This study aims to get an insight into the particle trajectories that microplastics follow, after having been released in the North Sea.

For the computations daily-mean values of the surface currents are used, retrieved from the Mercator global ocean model. 2D particles trajectories are simulated for a year, with a 3rd party Python toolbox for Lagrangian simulation of particles: OceanParcels. Particles released from any location in the North Sea eventually get trapped in the Norwegian Coastal Current (NCC). From here they are being further advected to the North, at different moments in time for the particles released at different locations. The coastal processes in the NCC are mainly linked to wind and stratification, hence variations in ow patterns near the coast are linked to the seasons. When these ow pattern include large scale eddies, the particles follow a meandering and erratic path. Floating plastic particles released in the North Sea will flow northwards along the coast of Norway. Eventually those particles will end up in the Arctic region or get
trapped in the Norwegian fjords, independently of the location of release. However, the time scale of the northward advection depends both on where the particle has been released and the environmental conditions.

Coastal bays in the Caribbean accommodate different marine ecosystems, including seagrass meadows and coral reefs, which provide important ecosystem services. However, these marine ecosystems are endangered. Seagrass ecosystems have a key role in coastal bays, but despite their alarming rates of loss, they receive little attention compared to other marine ecosystems. This study aims to provide a better understanding of the role of seagrass ecosystems in coastal bays by assessing their impact on the morphodynamic behavior. In order to achieve this, an existing hydrodynamic model has been extended to include morphodynamics. Two different bays have been investigated: Baie Orientale and Baie de l’Embouchure (St. Martin). These bays represent a partially exposed and fully sheltered bay, respectively. Both regular wave conditions, as well as extreme storm conditions, have been investigated to understand the consequences of seagrass loss on coastal erosion for different environmental climates. The coastal erosion has been found to be more prominent in the exposed region, whereas the more sheltered areas are more resilient. The erosion takes place in shallow waters but remains limited under regular swell conditions. The increased wave energy, during the extreme storm event, increases the erosion rates considerably. However, the regular swell conditions are normative in shaping the morphological development of these coastal bays when longer timescales are considered. The seagrass counters erosion most effectively in the foreshore and much less in deeper regions. Removal of seagrass in the foreshore (between 1-3m) halves the sediment stabilization. In contrast, the sediment stabilization increases if the meadows are able to spread especially towards the shore. In addition, the wave energy and waveform have a significant impact on the sediment stabilization. The stabilization typically decreases for higher and shorter (storm) waves, whereas it increases for smaller and longer (swell) waves. The long-distance interactions between seagrass meadows and coral reefs have led to their mutual coexistence, which is also found to be beneficial for the erosion control of the coastal bays. The dissipation of wave energy on top of the reefs fosters the sediment stabilization by seagrass. Moreover, the impact of the reefs on sediment stabilization also increases in the presence of seagrass meadows due to the additional drag exerted by the seagrass. The seagrass meadows are typically more effective under swell waves, whereas the reefs are more dominant in the dissipation of storm waves. Seagrass meadows and coral reefs form thus a synergy, in which the stabilization of sediments provided by the individual ecosystems is facilitated, reinforced, and complemented by the proximate presence of the other ecosystem. Finally, the role of seagrass on sediment stabilization has been explored under climate change. The coastal erosion increases for the considered sea-level rise scenarios. The impact of the seagrass on sediment stabilization decreases when the bays, seagrass and reef ecosystems are not able to keep up with sea-level rise. The synergy between seagrass and reefs emphasizes that the responses of both ecosystems are of importance for the future of tropical sheltered bays and should therefore not be managed in isolation.