CONTENTS & ABSTRACTS
In English. Summaries in Estonian
Proceedings of the Estonian Academy of Sciences.
Volume 49 No. 3 September 2000
Exchange processes in the Väike Strait (Baltic Sea): Present, past, future;
Ülo SUURSAAR, Mikk OTSMANN, and Tiit KULLAS
Abstract. The Väike Strait has been closed by a road-dam since 1896. During the last decade acceleration of eutrophication processes has been observed in the strait. Using hydrodynamic models the pre-dam flow characteristics were reconstructed and the possible future developments are discussed in relation to the plans to make openings into the dam. In the openings the flow with an average velocity of 50 cm/s will appear. The direction of the flow will change rapidly, but the resulting annual water flux of about 0.1 km3 and 1000 tonnes of sediments will be directed from the Gulf of Riga to the Väinameri sub-basin. The desired positive ecological effect will remain modest and it will be limited to the vicinity of the openings. A slight improvement may occur in the southern part of the Väike Strait. To the north from the dam (near Orissaare), the temporal variability of hydrochemical parameters will increase, and the situation may even deteriorate.
Key words: currents, sea level, modelling, nutrients, resuspension, straits, Baltic Sea.
Factors affecting the distribution of benthic invertebrates in the phytal zone of the north-eastern Baltic Sea; 253–269
Helen ORAV, Jonne KOTTA, and Georg MARTIN
Abstract. Macrozoobenthos was studied in the coastal sea of the north-eastern part of the Baltic Sea. Using permutation procedure the structure of macrozoobenthic assemblages was compared at 14 different phytobenthic assemblages and the contribution of different environmental factors to the variability in macrozoobenthos was computed. The transitions in macrozoobenthic assemblages between different vegetation types were gradual. Macrozoobenthos in Fucus vesiculosus, Furcellaria lumbricalis, Pilayella littoralis, and Polysiphonia nigrescens dominated assemblages differed significantly from other phytobenthic assemblages. As compared to abiotic variables biotic factors, e.g. the biomass structure of phytobenthos, described the structure of macrozoobenthic assemblages in the phytal zone better. Generally, Chara spp., Pilayella littoralis, and Furcellaria lumbricalis dominated assemblages were preferred by macrozoobenthos over other habitats and species with strong thalli over filamentous algae.
Key words: Baltic, distribution, macrozoobenthos, macrophytobenthos.
Migrations of the perch
Abstract. Migration of perch was studied by tagging 2146 fish in Matsalu Bay in 1994–95. The tagging was made mainly during the spawning time. Until May 1999, 286 recoveries had been reported. Annual migrations take place between shallower spawning and feeding areas and deeper wintering areas. Differences in migration distances depending on migration direction were revealed. The homing of perch was also observed.
Key words: freshwater fish, perch, migration, homing, Moonsund Archipelago.
Distribution of stoneflies (Insecta: Plecoptera) in Estonia; 277–288
Abstract. Twenty-two species of stoneflies belonging to five families were found in more than 1200 samples (mainly from 1985–99). Six of them were recorded for the first time in Estonia. The majority of the species inhabited only running waters and preferred moderate or fast flow, and stony or gravelly bottom, water moss, or twigs as a substrate. The commonest species were Nemoura cinerea (the only species occurring also on western islands), Isoperla grammatica, Taeniopteryx nebulosa, Leuctra digitata, and Nemurella pictetii. Most of the Estonian species are common in neighbouring areas. Diura nanseni is of northern and Perlodes microcephala of southern distribution. As occurrence of stoneflies always indicates high or very high water quality, the knowledge on their presence or absence in different regions of the country is necessary in environmental monitoring.
Key words: Plecoptera, Estonia, fauna, distribution.
Study of the multivariate structure of the Estonian Alchemilla L. (Rosaceae) microspecies: An example of the structural indices approach; 289–301
Silvia SEPP, Tatjana NAHTMAN, Tõnu MÖLS, and Jaanus PAAL
Abstract. The structural indices approach was used in the taxonomy of 23 microspecies of Alchemilla L. to overcome the problem of the statistical incorrectness caused by testing the objectivity of taxa applying the same morphometric variables as those used to define them. We tried to find answers to the following questions: How distinct are the microspecies according to the metric and count variables? How do the structural indices distinguish microspecies? What are the most stable proportions between the characters? Which characters are most informative in microspecies distinction? The structural indices proved to be better for taxon discrimination than the first principal components and single variables. The pairs of indistinct microspecies found in discriminant analysis were confirmed by structural indices analysis, but additionally many indistinct species pairs appeared. The hairiness characters were effective for microspecies discrimination while flower measurements were the poorest discriminators; all the metric variables and counts together were the most effective of all.
Key words: morphological variation, plant taxonomy, principal components analysis.
Jüri Martin 60; 302–303