluble reactive phosphorus (SRP) have been measured twice a week. The other parameters were introduced later (dissolved silicate (Si) since 1974, pH since 1979, dissolved organic nitrogen (DON) since 1996, dissolved organic phosphorus (DOP) since 2001, chlorophyll a since 1979, and suspended particulate matter (SPM) since 1975), and in the case of dissolved oxygen, were already discontinued (1979–1983). In the years 1977, 1978, and 1983, no sampling took place. Since the start of the continuous sampling in 1984, the sea surface temperature in the bight has risen by +1.11 ∘C, with the highest increases during the autumn months, while the pH and salinity decreased by 0.23 and 0.33 units, respectively. Summer and autumn salinities are generally significantly elevated compared to spring and winter conditions. Dissolved nutrients (ammonium, nitrite, nitrate, and SRP) have displayed periods of intense eutrophication (1973–1998) and de-eutrophication since 1999. Silicate has shown significantly higher winter levels since 1999. Interestingly, phytoplankton parameters did not mirror these large changes in nutrient concentrations, as a seasonal comparison of the two eutrophication periods showed no significant differences with regard to chlorophyll a. This phenomenon might be triggered by an important switch in nutrient limitation during the time series. With regard to nutrients, the phytoplankton was probably primarily limited by silicate until 1998, while, since 1999, the SRP limitation has become increasingly important. All data are available in Rick et al. (2017b–e, 2020a–o) from https://doi.org/10.1594/PANGAEA.150032, https://doi.org/10.1594/PANGAEA.873549, https://doi.org/10.1594/PANGAEA.873545, https://doi.org/10.1594/PANGAEA.873547, https://doi.org/10.1594/PANGAEA.918018, https://doi.org/10.1594/PANGAEA.918032, https://doi.org/10.1594/PANGAEA.918027, https://doi.org/10.1594/PANGAEA.918023, https://doi.org/10.1594/PANGAEA.918033, https://doi.org/10.1594/PANGAEA.918028, https://doi.org/10.1594/PANGAEA.918024, https://doi.org/10.1594/PANGAEA.918034, https://doi.org/10.1594/PANGAEA.918029, https://doi.org/10.1594/PANGAEA.918025, https://doi.org/10.1594/PANGAEA.918035, https://doi.org/10.1594/PANGAEA.918030, https://doi.org/10.1594/PANGAEA.918026, https://doi.org/10.1594/PANGAEA.918036, and https://doi.org/10.1594/PANGAEA.918031.

• An entire ecosystem approach in management and policy is gained by indicators from the Ecological Network Analysis (ENA).

Germany is an EU member state and is thus obliged to monitor and protect its marine and coastal areas in the context of international treaties (e.g. EU Marine Strategy Framework Directive, EU Natura2000 directives, Trilateral Monitoring and Assessment Programme, OSPAR) to achieve the good environmental status (GES). Suitable indicators thus need to be developed to assess the status of relevant ecosystems. Intertidal bivalve beds belong to the most productive habitats in the shallow coastal waters of the Wadden Sea but are highly dynamic and difficult to monitor. Extensive benthos and sediment sampling are required to study their development and distribution. We therefore evaluated the suitability of herring gulls (Larus argentatus) as a bioindicator species for monitoring these habitats. As flexible and opportunistic top-predators, herring gulls prefer to forage on intertidal flats and feed on bivalves (Cerastoderma edule, Mytilus edulis, Ensis leei) and crustaceans, with intertidal habitats near the breeding colony preferred during the incubation period. We used state of the art tracking devices to analyse habitat selection by herring gulls, and assessed how this was driven by biotic and abiotic factors. We then designed a habitat model to predict the occurrence of intertidal bivalve beds for directed monitoring, based on GPS logger data from herring gulls and hydrodynamic data. Both methods showed high correlations of herring gull foraging patterns with bivalve biomass and inundation time, depending on the distance from the breeding colony. The movement patterns of herring gulls clearly mirrored intertidal bivalve distributions. These results showed that combining GPS-logger data for top-predators, such as birds, with environmental data has great potential for monitoring and assessing the GES. We propose that herring gulls may be used as an indicator to locate bivalve beds in the Wadden Sea and to detect changes in the food web.

Ever-expanding human activities on land and at sea have amplified the need for easily applicable proxies to effectively predict human mediated changes in ecosystem functioning and biogeochemical cycling. Here we investigate the ability of different proxies to predict macrofaunal impact on nutrient fluxes of ammonium, nitrate, nitrite, silicate and phosphate under different environmental conditions. As proxies we chose simple community descriptors (i.e. density, wet biomass, ash free dry mass) as well as two trait-based indices that were created to describe macrofauna-sediment interactions (i.e. community bioturbation potential (BPc) and community irrigation potential (IPc)). We hypothesize that trait based indices, will increase the predictability of macrofaunal impact on nutrient fluxes compared the more simple community descriptors. We correlate all proxies with experimental nutrient flux data measured under different environmental conditions using generalized linear models. Generally environmental conditions significantly affected all analysed nutrient fluxes and mostly provided better predictions than any of the proxies for macrofaunal impact by itself. Yet a combination of the proxies and the environmental conditions always increased prediction accuracy. Hereby the irrigation trait based indices enhanced the predictability of the nutrient fluxes of ammonium, nitrate, nitrite, silicate and phosphate most.

Meiofauna are known to have an important role on many ecological processes, although, their role in food web dynamics is often poorly understood, partially as they have been an overlooked and under sampled organism group. Here, we used quantitative food web modeling to evaluate the trophic relationship between meiofauna and their food sources and how meiofauna can mediate the carbon flow to higher trophic levels in five contrasting soft-bottom intertidal habitats (including seagrass beds, mudflats and sandflats). Carbon flow networks were constructed using the linear inverse model-Markov chain Monte Carlo technique, with increased resolution of the meiofauna compartments (i.e. biomass and feeding ecology of the different trophic groups of meiofauna) compared to most previous modeling studies. These models highlighted that the flows between the highly productive microphytobenthos and the meiofauna compartments play an important role in transferring carbon to the higher trophic levels, typically more efficiently so than macrofauna. The pathway from microphytobenthos to meiofauna represented the largest flow in all habitats and resulted in high production of meiofauna independent of habitat. All trophic groups of meiofauna, except for selective deposit feeders, had a very high dependency on microphytobenthos. Selective deposit feeders relied instead on a wider range of food sources, with varying contributions of bacteria, microphytobenthos and sediment organic matter. Ecological network analyses (e.g. cycling, throughput and ascendency) of the modeled systems highlighted the close positive relationship between the food web efficiency and the assimilation of high-quality food sources by primary consumers, e.g. meiofauna and macrofauna. Large proportions of these flows can be attributed to trophic groups of meiofauna. The sensitivity of the network properties to the representation of meiofauna in the models leads to recommending a greater attention in ecological data monitoring and integrating meiofauna into food web models.

In this paper, we identified seven ecological network analysis (ENA) metrics that, in our opinion, have high potential to provide useful and practical information for environmental decision-makers and stakeholders. Measurement and quantification of the network indicators requires that an ecosystem level assessment is implemented. The ENA metrics convey the status of the ecological system state variables, and mostly, the flows and relations between the various nodes of the network. The seven metrics are: 1) Average Path Length (APL), 2) Finn Cycling Index (FCI), 3) Mean Trophic level (MTL), 4) Detritivory to Herbivory ratio (D:H), 5) Keystoneness, 6) Structural Information (SI), and 7) Flow-based Information indices. The procedure for calculating each metric is detailed along with a short evaluation of their potential assessment of environmental status.

Arctic kelp belts, made of large perennial macroalgae of the order Laminariales, are expanding because of rising temperatures and reduced sea ice cover of coastal waters. In summer 2013, the trophic relationships within a kelp belt food web in Kongsfjorden (Spitsbergen) were determined using fatty acid and stable isotope analyses. Low relative proportions of Phaeophyta fatty acid trophic markers (i.e. 20:4(n-6), 18:3(n-3) and 18:2(n-6)) in consumers (3.3−8.9%), as well as low 20:4(n-6)/20:5(n-3) ratios (<0.1−0.6), indicated that Phaeophyta were poorly used by macrozoobenthos as a food source, either fresh or as detritus. Relatively high δ13C values measured in macrozoobenthos (−22.5 to −16.1‰) ruled out an important role of erect Rhodophyta, which were much more 13C depleted (−37.1 to −35.8‰). Instead, δ13C values and relatively high abundances of typical diatom (14:0, 16:1(n-7), 20:5(n-3)) and flagellate (18:4(n-3), 22:6(n-3)) fatty acid trophic markers in consumers pointed out an important use of microalgae, likely of pelagic and benthic origin (i.e. senescent phytoplankton bloom, eroded epiphytes and suspended epilithic material). The use of these food resources may be fostered by their trapping under the kelp canopy.

Neobiotic species can have profound impacts on food webs and entire ecosystems. The American razor clam Ensis leei was introduced into the Wadden Sea by vessels in the late 1970s and has since spread widely. It has been suggested that Ensis does not interact strongly with other benthic species. The abundance and biomass of E. leei were recorded in 2393 samples in the north-eastern Wadden Sea and 800 samples in the south-eastern Wadden Sea over a total period of 9 years. Using an interdisciplinary approach, we developed a habitat prediction model using sedimentological and hydrodynamic predictors to help understand the shape of the ecological niche occupied by Ensis in the Wadden Sea. Our model showed that Ensis preferred areas with moderately high bed shear stress and prolonged or constant water coverage. Ensis preferred coarse sediments in the northern sub-area but coarse and muddy sediments in the southern sub-area and was negatively affected by the sand mason worm Lanice conchilega in the northern sub-area. Predictions of the spatial distribution of Ensis using the northern and southern datasets revealed major differences in predicted hot-spots throughout the entire study site. This study thus highlights the need to collect a sufficiently large dataset from different sub-areas of the Wadden Sea to allow valid conclusions to be drawn regarding the spatial distribution of Ensis. The negative effects of L. conchilega on Ensis abundance and biomass as well as the occurrence of Ensis in muddy sediments in the south suggest that the ecological niche of this neobiotic species is likely to overlap partly with the native fauna of the Wadden Sea.