Irena V. Telesh

Status of Biodiversity in the Baltic Sea

The brackish Baltic Sea hosts species of various origins and environmental tolerances. These immigrated to the sea 10,000 to 15,000 years ago or have been introduced to the area over the relatively recent history of the system. The Baltic Sea has only one known endemic species. While information on some abiotic parameters extends back as long as five centuries and first quantitative snapshot data on biota (on exploited fish populations) originate generally from the same time, international coordination of research began in the early twentieth century. Continuous, annual Baltic Sea-wide long-term datasets on several organism groups (plankton, benthos, fish) are generally available since the mid-1950s. Based on a variety of available data sources (published papers, reports, grey literature, unpublished data), the Baltic Sea, incl. Kattegat, hosts altogether at least 6,065 species, including at least 1,700 phytoplankton, 442 phytobenthos, at least 1,199 zooplankton, at least 569 meiozoobenthos, 1,476 macrozoobenthos, at least 380 vertebrate parasites, about 200 fish, 3 seal, and 83 bird species. In general, but not in all organism groups, high sub-regional total species richness is associated with elevated salinity. Although in comparison with fully marine areas the Baltic Sea supports fewer species, several facets of the systems diversity remain underexplored to this day, such as micro-organisms, foraminiferans, meiobenthos and parasites. In the future, climate change and its interactions with multiple anthropogenic forcings are likely to have major impacts on the Baltic biodiversity.

Principal processes within the estuarine salinity gradient: a review.

The salinity gradient is one of the main features characteristic of any estuarine ecosystem. Within this gradient in a critical salinity range of 5-8 PSU the major biotic and abiotic processes demonstrate non-linear dynamics of change in rates and directions. In estuaries, this salinity range acts as both external ecological factor and physiological characteristics of internal environment of aquatic organisms; it divides living conditions appropriate for freshwater and marine faunas, separates invertebrate communities with different osmotic regulation types, and defines the distribution range of high taxa. In this paper, the non-linearity of biotic processes within the estuarine salinity gradient is illustrated by the data on zooplankton from the Baltic estuaries. The non-tidal Baltic Sea provides a good demonstration of the above phenomena due to gradual changes of environmental factors and relatively stable isohalines. The non-linearity concept coupled with the ecosystem approach served the basis for a new definition of an estuary proposed by the authors.

Distribution and seasonal dynamics of the Ponto-Caspian invader Cercopagis pengoi (Crustacea, Cladocera) in the Neva Estuary (Gulf of Finland)

The Ponto-Caspian predatory cladoceran Cercopagis pengoi was first recorded in the Baltic Sea in 1992 (Gulf of Riga). In 1995 it reached high densities in the eastern Gulf of Finland. Seasonal abundance and distribution of Cercopagis in the Neva Estuary were studied in June—October 1996. Until 21 July densities fluctuated between 0.0 and 4.2 ind m−3. Maximum densities (up to 305 ind. m−3 were observed in August—September, the period of maximum water temperature. On 15 October (surface water temperature 8°C), Cercopagis was still present in plankton at low densities. C. pengoi was present at almost all stations both in the central gulf and in inshore areas along southern and northern coasts. Although Cercopagis was present throughout the water column, its abundance in the upper 10-m was usually higher than deeper down.

Macroalgal diversity along the Baltic Sea salinity gradient challenges Remane's species-minimum concept

Remanes species-minimum concept, which states that the lowest number of taxa occurs at the horohalinicum (5-8psu), was tested by investigating macroalgal diversity on hard substrates along the natural salinity gradient in the Baltic Sea. Field data on species occurrence and abundance were collected by SCUBA diving along 10 transects of the Finnish, Swedish and German coasts, covering a salinity range from 3.9 to 27psu. Macroalgal species numbers declined steadily with salinity, decreasing until 7.2psu was reached, but in the horohalinicum, a marked reduction of species number and a change in diversity were indicated by the Shannon index and evenness values. The non-linear decrease in macroalgal diversity at 5-8psu and the lack of increase in species numbers at salinities below 5psu imply a restricted applicability of Remanes species-minimum concept to macroalgae.

Carbon content of some freshwater rotifers

Carbon content of rotifers from 14 species ( Keratella cochlearis, K. c. tecta, K. c. hispida, K. ticinensis, K. quadrata, Polyarthra remata, P. vulgaris, P. major, P. euryptera, Synchaeta sp., S. stylata, S. pectinata, Trichocerca capucina, Asplanchna priodonta) was determined with the high temperature combustion method of Salonen (1979). Rotifers for the carbon analysis were collected from different fresh water bodies in Russia (Lake Ladoga) and Finland (lakes Pohjalampi, Varaslampi, and two small ponds in Lammi). Average individual carbon mass of rotifers varied between 0.0064 and 0.058 μg in Keratella spp., 0.012 and 0.051 μg in Polyarthra spp., 0.020 and 0.133 μg in Synchaeta spp., 0.162 and 0.555 μg in A. priodonta. The carbon level in the studied rotifer species differed 100-fold ranging from 0.31% WW in A. priodonta to 31.5% WW in K. c. tecta. Body length/carbon mass and body volume/carbon mass regressions were established for the studied rotifers.

The effect of fish on planktonic rotifers

The dynamics, community structure, and productivity of planktonic rotifers were studied during 3 years in two lakes near St. Petersburg (Russia). One lake was repeatedly stocked with larvae of the fish Coregonus peled; the other contained no fish. Fish addition led to a shift in plankton community structure.Population densities of some rotifer species (Keratella cochlearis, K. irregularis, Asplanchna priodonta) increased as a result of the elimination of large crustaceans by fishes during summer and autumn.An inverse relationship was found between the biomass of rotifers and Daphnia.

Planktonic Ciliates of the Baltic Sea (a Review)

The data on the ciliates species composition are given for the Baltic Sea, a brackish-water semi-closed water body where a considerable part of the planktonic fauna is presented by freshwater species. During the observation period, 789 species of ciliates were found, 160 of which are typical planktonic forms. The ecological characteristics of ciliates are given, along with an assessment of their role in the productivity of the Baltic Sea pelagic communities.

The Predatory Water Flea Cercopagis Pengoi in the Baltic Sea: Invasion History, Distribution and Implications to Ecosystem Dynamics

Cercopagis pengoi, a predatory cladoceran from the Ponto-Caspian basin, invaded the northeastern Baltic Sea in 1992 due to ballast water discharges, and by the end of the 1990s formed several permanent populations in different gulfs and lagoons of the sea. The present-day distribution of C. pengoi witnesses for its high ecological plasticity. Evaluation of predation pressure of C. pengoi on its potential preys (younger larval stages of copepods, Daphnia spp., Bosmina spp. and rotifers) demonstrated significant impact of this alien species on native Zooplankton communities and the pelagic food webs in general. A considerable dietary overlap of C. pengoi and planktivorous fish may contribute to a decline of food resource for important commercial fish — herring and sprat. On the other hand, during the population maximum C. pengoi forms an important portion of the diet of these fish. This invasion has increased species diversity of the pelagic fauna of the Baltic Sea and incorporated an additional element to the trophic link of carnivores in the pelagic food web. Due to high population densities in some localities and considerable predation pressure on plankton communities, invasion of C. pengoi is likely to cause important structural and functional ecosystem alterations in the Baltic Sea.

Species composition of planktonic Rotifera, Cladocera and Copepoda in the littoral zone of Lake Ladoga

A species list of zooplankton from the littoral zone of Lake Ladoga is presented, with notes on population densities and distribution. The list, totalling 141 taxa of Rotifera, Cladocera and Copepoda, includes 36 taxa reported for the first time in Lake Ladoga. An inverse relationship has been observed between the values of Shannon-Weaver index of species diversity and mean individual body mass of zooplankton organisms in the communities associated with macrophytes.

Environmental Problems and Challenges for Coastal Zone Management in the Neva Estuary (Eastern Gulf of Finland)

Heavy nutrient and organic matter loading, resulting in enhanced primary productivity, is currently recognised as the most serious environmental problem for the Neva Estuary and adjacent parts of the eastern Gulf of Finland. The introduction of alien species is an emerging issue for the Neva Estuary and should seriously be taken into account, considering the rapid development of the shipping industry in the area. These environmental problems along with the prevailing strategy of transport-oriented development of the coastal zone in the Neva Estuary and insufficient legislative background are the main challenges for coastal zone management in the eastern Gulf of Finland. The development of comprehensive management plans could serve as an essential step toward effective coastal zone management in the Neva Estuary and adjacent areas. Management approaches to control eutrophication in the Neva Estuary coastal zone should consider the development of filamentous algae mats and emergent macrophytes in the littoral zone as the most appropriate indicator of the ecosystem state and measure of effectiveness of management actions. Management actions should be based on the scientific knowledge of the main factors controlling the development of filamentous algae, which needs further research. The management of the introduction of alien species requires different approaches and should mainly be based on preventive actions, including ballast-water control.