ALBERT

Description: Hypoxia is an increasing problem in marine ecosystems around the world. While major advances have been made in our understanding of the drivers of hypoxia, challenges remain in describing oxygen dynamics in coastal regions. The complexity of many coastal areas and lack of detailed in situ data have hindered the development of models describing oxygen dynamics at a sufficient spatial resolution for efficient management actions to take place. It is well known that the enclosed nature of seafloors and reduced water mixing facilitates hypoxia formation, but the degree to which topography contributes to hypoxia formation and small-scale variability of coastal hypoxia has not been previously quantified. We developed simple proxies of seafloor heterogeneity and modeled oxygen deficiency in complex coastal areas in the northern Baltic Sea. According to our models, topographical parameters alone explained ∼80 % of hypoxia occurrences. The models also revealed that less than 25 % of the studied seascapes were prone to hypoxia during late summer (August–September). However, large variation existed in the spatial and temporal patterns of hypoxia, as certain areas were prone to occasional severe hypoxia (O2 

Description: Peltonen, H., Luoto, M., Pääkkönen, J.-P., Karjalainen, M., Tuomaala, A., Pönni, J., and Viitasalo, M. 2007. Pelagic fish abundance in relation to regional environmental variation in the Gulf of Finland, northern Baltic Sea. – ICES Journal of Marine Science, 64: 487–495. This study applies variation partitioning to analyse spatial patterns in hydroacoustic estimates of fish abundance in relation to regional variation in the hydrography, food resources, and geography of the Gulf of Finland, northern Baltic Sea. Using variation partitioning based on generalized additive models, daily fluctuations in hydroacoustic abundance estimates were first eliminated, and the remaining variation in fish abundance was decomposed into independent and joint effects of hydrography, food resources, and geography. The independent effect of geographic variables (spatial location and water depth) captured the largest fraction of the variation (9.3%) in the fish-abundance patterns, whereas the independent effects of hydrography (5.8%) and food resources (5.6%) captured slightly less. However, a considerable portion of the variation in fish-abundance patterns was accounted for by the joint effects of explanatory variables and may therefore be causally related to two or all three groups of variables. The model applied efficiently eliminated the spatial autocorrelation in the fish abundance between sampling units, especially at distances 〉2000 m. At smaller scales, the residual autocorrelation may have been due to fish behavioural patterns independent of the explanatory variables in this analysis.

Description: Hypoxia is an increasing problem in marine ecosystems around the world, and recent projections indicate that anoxic dead zones will be spreading in the forthcoming decades. While major advances have been made in our understanding of the drivers of hypoxia, it fundamentally hinges on patterns of water circulation that can be difficult to resolve in coastal regions. The complexity of many coastal areas and lack of detailed in situ data has hindered the development of models describing oxygen dynamics at a sufficient resolution for efficient management actions to take place. We hypothesized that the enclosed nature of seafloors facilitates hypoxia formation. We developed simple proxies of seafloor heterogeneity and modelled oxygen deficiency in complex coastal areas in the northern Baltic Sea. We discovered that topographically sheltered seafloors and sinkholes with stagnant water are prone to the development of hypoxia. Approximately half of the monitoring sites in Stockholm Archipelago and one third of sites in southern Finland experienced severe hypoxia (O2 

Description: Climate change influences the Baltic Sea ecosystem via its effects on oceanography and biogeochemistry. Sea surface temperature has been projected to increase by 2 to 4 °C until 2100 due to global warming; the changes will be more significant in the northern areas and less so in the south. The warming up will also diminish the annual sea ice cover by 57% to 71%, and ice season will be one to three months shorter than in the early 21st century, depending on latitude. A significant decrease in sea surface salinity has been projected because of an increase in rainfall and decrease of saline inflows into the Baltic Sea. The increasing surface flow has, in turn, been projected to increase leaching of nutrients from the soil to the watershed and eventually into the Baltic Sea. Also, acidification of the seawater and sea-level rise have been predicted. Increasing seawater temperature speeds up metabolic processes and increases growth rates of many secondary producers. Species associated with sea ice, from salt brine microbes to seals, will suffer. Due to the specific salinity tolerances, species’ geographical ranges may shift by tens or hundreds of kilometres with decreasing salinity. A decrease in pH will slow down calcification of bivalve shells, and higher temperatures also alleviate establishment of non-indigenous species originating from more southern sea areas. Many uncertainties still remain in predicting the couplings between atmosphere, oceanography and ecosystem. Especially projections of many oceanographic parameters, such as wind speeds and directions, the mean salinity level, and density stratification, are still ambiguous. Also, the effects of simultaneous changes in multiple environmental factors on species with variable preferences to temperature, salinity, and nutrient conditions are difficult to project. There is, however, enough evidence to claim that due to increasing runoff of nutrients from land and warming up of water, primary production and sedimentation of organic matter will increase; this will probably enhance anoxia and release of phosphorus from sediments. Such changes may keep the Baltic Sea in an eutrophicated state for a long time, unless strong measures to decrease nutrient runoff from land are taken. Changes in the pelagic and benthic communities are anticipated. Benthic communities will change from marine to relatively more euryhaline communities and will suffer from hypoxic events. The projected temperature increase and salinity decline will contribute to maintain the pelagic ecosystem of the Central Baltic and the Gulf of Finland in a state dominated by cyanobacteria, flagellates, small-sized zooplankton and sprat, instead of diatoms, large marine copepods, herring, and cod. Effects vary from area to area, however. In particular the Bothnian Sea, where hypoxia is less common and rivers carry a lot of dissolved organic carbon, primary production will probably not increase as much as in the other basins. The coupled oceanography-biogeochemistry ecosystem models have greatly advanced our understanding of the effects of climate change on marine ecosystems. Also, studies on climate associated “regime shifts” and cascading effects from top predators to plankton have been fundamental for understanding of the response of the Baltic Sea ecosystem to anthropogenic and climatic stress. In the future, modeling efforts should be focusing on coupling of biogeochemical processes and lower trophic levels to the top predators. Also, fine resolution species distribution models should be developed and combined with 3-D modelling, to describe how the species and communities are responding to climate-induced changes in environmental variables.