Pressures on the Baltic Sea
The Baltic Sea is one of the world´s largest brackish water areas. It is inhabited by both marine and freshwater species, but the number of species is low compared to most other seas due to the low salinity. The drainage area is inhabited by around 85 million people, influencing on the status of the Baltic Sea via human activities on land and sea. Due to the limited level of water exchange, nutrients and other substances from the drainage area accumulate in the Baltic Sea and are only slowly diluted. The status of seven distinct pressures on the Baltic Sea are assessed in this report (Figure ES2). In addition, a particular concern for the Baltic Sea is the wide and increasing distribution of areas with poor oxygen conditions. Climate-related increases in water temperature, and decreases in salinity due to increased input of freshwater, are further expected to affect the distribution of species over time, as well as their physiology and food availability.
Eutrophication has been evident in the Baltic Sea for many decades, due to past high and still excessive input of nitrogen and phosphorus. Over 95% of the Baltic Sea region is affected by eutrophication. Inputs of nutrients from land have decreased, but effects of these measures are not yet generally reflected in the status of the marine environment. The eutrophication status has deteriorated in seven out of the seventeen open-sea assessment units since the last five year period (2007–2011) to the present (2011–2015), whereas it has improved in only two assessment units. Only a few coastal areas are currently unaffected by eutrophication, but an improving trend is seen in some indicators and sub-basins.
Levels of contaminants are elevated and continue giving cause for concern. However, the analysis suggests that the situation is not generally deteriorating, as reflected in slightly more improving than deteriorating trends in the monitored hazardous substances. The integrated contamination status is mainly influenced by poly-brominated flame retardants and mercury. Cesium (137Cs) deposited after the accident at the Chernobyl nuclear power plant in 1986 is now at acceptable levels in some sub-basins, and can be expected to be so in all of the Baltic Sea by 2020. Acute pollution events from oils spills have decreased.
HELCOM is developing core indicators for assessing marine litter, but they are not yet operational and thus no assessment of status has been possible at this time. Beach litter monitoring is ongoing in several countries, showing that the number of beach litter items ranges from around 10 to 160 per 100 m beach in the different sub-basins. Plastic litter is a special concern due to its risk to the environment and its slow rate of degradation. Around 70% of the litter items in the Baltic Sea are derived from plastic materials.
Underwater sound is among the most widely-distributed pressures in the Baltic Sea, caused by various human activities. Areas with high levels of continuous sound have been mapped and they mainly coincide with areas of high vessel traffic. Out of 350 impulsive sound events registered in a newly established HELCOM registry, 167 are linked to pile driving in connection with construction activities. It is not known how many marine species are impacted and thus no assessment of status has been possible at this time.
Around 140 non-indigenous species have so far been recorded in the Baltic Sea. Of these, 14 are new for the Baltic Sea during the assessment period (2011–2015). In addition, an unknown number of previously arrived non-indigenous species have expanded their distribution range to new sub-basins in the Baltic Sea. The regional objective is that there should be no primary introductions of non-indigenous species due to human activities during an assessment period and thus, good status is not achieved.
Species removal by fishing and hunting
Three out of eight assessed commercial fish stocks are in good status with respect to both biomass and fishing mortality rates. However, fourteen stocks are currently lacking evaluation. In addition to the targeted species, unselective fishing methods cause mortality of non-target fish species and size classes. Hunting has a relatively small role today. Seals are generally protected, but hunting is permitted in some countries, restricted to populations above a limit reference level and with a positive growth rate. Waterbirds are hunted in some countries, whereas in others they have strict protection.
Seabed loss and disturbance
Less than one percent of the Baltic Sea seabed was estimated as being lost due to human activities by 2015 while around half of the Baltic Sea seabed was estimated as potentially disturbed in the assessment period. The estimates are based on the spatial extent of human activities but have not been linked to pressure intensity. Hence, no assessment of adverse effects on the seabed has been made at this time.
For the biodiversity core indicators there are cases of inadequate status in all levels of the food web; only a few core indicators have acceptable levels in part of the Baltic Sea, and none of them in all assessed areas. Although the results for different indicators are not directly comparable, as their assessment methods have been developed independently, the overall result suggests that the environmental impacts on species in the Baltic Sea are wide-reaching and not restricted to certain geographic areas or certain parts of the food web (Figure ES3).
For benthic habitats, there is indication of good status in five of twelve assessed open sea areas based on estimates limited to soft bottom habitats. Coastal areas show good status in about half of the assessed Baltic Sea region. Pelagic habitats are assessed based on core indicators representing primary productivity, and in some sub-basins also zooplankton. Based on the available indicators, good status of open-sea pelagic habitats has been achieved only in the Kattegat. Coastal areas show good integrated status in about one quarter of the assessed areas. The assessments of benthic and pelagic habitats are still under development and additional elements will be included in assessments in the future.
The assessment of fish from a biodiversity perspective indicates good status in about half of the assessed coastal areas. In the open sea, good status is not achieved in any assessment area. Two out of five assessed pelagic fish stocks (herring in the central Baltic Sea and Bothnian Sea) have good status, and one of three assessed demersal stocks (plaice in the Kattegat, Sound and Belt Sea). Demersal fish are only assessed in the Kattegat and the western Baltic Sea, and an assessment for the eastern parts of the Baltic Sea is currently lacking (Figure ES4). Core indicators for the migratory species salmon and sea trout show that good status is not achieved in most areas where they are assessed.
Among the marine mammals, grey seals and harbour seals show increasing population sizes, but the assessment for grey seal indicates that the nutritional and reproductive status is not good. Of the three management units of harbour seals in HELCOM area, only the Kattegat population shows good status. The population of ringed seal in the Gulf of Finland is of concern. The population is sensitive to climate change, and it is decreasing and currently represented by around 100 animals. A particular concern is also the Baltic Proper population of harbour porpoise, with a population size recently estimated at around 500 animals. The Kattegat-Belt-Sea-Western Baltic subpopulation is also assessed as threatened by HELCOM, but the sub-population is estimated at around 40 500 animals and the sub-population is stable.
Water birds are assessed by their abundance during the breeding and the wintering season. Both indicators failed the threshold values, particularly due to a decline in benthic feeding birds during both seasons, as well as a decline in surface feeders and waders during the breeding season, and in grazing feeders during the wintering season. Pelagic feeding birds as a group shows good status.
Food web aspects
Since species are dependent on each other (for food, and via competition, for example) it can be expected that changes in one species will also influence the status of other species. Changes in the abundance of species from different feeding groups may signal such changes at food web level. In addition, altered nutritional status, growth rate or size structure are important indications that the function of the food web may have changed. Although further work is required for an indicator-based assessment of food web status in the Baltic Sea, available data for some geographic areas and species indicate a decreased nutritional status and size structure in fish (such as Eastern Baltic cod), decreased nutritional status in mammals (such as grey seal) and decreased size structure in zooplankton, all pointing towards a deteriorating food web status.
Cumulative impacts and spatial aspects
The indicator-based assessments of pressures show their status when assessed individually, without comparing their total impact or their level of spatial overlap with sensitive habitats. The Baltic Sea Impact Index is an assessment component that additionally describes the potential cumulative burden on the environment in different parts of the Baltic Sea, with the use of more detailed spatial information than can be provided by the core indicators. The results indicate that the highest potential environmental impacts currently occur in the southwestern parts of the Baltic Sea, and that the pressures causing most impacts on species are concentration of nutrients (representing inputs of nutrients), contamination, underwater noise, non- indigenous species, and the extraction of fish. Other pressures have high influence on specific species and species groups but are less widely distributed.
Impacts on human well-being
Human activities in the Baltic Sea and its drainage area contribute to pressures that act on the Baltic Sea environment but are also in many cases dependent on a healthy state of the marine environment. The cost of degradation with respect to eutrophication in the Baltic Sea region is estimated as total losses of around 3.8–4.4 billion euros annually. In other words, the citizens’ welfare would increase by this much each year if good eutrophication status was achieved (See Figure 4.1.10 in Chapter 4.1 Eutrophication). Estimates for selected biodiversity components suggest that citizens’ welfare would increase by 1.8–2.6 billion euros annually in the Baltic Sea region if the state of marine vegetation and fish stocks improved to a good status (see Chapter 5.6 Biodiversity summary and food web aspects). The current recreational benefits of the Baltic Sea are estimated at around 15 billion euros annually, and the current losses of recreation values due to the deterioration of the marine environment are estimated to around 1–2 billion euros annually (Chapter 3 Human activities and the ecosystem).