Opening statement for Topic 1: " What is the Baltic contribution to the European marine biodiversity? What is the marine biodiversity knowledge in NAS countries?"
Author: Dr. Evald Ojaveer, Estonian Marine Institute, University of Tartu, Estonia
Dear colleagues,
In the list of European seas, the Baltic Sea stands side by side with the North Sea, Norwegian Sea etc. However, concerning ecosystems (below biodiversity has been considered in the ecosystem's framework), the shallow brackish Baltic Sea is a sea like no other. The Baltic ecosystems have developed only for 10-12 000 years, in very variable conditions, incl. the Ancylus Lake stage. The species richness of the Baltic ecosystems cannot be compared with other seas, even not with the Mediterranean, another semienclosed sea in Europe, the ecosystem of which has formed for 70 million years in much more stable conditions. The ecosystems of the Baltic Sea are unique brackishwater systems in the stage of rapid development and differentiation.
The largely differing salinity by areas of the sea (in the Kattegat the salinity varies from 12-34 ‰ but decreases to 2-3 ‰ in the easternmost part of the Gulf of Finland and the northernmost Bothnian Bay), create very specific osmotic conditions for aquatic organisms in the Baltic Sea. Considerable variations in the temperature induced by the wide N-S range of the sea, and in the oxygen concentration because of the existence of two principal water layers separated by halocline, sophisticate the adaptations. Only a limited number of species have been able to adapt to a wide range of salinity and rather severe temperature conditions in winter. Therefore, the number of species in the Baltic Sea is rather moderate. Many of them occur in the border zone of its area. The relatively small number of species and their harsh living conditions limit the possible links in food chains increasing the risk for disruptions. During the adaptation to the stressful environmental conditions, the features of a number of species have changed, e.g. their metabolism has slowed down and the body size decreased.
The long estuary-like Baltic Sea involves largely differing habitats. The SW part of the sea receiving the North Sea water is the most acceptable habitat for marine organisms in the Baltic. There the number of marine species is the highest (in Kattegat the number of marine fish species is approximately 80). In this area Laminaria, Calanus , Oithona, Sagitta, Scoloplos, Abra, Astarte, cod, plaice and other marine species have started their adaptations to the Baltic conditions. In the northern and NW parts of the sea with severe/arctic climate, rather marginal influence of the modified marine waters and large freshwater input, only a few marine species have permanently established and can produce their offspring (in the Bothnian Sea the number of marine fish species is about 15). In the coastal zone with numerous archipelagoes and skerries mainly the organisms with freshwater background are abundant. Because of the mechanical influence of ice, harsh conditions in shallow areas favour species with short life cycle, influencing biodiversity and the related phenomena.
The bottom relief divides the Baltic Sea into a number of basins with separate circulation systems and the continuously renewing hydrological borders. The heterogeneity in biotopes is much larger than in eumarine seas. As a result the Baltic ecosystem consists of a number of ecological subsystems notably differing in basic parameters (salinity, temperature, oxygen conditions, the pattern of energy flow in the ecosystem, etc.). Formation of infraspecific groups in species by means of adaptation to the conditions of the local subsystems is intense. However, owing to the short history of the sea, in general the differentiation of the endemic groups has not yet reached the species level.
In the contemporary Baltic Sea the most ancient component of the biota consisting of very euryhaline species immigrated into the Baltic during its initial stages of development (the glacial relicts), is distributed mainly in the gulfs of Bothnia, of Finland and of Riga. There the temperature and oxygen conditions are acceptable for them. A continuous natural immigration occurs mainly from two sources: 1) marine boreal and migratory species penetrating into the Baltic via Danish straits; 2) freshwater species which occupy mainly coastal areas, especially in the northern Baltic with lower salinity. In addition, certain exotic species, recently favoured by man in crossing their distribution borders (with ships, mainly in the ballast water) have colonized large areas of the Baltic Sea. Historically, the success of the colonization is connected with the developmental stages of the sea and oscillations of climatic periods. Also, in the contemporary stage of the sea, the dependence of the biota on the temperature regime and the type of circulation of air masses over the Baltic Sea is obvious. In the periods of good water exchange between the Baltic and the North Sea marine species have had better possibilities for the increase of their abundance. In the periods of freshening of the Baltic Sea, marine species retreated and freshwater species widened their area. Studies on the formation of fauna and flora in the Baltic Sea (including introduction of alien species) during different climatic periods are very important and they should be encouraged.
In the subsystems of the Baltic Sea the biological productivity is highly variable both in time and space. The most productive areas are confined to the archipelagoes and estuaries and the zones of violent vertical mixing of water layers on the coastal slope and banks in the open sea where upmixing of nutrients from below the halocline takes place year round. Such areas accommodate diverse flora and fauna. Also, ecosystems of the Baltic Sea (incl. their biodiversity) readily react to the anthropogenic impacts the importance of which in concrete areas during different climatic periods needs better be quantified
The items to be commented:
1. A reasonable scheme for the studies of the Baltic ecosystems. Is it justified to make conclusions on the whole Baltic Sea based on materials collected in a limited area, e. g. in the Gulf of Finland or SW Baltic?
2. What is the importance of infraspecific groups and higher taxonomic units in marine biodiversity assessments?
3. How should the assessments of living resources and their sustainable management be organized in the Baltic?
4. Biodiversity assessments in the Baltic.
5. The possible areas of estimation of the biodiversity and habitat variation in the Baltic.
6. The periodic nature of development of the Baltic ecosystems (incl. the dynamics in their components: phytoplankton, macrovegetation, bacteria, zooplankton, zoobenthos, fish, alien species, etc.).
7. Define the term alien (non-indigenous, exotic) species for the Baltic ecosystems.
In the Baltic Sea countries the history of marine science has developed well over a century. In the second half of the 20th century, the contacts between the east-coast and west-coast countries in marine science were weak and the corresponding developments differed. In the east-coast countries a large part of the studies was aimed at practical goals (e.g. the creation of scientific basis for the exploitation of living resources). The studies resulted in rather detailed knowledge of some ecological subsystems and the understanding that in the Baltic Sea certain fish species have local populations that should be assessed and managed separately. The majority of the results were published in Russian, Polish, Estonian, German, and other languages not understood by all scientists.
Today a rather rich literature is available on a number of ecological subsystems (incl. biodiversity), on the assessment and management of some living resources in the Baltic Sea, etc. However, because of language problems, the access to all of these materials by some scientists may be somewhat complicated.
Comments expected:
1. Is the problem concerning the availability of a part of the literature on the Baltic ecosystems important?
2. Suggestions. |
