No abstract

Since the last decades, previous long-term Wadden Sea studies revealed significant changes in the abundance, biomass and spatial distribution of characteristic macrofauna communities in response to environmental changes and anthropogenic stressors. In this study, we performed statistical community analysis for the East-Frisian Wadden Sea (EFWS, southern North Sea) on two reference datasets across a period with severe climatic and environmental changes (1980s-2018). Therefore, historical macrofauna data from the Quantitative Sensitivity Mapping (1980s, SENSI 1) were reanalyzed and compared with data from the Synoptic Intertidal Benthic Survey (SIBES/SENSI 3) collected in 2018. Our results revealed significant quantitative and spatial changes in the characteristic macrofauna communities between the 1980s and 2018, most likely in response to de-eutrophication and sea level rise mediated habitat changes. Since the 1980s, the total number of taxa remained relatively stable (1980s: 90, 2018: 81), but the total abundance decreased by ca. -31% and the total biomass decreased by ca. -45%, particularly in the eastern regions of the study site probably due to de-eutrophication processes. Thereby, the mean abundances/m2 of ≥ -80% (1980s-2018) in the EFWS of several dominant species decreased: e.g. the gastropod Peringia ulvae, the polychaete Lanice conchilega and the bivalve Mya arenaria. In contrast, the mean abundance/m2 of one dominant species increased by ≥ +80% (1980s-2018): the invasive bivalve Ensis leei. The mean biomass [g/m2] of three dominant species decreased by ≥ -80% (1980s-2018): P. ulvae, L. conchilega and the amphipod Corophium volutator. In contrast, the mean biomass [g/m2] of one dominant species increased by ≥ +75% (1980s-2018): the polychaete Arenicola marina. In the western part of the EFWS, not only higher abundances of A. marina, but also of L. conchilega and P. ulvae were found in 2018, caused i.a. by sea level rise mediated decreasing mud contents and sand accretion on tidal flats. At the community level, the Oligochaeta/Heteromastus community increased in spatial distribution in the western EFWS in 2018 in the vicinity of increasing mussel/oyster beds.

<p>A coupled wave and ocean model within the COAWST Modelling System is used in a one-way nesting scenario to investigate the importance of wind, surface currents and Stokes drift for the distribution of surface drifting objects in the nearshore region of the East Frisian barrier island Spiekeroog in the North Sea. Stokes drift and surface currents are computed on a high resolution grid. Combination with meteorological data, Lagrangian floats and in situ data of surface drifters and wave radar measurements allows for a realistic estimation of wind drag coefficients and Stokes Drift. Therefore GPS-Box Drifters have been developed which resemble surface floating macroplastics. Complex topographic features with shallow areas and deep channels within this coastal region lead to strongly heterogeneous wave and current fields. Due to the high resolution of our numerical model these features can be described with the needed accuracy. At the same time computational costs are minimized by using a two-step nesting approach. We show that Stokes Drift becomes a major role in shallow coastal regions, even exceeding the influence of the wind drag, hence playing a key role for realistic descriptions of beaching and the recognition of litter accumulation.</p><p> </p>

<p>Since 2016, an interdisciplinary consortium at the Carl von Ossietzky University in Oldenburg has been funded by the Lower Saxony Ministry for Science and Culture in order to provide solid, scientific knowledge of the sources, pathways and accumulation zones of plastic litter. This team consists of physical oceanographers, geoecologists, biologists and environmental planners.</p><p>Using simple wooden drifters, GPS-drifters and high resolution, numerical modelling, the consortium studied the dispersal of floating macroplastics (i.e. visible plastic fragments and objects) and accumulation areas within the German Bight and the Wadden Sea. Furthermore, coastal sensors and observation systems were employed to gather data of hydrodynamic parameters. In addition, the general public has actively participated in the collection of litter data via a web-based registration system for reporting the findings of wooden drifters.</p><p>In this presentation we will highlight some of the most important results of the project amongst them the surprising observation of a complete reversal of the circulation in the southern North Sea in March 2018, supported by drifter reports from citizen scientists from Britain. We will also shortly shed light on the heavy workload involved with presentations to the public (Radio, TV, print media, presentations to various stakeholder groups) which future projects should anticipate already at the planning stage.</p>

The issue of marine plastic pollution has been extensively studied by various scientific disciplines in recent decades due to its global threat. However, owing to its complexity, it requires an interdisciplinary approach to develop effective management strategies. The multidisciplinary scientific approach presented here focuses on understanding the sources and pathways of macroplastic litter and developing abatement strategies in the southern North Sea region. Over 2.5 years, more than 63,400 biodegradable wooden drifters were deployed with the help of citizen science to study the sources, pathways, and accumulation areas of floating marine litter. Rivers act as sinks of most of the floating marine litter released within their waterways. Short-term field experiments were also conducted to analyse the hydrodynamic and atmospheric processes that govern the transport of floating litter particles at the sea surface. Numerical models were used to examine the transport of virtual litter particles in the entire North Sea and in coastal regions. It was found that there are no permanent accumulation areas in the North Sea, and the Skagerrak and fronts can increase the residence times of floating marine litter and favour sinking. Field surveys revealed that the majority of litter objects originate from fisheries and consumer waste. To develop effective abatement strategies, the key stakeholder landscape was analysed on a regional level. The interdisciplinary approach developed in this study highlights the importance of synergizing scientific resources from multiple disciplines for a better understanding of marine plastic pollution and the development of effective management strategies.