Hydrobiologia 434: 41–54, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands.
41
Species richness of pelagic Cladocera of large lakes in the eastern hemisphere N. M. Korovchinsky A. N. Severtsov Institute of Ecology and Evolution of Russian Academy of Sciences, Leninsky prospect 33, 117071 Moscow, Russia E-mail:
[email protected] Received 22 November 1999; in revised form 3 April 2000; accepted 10 May 2000
Key words: pelagic Cladocera, species richness, large lakes, eastern hemisphere
Abstract The composition of the pelagic cladoceran species assemblages in some large, well-studied, lakes of Europe, Asia and Africa is reviewed based on original and literature data. In general, pelagic cladocerans are taxonomically less well studied than some littoral groups. Only the limnetic members of the family Sididae and some Daphnia have recently been revised, whereas knowledge of species diversity of other Daphniidae (including moinas) and Bosminidae is missing. Future detailed taxonomic studies may lead to considerable changes in understanding of limnetic zooplankton composition.
Introduction Large lakes accumulate most of the surface waters of the world (Herdendorf, 1990) and the deep ancient lakes produce some of the best examples of adaptive radiation known (Brooks, 1950; Kozhov, 1963; Dumont, 1994). At the same time, because of the small surface–volume ratio in large lakes, their pelagic communities are usually of considerably greater importance than benthic communities. Cladocerans represent a typical component of the pelagic zooplankton, and are usually more diverse there than copepods, although they may be rare or absent in the limnetic zone of some ancient lakes (Dumont, 1994). The investigation of pelagic crustaceans of large lakes started in Europe (Lakes Constance, Onega and Geneva), and later extended to other regions, approximately from the1850s to the 1930s. In many lakes, the pelagic community and its members was subjected to long-term studies. As a result, cladocerans together with Copepoda and Rotifera may be regarded as the best studied component of continental waters. One might think that the species of cladocerans should be especially well known, but recent taxonomic
revisions demonstrate an insufficient present knowledge of species diversity of the group (Frey, 1982, 1987; Korovchinsky, 1996). Modern taxonomic studies improved the situation. However, the involvement of different cladoceran taxa in their modern understanding seems rather irregular and our notions of taxonomic structure of many groups and assemblages are still far from reality (Frey, 1987; Korovchinsky, 1996; Hebert & Taylor, 1997; Dumont, 1997). The objectives of the present paper are to review the current knowledge of species composition of the pelagic cladocerans of some large lakes situated in the eastern hemisphere and to present some new data to show the perspectives of further studies in this field.
Materials and methods Material for this study was borrowed from specialists named below and from extensive collections indicated as follows: ZIN – Zoological Institute (S.-Petersburg, Russia), NHM – Natural History Museum (London, England), HNHM – Hungarian Natural History Museum (Budapest, Hungary), HJD – Prof. H. J. Dumontcollection (University of Ghent, Belgium), DGF –
42 Prof. D. G. Frey – collection (Indiana University, U.S.A.), CHF – Prof. C. H. Fernando - collection (Waterloo University, Canada). Europe 1. Lago Maggiore (Italy): 9.10.1973, leg. N. N. Smirnov. 2. Neusiedlersee (Austria): 26.08.1988, leg. L. Forro; 2.07 and 17.08.1972 (HJD). 3. Lake Balaton (Hungary): 13.09.1956 (NHM), leg. G. Boxshall; June and November 1983, leg. L. Toth. 4. Lake Onega: 9.03.1973, leg. O. Zhavoronkova. Asia 1. Lake Baikal (Eastern Siberia, Russia): 20.08.1998, leg. N.G. Sheveleva. 2. Lake Khanka (Far East, Russia - China): 4 samples of 14. 07–28. 09. 1932 (ZIN), leg. L. A. Kutikova; 30.07.1981, leg. Wong Quangxi. 3. Lake Issyk - Kul (Kirkhizia), 28.07.1976, leg. A.V. Makrushin. 4. Lake Balkhash (Kazakhstan): July 1991, leg. T. S. Stuge. 5. Lake Kinneret (Israel), 1.04.1984 and 3.01.1985, leg. M. Gophen. 6. Lake Biwa (Japan): 27.08.1917 (ZIN), leg. L. A. Kutikova; one sample without the date, leg. O. A. Timoshkin and N. G. Sheveleva. 7. Lake Lanao (Philippines): 8 samples from 13.08.1967 to 14.06.1968 (DGF). 8. Lake Toba (Indonesia): 3 samples from 8.04 to 23.04.1929, leg. P. Adamicka; 6 samples from 3.07.1977 to 6.09.1984 (CHF); 1 sample, 9.11.1986 (DGF). Africa 1. Lake Victoria (Kenia): total mounts V-89, V-90 (HNHM), leg. L. Forro; N 222 - 1915 (ZIN), leg. L. A. Kutikova; March 1995 (HJD). 2. Lake Albert (Uganda): 13.05.1991, leg. L. Mwebaza-Ndawula, 29.03.1995, leg. A. Litt. 3. Lake Edward (Uganda): 21.03 and 25.03.1995, leg.A. Litt. 4. Lake Tana (Ethiopia): 8.05.1981 and 1.05.1982 (HJD), 23.01 and 3.02.1992, leg. V. Mikheev, March 1997, leg. A. Golubtsov.
5. Ethiopian Rift Valley lakes: Lake Langano, 2.11.1984, leg. V. Mikheev; Lake Zwai, 24.06.1982, leg. D. Pavlov; Lake Abijata, 10. 11. 1981 (HJD); Lake Abaya, March 1982 (HJD); Lake Awassa, 6.10.1982 (HJD), 14.10.1993, leg. S. Bekelie; Lake Chamo, 28.09.1982, leg. V. Mikheev. The material was represented by specimens in formalin, alcohol or, rarely, as total mounts. All available taxa were registered but the family Sididae (Sida, Limnosida, Diaphanosoma) was studied in detail. Apart from this material, the literature sources on lakes mentioned above and some other large lakes (Geneva, Constance, Ohrid, Ladoga, Sevan) have been analysed. Such species as Ceriodaphnia laticaudata and Polyphemus pediculus were excluded from the observation due to their primary predomination in littoral habitats.
Results European lakes Lake Geneva Eight species permanently inhabit the pelagic zone (Balvay, 1984; Balvay et al., 1985) (Table 1). Most were recorded in the second half of the 19th–early 20th century, and since that time have not been restudied taxonomically. Only the littoral Sida, also numerous in open waters and originally described as S. limnetica by Burckhardt (1899), was recently re-assigned to typical S. crystallina (O.F.Müller, 1776) ( Balvay, 1984; Korovchinsky, 1986a). Lake Constance (Obersee) Seven species occur in the open lake (Einsle, 1978, 1988; Straile & Geller, 1998) (Table 1). Hybrids D. galeata x D. hyalina have also been found here (Wolf, 1987). Other hybrids D. cucullata x D. galeata (Flössner & Kraus, 1986) probably originate from the Untersee. A genetic analysis has shown a high heterogeneity of the Daphnia populations (Weider & Stich, 1992). Question with the species composition of Bosmina still remains unclear. In particular, taxon kessleri named variously (Flössner, 1972; Einsle, 1988; Lieder, 1996; Straile & Geller, 1998) may to be just the hybrid of B. longispina and B.coregoni (Hofmann, 1998). Diaphanosoma brachyurum had disappeared from the lake by 1957 and a new species, the North Amer-
43
Table 1. Species composition of pelagic cladocerans of large European lakes Species / Lakes
Currently known taxa: Limnosida frontosa Sars, 1865 Diaphanosoma brachyurum (Lievin, 1848) Holopedium gibberum Zaddach, 1855 Daphnia longiremis Sars, 1862 Daphnia cristata Sars, 1862 Daphnia cucullata Sars, 1862 Daphnia longispina O.F. Muller, 1785 Daphnia galeata Sars, 1864 Daphnia hyalina Leydig, 1860 Daphnia pulex Leydig, 1860 Daphnia atkinsoni Baird, 1859 Ceriodaphnia pulchella Sars, 1862 Ceriodaphnia affinis Lilljeborg, 1901 Ceriodaphnia quadrangula O.F. Muller, 1785 Ceriodaphnia reticulata (Jurine, 1820) Bosmina berolinensis Imhof, 1888 Bosmina coregoni Baird, 1857 Bosmina crassicornis Lilljeborg, 1887 Bosmina kessleri Uljanin, 1874 (or B. longicornis kessleri Uljanin, 1874) Bosmina longicornis Schodler, 1865 Bosmina longispina Leydig, 1860 Bosmina obtusirostris Sars, 1862 Bosmina longirostris (O.F.Muller, 1785) Chydorus sphaericus (O.F.Muller, Bythotrephes longimanus Leydig, 1860 Leptodora kindti (Focke, 1844) Recently identified taxa:
Geneva
Constance (Obersee)
+
Lago Neusiedlersee Maggiore
+
+
+
Balaton
+
+
+ + +
Ohrid
? + +
+ +
+ +
+
Ladoga Onega
+ +
+ +
+ + + + +
+ + + + +
+ +
+
+
+ + + + +
+
+
+
+ + +
+ +
+
+
+ + + +
+ + + +
+ +
+ +
+
+
+
+
+
+
+
+
+
+
+
+
+ +
+
+
+
−
Daphnia galeata x Daphnia hyalina, Daphnia parvula Fordyce, 1901
−
+
+
+
DiaphanoDiaphanoDaphnia Daphnia soma soma lacustris pulicaria galeata mongolianum Korinek, 1981; Forbes, 1983 Ueno, 1938; D. mongoliaMoina num?, brachiata Daphnia (Jurine, 1820) cucullata x D. galeata
−
44 ican D. parvula, was found here in one bay in 1974 (Einsle, 1978). This long-studied lake is the type locality for three species, viz. Daphnia hyalina, Bosmina longispina and Bythotrephes longimanus (Leydig, 1860). Recent taxonomic studies of the local fauna mostly focused on representatives of the genus Daphnia (Flössner, 1972; Flössner & Kraus, 1986). In particular, the typical two former species have been drawn with a supplement of genotypic characteristics of D. hyalina (Wolf, 1987; Weider & Stich, 1992). Lago Maggiore Recent overviews yielded six pelagic species (DeBernardi et al., 1989; Manca et al., 1992) (excluding Alona affinis as a facultative taxon) (Table 1). Dodson (1991) also lists Bosmina coregoni based on older records. Analysis of a single sample confirmed the presence of typical Diaphanosoma brachyurum (pers. unpubl. data). Bosmina and Daphnia need further taxonomic studies. Neusiedlersee The zooplankton composition of the lake has been summarised by Ponyi & Devai (1979), Herzig (1979) and Forro & Metz (1987). Both latter include Daphnia longispina although Herzig mentions that, based on unpublished Hrbacek’s definition, two species, D. cucullata and D. galeata, are disguised under this name. On the other hand, Ponyi & Devai (op. cit.) list only D. hyalina which unusually absent in open water. Representatives of Moina named M. rectirostris and M. micrura, and extinct since the 1950s were recently classified as M. brachiata (Forro & Metz, 1987). Diaphanosoma identified as ‘D. brachyurum’ dominates the zooplankton. I recently studied samples, including one of the last century, and found only D. mongolianum (pers. unpubl. data). This identification was accepted in recent hydrobiological studies (Herzig, 1995). Lake Balaton Five species occur in the limnetic zone (Zankai & Ponyi, 1986) (Table 1). Modern analysis confirmed the presence of D. cucullata and revealed hybrids D. cucullata x D. galeata (Schwenk et al., 1998). The identification of local Diaphanosoma was rather complicated. For a long time it was named ‘D. brachyurum’, later ‘D. birgei lacustris’, and finally D. lacustris (Korovchinsky, 1987). Possibly D. mongolianum occurs too, but this still remains uncertain in
spite of recent taxonomic study (Nedelkovic & Ponyi, 1997). Lake Ohrid Only two planktonic species (excluding the littoral Scapholeberis mucronata) have been recorded in the pelagic zone (Daphnia pulex and Bosmina longirostris); the presence of D. longispina was suspected (Stankovic, 1960; Green, 1960). Later, ‘D. pulex’ was reidentified as D. pulicaria (Hrbacek, 1987). Lake Ladoga Pelagic cladocerans number 22 species (Den’gina & Sokolova, 1968; Telesh, 1996). Of these, only nine (Holopedium gibberum, Daphnia cristata, D. cucullata, Bosmina coregoni, B. crassicornis, B. longispina, B. obtusirostris, Bythotrephes longimanus, Leptodora kindti) are characteristic of the central part of the lake. The others species prefer bays and inshore zones. The ctenopods include Diaphanosoma brachyurum, the only species of the genus known at this northern latitude. Most other taxa present taxonomic problems, especially Bosmina and the species group Daphnia cucullata - D. longispina - D. galeata. Bosmina is represented by eight morphologically variable ‘species’ but none of these was the subject of a detailed taxonomic analysis. Lake Onega The species composition is as diverse as in Ladoga (23 taxa of species rank excluding occasional littoral forms (Smirnova, 1972; Kulikova et al., 1997), and is dominated by morphologically variable Daphnia and Bosmina (six and seven species, respectively). Only six species (Limnosida frontosa, Holopedium gibberum, Daphnia cristata, Bosmina obtusirostris lacustris, Chydorus sphaericus and Leptodora kindti) are numerous throughout the lake, while others tend to be distributed in bays and closer to the shore. Among Daphnia species, the record of D. atkinsoni looks curious, it normally occurs in more southern, temporary water bodies (Hrbacek, 1987). Asian lakes Lake Kinneret Daphnia lumholtzi disappeared in the late 1950s or early 1960s (Gophen, 1978), leaving only five species (Gophen, 1978; Gophen et al., 1990) (Table 2).
45 Table 2. Species composition of pelagic cladocerans of large Asian lakes Species / Lakes Currently known taxa: Diaphanosoma brachyurum Diaphanosoma chankensis Ueno, 1939 Diaphanosoma modigliani Richard, 1895 Diaphanosoma sarsi Richard, 1895 Holopedium gibberum Daphnia longispina Daphnia cucullata Daphnia galeata Daphnia hyalina Daphnia balchashensis Manuilova, 1948 Daphnia cristata Daphnia biwaensis Ueno, 1937 Ceriodaphnia reticulata Ceriodaphnia pulchella Ceriodaphnia quadrangula Ceriodaphnia cornuta Sars, 1885 Ceriodaphnia dubia Richard, 1895 Moina rectirostris Leydig, 1860 Moina dubia Guerne et Richard, 1892 Moina micrura Kurz, 1874 Moina macrocopa (Straus, 1820) Bosmina obtusirostris Bosmina longispina Bosmina coregoni Bosmina fatalis Burckhardt, 1924 Bosmina longirostris Bosminopsis deitersi Richard, 1897 Chydorus sphaericus Leptodora kindti Recently identified taxa:
Kinneret
Sevan
+
Issyk-Kul
Balkhash
+
+
Baikal
Khanka
Biwa
Lanao
Toba
+
+
+
+
+ +
+
+
+ +
+ + + + + + +
+
+ + +
+ + +
+ + +
+
+ + + +
+
+
+
+ +
+
+ +
Diaphano- Daphnia Diaphanoso Diaphanoso Daphnia Diaphanoso soma hyalina ma ma cucullata x ma dubium lacustris, D, mongolia- mongolia- Daphnia Manuilova, orghidani? num num, galeata 1964, Daphnia D. orghidani galeata transamurensis Korovchinsky 1986, Limnosida frontosa. Daphnia galeata
+
+
+ +
? ?
+ + Diaphanoso Diaphanoso ma cf. ma orientalis, orghidani D. cf. transamuorghidani, rensis D. dubium, Daphnia galeata, Moina micrura
+
46 Moina rectirostris is the least numerous and renamed as M. dubia by Serruya (1978). Both these names are currently regarded as synonyms of M. brachiata, M. micrura or M. affinis (Smirnov, 1976). Of other species, ‘Diaphanosoma brachyurum’ has recently been assigned to D. lacustris (Korovchinsky, 1987). Possibly another species, D. orghidani, also inhabits this lake (Bromley, 1993). According to Rzoska’s revision ( 1956a), Ceriodaphnia rigaudi should be C. cornuta, but this taxon represents a species complex (Berner, 1985, 1999). Lake Sevan The pelagic zone is dominated by only one cladoceran species previously named Daphnia longispina sevanica (Meshkova, 1968; Nikogosjan, 1985), but recently considered as D. hyalina (Glagolev, 1986). Lake Issyk-Kul Only few species of rotifers and copepods inhabit the open water of the brackishwater lake while planktonic cladocerans populate bays and the littoral zone (Folyjan, 1973) (Table 2). Diaphanosoma brachyurum has been reidentified as D. mongolianum (Korovchinsky, 1987). Lake Balkhash Eleven planktonic species of Cladocera have been recorded in the lake having peculiar salinity gradient (Saduakasova, 1972) (Table 2), without indication of habitat preferences. Daphnia balchashensis Manuilova is probably conspecific with D. galeata (Glagolev, 1986). The record of D. cristata seems curious because the southern limit of the species’ range just reaches northern Kazakhstan (Korovchinsky et al., 1995), and it might be easily confused with other helmeted Daphnia species. The taxonomic status of ‘Moina rectirostris’ also remains unclear. A reinvestigation of the Diaphanosoma in the lake has revealed D. mongolianum instead of D. brachyurum (pers. obs.). Lake Baikal Reviewers (e.g. Kozhov, 1962; Dumont, 1994) often ignored facultative presence of five cladoceran species in the pelagic zone where they may be quite abundant (Chydorus sphaericus is added to this assemblage in late summer) (Smirnov, 1984; Glagolev, 1986; Sheveleva & Pomazkova, 1995) (Table 2). Their presence is connected with the population dynamic of the species in the littoral zone and with the hydrological
characters of the year. Daphnia galeata and Bosmina longirostris predominate. Another 12 planktonic species and hybrids D. cucullata x D. galeata mostly inhabit bays and the littoral zone. In spite of recent reviews (Sheveleva & Pomazkova, op.cit.), all species, especially Bosmina and Daphnia, need further work. Lake Khanka There is no a modern review of the pelagic fauna of the lake and brief overview is needed. Ueno (1937a) first recorded Diaphanosoma brachyurum and Bosmina coregoni longispina, which are probably synonymous with later collected species, two of which were described as a new (D. chankensis, Moina chankensis and B. fatalis f. chankensis) (Ueno, 1939). A year later, Daphnia longispina and Leptodora kindti were added to the list (Ueno, 1940). A survey by Borutsky (1952) confirmed previous identifications and added Chydorus sphaericus. Goulden (1968) considered the local Moina as specific, although he had no gamogenetic specimens for a conclusive definition; Smirnov (1976) synonymised it with M. micrura. Later, Daphnia galeata (probably is conspecific with the earlier recorded D. longispina) and Diaphanosoma orghidani transamurensis n. ssp. were recorded (Glagolev, 1986; Korovchinsky, 1986b). Finally, the species list was supplemented with Diaphanosoma dubium and Limnosida frontosa (Korovchinsky, submitted). Thus, nine pelagic cladoceran species, including three Diaphanosoma, are known. Most of them need reinvestigation which has only been provided for Diaphanosoma chankensis (Korovchinsky, 1992, 1998a). Lake Biwa Ten species have been recorded (Narita & Okamoto, 1984). Among them, Daphnia biwaensis Ueno, originally considered as a pelagic race D. pulex biwaensis (Ueno, 1937b), only slightly differs from D. pulex and is possibly conspecific with it or another closely related species. D. longispina, known under different names (D. longispina hyalina, D. longispina galeata, D. hyalina) has been reassigned to D. galeata (Tanaka, 1992). Moina dubia Guerne et Richard, now considered a subspecies of M. micrura, has never been recorded in Eastern Asia before (Smirnov, 1976). It lacks from later corrected species lists which, however, include one extra species – Bosmina fatalis (Mori & Miura, 1990). The analysis of few samples from the lake did not reveal Diaphanosoma brachyurum, but D. dubium, D.
47 cf. orientalis and D. cf. orghidani (pers. obs.), which need further studies. Lake Lanao The original survey yielded four pelagic species (Woltereck, 1941) but the present list is fully revised (Table 2). Thus, Moina micrura was listed instead of M. macrophthalma and Bosmina fatalis instead of Bosmina longirostris and Bosminopsis deitersi (Lewis, 1979). Frey (1969) recorded B. deitersi shortly before Lewis’ investigations. Further studies also revealed Diaphanosoma orghidani transamurensis instead of D. modigliani (Korovchinsky, 1991). It co-exists here with the much less numerous D. sarsi. Lake Toba This lake is the type locality of three species described by Richard (1894): Diaphanosoma modigliani, D. sarsi and Ceriodaphnia dubia. In addition, Bosmina longirostris was recorded (Brehm, 1933). D. modigliani has recently been redescribed and considered as known only in the lake (Korovchinsky, 1991), although later it was also found in Lake Tempe (Sulawesi, Indonesia) (Korovchinsky, 1998b). The taxonomic status of C. dubia remains unclear. Johnson (1956) suggested its conspecificity with C. affinis. African lakes Lake Victoria Several reviews (Rzoska, 1956b; Green, 1971; Dumont, 1986; Mavuti & Litterick, 1991; MwebazaNdawula, 1994) list 10 species, although two more (Ceriodaphnia quadrangula and Moina hartwigi) had been recorded earlier (Werestchagin, 1916) (Table 3). Among others, only Daphnia barbata and D. lumholtzi seem not to rise a taxonomic problem. D. longispina (D. longispina hyalina in Delachaux (1917)) undoubtedly requires more attention as well as taxa of Moina, Ceriodaphnia and Bosmina. Recent analysis of the lake’s zooplankton gave me an opportunity to find one extra species of Diaphanosoma – D. mongolianum (pers. unpubl. data), which had possibly been confused with D. sarsi earlier. Moreover, an investigation of old total mounts by Daday revealed specimens of D. brachyurum s.l. together with the common D. excisum. Lakes Albert and Edward Their pelagic cladoceran assemblage is more or less similar to that of Lake Victoria (Table 3). Daphnia
lumholtzi in Lake Albert has two morphs (typical and monacha) (Green, 1967). Again, in both lakes, Diaphanosoma excisum co-occurs with D. mongolianum (pers.obs.). Lake Tana The first survey of its zooplankton (Brunelli & Canicci, 1940) revealed 10 species including five Ceriodaphnia, two of which (C. rigaudi and C. cornuta) are probably conspecific (Rzoska, 1956a). A recently compiled species list (Dumont, 1986) comprises nine taxa of species rank (Table 3), most of which need revision. Modern morphological and genetic analysis revealed D. hyalina (Schwenk et al., 1998) instead of the long-recorded D. longispina. My analysis of Diaphanosoma confirmed the presence of D. excisum and D. sarsi together with one additional species, D. orghidani (subspecies D. orghidani orghidani). Ethiopian Rift Valley lakes Of eight lakes of the group, only four (Zwai, Abijata, Langano and Awassa) have been surveyed for their zooplankton. Lake Abijata was reported as lacking Cladocera (Wodajo & Belay, 1984), and in others they are not diverse, with six species most (Table 3). These include the littoral Chydorus sphaericus and Alona diaphana (Wodajo & Belay, 1984; Fernando et al., 1990; Mengestou & Fernando, 1991). Recent studies (Korovchinsky, 1987, unpubl. data) revealed Diaphanosoma mongolianum in five lakes, in two of which it co-occurs with D. excisum (Table 3). D. mongolianum has also been found in the Ethiopian non-Rift Valley Lake Haik and crater Lake Zengana (pers. obs.).
Discussion All European lakes considered except Ohrid, Ladoga and Onega are of similar size and at latitudes 46– 48◦ N, while the latter two are much larger and more northern in location (60–62◦ N). Lake Ohrid is unic in respect of its antiquety and low diversity of pelagic cladoceran assemblage (two or three species). In West and Central European lakes, five–nine species inhabit pelagic zone, whereas 21 and 23 species were recorded in lakes Ladoga and Onega, although some of them seem to be more littoral in their distribution. In general, 31 cladoceran taxa of species rank have been recorded in European lakes, most of which are
48 Table 3. Species composition of pelagic cladocerans of large African lakes Species/Lakes
Currently known taxa: Diaphanosoma excisum Sars, 1885 Diaphanosoma sarsi Daphnia longispina Daphnia barbata Weltner, 1898 Daphnia lumholtzi Sars, 1885 Ceriodaphnia reticulata Ceriodaphnia quadrangula Ceriodaphnia dubia Ceriodaphnia cornuta Moina micrura Moina hartwigi Weltner, 1898 Bosmina longirostris Chydorus sphaericus Recently identified taxa:
Victoria
Albert
Edward
Tana
Ethiopian Rift Valley lakes
+ + + + +
+ +
+
+ + +
+
+ + + + + + + Diaphanosoma mongolianum, D. cf. brachyurum
members of families Daphniidae (13 species) and Bosminidae (eight species). Apart from this, the hybrids Daphnia galeata x D. hyalina and D. cucullata x D. galeata supplemented the list. Representatives of Diaphanosoma have been recorded in all except Ohrid and Constance (in the latter they had disappeared in the 1950s probably due to eutrophication (Einsle, 1988; Straile & Geller, 1998)). Lakes Neusiedlersee and Balaton have proved to be occupied by D. mongolianum and D. lacustris instead of the previously listed D. brachyurum. Typical representatives of the latter species occur only in Lago Maggiore while in Lake Geneva the species status of these crustaceans remains unclear. In spite of such changes, additional material would to be studied to reveal the real local species diversity of the group because two or three Diaphanosoma species may co-occur in each lake (e.g. a second species D. mongolianum seems present in Lake Balaton) (Korovchinsky, 1987).
+ +
+ + + +
+ +
+ + +
Diaphano soma mongolianum
Diaphano soma mongolianum
+ +
+
+ + +
+ +
+ +
+ +
Diaphano soma orghidani Negrea, 1982 Daphnia hyalina
Diaphano soma mongolianum
The discovery of interspecific Daphnia hybrids (Hebert, 1985; Wolf & Mort, 1986; Wolf, 1987) was an important event in modern cladoceran taxonomy. They have been found in Lake Constance (D. galeata x D. hyalina) (Wolf, 1987; Weider & Stich, 1992) and Lake Balaton (D. cucullata x D. galeata) (Schwenk et al., 1998); they are almost certaily widely distributed. The parental Daphnia species also need further attention from the taxonomic point of view. Thus, in Neusiedlersee D. cucullata and D. galeata have been recorded instead of long known ‘D. longispina’ (Herzig, 1979), and D. galeata was recently found in Lake Ladoga (Telesh, 1996). The type population of D. hyalina from Lake Constance was studied morphologically (Flössner & Kraus, 1986) and genetically (Wolf, 1987; Weider & Stich, 1992), but requires more detailed redescription. D. pulex is typical for ponds and temporary waters, and records from lakes may belong in fact to D. pulicaria (Hrbacek, 1987). Indeed, the latter author has
49 found the species in Lake Ohrid, whereas the status of D. pulex from Neusiedlersee remains unclear. On the other hand, the problem of conspecificity of the European and typical American representatives of D. pulicaria is unsolved. The latter frequently hybridises with D. pulex (Hebert et al., 1989) and was long confused with D. pileata (Hebert & Finston, 1996). The American and European members of this complex differ much genetically (Colbourne et al., 1998). Species of Ceriodaphnia are not recorded in the pelagic zone save for in the shallow Neusiedlersee and Lakes Ladoga and Onega where they are mostly distributed closer to the shore. So far, this genus has not been revised taxonomically (Korovchinsky, 1996). The genus Bosmina provides an example of high species diversity, especially in Lakes Ladoga and Onega, where it is represented by eight and seven taxa of species rank, respectively. Morover, some of them have by two or three stable morphological forms usually listed as subspecies, thus increasing the general number of taxa up to 14 and 10, respectively. Last time, the taxonomy of this genus, especially in Europe, was attempted to be revised (Lieder, 1983a, 1996), however, many questions remained unsolved. In particular, the enormous variability of European forms of Bosmina is suggested to be a result of extensive introgressive hybridization (Lieder, 1983b, 1996; Hofmann,1991). Hybrids have now been detected in Arctic Bosmina (Little et al., 1997) but probably they are not widely distributed because genetic analysis of North American Bosmina did not reveal evidence of interspecific hybridization (DeMelo & Hebert, 1994). Lakes Ladoga and Onega are listed among the few well studied lakes with respect to total cladoceran species richness (Dumont & Segers, 1996). However, it is evident that all species identifications of their fauna are routine and those of Daphnia and Bosmina need further attention. The example of Neusiedlersee is especially typical of the necessity of further taxonomic reevaluation. Past identifications of its three cladoceran taxa were all incorrect (Ponyi & Devai, 1979; Herzig, 1979; Forro & Metz, 1987; Korovchinsky, unpubl. data) (Table 1), Daphnia pulex awaits further reidentification. Nine large Asian lakes are comparatively more diverse in their size, morphometry, hydrochemistry, and geographic location, being situated both in the temperate and tropical zones. On the whole, 30 cladoceran taxa of species rank have been recorded in these lakes, of which from one (Sevan) to 12 (Biwa) are known in particular sites (Table 2).
The Diaphanosoma are especially diverse here: four previously known species were recently supplemented by D. mongolianum, D. orghidani, D. cf. orientalis and D. dubium. Members of the D. brachyurum-species group occur in Baikal in the inshore zone only, and possibly in Lake Khanka but need further confirmation. Of seven Daphnia taxa, two (D. balchashensis and D. biwaensis) seem to be synonyms of D. galeata and D. pulex-like species, although their exact status is not clear. Records of D. cucullata and D. cristata in Lake Balkhash also require confirmation. ‘D. longispina’ in Lakes Sevan and Biwa turned out to be D. hyalina and D. galeata, respectively (Glagolev, 1986; Tanaka, 1992) (Table 2). Many Ceriodaphnia species are mainly littoral, although C. reticulata, C. cornuta and C. dubia permanently live in the pelagic zone of Lakes Kinneret and Toba. The taxonomic status of these species includes species complexes (Berner, 1985, 1999), and remains unclear. According to Smirnov (1976), several Moina (M. dubia, M. rectirostris, M. macrophthalma, M. chankensis) have been synonymised with M. micrura, thus reducing the composition of the group in different lakes to a rather uniform state. However, the latter variable taxon needs further revision as potential species-group. The presence of M. macrocopa among planktonic species in Lake Biwa seems odd, as normally it is restricted to ponds and temporary waters. The identity of Chydorus sphaericus and Leptodora kindti in Lakes Khanka and Biwa with the typical forms of these species also needs confirmation as the cladoceran fauna of Eastern Asia is supposed to be specific (Korovchinsky, 1996). In the result of recent revisions, the species composition of Khanka and Biwa has mostly been changed compareing with other reviewed Asian lakes: four and six taxa appeared to be new for each, respectively (Table 2). The species composition of East African plateau lakes is comparatively less diverse consisting of 17 taxa. Each particular lake yields from two (Lake Zwai, Ethiopia) to 12 (Lake Victoria) pelagic cladoceran species. Diaphanosoma mongolianum and D. excisum are prominent common lake species. The former has been recorded in all Ethiopian Rift Valley lakes except Chala, Koka, and Abijata (Korovchinsky, 1987, unpubl. data). The latter lake was reported as lacking
50 cladoceran fauna at all (Wodajo & Belay, 1984) but my examination of a sample from the lake revealed Daphnia barbata (unpubl. data). The presence of D. orghidani in Lake Tana is the second record of this species in Africa. Also, the finding of representatives of D. brachyurum-group in Lake Victoria seems unusual but in fact similar diaphanosomas had been described from some lakes of the east (Harding, 1942) and south (Korinek, 1984) of the continent. Preliminary examination of daphnids from Lake Tana revealed D. hyalina instead of the usually listed D. longispina (Schwenk et al., 1998), a taxon which needs further revision throughout the continent. On the whole, the status of only few pelagic cladoceran species of large lakes is stable in any degree, first of all the representatives of Diaphanosoma and Daphnia. The species composition of Ceriodaphnia, Moina and the Bosminidae usually remains to be known. In fact, most of modern taxonomic studies mainly focused on the cladoceran groups characteristic of temporary, littoral, and benthic habitats (e.g. Frey, 1973, 1980, 1991; Hann, 1982, 1995; Berner, 1985, 1999; Smirnov, 1992, 1996; Orlova-Bienkowskaja, 1998). Thus, at least in the eastern hemisphere pelagic cladocerans (North American representatives of Daphnia and Bosmina are extensively studied by Prof. P.D.N. Hebert and his followers: e.g. Hebert et al., 1989; DeMelo & Hebert, 1994; Hebert & Finston, 1996; Little et al., 1997; Colbourne et al., 1998) appear to be much less studied taxonomically in spite of their primary use in hydrobiological surveys. In general, seventeen lakes of twenty nine under consideration proved to have species of diaphanosomas (D. mongolianum, D. lacustris and D. orghidani) different from those previously listed (D. brachyurum, D. modigliani and possibly D. sarsi). New Daphnia species (mostly D. hyalina and D. galeata) have been found in seven lakes, and their hybrids in three lakes (Constance, Balaton and Baikal). being studied morphologically and genetically only in Constance (Flössner & Kraus, 1986; Wolf, 1987; Weider & Stich, 1992). For most European and Asian lakes, only the species attribution is verified in the present faunistic revision. Only in Lakes Constance, Khanka and Biwa, the cladoceran species diversity has been enriched by one to three species of Limnosida and Diaphanosoma, and two kinds of Daphnia hybrids. On the other hand, the cladoceran fauna of practically all African lakes under consideration has been supplemented by one to two Diaphanosoma species.
The complex nature of large lakes includes differences in morphology, geology, climate, and the location of river inflows within the systems which much influence patterns of distribution of individual species in space and time (Patalas & Salki, 1992). Lewis (1987) suggested succession as the main mechanism that maintains species diversity in fresh waters; in the tropics episodes of succesion are more numerous and irregular. All these factors complicate species inventory. It should be stressed that only small numbers of samples from large lakes have been analysed in the course of modern studies. Further investigation of material collected in different seasons, may possibly reveal additional unknown taxa. Reference data for the revision of zooplankton composition of lakes studied for many years are limited. Old samples are either not available or hardly accessible. Descriptions and drawings of particular cladoceran are not detailed enough or lacking (e.g. for Lakes Ohrid, Kinneret, Lanao). Some old descriptions undoubtedly may be useful for comparisons (e.g. those of Daday, 1907; Werestchagin, 1916; Green, 1967 on African lakes, Ueno, 1939 on Lake Khanka or Richard, 1894, Brehm, 1933, and Johnson, 1956 on Lake Toba). Recent and adequate data are few, and available only on daphnids of Lakes Constance (Einsle, 1978; Flössner & Kraus, 1986; Wolf, 1987; Weider & Stich, 1992), Balkhash (Glagolev, 1986), Baikal (Smirnov, 1984), Biwa (Tanaka, 1992), Diaphanosoma of Lakes Balaton, Kinneret, Issyk-Kul, Khanka, Toba, Zwai (Korovchinsky, 1987, 1991, 1992, 1998a,b), and Moina of Lake Khanka (Smirnov, 1976). Thus, the bulk of cladoceran identifications in large lakes is not documented well enough, whereas modern taxonomic practice demands analysis of local populations in morphological and molecular details (Frey, 1982, 1987; Hebert, 1985; Korovchinsky, 1996; Hebert & Taylor, 1997; Weider et al., 1999). In general, usually five to eight cladoceran species inhabit the pelagic zone of large European lakes with the exception of Lake Ohrid (two or three species). In more northern, very large, lakes, Ladoga and Onega species richness is higher, although only six to nine species permanently dominate their open parts. Presumably an equal species number is present in temperate Asian lakes, although the exact species number distributed in the pelagic zone of Balkhash and Biwa is not known. At the same time, Lakes Sevan and IssykKul seem exceptional, housing just one or no species in the open part (in the latter lake cladocerans seem to be distributed in bays and closer to the shore). On
51 the other hand, the presence of three or four species in the tropical Lakes Lanao and Toba indicates comparatively lower species diversity, although this requires more precise definition. Seven to 14 species have been recorded in larger African lakes Victoria, Albert, Edward, and Tana and two to five species in smaller Ethiopian lakes Zwai, Langano, and Awassa (excluding Chydorus present sporadically). All these lakes are more or less elevated and their cladoceran fauna is mixed with tropical–subtropical and temperate species complexes. The outcome of present faunistic review supports rather than refute the suggestions of interlatitudinal equivalency of planktonic species diversity (Lewis, 1987; Dodson, 1992; Dumont & Segers, 1996) and its simplification in ancient lakes (Dumont, 1994), although such comparisons may still suffer from a small number and natural diversity of lakes under consideration. Undoubtedly, such generalizations will become more substantial after taxonomic revisions in groups of pelagic taxa which are currently erroneously regarded as rather well investigated.
Addendum Very recent study of one additional sample from the northern part of Lake Biwa (12.11.1993, leg. Dr S. Tanaka) revealed Diaphanosoma macrophthalma Korovchinsky et Mirabdullaev, 1995, another new species for this lake and Japan in general.
Acknowledgements I thank all colleagues for materials sent at my disposal and also Prof. H. J. Dumont (Univ. of Ghent, Belgium), Dr N. G. Sheveleva (Inst. of Limnology, Irkutsk, Russia), W. Hollwedel (Varel, Germany), and Dr A. S. Golubtsov (Inst. of Ecology and Evolution, Moscow, Russia) for valuable consultations and literature support. Prof. H. J. Dumont and Prof. N. N. Smirnov have kindly edited the first draft of the manuscript. Corrections of one of the anonymous reviewer greatly emended the manuscript too. This work was supported by the Russian Foundation for Basic Research (grant N 99-04-48969).
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