Printer Friendly

Meiobenthos of some Estonian coastal lakes/Monede Eesti rannikujarvede meiobentosest.

INTRODUCTION

Meiobenthos is a term to denote submicroscopic, multicellular bottom animals usually ignored in regular studies of macrozoobenthos. The word 'microbenthos' has been used with the same meaning to distinguish it from macrobenthos, i.e. bottom animals that are distinctly visible without any magnification (e.g., Stanczykowska, 1967; Mikhajlov, 1970; Babitskij, 1980). However, the term 'microbenthos' fits better the bottom-inhabiting unicellular Protoctista. Meiobenthos includes, besides several specific animal groups (eumeiobenthos), also numerous young submicroscopic stages of various macroscopic animals (pseudomeiobenthos), as well as representatives of zooplankton when they spend some time on bottom. Discrimination between macrozoobenthos and pseudomeiobenthos is conventional. A survey of the role of meiobenthos in freshwater lakes is given by Kurashov (1994, 2002).

Meiobenthos is poorly studied in Estonia. Short notes on the 'microbenthos' of Lake Peipsi-Pihkva, situated on the border between Estonia and Russia, were published by Mikhajlov (1970, 1973). Timm (2002) treated the meiobenthos of the transition zone between the deeper littoral and the profundal in 10 small Estonian lakes. A meiobenthoc animal group, Ostracoda, was identified in the samples of macrozoobenthos from the Baltic Sea, and from the rivers and springs studied by Jarvekulg (1979, pp. 91-92; 2001, p. 164; Timm & Jarvekulg, 1975, p. 84).

The present study is part of a comprehensive research of the Estonian coastal halotrophic lakes, initiated by the Centre for Limnology of the Estonian University of Life Sciences. It is an attempt to give a preliminary survey of the submicroscopic bottom fauna of these lakes and its changes in the course of gradual isolation from the Baltic Sea due to isostatic land uplift.

STUDY AREA

Twenty brackish-water and freshwater bays, lagoons, and relic lakes were under study. These water bodies are located on the islands of Hiiumaa and Saaremaa and in the northwestern part of the Estonian mainland, between 58[degrees]10'-59[degrees]15' N and 21[degrees]45'-23[degrees]45' E. Many of them still bear a name indicating their recent marine nature, like laht (bay) or meri (sea). Others are called jarv (lake) or lais (coastal lake), while one lake is simply named auk (pit). Three hydrological categories can be distinguished under these sampling sites: 2 open bays, 5 lagoons receiving irregularly some brackish water from one or two canals, and 13 entirely freshwater lakes lying already above sea level. The lagoons and the lakes belong to different succession stages of the halotrophic lake type sensu Maemets (1974) and Ott & Koiv (1999). Their location is shown in Fig. 1. Most of them are very shallow, less than 1 m, while the depth of some others reaches 2-3 m. The bottom is usually sandy or clayey, often silted, seldom with a thick mud layer. The water is unstratified and rich in oxygen, mostly transparent to the bottom. The concentration of HC[O.sub.3.sup.-] in the lakes and lagoons fluctuated mostly between 61 and 348 mg [L.sup.-1], [COD.sub.Cr] was 39-102 mg [L.sup.-1], pH 7.2-9.9, Ptot 0.010-0.039 mg [L.sup.-1], and Ntot 400-2748 mg [L.sup.-1] (data of the Centre for Limnology).

Among the open bays, Reigi laht on the northwestern coast of Hiiumaa Island is a part of the open Baltic Sea, with a salinity of about 6-7%0. The sampling site is enriched by the effluent of a fish factory. The other bay, Rame laht, belongs to the Gulf of Riga and borders on the mainland. Its salinity is slightly lower (up to 5%0), and the water is unpolluted.

Of the lagoons Kirikulaht on Hiiumaa Island receives fresh water from a stream but is also connected with Reigi laht by a strait. The Kaina laht on Hiiumaa Island is connected with the sea by two short ditches. The Laialepa laht on Saaremaa Island is connected with the sea by a short ditch. All three lagoons have extensive, very shallow open water regions. The largest lagoon (area about 5 [km.sup.2], depth about 2 m), Suurlaht in Saaremaa has a 3 km outflow changing occasionally its direction. The Moisalaht on the mainland is isolated from Rame laht with a half a kilometre long railway embankment; however, a small bridge enables some water exchange. The Moisalaht is very muddy and mostly overgrown with reeds. The salinity of water varied mostly between 210 and 3380 mg [L.sup.-1] [Cl.sup.-] in different lagoons but was only 120-150 mg [L.sup.-1] in the Suurlaht.

[FIGURE 1 OMITTED]

Among the conventional freshwater lakes (without direct contact with sea water, concentration of [Cl.sup.-] 7-234 mg [L.sup.-1]), Tammelais and Veskilais in Hiiumaa, and Kooru jarv in Saaremaa are shallow and rich in vegetation. Sarapiku jarv, Kiljatu jarv, and Nonni jarv in Saaremaa are shallow but mostly with open water. Linnulaht (Bird Bay), enriched by numerous nesting waterfowl, has a thick layer of watery mud, and is fringed with lush reed thickets. In the mainland, the shallow lakes of Kaomardi laht and Kussa laht are completely overgrown with reeds and dense Chara, while the lakes of Sutlepa meri and Pikane jarv have also extensive but shallow open-water areas. Two of the mainland lakes, Allikajarv and Lepaauk, are most similar to small lakes of glacial origin, with a developed littoral vegetation zone well distinguished from the central deeper, profundal-like hollow. Their water is brownish, with HC[O.sub.3.sup.-] content ranging between 70 and 90 mg [L.sup.-1], and with a pH of about 7.

MATERIAL AND METHODS

Sampling was performed on 10-20 August 2004, always in shallow water (0.2-0.7 m). The sediment corer, made of a 48 cm long aluminium pipe with an inner diameter of 2.75 cm, took a core with a surface of 5.94 [cm.sup.2]. Only the uppermost, soft sediment layer (2-10 cm thick) was sampled. One sample consisting of 5 replicate cores, randomly located several metres from each other, was taken from each water body. The whole material comprised 100 cores. They were fixed separately with a small amount of formalin, and were sieved later in the laboratory under tap water, on a double silk sieve with mesh sizes of about 400-500 and 60 [micro]m. The sieving residues were studied using a Bogorov counting plate under x20 magnification of a dissection microscope. The animals were picked out, measured, and the largest macrozoobenthic individuals were also weighed on a torsion balance with 1 mg accuracy. The weight of smaller animals was either calculated after their approximate body volume, particularly in the case of the cylindrical forms like Chironomidae and Oligochaeta (Smit et al., 1993; Timm, 2002), or by using standard tables (Kurashov, 1994). Application of a double sieve facilitated sorting but did not allow us to distinguish any size classes; thus both fractions were pooled in the calculations. Abundance and wet biomass were calculated per square metre.

In the calculations, all animals too small to belong to macrozoobenthos were divided into pseudomeiobenthos, eumeiobenthos, and plankton. Pseudomeiobenthos was limited to the individuals of Oligochaeta, Chironomidae, and other Insecta, as well as Malacostraca, etc., all shorter than 3 mm, while larger individuals were considered macrozoobenthic (as in Gusakov, 1993, 2005). Gastropoda, Sphaerium, and the adult Hydracarina as heavier animals were considered as macrozoobenthos regardless of their size. Eumeiobenthos was represented by Ostracoda, Harpacticoida, Hydra sp., and Nematoda without the large Mermithidae. All Copepoda (except Harpacticoida) and Cladocera were treated as planktic animals. Rotatoria were not detected with this method.

The animals were mounted on slides in glycerine and identified under a microscope using magnifications suitable for a particular taxonomic group. Most taxa were identified to the species level: Oligochaeta and some smaller groups, by Tarmo Timm; Chironomidae, by Margit Kumari; Cladocera and Copepoda, by Kaidi Kubar; Ostracoda, by Kadri Sohar; and Nematoda, by Walter Traunspurger.

RESULTS

Fauna

Altogether 122 taxa were found, among them 70 nominal species (Appendix). Part of the individuals remained undetermined to the species level due to their small size or poor preservation, but they may belong to some of the identified species. Most of the taxa, 69 of 103, are macrobenthic when reaching their full size but belong to pseudomeiobenthos when young. Nine more macrobenthic taxa (mostly molluscs, and a large polychaete) were never considered meiobenthic due to their high biomass. The diversity of eumeiobenthos was limited to 22 taxa. Plankton was represented with 22 taxa, too.

Oligochaeta was the most diverse group, with 28 taxa (24 of them identified to the species level). Most of them represented meiobenthos-sized Naididae. The Oligochaeta accounted for about 21% of the macrobenthic and 20% of the pseudomeiobenthic specimens in the material. Four marine and brackish-water oligochaetes (Heterochaeta costata, Paranais litoralis, Amphichaeta sannio, and Lumbricillus sp.) were observed only in Reigi laht, the most typical marine site. A species usually limited to very slightly brackish water, Potamothrix bavaricus, was recorded from at least four lagoons and lakes. Besides it, immature Potamothrix sp. occurred in seven more lakes; they may belong either to P. bavaricus, or to its freshwater counterpart P. hammoniensis (Michaelsen, 1901); no mature individuals of the latter were found in this material. The rest of the oligochaetes live generally in fresh water, although some of them can tolerate also low salinity in the Baltic Sea bays (Jarvekulg, 1979).

The larval Chironomidae were another dominant group of larger animals, with 19 taxa, among them 10 identified to the species or the larval form. They made up about 60% of the macrobenthic and 22% of the meiobenthic specimens. Many of the smallest individuals remained unidentified. Among the identified species, Tanytarsus verralli was the commonest, observed at 10 sites of 20. All of these chironomid taxa inhabit mostly fresh water, although some are slightly euryhaline. Chironomids were very scarce in the samples taken from both brackish water bays. On the other hand, their share was even higher in the lagoons than in the entirely separated lakes, both on the macrobenthic and pseudomeiobenthic levels.

Among the other macrobenthic and pseudomeiobenthic groups, three taxa were the most frequent in the samples: the crustacean Asellus aquaticus (8 sites, in the lagoons and lakes), the ephemeropteran Caenis sp. (6 sites, in the lagoons and lakes), and the bivalve mollusc Sphaerium corneum (6 sites, in the lakes only). Representatives of some other freshwater Insecta and Mollusca, as well as Hirudinea, Mermithidae, Hydracarina, Gammarus, and Bryozoa were observed seldom and as single individuals. In the cores taken from the bay of Reigi laht, a very large polychaete worm, Hediste diversicolor, was abundant, accompanied with an unidentified gastropod. Hediste was also observed in a qualitative sample from the lagoon of Kirikulaht, but was lacking in the cores. Another marine worm, the priapulid Halicryptus spinulosus, was found in Reigi laht.

The eumeiobenthic crustacean group of Ostracoda was represented with 8 species and with some unidentified individuals. Darwinula stevensoni was the most frequent species (6 sites), followed by Cyprideis torosa (5 sites) and Candona candida (4 sites). Most of them are known as euryhaline freshwater species but Cyprideis torosa prefers brackish water. In our material, these euryhaline ostracods were found both in the lakes and in the lagoons. Cyprideis torosa was the only ostracod at the most marine site, Reigi laht. The only true freshwater species in this list, Cypria exsculpta, was found once in the lake of Allikajarv. Ostracoda accounted for about 25% of the abundance of the meiobenthic animals both in the lagoons and in the lakes, but for much less in the open bays. The lagoon of Suurlaht and the lake of Kussa laht were the richest in ostracods.

The small (non-mermithid) Nematoda, all in all 22 taxa, were observed at 13 sites of 20, most abundantly in the bay of Reigi laht and in the lagoon of Kirikulaht connected with each other. Owing to these two water bodies, the total share of Nematoda among meiobenthos was 39%. In the freshwater lakes, small nematodes were scarce, making up only 2.5% of the meiobenthos. Nine freshwater taxa were identified, among them Dorylaimus stagnalis and Tobrilus cf. gracilis being the commonest. Freshwater species were even found in the open bay of Rame laht and in the lagoon of Kirikulaht connected closely with the open bay of Reigi laht. At the same time, the highly abundant nematode fauna of Reigi laht itself consisted exclusively of marine taxa, 12 in number, but mostly not identified to the species level.

Two more eumeiobenthic taxa, Hydra sp. and unidentified Harpacticoda, were found only once and as single individuals.

Cladocera accounted for about 2/3 of the planktonic Crustacea in our samples, and about 6% of all meiobenthic animals. Nine taxa were registered, among them six identified to the species level. All of them are common freshwater species. Alona costata and Sida crystallina were the commonest, both registered from 6 sites--the former from the lagoons and lakes, and the latter only from the lakes.

Copepoda, another order of planktonic Crustacea, made up about 4% of the meiobenthos. Of the 13 taxa 4 belonged to the suborder Calanoida, and 9 to Cyclopoida (the third suborder, Harpacticoida, is eumeiobenthic). The cyclopoids were represented only with freshwater species, even in the open bays. Megacyclops viridis (7 sites) and Mesocyclops leuckarti (5 sites) were the most frequent. Among the three calanoids identified, two belong to the brackish-water fauna: Limnocalanus grimaldu (in two lagoons) and Centropages sp. (remarkably, in the freshwater lake of Allikajarv).

Abundance and biomass

The average abundance of all animals for all studied 100 cores was 53 973 [+ or -] 17 244 individuals per square metre, macrobenthos constituing about 15%, pseudomeiobenthos 30%, eumeiobenthos 47%, and plankton 9% (Table 1). The share of eumeiobenthos, mostly nematodes, was very high in the open bay of Reigi laht. Without the open bays, the percentage of eumeiobenthos was lower: 34% of all animals (or 41% of the meiobenthic animals) in the lagoons, and 20% (or 27%) in the freshwater lakes (Table 1). Nematoda accounted for about 39% of the meiobenthos-sized animals (but only 2.5% in the freshwater lakes); small Chironomidae, 23%; Ostracoda, 16%; Oligochaeta, 7%; Cladocera, 6%; and Copepoda, 4% (Table 2).

Total average biomass in all cores was calculated as 25 046 [+ or -] 13 928 mg [m.sup.-2]. However, 93% of it was formed of macrozoobenthos, particularly larger Chironomidae (but Polychaeta in Reigi laht). The remaining 1797 [+ or -] 391 mg [m.sup.-2] of meiobenthos consisted of pseudomeiobenthos (50%), eumeiobenthos (23%), and plankton (27%) (Table 3). Small chironomids and ostracods were the most important taxonomic groups in the biomass of meiobenthos, both accounting for 22%; Cladocera made up 17%, Copepoda 10%, and Oligochaeta 9%. The share of Nematoda in the biomass was negligible (Table 2).

A rich benthic fauna of animals typical of the Baltic Sea was found in the cores taken from the open bay of Reigi laht: the polychaete Hediste diversicolor, the oligochaetes Heterochaeta costata, Paranais litoralis, Amphichaeta sannio, and Lumbricillus sp., the priapulid Halicryptus spinulosus, a poorly preserved and hence unidentified prosobranchian gastropod, the meiobenthic ostracod Cyprideis torosa, and a number of marine nematodes. In another, more sheltered, bay of Rame laht, the fauna was very different: low in numbers and consisting mostly of freshwater animals including small chironomid larvae, nematodes, and planktonic cyclopoids.

Kirikulaht, a lagoon closely connected with the bay of Reigi laht, revealed a diverse freshwater fauna dominated by chironomid and ephemeropteran larvae, nematodes, and planktonic cladocerans. No brackish-water animals (except for a few nematodes), common with Reigi laht, were found in the cores, although some were recorded from the qualitative samples from the lagoon.

In the other four lagoons, too, the fauna consisted largely of diverse, and often abundant, freshwater animals. Besides, there occurred a few brackish-water species such as the oligochaete Potamothrix bavaricus, ostracod Cyprideis torosa, and calanoid Limnocalanus grimaldii.

The samples from the lakes contained some more freshwater animals not met in the lagoons, including several species of molluscs, oligochaetes, and cladocerans, as well as the ostracod Cypria exsculpta. However, also the brackish-water oligochaete Potamothrix bavaricus was repeatedly found here; the ostracod Cyprideis torosa and the calanoid Centropages sp., domestic in the Baltic Sea but not observed in the lagoons, were found on one occasion each. The average abundance and biomass of macro--and meiozoobenthos were higher in the lagoons than in the lakes (Tables 1 and 3).

DISCUSSION

There are no comparable data on the zoobenthos of small lakes on the Baltic coast. The best equivalent may be Lake Lebsko near Slupsk, Poland. This lake is much larger than the studied Estonian lakes (71.4 [km.sup.2], depth 6.3 m), and its water is slightly brackish (maximum salinity amplitude 0.021-2.574 g [L.sup.-1] [Cl.sup.-] in different parts) like in the lagoon of Suurlaht in Saaremaa. The abundance of the littoral macrozoobenthos has been very similar (11 000 ind. [m.sup.-2]) to that of Suurlaht while the biomass has been about twice higher, about 30 g [m.sup.-2]. The bottom fauna consists exclusively of freshwater species, except for the single brackish-water oligochaete Potamothrix bavaricus common also in Suurlaht. Unfortunately, the meiobenthos of this Polish lake has not been studied (Dobrowolski, 1995).

Zhadin et al. (1972) studied the psammon of the largest lagoon of the Baltic, the Curonian Lagoon (Bay). The psammon here means the hygrophilous fauna of the moist sand in supralittoral and above the coastal groundwater. A rich fauna was found, consisting mostly of Aeolosomatida, Oligochaeta, Rotatoria, Nematoda, and Harpacticoida. No data on the true meiobenthos ofthis lagoon are available.

The open brackish-water bays of the Baltic Sea in Finland (Tvarminne Bay and the mouth of the Kyrojoki River) harbour a meiofauna consisting of a mixture of brackish--and freshwater species (Keynas & Keynas, 1978; Merilainen, 1988). The bulk of the abundance is formed of small Nematoda; the brackish-water oligochaetes Amphichaeta sannio and Paranais litoralis were recorded as abundant in the Kyrojoki estuary, like in Estonian Reigi laht. However, the nematode species were different. The total abundance of meiobenthos in the Kyrojoki (38 300-2 398 800 ind. [m.sup.-2]) was roughly comparable to that in Reigi laht, but much lower in Tvarminne Bay, evidently owing to the larger depth of the latter site.

The true brackish-water meiofauna typical of the Baltic Sea was investigated by Pallo et al. (1998) at 30 stations of the open Gulf of Riga, immediately near our study area, at depths of 13-54 m. The average abundance of metazoan meiobenthos was 4.8 million ind. [m.sup.-2]; 86% of this was formed by Nematoda and 9% by Harpacticoida. This fauna was similar to that on the most 'marine' site in our material, Reigi laht, with a strong dominance of Nematoda. However, the abundance was even higher there, about by an order of magnitude. Shallowness of our sampling point can be a reason, but so can the difference in sample processing. Some part of the smallest nematodes may have been omitted during hand-sorting used by us while Pallo et al. (1998) practised elutriation of sieved samples in a denser solution.

Mikhajlov (1970, 1973) treated the 'microbenthos' (in fact, meiobenthos) of large unstratified Lake Pihkva (Pskovskoe) lying on the border of Russia and Estonia. A diverse fauna inhabited the sandy bottom, while small chironomids and oligochaetes prevailed on mud. The average abundance was 56 100 ind. [m.sup.-2] for the whole lake in July 1967, which is comparable to the respective average figure for Estonian coastal lakes and lagoons. However, the average biomass of meiobenthos was about three times larger there, 5470 mg [m.sup.-2].

The data by Timm (2002) for ten small Estonian inland stratified lakes were collected in deeper muddy zones, which are lacking in the shallow coastal lakes and lagoons. These zones are expected to be quantitatively poorer in zoobenthos than the littoral. Indeed, the average abundance of macrozoobenthos + pseudomeiobenthos was about three times lower there than in the coastal lakes (4937 versus 16 120 ind. [m.sup.-2], respectively), and nine times lower than in the lagoons (44 646 ind. [m.sup.-2]). The abundance of eumeiobenthos + planktic animals in these stratified lakes was slightly higher (11 580 versus 8573 ind. [m.sup.-2]), mostly due to Cyclopoida abundant in the deeper zones of the stratified lakes, but again three times lower than in the lagoons rich in Nematoda and Ostracoda (36 430 ind. [m.sup.-2]). The length of the taxon list for the inland lakes was similar to that for the coastal water bodies (120 versus 122), despite the lack of brackish-water species in the former. The major animal groups were the same, as were about 50 of the identified taxa.

Six small inland lakes in eastern Latvia (Kurashov & Belyakov, 1987) revealed high figures for the abundance and biomass of meiobenthos in the littoral, from 21 920 to 147 070 ind. [m.sup.-2], and from 0.75 to 5.43 g [m.sup.-2], with higher figures being registered for more eutrophied lakes. In the profizndal mainly cyclopoids occurred, like in the small Estonian lakes studied by Timm (2002).

In deep mesotrophic Lake Verkhnee Vrevo in the Leningrad Region, Russia (Zakhodnova et al., 1984), high abundance and biomass figures, 160 000900 000 ind. [m.sup.-2] and 1.58-21.39 g [m.sup.-2], were recorded in different seasons, with a maximum in June. Nematoda formed an overwhelming majority of the meiobenthos there like in the Estonian bay of Reigi laht, with 142 000-730 000 ind. [m.sup.-2] and 0.14-1.05 g [m.sup.-2]. However, the nematode species were different from those found in the present study. Ostracods and cyclopoids were abundant too; oligochaetes, chironomids, and tardigrades were less numerous. Although it was not clearly indicated, the above study was limited to shallows like the present article.

In Finnish Lake Paajarvi, 78 900-625 000 ind. [m.sup.-2] of meiobenthic animals were found at different depths (Holopainen & Paasivirta, 1977). Nematoda formed the bulk of this amount, except at a depth of 2 m, where Ostracoda, particularly Darwinula stevensoni, which was also abundant in our material, dominated.

The average abundances and biomasses of meiobenthos for five small lakes on the Karelian Isthmus measured from 1200 to 14 900 ind. [m.sup.-2] and from 0.15 to 0.92 g [m.sup.-2] (Skvortsov, 1984). These figures are much smaller than those for Lake Vrevo, as well as for Estonian coastal water bodies. Yet they are rather similar to the corresponding figures for the deeper zones of small Estonian lakes (Timm, 2002); apparently, in the above study different depth zones were lumped. The author states that the share of meiobenthos in total benthos decreases with eutrophication of lakes.

Gusakov (1993) studied meiobenthos in a section of the Rybinsk Reservoir on the Volga River, northern Russia. In 26 cores taken seasonally from four unvegetated sites with depths of 2-12 m, 139 taxa (113 species) were registered--a number slightly higher than that based on our material. The species list included only freshwater taxa, among them several eumeiobenthic Harpacticoida and Tardigrada rare or lacking in our material, and much more species of Nematoda, while not all Oligochaeta were identified. However, the number of taxa registered from the shallow-water sites was only 87--thus considerably less than registered from the Estonian coastal lakes and lagoons due to the higher ecological diversity of the latter. The average number of meiobenthic animals at these two shallow-water sites, 31 400 and 81 600 ind. [m.sup.-2], and the biomass, 480 and 1630 mg [m.sup.-2], were well comparable to the respective figures for the coastal lakes and lagoons studied here. For the deeper stations, the corresponding figures were markedly higher. Eumeiobenthos (together with planktonic animals) accounted for 85% and 78% of the number of individuals, and 40% and 19% of the biomass in the Rybinsk Reservoir. Nematoda were responsible for the bulk of total abundance, and Chironomidae, for the biomass.

Gusakov (2005) studied, using the same methods, also the Gor'kij Reservoir on the Volga River. The material was larger, 73 cores from ecologically different sections. Consequently, the species list was much longer, 223 taxa, including 170 taxa at the shallow-water sites of the river bed section. At these sites, best comparable to ours, the average abundance of meiobenthos fluctuated between 231 700 and 310 700 ind. [m.sup.-2] and the biomass between 4900 and 7700 mg [m.sup.-2] in different seasons, while eumeiobenthos (together with planktic animals) always made up more than 90% of the abundance and 50% of the biomass. Besides the Nematoda, also Oligochaeta, Cladocera, Cyclopoida, and Harpacticoida were abundant on the shallows of the Gor'kij Reservoir.

CONCLUSIONS

The meiobenthos of the Estonian coastal water bodies is comparable to that of many other shallow water bodies of neighbouring regions, regarding both quantity and diversity. The bulk of it is usually formed of the first stages of macrozoobenthic animals such as chironomids and oligochaetes; the near-bottom planktic crustaceans also build up its amount, while eumeiobenthic animal groups (mainly Ostracoda and Nematoda in this study) are outnumbered. The only site where small Nematoda gained an overwhelming majority, like in some inland freshwater lakes and in the Baltic Sea, was the brackish-water open bay of Reigi laht. This was also the only site where brackish-water taxa dominated, although their abundance remained considerably lower than in the open sea. At all other sites the fauna consisted of freshwater taxa, with a small addition of brackish-water species, mostly in the lagoons still weakly connected with the sea. The lagoons also revealed a significantly higher average abundance and biomass of meiobenthos than the coastal but entirely separated freshwater lakes.

APPENDIX

LIST OF TARA FOUND IN THE WATER BODIES STUDIED

Numbers of water bodies as in Fig. 1

Coelenterata

Hydra findet.-5

Nematoda

Dorylaimus stagnalis Duj ardin, 1845-2, 3, 4, 8, 9, 20

Paractinolaimus macrolaimus (DeMan, 1880)-10, 16

Tobrilus cf. gracilis (Britain, 1865)-3, 7, 15, 16

Oncholaimus cf. oxyuris-1

Adoncholaimus sp.-1

Anoplostoma sp.-1

Chromadorita sp.-1, 3

Daptonema sp.-1

Laimydorus sp.-1

Laimydorus/Mesodorylaimus sp.-3

Microlaimus sp.-1

Oncholaimus sp.-7

Plectus sp.-3

Theristus sp.-1, 3

Chromadoridae gen. sp.-1

Mermithidae gen. sp.-2, 6

Nematoda gen. sp. No 1-1 (marine)

Nematoda gen. sp. No 2-1 (marine)

Nematoda gen. sp. No 3-1 (marine)

Nematoda gen. sp. No 4 (cf. Daptonema, marine)-1

Nematoda findet.-4, 5, 6

Priapulida

Halicryptus spinulosus Siebold, 1894-1

Polychaeta

Hediste diversicolor (Muller, 1776)-1

Oligochaeta

Stylaria lacustris (Linnaeus, 1767)-3, 6, 10, 16, 19

Vejdovskyella comata (Vejdovsky, 1884)-8, 18

Slavina appendiculata (Udekem, 1855)-6, 8, 19

Dero obtusa Udekem, 1855-8, 18

Naffs communis Piguet, 1906-8, 15, 16

Naffs pardalis Piguet, 1906-13, 14

Naffs variabilis Piguet, 1906-6, 9, 17, 19

Naffs simplex Piguet, 1906-6, 8

Naffs pseudobtusa Piguet, 1906-6

Specaria josinae (Vejdovsky, 1884)-18, 19

Paranais litoralis (Muller, 1780)-1

Chaetogaster diaphanus (Gruithuisen, 1828)-3, 6, 19

Chaetogaster diastrophus (Gruithuisen, 1828)-5, 20

Chaetogaster langi Bretscher, 1896-10

Amphichaeta sannio Kallstenius, 1892-1

Pristina longiseta Ehrenberg, 1828-6

Pristina aequiseta Bourne, 1891 forma foreli (Piguet, 1906)-8, 20

Limnodrilus hoffmeisteri Claparede, 1862-20

Tubifex ignotus (Stolc, 1886)-20

Heterochaeta costata Claparede, 1863-1

Psammoryctides barbatus (Grube, 1861)-10, 11, 20

Potamothrix bavaricus (Oschmann, 1913)-5, 14, 15, 16

Potamothrix sp.-7, 11, 12, 13, 17, 18, 19

Tubificidae gen. sp.-8, 20

Cognettia glandulosa (Michaelsen, 1888)-20

Marionina argentea (Michaelsen, 1889)-20

Marionina sp.-8

Lumbricillus sp.-1

Hirudinea

Helobdella stagnalis (Linnaeus, 1758)-14

Chelicerata

Hydracarina indet.-2, 9, 11, 17, 19

Cladocera

Alona costata Sars, 1862-3, 4, 8, 9, 10, 14

Aeroperus elongatus (Sars, 1862)-8

Daphnia longispina (Muller, 1776)-3

Diaphanosoma brachyurum (Lievin, 1848)-20

Sida crystallina (Muller, 1776)-10, 12, 14, 18, 19, 20

Simocephalus exspinosus (Koch, 1841)-14, 16

Camptocercus sp.-20

Ceriodaphnia sp.-19

Cladocera indet.-12

Copepoda

Eudiaptomus gracilis (Sars, 1863)-4

Limnocalanus grimaldu (De Guerne, 1886)-5, 6

Centropages sp.-19

Calanoida indet.-2

Cyclops insignis Claus, 1857-14

Eucyclops serrulatus (Fischer, 1851)-8

Mesocyclops viridis (Jurine, 1820)-2, 8, 9, 10, 12, 15, 16

Mesocyclops leuckarti (Claus, 1857)-2, 3, 6, 14, 19

Mesocyclops oithonoides (Sars, 1863)-20

Microcyclops gracilis (Lillj eborg, 1853)-14

Paracyclops affinis (Sars, 1863)-7

Paracyclops fimbriatus (Fischer, 1853)-7, 20

Cyclopidae indet.-1

Harpacticoida indet.-5

Ostracoda

Candona angulata Muller, 1900-16

Candona candida (Muller, 1776)-6, 15, 16, 18

Eabaeformicandona protzi (Hanwig, 1989)-4, 6, 18

Cypria exsculpta (Fischer, 1855)-19

Cyprfia ophthalmica (Jurine, 1820)-3, 6, 16

Cyprideis torosa (Jones, 1850)-1, 4, 5, 7, 16

Potamocypris unicaudata Schafer, 1943-6

Darwinula stevensoni (Brady et Robenson, 1870)-4, 5, 9, 11, 12, 19

Ostracoda indet.-14

Malacostraca

Asellus aquaticus (Linnaeus, 1758)-3, 4, 8, 10, 12, 14, 19, 20

Gammarus sp.-2, 7, 17

Chironomidae

Chironomus plumosus (Linnaeus, 1758)-6, 7, 14, 15

Chironomus sp.-2, 4, 7, 15, 16

Glyptotendipes paripes (Edwards, 1929)-4, 11

Glyptotendipes sp.-5, 7, 11

Stictochironomussticticus(Fabricius, 1781)-20

Stictochironomus rosenschoeldi (Zetterstedt, 1838)-3, 5

Einfeldia sp.-10

Microchironomus sp.-7

Chironomini indet.-10

Tarrytarsus verralli Goethgebuer, 1928-3, 4, 6, 8, 9, 11, 13, 14, 17, 20

Tanytarsus ex gr. holochlorus Edtyards, 1929-15, 16

Tarrytarsus sp.-6, 19

Ablabesmyia phatta (Eggen, 1863)-18

Ablabesmyia sp.-2, 9, 17

Procladius ferrugineus (Kieffer, 1918)-14, 17

Procladius sp.-3, 6, 8, 16, 18

Cricotopus bicinctus (Meigen, 1818)-4

Psectrocladius ex gr. sordidellus (Zetterstedt, 1838)-4, 5, 9, 17

Chironomidae indet.-1, 4, 5, 8, 9, 10, 11, 12, 13, 17, 18, 20

Insecta div.

Caenis sp.-3, 5, 8, 9, 14, 19

Leptocerus tineiformis Curtis, 1834-15

Polycentropodidae gen. sp.-3

Trichoptera indet.-11

Sigara striata (Linnaeus, 1758)-16

Corixidae gen. sp.-3

Coleoptera indet.-11

Ceratopogonidae indet.-3, 5, 9, 10, 14, 16

Diptera indet.-7

Mollusca

Bithynia tentaculata (Linnaeus, 1758)-11, 12

Planorbidae indet.-19, 20

Gastropoda indet.-1

Sphaerium corneum (Linnaeus, 1758)-8, 9, 14, 18, 19, 20

Pisidudae indet.-11, 17

Bryozoa

Bryozoa indet.-7

ACKNOWLEDGEMENTS

The study was financed by the Core Grant 0362482x03 "Formation and changes of the biological diversity under the human impact in different lake types (Estonia-Denmark-Netherlands)" of the Estonian Ministry of Education and Research. We thank Mrs Katrin Ott (Centre for Limnology, Estonian University of Life Sciences) for the hydrochemical data. Mrs Ester Jaigma kindly revised the English text of the paper.

Received 3 January 2007, in revised form 24 April 2007

REFERENCES

Babitskij, V. A. 1980. Microzoobenthos in three lakes of different types. Gidrobiol. Zh., 16(1), 37-45 (in Russian).

Dobrowolski, Z. 1995. Occurrence of macrobenthos in different littoral habitats of the polymictic Lebsko Lake. Ekol. polska, 42(1-2), 19-40.

Gusakov, V. A. 1993. Species content and distribution of meiobenthos of the Volga section of the Rybinsk Resevoir. In Zoocenoses of the Upper Tjolga Basin Water Bodies under the Human Impact. L D. Papanin Institute for the Biology of Inland Waters, Trudy, 69(72), 74-93. Gidrometeoizdat, Sankt-Peterburg (in Russian).

Gusakov, V. A. 2005. Meiobenthos of the Gor'kij Reservoir. In Biological Resources of Fresh Waters: Invertebrates, pp. 98-141. Institut biologu vnutrennikh vod, Rybinsk (in Russian).

Holopainen, I. J. & Paasivirta, L. 1977. Abundance and biomass of the meiozoobenthos in the oligotrophic and mesohumic lake Paajarvi, southern Finland. Ann. Zool. Fenn., 14(3), 124-134.

Jarvekulg, A. 1979. Bottom Fauna of the Eastern Part of the Baltic Sea. Valgus, Tallinn (in Russian).

Jarvekulg, A. (ed.) 2001. Estonian Rivers. Tartu Ulikooli Kirjastus, Tartu.

Keynas, K. & Keynas, L. 1978. Meiofauna in soft bottom sediments at Tvarminne, northern Baltic. Methods and preliminary results. Mem. Soc. Fauna Flora Fenn., 54(2), 658.

Kurashov, E. A. 1994. Meiobenthos as a Component of Lake Ecosystem. Institute of Limnology of RAS, St. Petersburg (in Russian).

Kurashov, A. A. 2002. The role of meiobenthos in lake ecosystems. Aquat. Ecol., 36(3), 447-463.

Kurashov, E. A. & Belyakov, V. P. 1987. Role of meiofauna in benthic community in the Latvian lakes of different type. Gidrobiol. Zh., 23(2), 46-50 (in Russian).

Maemets, A. 1974. On Estonian lake types and main trends of their evolution. In Estonian Wetlands and Their Life, Estonian Contributions to the International Biological Programme No. 7, pp. 292. Valgus, Tallinn.

Merilainen, J. J. 1988. Meiobenthos in relation to macrobenthic communities in a low saline, partly acidified estuary, Bothnian Bay, Finland. Ann. Zool. Fenn., 25(4), 277-292.

Mikhajlov, A. E. 1970. Oligochaetes in the microbenthos of Lake Pskov. In Biological Processes in the Marine and Continental Water Bodies. Abstracts of the II Congress of the All-Union Hydrobiological Society, p. 269. Kishinev (in Russian).

Mikhajlov, A. E. 1973. On the microbenthos of Lake Pskov. In Biological Researches on the Baltic Inland Water Bodies. Proceedings of the XV Scientific Conference on the Baltic Inland Water Bodies, pp. 73-75. Minsk (in Russian).

Ott, I. & Koiv, T. 1999. Estonian Small Lakes: Special Features and Changes. Estonian Environment Information Centre, Tallinn.

Pallo, P., Widbom, B. & Olafsson, E. 1998. A quantitative survey of the benthic meiofauna in the Gulf of Riga (Eastern Baltic Sea), with special reference to the structure of nematode assemblages. Ophelia, 49(2), 117-139.

Skvortsov, V. V. 1984. Quantitative evaluation of the meiobenthoc community in the processes of organic matter transformation in the lacustrine ecosystems. Sb. nauchn. trud. GosNlORKh, 223, 108-111 (in Russian).

Smit, H., Dudok van Heel, E. & Wiersma, S. 1993. Biovolume as a tool in biomass determination of Oligochaeta and Chironomidae. Freshwater Biol., 29, 376.

Stanczykowska, A. 1967. Comparison of the zoomicrobenthos occurring in the profundal of several lakes in Northern Poland. Bull. Acad. polon. Sci., cl. II, 15, 349-353.

Timm, T. 2002. Meiobenthos in some Estonian small stratified lakes. Proc. Estonian Acad. Sci. Biol. Ecol., 51, 184-203.

Timm, T. & Jarvekulg, A. 1975. Die Quellen Estlands als extreme Biotope and ihr Schutz. In Eesti loodusharulduste kaitseks, pp. 76-89. Valgus, Tallinn.

Zakhodnova, T. A., Petukhov, V. A. & Alekseev, V. P. 1984. Consumption of the production of microphytobenthos by meiobenthos and protozoans in the littoral of Lake Verkhnee Vrevo (according to the data from 1982). Sb. nauchn. Lrud. GosNlORKh, 224, 87-97 (in Russian).

Zhadin, V. L, Akatova, N. A., Kutikova, L. A. & Ozeretskovskaya, N. G. 1972. Freshwater psammon of the coast of the Curonian Spit. Gidrobiol. Zh., 8(6), 74-87 (in Russian).

Tarmo Timm (a) *, Margit Kumari (a), Kaidi Kubar (a), Kadri Sohar (b), and Walter Traunspurger (c)

(a) Centre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, 61117 Rannu, Tartumaa, Estonia

(b) Institute of Geology, University of Tartu, Vanemuise 46, 51014 Tartu, Estonia

(c) Abteilung Tierokologie, Universitat Bielefeld, Morgenbreede 45, D-33615 Bielefeld, Germany

* Corresponding author, tarmo.timm@emu.ee
Table 1. Average abundance of animals, ind. [m.sup.-2]
([+ or -] standard error)

Water body Macrozoobenthos Pseudomeiobenthos

 1. Reigi laht 16 835 23 569
 2. Rame laht 1 010 1 010

 3. Kirikulaht 16 162 67 003
 4. Kaina laht 4 040 16 498
 5. Laialepa laht 20 202 37 037
 6. Suurlaht 11 448 30 303
 7. Moisalaht 11 784 8 754

 8. Tammelais 4 714 15 825
 9. Veskilais 3 030 8 080
10. Kooru jarv 5 050 12 458
11. Sarapiku jarv 3 367 24 242
12. Kiljatu jarv 19 192 31 313
13. Nonni jarv 1 010 10 438
14. Linnulaht 8 081 5 387
15. Kaomardi laht 1 683 3 704
16. Kiissa laht 7 071 1 683
17. Sutlepa meri 12 121 8 417
18. Pikane jarv 5 387 2 357
19. Allikajarv 4 040 5 387
20. Lepaauk 3 704 5 387

Open bays (1, 2) 8 922 12 289
 [+ or -] 7 912 [+ or -] 11 279

Lagoons (3-7) 12 727 31 919
 [+ or -] 2 699 [+ or -] 10 085

Lakes (8-20) 6 035 10 360
 [+ or -] 1 359 [+ or -] 2 445

 Total (1-20) 7 997 15 943
 [+ or -] 1 379 [+ or -] 3 602

Water body Eumeiobenthos Plankton

 1. Reigi laht 301 683 337
 2. Rame laht 1 010 4 040

 3. Kirikulaht 35 017 22 222
 4. Kaina laht 10 101 1 684
 5. Laialepa laht 7 407 1 010
 6. Suurlaht 69 360 17 508
 7. Moisalaht 17 172 673

 8. Tammelais 2 694 21 549
 9. Veskilais 3 704 1 684
10. Kooru jarv 673 3 367
11. Sarapiku jarv 337 0
12. Kiljatu jarv 337 1 347
13. Nonni jarv 0 0
14. Linnulaht 8 417 5 724
15. Kaomardi laht 673 1 683
16. Kiissa laht 39 057 3 367
17. Sutlepa meri 0 0
18. Pikane jarv 7 071 337
19. Allikajarv 2 357 2 694
20. Lepaauk 1 010 3 367

Open bays (1, 2) 151 346 2 188
 [+ or -] 150 336 [+ or -] 1 851

Lagoons (3-7) 27 811 8 619
 [+ or -] 11 449 [+ or -] 4 654

Lakes (8-20) 5 102 3 471
 [+ or -] 2 927 [+ or -] 1 580

 Total (1-20) 25 404 4 630
 [+ or -] 15 067 [+ or -] 1 571

Water body Total meiobenthos All animals

 1. Reigi laht 325 589 342 424
 2. Rame laht 6 060 7 070

 3. Kirikulaht 124 242 140 404
 4. Kaina laht 28 283 32 323
 5. Laialepa laht 45 454 65 656
 6. Suurlaht 117 171 128 619
 7. Moisalaht 26 599 38 383

 8. Tammelais 40 068 44 782
 9. Veskilais 13 468 16 498
10. Kooru jarv 16 498 21 548
11. Sarapiku jarv 24 579 27 946
12. Kiljatu jarv 32 997 52 189
13. Nonni jarv 10 438 11 448
14. Linnulaht 19 528 27 609
15. Kaomardi laht 6 060 7 743
16. Kiissa laht 44 107 51 178
17. Sutlepa meri 8 417 20 538
18. Pikane jarv 9 765 15 152
19. Allikajarv 10 438 14 478
20. Lepaauk 9 764 13 468

Open bays (1, 2) 165 824 174 747
 [+ or -] 159 764 [+ or -] 167 677

Lagoons (3-7) 68 350 81 077
 [+ or -] 21 657 [+ or -] 22 603

Lakes (8-20) 18 932 24 967
 [+ or -] 3 522 [+ or -] 4 204

 Total (1-20) 45 976 53 973
 [+ or -] 16 472 [+ or -] 17 244

Table 2. Percentage of animal groups in the abundance and
biomass of meiobenthos

Type of water
bodies Oligochaeta Chironomidae

 Abundance:
Open bays 6.90 0.20
Lagoons 3.74 33.20
Lakes 10.95 41.04
 Total 6.81 23.40

 Biomass:
Open bays 43.48 0.67
Lagoons 6.02 23.55
Lakes 9.14 22.32
 Total 9.27 21.89

Type of water Other
bodies pseudomeiobenthos Ostracoda

 Abundance:
Open bays 0.30 1.22
Lagoons 9.75 24.83
Lakes 2.74 24.49
 Total 4.47 16.22

 Biomass:
Open bays 9.48 26.42
Lagoons 24.09 20.55
Lakes 13.93 22.48
 Total 18.93 21.66

Type of water Other
bodies Nematoda eumeiobenthos

 Abundance:
Open bays 90.05 0.00
Lagoons 15.57 0.30
Lakes 2.46 0.00
 Total 38.90 0.11

 Biomass:
Open bays 9.92 0.00
Lagoons 0.22 1.19
Lakes 0.17 0.00
 Total 0.67 0.61

Type of water
bodies Cladocera Copepoda

 Abundance:
Open bays 0.10 1.22
Lagoons 6.40 6.21
Lakes 12.30 6.02
 Total 5.71 4.36

 Biomass:
Open bays 0.00 10.03
Lagoons 12.20 12.18
Lakes 24.33 7.63
 Total 16.86 10.11

Table 3. Average wet biomass of animals, mg [m.sup.-2]
([+ or -] standard error)

Water body Macrozoobenthos Pseudomeiobenthos

 1. Reigi laht 284 637 788
 2. Rame laht 428 178

 3. Kirikulaht 14 214 4 504
 4. Kaina laht 2 134 1 107
 5. Laialepa laht 6 959 1 613
 6. Suurlaht 14 523 922
 7. Moisalaht 40 664 1 790

 8. Tammelais 6 104 1 263
 9. Veskilais 6 871 446
10. Kooru jarv 4 094 216
11. Sarapiku jarv 11 656 1 082
12. Kiljatu jarv 10 765 1 407
13. Nonni jarv 740 255
14. Linnulaht 21 791 272
15. Kaomardi laht 2 752 172
16. Kiissa laht 17 226 146
17. Sutlepa meri 7 561 548
18. Pikane jarv 2 013 130
19. Allikajarv 7 319 879
20. Lepaauk 2 501 228

Open bays (1, 2) 142 532 483
 [+ or -] 142 104 [+ or -] 305

Lagoons (3-7) 15 699 1 987
 [+ or -] 6 660 [+ or -] 649

Lakes (8-20) 7 799 542
 [+ or -] 1 723 [+ or -] 127

Total (1-20) 23 247 897
 [+ or -] 13 891 [+ or -] 224

Water body Eumeiobenthos Plankton

 1. Reigi laht 651 27
 2. Rame laht 2 255

 3. Kirikulaht 94 2 487
 4. Kaina laht 720 48
 5. Laialepa laht 508 39
 6. Suurlaht 2 175 1 933
 7. Moisalaht 569 10

 8. Tammelais 21 1 072
 9. Veskilais 138 79
10. Kooru jarv 0 560
11. Sarapiku jarv 20 0
12. Kiljatu jarv 26 489
13. Nonni jarv 0 0
14. Linnulaht 360 734
15. Kaomardi laht 61 170
16. Kiissa laht 2 514 1 256
17. Sutlepa meri 0 0
18. Pikane jarv 230 168
19. Allikajarv 144 151
20. Lepaauk 2 275

Open bays (1, 2) 326 247
 [+ or -] 324 [+ or -] 219

Lagoons (3-7) 813 903
 [+ or -] 356 [+ or -] 541

Lakes (8-20) 270 381
 [+ or -] 189 [+ or -] 116

Total (1-20) 411 498
 [+ or -] 157 [+ or -] 155

Water body Total meiobenthos All animals

 1. Reigi laht 1 466 286 103
 2. Rame laht 435 863

 3. Kirikulaht 7 085 21 299
 4. Kaina laht 1 875 4 009
 5. Laialepa laht 2 160 9 119
 6. Suurlaht 5 030 19 553
 7. Moisalaht 2 369 43 033

 8. Tammelais 2 356 8 460
 9. Veskilais 663 7 540
10. Kooru jarv 776 4 870
11. Sarapiku jarv 1 102 12 758
12. Kiljatu jarv 1 922 12 687
13. Nonni jarv 255 995
14. Linnulaht 1 366 23 157
15. Kaomardi laht 403 3 184
16. Kiissa laht 3 916 21 142
17. Sutlepa meri 548 8 109
18. Pikane jarv 528 2 541
19. Allikajarv 1 174 8 493
20. Lepaauk 505 3 006

Open bays (1, 2) 950 143 483
 [+ or -] 515 [+ or -] 142 620

Lagoons (3-7) 3 704 19 403
 [+ or -] 1 017 [+ or -] 6 726

Lakes (8-20) 1 193 8 996
 [+ or -] 285 [+ or -] 1 914

Total (1-20) 1 797 25 046
 [+ or -] 391 [+ or -] 13 928
COPYRIGHT 2007 Estonian Academy Publishers
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2007 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Timm, Tarmo; Kumari, Margit; Kubar, Kaidi; Sohar, Kadri; Traunspurger, Walter
Publication:Proceedings of the Estonian Academy of Sciences: Biology/Ecology
Date:Sep 1, 2007
Words:7004
Previous Article:Detrimental effect of peritrich ciliates (Epistylis sp.) as epibionts on the survival of the copepod Acartia bifilosa/Aerjalalise Acartia bifilosa...
Next Article:Effect of cyanobacterial blooms on the abundance of the flounder Platichthys flesus (L.) in the Gulf of Finland/Sinivetikaoitsengute mojust lesta...

Terms of use | Copyright © 2017 Farlex, Inc. | Feedback | For webmasters