Proceedings of the Estonian Academy of Sciences

CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Biology. Ecology

Volume 52 No. 4 December 2003

Changes in the benthic community structure and assessment of the water quality and the state of the ecosystems of Neva Bay and the eastern Gulf of Finland in 1994–2001; 365–377

Evgeniya V. Balushkina and Nonna P. Finogenova

Abstract. Zoobenthic communities of Neva Bay and the eastern Gulf of Finland were determined using a complex of structure indices, such as species composition, number of species, abundance, biomass, and indices calculated on their basis, in particular the Shannon diversity index. The state of the ecosystems and the quality of the water of Neva Bay and the eastern Gulf of Finland were assessed using the Integrated Index (IP) specially devised for these ecosystems. It was shown that in 1994 through 2001 the role of oligochaetes in Neva Bay increased gradually, whereas the role of other taxa of benthic invertebrates declined. The water quality in the major part of Neva Bay was assessed by IP for 2001 as “polluted–dirty” and the state of the ecosystem as “crisis”. In the northern shallow area of the eastern Gulf of Finland eurybiont species of the freshwater complex, i.e. oligochaetes, chironomid larvae, and molluscs of the Рisidiidae family, dominated in terms of biomass over other groups of aquatic organisms during the study period. The assessment of the state of the eastern Gulf of Finland in 2001 showed that with an increase of depth and salinity in the western direction the degree of pollution declined.

Key words: zoobenthos, pollution, water quality assessment, ecosystem.

Changes of the bottom macrofauna in the eastern Gulf of Finland in 1985–2002; 378–393

Alexey A. Maximov

Abstract. Long-term changes of macrozoobenthos in the eastern Gulf of Finland are described on the basis of field observations during 1985–2002. Deep-water bottom communities were radically changed by the oxygen deficit in 1996. Deterioration of oxygen conditions was responsible for the strong impoverishment (biomass less than 1 g/m²) and complete disappearance of macrofauna in large bottom areas. Outside the confines of these areas no distinct difference was observed between the 2000s and the beginning of the study period; however, macrozoobenthos showed considerable interannual variations because of population fluctuations of dominant species.

Key words: Baltic Sea, Gulf of Finland, macrozoobenthos, population dynamics, long-term changes.

Dynamics of Marenzelleria viridis (Polychaeta: Spionidae) pelagic larvae in Pärnu Bay, NE Gulf of Riga, in 1991–99; 394–406

Mart Simm, Henn Kukk, and Markku Viitasalo

Abstract. Marenzelleria viridis, a polychaete species originating from North America, was found in the Baltic Sea in 1985 and in the Gulf of Riga in 1988. In Pärnu Bay, the NE Gulf of Riga, pelagic larvae of Marenzelleria were first discovered in 1991 and have since then been annually present in the plankton community. The abundance of larvae remained relatively constant during the first 6 years, but increased abruptly in 1998–99. This interval between the recording of the first larvae and mass development of the species is extraordinarily long for the Baltic, and was possibly caused by the low salinity of Pärnu Bay. In the North and Baltic seas, two sibling species of Marenzelleria have been identified. The North Sea form, M. cf. wireni, breeds in spring, while the Baltic Sea form, M. cf. viridis, has only been reported to breed in autumn. In Pärnu Bay, fertilized eggs and trochophores of Marenzelleria occurred in plankton both in spring and in autumn, which raises a question of the identification of the spring larvae. Earlier genetic analyses have however indicated that only M. cf. viridis is found in the Gulf of Riga. Therefore the species is, in suitable environmental conditions, capable of reproducing two times a year. The spawning season of the Baltic M. cf. viridis is thus not genetically determined, but is caused by exogenous factors, such as temperature and possibly also food conditions.

Key words: Marenzelleria viridis, introduced species, reproduction, pelagic larvae, Gulf of Riga, Baltic Sea.

Nutrient budget of Lake Peipsi in 1998; 407–422

Peeter Nõges, Ülle Leisk, Enn Loigu, Alvina Reihan, Boris Skakalski, and Tiina Nõges

Abstract. In the wet year of 1998, Lake Peipsi (3555 km²) received 23 800 t (67 kg ha^–1) of total nitrogen (Ntot) and 1300 t (3.6 kg ha^–1) of total phosphorus (Ptot). The area-specific loading of Ntot was higher from the Estonian part of the watershed while that of Ptot was higher from the Russian part. Precipitation contributed 11% of the Ntot load and 4% of the Ptot load. Since 1985–89, Ntot loads had decreased three times but Ptot loads had remained on the previous level. The resulting decrease in the N/P loading ratio has led to heavy blooms of nitrogen-fixing cyanobacteria in recent years. For the lake to reach mesotrophic status, the P load should be decreased 1.7 times.

Key words: water balance, mass balance of nutrients, N/P loading ratio, nutrient retention, Vollenweider’s model.

Influence of light intensity on in vivo fluorescence characteristics of cyanobacteria; 423–436

Aina Leeben

Abstract. A laboratory experiment was carried out to estimate the extent of changes in fluorescence characteristics of three oscillatorian strains (Planktothrix mougeotii, P. prolifica, and Tychonema bourrellyi) grown in batch culture at two light intensities (9 and 39 μE m^–2 s^–1). The following set of measurements was performed in the late log-phase of the growth of the cultures: recording of in vivo fluorescence spectra at 680 nm by excitation in the range 400–660 nm, determination of chlorophyll a and phycobilin concentrations, cells and trichome numbers, mean cellular volume, and dry weight of the culture. In T. bourrellyi and P. prolifica the lower light intensity stimulated the synthesis of phycoerythrin, and as a consequence the fluorescence response. Negligible changes in the pigment composition and shape of spectra of the P. mougeotii strain were observed. Differences in quantitative fluorescence characteristics normalized to phytoplankton biomass equivalents for cyanobacterial cultures grown at two light intensities are presented.

Key words: in vivo fluorescence, cyanobacterial phycobilins, light adaptation, monitoring of cyanobacterial blooms.

Urban trees of Tallinn, Estonia; 437–452

Heldur Sander, Jüri Elliku, Alar Läänelaid, Vaike Reisner, Ülo Reisner, Mart Rohtla, and Marina Šestakov =

Abstract. In Tallinn (without Tallinn Botanic Garden) 1275 taxa of native and introduced woody plants have been registered. Out of these 480 taxa are trees. The most widespread tree species is Pinus sylvestris. A hundred and forty-two rare trees belonging to 70 species, hybrids, varieties, and cultivars are of a remarkable age and/or dimensions. Among them 71 trees (27 taxa) are younger than 60 years, 41 trees (23 taxa) are 60–80 years old, and 30 trees (20 taxa) are older than 80 years. The species with the oldest specimens, which are over 200 years of age, belong to 5 taxa, 100–200 year old trees to 24 taxa, 60–100 year old trees to 89 taxa, and trees under 60 years of age to 360 taxa. The species with the highest specimens reaching 30–35 m belong to 5 taxa, those of 20–30 m to 35 taxa, and those of 10–20 m to 105 taxa. We have registered about 800 trees with the stem perimeter of 300 cm or more. These trees belong to 11 genera.

Key words: urban trees, predominant trees, rare trees, tree age, dimensions of trees.

Instructions to authors; 453–455

Contents of volume 52; 457–459