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In the Baltic Sea, cyanobacteria regularly form massive blooms in late summer. These blooms can produce toxins and have the potential to counteract management efforts to limit eutrophication because they add bioavailable nitrogen (fixed from the atmosphere) to an already over-fertilized system. Despite their critical role and substantial research progress, the controls on cyanobacteria are still not comprehensively understood. This can limit the accuracy of model-based projections. Our study adds to the ongoing discussion by providing a comparison of existing contemporary model formulations. This comparison is supplemented by a unique combination of satellite estimates of cyanobacteria blooms, in-situ nutrient observations and output of a high-resolution general ocean circulation model (MOMBA). We retrace bloom origins and conditions by calculating the trajectories of respective water parcels backwards in time. In an attempt to identify drivers of bloom development, we find that blooms originate and manifest themselves predominantly offshore. Potential implications for contemporary modelling approaches are discussed.

The ecosystem of the Baltic Sea is endangered by eutrophication. This has triggered expensive international management efforts. Some of these efforts are impeded by natural processes such as nitrogen-fixing cyanobacteria blooms that add bioavailable nitrogen to the already over-fertilised system and thereby enhance primary production, export of organic matter to depth and associated oxygen consumption. Controls of cyanobacteria blooms are not comprehensively understood and this adds to the uncertainty 5 of model-based projections into the warming future of the Baltic Sea. Here we review our current understanding of cyanobacteria bloom dynamics. We summarise published field studies, laboratory experiments and dissect the basic principles ingrained in state-of-the-art coupled ocean-circulation biogeochemical models.

Seagrass meadows, one of the worlds most important and productive coastal habitats, are threatened by a range of anthropogenic actions. Burial of seagrass plants due to coastal activities is one important anthropogenic pressure leading to decline of local populations. In our study, we assessed the response of eelgrass Zostera marina to sediment burial from physiological, morphological, and population parameters. In a full factorial field experiment, burial level (5-20 cm) and burial duration (4-16 weeks) were manipulated. Negative effects were visible even at the lowest burial level (5 cm) and shortest duration (4 weeks), with increasing effects over time and burial level. Buried seagrasses showed higher shoot mortality, delayed growth and flowering and lower carbohydrate storage. The observed effects will likely have an impact on next years survival of buried plants. Our results have implications for the management of this important coastal plant., 26 pages, 5 figures, 1 table

Artificial reefs, in the Eastern Mediterranean (Cyprus,) became a popular and frequently used tool, in fisheries and biodiversity conservation management. Even though evaluation studies about the efficacy of artificial reefs are plentiful in the rest of the Mediterranean (Central and Western), in the Eastern Basin they are largely absent. As the Eastern part of the Mediterranean Sea is characterised by unique physical parameters, the necessity to study artificial reefs under these contrasting regimes increases. The epibenthic communities of two unintentional artificial reefs (modern shipwrecks) in Cyprus (Zenobia) and Lebanon (Alice-B) were evaluated in 2010. Both shipwrecks are at similar depth, type of sea bottom, made of the same material (steel) and were sunk approximately the same period of time. However, Alice-B shipwreck off the coast of Lebanon is constantly exposed to higher levels of nutrients than Zenobia in Cyprus. Significant dissimilarities were observed in the composition, percentage of benthic cover of predominant taxonomic groups and development of the epibenthic communities. Differences in physical and chemical parameters between sides lay mainly in the nutrient and thermal regimes affecting the shipwrecks and most likely bring about the differences in the observed community structure. The results of this study suggest that epibenthic communities could be highly impacted by eutrophication caused by anthropogenic activities, leading to less biodiverse communities dominated by specific species that are favoured by the eutrophic conditions.

Between the 1950s and 1980s concentrations of inorganic nutrients increased in the coastal areas of the Baltic Sea, including the Greifswalder Bodden. As a consequence, phytoplankton concentrations and suspended solids increased strongly and the light penetration decreased substantially. An increased turbidity led to a phase shift from a macrophyte-dominated to a phytoplanktondominated ecosystem. Within 30 years, macrophyte cover declined from 90% to 15%. Macrophyte depth limit decreased from 14 m to 6 m in the Bodden. After 1985, nutrient loading declined strongly. Although nutrient loads in the Greifswalder Bodden were reduced (a 50% decrease in phosphate concentration and a 40% decrease in nitrogen concentration) in the last 15 years, an expected improvement in water quality did not coincide. Light conditions improved slightly and macrophytes showed no recovery. Possible reasons for the slow improvement are internal loading and subsequent release of iron-bound phosphorus from sediments. This process sustains continuous high nutrient concentrations in the water column and facilitates the high growth and dominance of phytoplankton. During summer, an abundant Cyanobacteria community fuels phytoplankton dominance. In addition, heavy losses in macrophyte cover result in an increase in sediment resuspensation, which leads to a reduced light penetration. There is no sign of any change in current conditions.