Beschreibung: The ever increasing impact of the marine industry and transport on vulnerable sea areas puts the marine environment under exceptional pressure and calls for inspired methods for mitigating the impact of the related risks. We describe a method for preventive reduction of remote environmental risks caused by the shipping and maritime industry that are transported by surface currents and wind impact to the coasts. This method is based on characterizing systematically the damaging potential of the offshore areas in terms of potential transport to vulnerable regions of an oil spill or other pollution that has occurred in a particular area. The resulting maps of probabilities of pollution to be transported to the nearshore and the time it takes for the pollution to reach the nearshore are used to design environmentally optimized fairways for the Gulf of Finland, Baltic Proper, and south-western Baltic Sea

Beschreibung: The Boknis Eck (BE) time series station, initiated in 1957, is one of the longest-operated time series stations worldwide. We present the first statistical evaluation of a data set of nine physical, chemical and biological parameters in the period of 1957–2013. In the past three to five decades, all of the measured parameters underwent significant long-term changes. Most striking is an ongoing decline in bottom water oxygen concentration, despite a significant decrease of nutrient and chlorophyll a concentrations. Temperature-enhanced oxygen consumption in the bottom water and a prolongation of the stratification period are discussed as possible reasons for the ongoing oxygen decline despite declining eutrophication. Observations at the BE station were compared with model output of the Kiel Baltic Sea Ice Ocean Model (BSIOM). Reproduced trends were in good agreement with observed trends for temperature and oxygen, but generally the oxygen concentration at the bottom has been overestimated.

Beschreibung: Hydrodynamic drift modeling was used to investigate the potential dispersion of Mnemiopsis leidyi from the Bornholm Basin in the Baltic Sea where it has been observed since 2007 further to the east and north. In the brackish surface layer dispersion is mainly driven by wind, while within the halocline dispersion is mainly controlled by the baroclinic flow field and bottom topography. Model runs showed that the natural spreading via deep water currents from the Bornholm Basin towards north and east is limited by topographic features and low advection velocities. Based on the information on ranges of salinity and temperature, which limit survival and reproduction of this ctenophore within the Baltic Sea, areas have been identified where the American comb jelly, M. leidyi could potentially survive and reproduce. While, we could show that M. leidyi might survive in vast areas of the northern Baltic Sea its reproduction is prevented by low salinity (〈10 psu) and temperature (〈12°C). Thus, due to the combined effect of low salinity and temperature, it is not probable that M. leidyi could establish permanent populations in the central or northern Baltic Sea. However, it seems that in the southern parts of the Baltic Sea environmental conditions are suitable for a successful reproduction of M. leidyi.

Beschreibung: The rapid spread of Mnemiopsis leidyi across the entire Baltic Sea after its first observation in 2006 gave rise to the question of its invasion pathway and the possible vector of its transport. To investigate pathways of M. leidyi invasion, the years 2005–2008 have been simulated by a three-dimensional coupled sea ice-ocean model of the Baltic Sea. In addition, a Lagrangian particle-tracking model has been utilized to test possible transport routes of this invader for 2006/2007. Based on the model, we exclude advection from the Kattegat as the main area of origin of M. leidyi and further spreading through the entire Baltic Sea. To explain the dispersion of M. leidyi in 2007 an earlier invasion already in 2005 is most probable. Alternatively, an invasion originating from main harbors with high ship traffic could also be a potential pathway. Drift simulations with drifter release in the main harbors are in good agreement with the observed distribution pattern of M. leidyi.

Beschreibung: The hydrography and dynamics of the Baltic Sea, although ruled by the same principles and forcing factors as any part of the World Ocean, contain several distinguishing features. Apart from the complicated geometry and bathymetry of the basin, two major factors contribute to the complexity of the processes here. The interplay between inflowing saline, dense waters from the North Sea in the bottom layer with the excess of light, and fresh riverine waters coming into the system in the upper layer leads to the formation of a permanent two-layer structure of density separated by a sharp jump layer (halocline). Due to the layered structure, the direct atmospheric forcing is restricted to the upper layer with a typical thickness of 40–80 m, while in the bottom layer advection and mixing processes govern the patterns of the hydrographic fields. On the top of the upper layer, a well-mixed surface layer, with a typical thickness of 15–20 m, is formed due to summer-time heating, whereas at the bottom of this layer a rather sharp jump layer of temperature (thermocline) exists. During autumn the vertical temperature gradient vanishes due to thermal convection and turbulent mixing. There are four mechanisms which induce currents in the Baltic Sea: the wind stress at the sea surface, the surface pressure gradient, the thermohaline horizontal gradient of density and the tidal forces. The currents are steered furthermore by the Coriolis acceleration, topography and friction, forming a general (cyclonic) circulation in this stratified system with positive fresh water budget. Due to the shallowness of the Baltic Sea, bottom friction damps the currents remarkably. Voluminous river runoffs can produce local changes in the sea level height and consequently also in currents. Inflowing waters penetrate at depths where the density of the ambient water matches the inflowing water masses. Due to the small baroclinic Rossby radius (2–10 km), the proper descriptions of mesoscale eddies, fronts and mixing processes need high-resolution modelling.

Beschreibung: This study applied the Systems Approach Framework (SAF) to address the issue of declining Atlantic cod fishery in coastal areas. Interviews of 58 fishers from 26 harbours and meetings with national fisheries organisations and managers revealed the perception of an offshore movement of coastal cod. Numerical modelling based on fishing survey data did not substantiate these perceptions in the data-poor coastal waters. However, Data Storage Tag (DST) information combined with bottom sea water temperature data from the spatio-temporal hydrodynamic Baltic Sea Ice-Ocean Model showed changes in potential cod habitat distribution in the Skagerrak-Kattegat and western Baltic from 1979 to 2016. Subsequently, cod habitats were defined in three categories: (i) potentially suitable (T 〈= 12 degrees C); (ii) episodic (12 〈 T 〈= 16 degrees C); and (iii) unsuitable (T 〉 16 degrees C). The environmental changes were linked to the socio-economic component of cod fishery. Cod catches (weight and monetary value) were retrieved using logbook information and data from the Vessel Monitoring System (VMS, 2005-2016) and the Automatic Identification System (AIS, 2006-2016). General additive modelling significantly showed the largest proportion of catches took place in the potentially suitable habitat whereas catches were lower in the episodic habitat and rare in the unsuitable habitat. The results of this first large-scale SAF application are highly valuable for adapting existing fisheries management by: (i) providing information on habitat shrinkage for Maximum Sustainable Yield (MSY) based stock assessments; (ii) adding a spatio-temporal dimension for coastal productivity relative to the vessel-based Individual Transferable Quota (ITQ) system; and (iii) providing a predictive scenario simulation tool for sustainable management under changing environmental conditions.

Beschreibung: In order to detect shifts in community structure and function associated with global change, the natural background fluctuation in these traits must be known. In a 6 yr study we characterized the composition of young benthic communities at 7 sites along the 300 km coast of the Kiel and Lübeck bights in the German Baltic Sea and we quantified their interannual variability of taxonomic and functional composition. Along the salinity gradient from NW to SE, the relative abundance of primary producers decreased while that of heterotrophs increased. Along the same gradient, annual productivity tended to increase. Taxonomic and functional richness were higher in Kiel Bight as compared to Lübeck Bight. With increasing species richness functional group richness showed saturation indicating an increasing functional redundancy in species rich communities. While taxonomic fluctuations between years were substantial, functionality of the communities seem preserved in most cases. Environmental conditions potentially driving these fluctuations are winter temperatures and current regimes. We tentatively define a confidence range of natural variability in taxonomic and functional composition a departure from which might help identifying an ongoing regime shift driven by global change. In addition, we propose to use RELATE, a statistical procedure in the PRIMER (Plymouth Routines in Multivariate Ecological Research) package to distinguish directional shifts in time ("signal") from natural temporal fluctuations ("noise")