the littorina transgression in the western baltic sea as indicated by subfossil chironomidae...

WOLFGANG HOFMANN1 and KYAW WINN2

1Max-Planck-Institute of Limnology, P.O. Box 165, D-24302 Plön, GermanyEmail: [email protected]

2Institute of Geosciences, Christian Albrecht University, Ludewig-Meyn-Straße 10, D-24118 Kiel, GermanyEmail: [email protected]

The Littorina Transgression in the Western Baltic Sea as Indicatedby Subfossil Chironomidae (Diptera) and Cladocera (Crustacea)key words: Western Baltic Sea, Littorina Transgression, Chironomidae, Cladocera, Foraminifera,

lithostratigraphy.

Abstract

Subfossil remains of chironomids, cladocerans and foraminifers found in four sediment cores fromthe Vejsnaes Basin, Neustadt Bay, Mecklenburg Bay, and Kiel Fjord were analyzed. The faunal assemb-lages from below the Littorina Transgression horizon represented a rich cladoceran and chironomidfauna typical of freshwater habitats. Above the transgression horizon chydorids disappeared, foramini-fers appeared and the diverse chironomid fauna was replaced by an assemblage of three taxa, Cluniomarinus, Chironomus salinarius, and Cricotopus/Halocladius, which are typical of brackish/marine con-ditions.

1. Introduction

With the retreat of the ice masses at the end of the late Weichselian glaciation, narrowand elongated freshwater lakes developed in the Western Baltic Sea, with the largest andbroadest in the Mecklenburg Bay (SAURAMO, 1958; KOLP, 1964; DIETRICH and KÖSTER,1974; WINN et al., 1984; BJÖRK, 1995). The presence of Hystrichosphaeridae (Dinoflagella-te cysts) in these older sediments in the westernmost area (WINN et al., 1982) should beattributed to reworked Eem sediments that ring the western Kiel Bay (LAFRENZ, 1963) rat-her than to interconnections with the open sea. Later Preboreal observations of brackishwater diatoms in the Mecklenburg Bay (ERONEN et al., 1990) could not be fully explainedand suggest a possible influence of the sea even at this early period. During the followingYoldia Sea phase (10,300–9,500 a BP, conventional 14C-age) of the Baltic when the seabroke through the Narke-Staits (BJÖRK, 1995), the morphological high in the Darss area formed a natural dam that separated the western area from it. The southward extent of thesea through the Kattegat up to the Great Belt could be documented through brackish waterForaminifera (WINN, 1974). With isostatic uplift, this seaway closed and during the follo-wing Ancylus Lake (9,500–8,000 a BP), the lake level rose above 12 m and broke throughthe Darss threshold (KOLP, 1986; ERONEN et al., 1990). Reflection seismic profiles sugge-sted that the now very large freshwater lake in the Mecklenburg Bay was probably inter-connected with the main Ancylus Lake, and was part of the outflow system through the KielBay and the Belt Seas to the North Sea (LEMKE, 1998).

The marine transgression into the Baltic Sea through the Great Belt took place around8,340 a BP conventional 14C-age (= 9,370 calibrated 14C-years BP) with a stagnation of thesea level to about 8,100 a BP. By 8,000 a BP, both the Kiel and the Mecklenburg Bays weremarine (WINN et al., 1983), with salinities and temperatures comparable to the present dayKiel Bay waters.

Internat. Rev. Hydrobiol. 85 2000 2 – 3 267–291

The aim of this study is to investigate whether the shift from freshwater habitats tobrackish water conditions is reflected by subfossil faunal assemblages from various areas ofthe present Western Baltic Sea. This will be demonstrated by a comparison of the faunalassemblages found before and after the transgression. In two cases, the cores reach back tothe Younger Dryas period and the faunal changes at the Late Glacial/Holocene boundariesare included in the analysis. The analysis is founded upon faunal elements from differenthabitats. The Bosmina species represent the plankton, the chironomids and Foraminiferabelong to the littoral and profundal benthos, and the chydorids are elements of the littoralbenthos.

An analysis of Holocene sediments from the Central Baltic Sea (Bornholm Basin, GdanskBay) has shown that high concentrations of subfossil remains from freshwater Cladocera(Crustacea) and Chironomidae (Diptera) in lower sediment sections represent a former di-verse freshwater fauna and thus reflect freshwater conditions at that time. An increase in thedensities of Bosmina longispina at the expense of B. longirostris and a drastic decrease inchydorid and chironomid densities indicated the shift to brackish conditions. Uncertaintiesremained concerning the demarcation of the freshwater/brackish horizon and the synchro-nization with the diatom zonation. The data also indicated that the endemic brackish waterform of Bosmina longispina descended from the freshwater population which occurredduring the freshwater phase of the Baltic Sea (HOFMANN, 1987a).

2. Material and Methods

The sediment core 15391 was taken from the Vejsnaes area (WINN et al., 1982; WINN and AVER-DIECK, 1984) while core nos. 15342 and 15386 were from the Neustadt Bay and the Sagas Bank areain the western Mecklenburg Bay, respectively (WINN et al., 1983). Core 14855 was raised from a waterdepth of 12 m in the Kiel Fjord off Hotel Maritim (SIMANOWSKY, 1985). The positions and waterdepths of the cores were listed in Table 1 of WINN et al. (1986) and shown in Fig. 1. The chronozonesand the position of the basal horizon of the transgression refer to WINN et al. (1982, 1983), WINN andAVERDIECK (1984), and SIMANOWSKY (1985).

The Littorina Transgression is manifested in the studied sediment cores, either through an erosionalcontact (e.g., core no. 15391) or through a gradational change from freshwater lake marls to detritalgyttjas (e. g., core no. 15342). In the latter case, the contact has been identified after careful study ofthe sediment X-ray radiographs supported by sedimentological and palaeontological/palynological evi-dence. The high proportion of detrital organic matter in the gyttja has been attributed to the erosion ofthe inundated land areas following the rapid rise of lake level after the breakthrough of the sea acrossthe thresholds in the Great Belt (WINN and AVERDIECK, 1984). The δ13C measurements carried out onorganic carbon from similar sediment sequences in the Kiel Bay (WINN et al., 1988) indicated a signi-ficant terrigenous provenance of the organic detritus.

About 5 to 20 g of fresh sediment sampled from the middle of the core was boiled in 10% KOH ona magnetic stirrer. The sediment fraction >200 µm was examined under a stereo-microscope at 20x forchironomid analysis. The larval head capsules were picked out, dehydrated in 96% alcohol and mount-ed in Euparal (HOFMANN, 1986a). In two profiles (Neustadt 15342, Mecklenburg 15386) the sedimentfraction 100–200 µm was also analyzed separately to estimate the losses through the coarse mesh sizeof 200 µm (WALKER and PATERSON, 1985). Chironomid taxonomy follows WIEDERHOLM (1983). Taxo-nomy of Tanytarsus, Chironomus salinarius, and Cricotopus/Halocladius is after HOFMANN (1971a,1985). The Clunio material mainly consisted in the ventral part of the head capsules with the mentum.For a few of the more complete specimens, identification was made on the basis of the S I seta of thelabrum which has numerous branches and the proportions of the antenna. Both characters differ fromanother marine taxon Thalassosmittia thalassophila (BEQUAERT and GOETGHEBUER), which is not knownfrom the Baltic Sea (STRENZKE and REMMERT, 1957).

The cladoceran remains were counted in the fraction >100 µm at 80× magnification in subsamplesequivalent to 0.04 to 3.5 g wet sediment (s. FREY, 1986). Chydorid taxonomy follows FLÖSSNER (1972)and Bosmina taxonomy refers to LIEDER (1996). Subfossil Foraminifera were also counted in the cla-

268 W. HOFMANN and K. WINN

doceran samples. They were not analyzed taxonomically and were considered as a group. All the For-aminifera remains were of the same type as were found in sediment cores from the Central Baltic (HOF-MANN, 1987a) and belonged to the genera Ammonia and/or Elphidium (s. LUTZE, 1965). The chydoridassemblages were compared by cluster analysis on the basis of their percentage composition with theEuclidean distance as distance measure and average linkage as linkage rule (software: Statistica). Thechydorid species diversity index (Hs) was calculated according to LLOYD and GHELARDI (1964).

3. Results

3.1. Neustadt Bay Core 15342

This core was raised from the southwestern depositional basin of the Neustadt-LübeckBay (WINN et al., 1983). From among the cores investigated during this study, this is theonly core where both the transgression horizon and the fresh-brackish water lake marls/gyt-tja/marine clay boundary are present. The stratigraphic succession with the pollen zonation(after OVERBECK, 1975) is given below:

Littorina Transgression in the Western Baltic 269

Figure 1. Western Baltic Sea – location of the cores: 15391 (Vejsnaes Basin), 15386 (MecklenburgBay), 15342 (Neustadt Bay), and 14855 (Kiel Fjord).

Pollen zones Depth (cm) Lithological description0 Sea bottom, 23 m water depth.0–8 Mud, dark grey with H2S smell.

X-XII 8–80 Clay, brownish grey, with H2S smell, alternately lighter anddarker

X 80–99 layers, with thin silty lenses, sandier to base. Thinly beddedbelow

IX-VIII 99–222 324 cm. Fragments of Artica islandica, Abra alba, andVIII 222–340 Cerastoderma edule in layers. Hydrobia ulvae at 308 cm.VIIIa 340–386 Clay gyttja, with abundant detritus, micro current bedded,

and fine sand laminations; upper part bioturbate.Transgressional contact.

VIIIa 386–415 Lake marl, alternately light and dark grey, partially laminat-ed with abundant well preserved shells of Valvata piscinalispiscinalis, V. cristata, Bithynia tentaculata, Lymnea baltica,Sphaerium corneum, and ostracods.

IV 415–429 Lake marl, very dry (water content <20%) and hard, withshell fragments.

IV 429–477 Clay gyttja, dark grey, well bedded (2–3 cm), with abundantdetritus, non-bedded in upper 14 cm.

477–481 Sand, greyish brown, medium grained with shell fragments.481–485 Sand, greyish brown, fine grained with ostracods.485–494 Silt, brown, slightly sandy, layered (1 cm).

The samples included sediments from the Younger Dryas, (Boreal 2), Atlantic and Sub-atlantic. The Preboreal was missing in this core. Because of this very large erosional gap inthe succession, we have had no opportunity to investigate the Preboreal brackish water influ-ence discovered by KOLP (1964) and confirmed by ERONEN et al., (1990) in the Mecklen-burg Bay, and also observed by WINN (1974) in the Great Belt. However, WINN (1974)attributed this brackish water incursion to a younger period (8,800 a B.P., conventional 14C-age) than ERONEN et al., (1990) who assigned it to an older phase (9,500 a B.P.).

The transgression horizon indicated by a change from lake marls to detrital gyttja wasobserved at 386 cm. The contact with the well-bedded grey clays at 340 cm marks the onsetof marine conditions in the area.

3.1.1. Chironomidae

In 17 samples from sediment depths of 30 to 460 cm 1,584 chironomid head capsuleswere found in sample sizes ranging from 6.4 to 17.9 g fresh sediment. The range of abun-dance of the remains (1.3–24.7 specimens per g sediment) decreased in the section above290 cm. With the exception of the samples from 190 cm (13.5 specimens) and 290 cm (12.5specimens), the number of head capsules per sample ranged from 29.5 to 191.5 specimensper sample (mean value: 111 specimens/sample). No head capsules were found in the490 cm sample (sand) (Fig. 2).

The chironomid material included 41 taxa. Their distribution indicated significant quanti-tative and qualitative changes through the core and four separate faunal zones.(1) In the Younger Dryas section (430–460 cm) a relatively poor fauna was found with only

11 taxa predominated by Tanytarsus spp. (45%), Corynocera ambigua (21%), Chiro-nomus gr. anthracinus (8%), and Cladopelma gr. lateralis (6%).

(2) A highly diverse assemblage with 34 taxa occurred in the Atlantic section (350–390 cm)the prevalent taxa being mostly Tanytarsini: Tanytarsus spp. (25%), Cladotanytarsus(12%), Tanytarsus gr. chinyensis (6%), and Psectrocladius (4%).


(3) A decrease in the number of taxa (10) and a shift in predominance of Chironomus gr.plumosus (36%) and Dicrotendipes (27%) was observed in the 330 cm sample.

(4) Fig. 2 indicates a fundamental change of the chironomid fauna in the following uppersection of the core (310–30 cm) where 96% of the head capsules belonged to only threetaxa: Clunio marinus (68%), Cricotopus/Halocladius (15%), and Chironomus salinari-us (13%).

In the 290–490 cm section 110 of 879 head capsules, i.e., 12.5% of the total, were foundin the 100–200 µm fraction. From 260 cm to the top of the core, this proportion was di-stinctly higher. The specimens from the 100–200 µm fraction accounted for 62.9% of thetotal, which was due to the high frequencies of Clunio marinus. 427 of 634 specimens(67.3%) of this species were found in this size fraction.

3.1.2. Cladocera and Foraminifera

A distinct peak in the density of cladoceran remains was observed in the 350–390 cm sec-tion ranging from 2340–3225 specimens/g sediment (Fig. 3). In the adjacent sections below(430–460 cm) and above (310–330 cm) 112–556 specimens/g were found. Towards thetop, densities rapidly decreased and in the 30–230 cm only 0–6 specimens/g were present.The proportion of the bosminids relative to total cladocerans decreased from 24–37% in the370–460 cm section to 11% at 330 cm. Above this horizon, percentages were not calculat-ed due to insufficient material.

The genus Bosmina was represented by three taxa: Bosmina longirostris (O. F. MÜLLER),Bosmina longispina (LEYDIG), and Bosmina longicornis kessleri (ULJANIN). They showed avery similar pattern of vertical distribution with peak densities in the 350–390 cm section.In this horizon, B. longispina had slightly higher densities (320–440 specimens/g) than theother two species (120–270 specimens/g). In the sections below (430–460 cm) and above(310–330 cm), B. longirostris was more abundant than B. longispina and B. l. kessleri. Thelatter was absent below 390 cm. Above 310 cm, only eight Bosmina specimens were foundin total.

The Chydoridae were represented by 27 taxa, only 12 of which were found in the Youn-ger Dryas layers with a density of 70–300 specimens/g. In the 350–390 cm section, a significant increase both in the number of taxa (26) and number of specimens (1700–2500 specimens/g sediment) occurred. Above this zone chydorid density decreased again(260–330 cm: 30–500 specimens/g) and above 260 cm only single specimens were recor-ded.

These quantitative changes were combined with shifts in the structure of the assemblages.At 430–460 cm Acroperus harpae, Chydorus sphaericus, Eurycercus lamellatus, and Alo-nella nana predominated and accounted for 89% of the material. In the 370–390 cm sec-tion there was a more even distribution of the taxa: seven species, each species was around10%, accounted for 58% of the chydorids: Eurycercus lamellatus, Camptocercus rectiro-stris, Acroperus harpae, Alona affinis, Alona quadrangularis, Alonella nana and Alonellaexcisa. In contrast, at 350 cm the three most abundant species (Alona quadrangularis, Alonaaffinis, Monospilus dispar) accounted for 59% of the material indicating significantly lowerdiversity.

A stronger shift occurred at 330 cm where 74% of the chydorids belonged to the two mostabundant species, Chydorus sphaericus and Alona rectangula. Above 330 cm the number ofspecimens counted was so low that a calculation of percentages was not meaningful. In the290–310 cm section Chydorus sphaericus remained the most abundant species.

Cluster analysis arranged the four samples from the 370–460 cm section on the samebranch. As Alona quadrangularis and Alona affinis were more frequent at 370–390 cm thanin the section below two subunits were separated within this Cluster. The 350 cm and



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330 cm samples each represent well isolated units based on their specific percentagedistribution, i.e., at 350 cm there were high frequencies of Alona quadrangularis, Alona affi-nis, and Monospilus dispar, and at 330 cm there was a particularly high proportion of Chy-dorus sphaericus.

The compositional changes in the chydorid assemblages are also reflected by the speciesdiversity index which was low in the Younger Dryas (Hs: 2.36–2.57), increased in the350–390 cm section (Hs: 3.40–3.89) and decreased again at 330 cm (Hs: 2.17). Above thishorizon the limited material prevented a calculation of the diversity index.

Remains of Foraminifera were only found in the 0–310 cm section with densities of 2–51specimens/g (mean value: 18) and peaks at 60 cm 230 cm.

3.2. Mecklenburg Bay Core 15386

This core was retrieved from the southwestern part of the Mecklenburg Bay where rem-nants of the older beds are present in the boomer profiles (WINN et al., 1983). Consequent-ly, we could recover the sediment sequence from glacial till to freshwater lake marls withthe Littorina Transgression horizon and some marine sediment cover. The succession isdescribed below.

Pollen zones Depth (cm) Lithological description0 Sea bottom, 21 m water depth.0–8 Mud, dark grey, sandy, with A. islandica.10–50 Sand, medium grained, silts with pebbles, badly sorted.

Trangression contact.VII 50–117 Lake marls, grey, alternating dark and light layers, with V.

piscinalis piscinalis, V. cristata, B. tentaculata, Planorbisgyraulis, S. corneum, Pisidium supinum; seeds of Najasmarina and oogonia of Characeae, especially in the upper-most and basal layers.

117–162 Sand, fine grained, grey, silty with plant matter.162–184 Paleosol with glacial till and sand, greenish to reddish yel-

low, with roots.184–268 Glacial till, grey, sandy.

Samples were taken from 10–185 cm sediment depth. The 50–113 cm section has beendesignated as the Boreal 2 period. The layers above and beneath have not been dated. Thetransgression horizon is situated at 50 cm (WINN et al., 1983).

3.2.1. Chironomidae

Sample sizes ranged from 8.2–25.1 g fresh sediment. The chironomid material consistsof 1232 head capsules from 38 taxa. Density was low in the 130–155 cm section (0.05–5.4specimens/g sediment) and above 50 cm where in three samples totalling 48 g sediment onlytwo head capsules were found (0.04 specimens/g) (Fig. 4).

Shifts in the predominating taxa divide the section below 50 cm into four zones:(1) At 145 cm Tanytarsus gr. chinyensis (31%) and Tanytarsus spp. (20%) were most fre-

quent.(2) The 100–120 cm section was characterized by predominance of Microtendipes

(21–31%), while in the samples from 90 cm and 100 cm Corynoneura was predomi-nant (29%).



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(3) Above this horizon (53–80 cm), percentages of Chironomus gr. plumosus increasedfrom about 30% to >50%. The two head capsules found above 50 cm were Clunio mari-nus.

In total, 438 of the 1232 head capsules from this core, i.e. 35.6%, were found in the100–200 µm size fraction. Percentages ranged from 13.6 to 60.1% and were particularlyhigh at 90 cm (49.5%) and 100 cm (60.1%) where Corynoneura was most frequent. 86 ofthe 98 specimens from this genus were from this sediment fraction and also 16 of 20 Para-kiefferiella specimens and 51 of 71 not identified small Orthocladiinae. In the Chironomi-nae the proportion of the head capsules from this fraction was generally lower and account-ed for 40.9% of the total material in Corynocera ambigua, 34.5% in Tanytarsus spp., 23.3%in Dicrotendipes, and 19.3% in Microtendipes.

These data as well as the results from core 15342 show that washing in a 200 µm sieveleads to substantial losses of chironomid head capsules as has been already demonstrated byWALKER and PATERSON (1985). Due to these losses density of head capsules per g sedimentare underestimated which is important if this parameter plays a major role with respect tothe interpretation of the results. However, if small Orthocladiinae are predominant neglectof the 100–200 µm fraction also affects the percentage structure of the subfossil assemblage.In the cores 15342 and 15386 the frequencies of Clunio marinus, Corynoneura, Parakief-feriella, and the group of unidentified Orthocladiinae were heavily underestimated if onlythe fraction >200 µm was considered. On the other hand, the major faunal shift observed,i.e., the change from a diverse chironomid fauna to a poor assemblage of three specific taxa,is not affected by the use of a coarse mesh size.


Density of cladoceran remains was low in the 130–155 cm section (15–198 specimens/g),increased in the 53–120 cm section to an average density of 2,900 specimens/g, (range:1,123–5,320) and was extremely low in the 0–50 cm section (0.4–10 specimens/g) (Fig. 5).

Bosmina remains were found from 53–155 cm and Bosmina longispina was present in the10 cm sample. The latter was the most abundant taxon among the bosminids with a maxi-mum density of 516 specimens/g, while maximum densities of B. longisrostris and B. l. kes-sleri were 73 and 15 specimens/g, respectively. B longirostris and B. longispina were mostabundant in the 100–120 cm section. B. l. kessleri was represented by only nine specimensand their distribution pattern within the 60–145 cm section had no significance.

In the 115–155 cm section, the Bosmina species accounted for 13.4–40.3% (mean value:26.8%) of total Cladocera. The proportion decreased towards the top to 0.7% at 53 cm.

The density distribution of the chydorids followed the pattern for total Cladocera: 13–123specimens/g in the 130–155 cm section, 1,000–5,200 specimens/g between 53–120 cm andonly 10 single specimens in total from 0–53 cm.

The subfossil material included 26 species. With respect to percentage species composi-tion of the assemblages the 120–145 cm section was characterized by predominance of Chy-dorus piger and Monospilus dispar, in the 120–130 cm section together with Alonella nana.The 155 cm sample was different due to the high abundance of Alona affinis, which mightbe an effect of the low number of counted specimens.

The 53–110 cm section represents a relatively uniform assemblage predominated byEurycercus lamellatus, Camptocercus rectirostris, Acroperus harpae, and one Alonella spe-cies. In the 70–110 cm section Alonella nana was predominant, while in the samples from53 cm and 60 cm A. excisa was more frequent.

Accordingly, cluster analysis allowed separation into two main units, e.g., the130–155 cm section characterized by predominance of Monospilus dispar and Chydoruspiger and the 53–120 cm section with high frequencies of the above mentioned species.



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Within the latter cluster, the 120 cm sample has an isolated position due to the high pro-portion of Alonella nana and low percentages of Eurycercus lamellatus, Camptocercus rec-tirostris, and Acroperus harpae. This is also true for the 53 cm and 60 cm samples that havehigher percentages of Alonella excisa than the other samples.

In the Foraminifera only a single occurrence is recorded from the 38 cm sample.

3.3. Vejsnaes Basin Core 15391

This core was raised from the Vejsnaes Channel in the northwestern part of the Kiel Bay(WINN et al. 1982). Boomer profiles showed that over 40 m of postglacial sediments werepresent over the acoustic basement in the channel, unfortunately beyond the reach of ourcorer. Pollen analyses were carried out between 50 cm and 185 cm of this core. The litho-logical succession is given below.

Pollen zones Depth (cm) Lithological description0 Sea bottom, 23 m water depth.0–12 Mud, dark grey, sandy, with A. islandica, Astarte elliptica.12–49 Mud, grey, sandy, strongly bioturbate; basal 1 cm gravelly

(3–5 mm).VII 49–63 Lake marls, light brownish grey, bedding 2–4 cm, with fresh-V–VI 63–97 water molluscs (B. tentaculata, V. piscinalus piscinalis and

S. corneum); plant matter abundant to 63 cm.IV 97–101 Sand, medium grained, with silty streaks.IV 101–110 Clay, grey, with plant remains and shell fragments.IV 110–169 Sand, grey, fine to medium grained, with “floating” coarse

grains (1–2 mm) and a coarse layer at 154–155 cm; someS. corneum.

169–209 Sand, fine grained, clayey in parts, with abundant “floating”coarse grains (1–2 mm).

209–240 Clay, grey, fairly hard, silty.240–250 Alternations (1 cm) of clay, grey, hard, and sand, grey,

medium to coarse grained; mollusc fragments.250–258 Clay, grey, hard.

The samples were taken from the 4–250 cm section of the core that covered the Youn-ger Dryas, Preboreal, Boreal 1 and Boreal 2 periods. The 169–250 cm section and theuppermost 49 cm have not been stratigraphically correlated. The position of the transgres-sion horizon was at 49 cm (WINN et al. 1982).

3.3.1. Chironomidae

In 31 samples with sample sizes between 4.0 and 20.6 g sediment, 588 chironomid headcapsules were recorded. In the 50–250 cm section mean density was 2.9 head capsules/g,with maxima at 55 cm (10.9 specimens/g), 110 cm (8.3 specimens/g), and 170 cm (9.2 spec-imens/g). Above 50 cm average density decreased to 0.4 specimens/g (Fig. 6). Numbers persample (range: 1–109) were mostly <20 with a mean value of 19.0 specimens per sample.Due to these low numbers percentages of the taxa were not calculated.

The numbers of head capsules in the 210–250 cm section, 120–150 cm section and at100 cm were too low to specify the species composition. The remaining sections may beseparated into four faunal zones.



Figu

re6.

Vej

snae

s B

asin

co

re

1539

1 –

Chi

rono

mid

ae

(fra

ctio

n >

200

µm

):

tota

l ch

iron

omid

s an

d m

ost

freq

uent

ta

xa

(num

bers

/g

wet

se

dim

ent)

(for

abb

revi

atio

ns s

ee F

ig.2

).

(1) In the 160–200 cm section (n = 318) Microtendipes (32.7%) and Tanytarsus spp.(17.3%) were the most frequent taxa and Psectrocladius (8.5%), Paratanytarsus (6.9%),and Micropsectra (5.3%) were dominant.

(2) In the 110 cm sample (n = 47) Corynocera ambigua (25.5%), Tanytarsus spp. (17.0%),and Microtendipes (12.8%) accounted for 55.3% of the chironomids.

(3) Above this zone (50–95 cm, n = 131) a compositional change towards predominance ofDicrotendipes (26.7%) and Chironomus gr. plumosus (24.4%) occurred.

(4) Finally, in the 0–50 cm section (n = 36) Clunio marinus (61.1%) clearly predominatedand Cricotopus/Halocladius was second in abundance (16.7%).


In the 50–120 cm section, the density of cladoceran remains ranged from 1,200 to 7,300specimens/g (mean value: 3,860 specimens/g) with an exceptionally low value (163 speci-mens/g) in a thin sand layer at 100 cm (WINN et al., 1982) while in the 160–190 cm sectiondensity was much lower (range: 78–320 specimens/g). In the remaining horizons, 4–45 cm,130–150 cm, and 200–250 cm, only less than 20 specimens/g were found in most cases(Fig. 7).

Bosmina species were not present in the 200–250 cm section. From 40 cm to 190 cm sedi-ment depth the proportion of Bosmina remains as percentage of total cladocerans averages5.2%, if the peak values of 21.4% at 100 cm and 20% at 150 cm are not included. In the50–75 cm section the values were particularly low (0.5–1.9%).

In this core, only two Bosmina species, B. longirostris and B. longispina were found thelatter of which predominated with maximum densities of 71–175 specimens/g in the65–95 cm section. Maximum frequencies of B. longirostris (36–63 specimens/g) occurredin the 95–120 cm section. This species was absent in the uppermost 33 cm section of thecore while B. longispina was still present at very low densities of 0.4–3.8 specimens/g.

The vertical distribution of chydorid densities follows the pattern of total cladocerans inFig. 7, as frequencies of Bosmina were very low. High densities of total cladocerans in the50–120 cm section were due to maximum densities of the chydorids ranging from1,100 –7,200 specimens/g. Densities sharply declined at 45 cm.

There were 25 chydorid species present in the material from this core. Some taxa wererestricted to the Holocene section and did not occur in the Younger Dryas: Alona guttata,Pleuroxus trigonellus, Anchistropus emarginatus, Pseudochydorus globosus, Leydigia acant-hocercoides, and Kurzia latissima. Species such as Camptocercus rectirostris, Alona costata,Alona rectangula, Graptoleberis testudinaria, and Alonella excisa were more frequent in theHolocene than in the Late-Glacial samples. A third group of species did not show clear diffe-rences in the frequencies from Holocene and Late-Glacial layers: Acroperus harpae, Alonaquadrangularis, Alona affinis, Monospilus dispar, Alonella nana, Chydorus piger, and Chy-dorus sphaericus, while Acroperus elongatus was frequently found in the Late Glacial period.The material from the upper 33 cm section of the core consists of single findings of 14 taxa.

Cluster analysis separated three units, i. e., the sections (1) 180–190 cm, (2) 95–170 cm,and (3) 40–85 cm. Cluster 1 is distinguished by high proportions of Acroperus elongatusand Monospilus dispar. Cluster 2 has high percentages of Alonella nana (mean percentage:26.3%) and low percentages for Alona rectangula (2.4%) and Chydorus sphaericus (9.4%).In Cluster 3 proportions of Alona rectangula (18.2%) and Chydorus sphaericus (22.7%)were high and the percentage of Alonella nana (15.1%) was lower than in the section below.

With respect to number of species and percentage distribution, the Late-Glacial and Holo-cene assemblages were rather similar, therefore there was only a slight difference in themean species diversity index which was Hs = 2.78 for the Late-Glacial (range: 2.47–3.14)and Hs = 2.95 for the Holocene (range: 2.60–3.21).



Figu

re7.

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e 15

391

– Fo

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Cla

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ra,

and

Bos

min

asp

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s (n

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sed

imen

t);

Bos

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aas

per

cent

age

of t

otal

Cla

do-

cera

(no

t ca

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ated

for

the

4–

33cm

, 13

0–

150

cm,

and

200

–25

0cm

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tions

); c

hydo

rid

spec

ies

dive

rsity

ind

ex (

not

calc

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he 4

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130

–15

0cm

, an

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0–

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per

cent

ages

of

chyd

orid

spe

cies

(+

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ates

occ

urre

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) (f

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ions

see

Fig

.2).

Foraminifers only appeared in the 0–45 cm section of the core. Mean density was 48 specimens/g (range: 10–110 specimens/g).

3.4. Kiel Fjord Core 14855–1

This gravity core was retrieved from the western flank of the inner Fjord. A change fromlimnetic gyttja/marls to marine muds was encountered at 420 cm (SIMANOWSKY, 1985). Pol-len analyses have not been carried out on this core. One 14C-date is available from the peatnear the base of the core. This succession is given below.

Depth (cm) Lithological description0 Sea bottom, 12 m water depth.0–8 Mud, dark grey, with silty to very fine grained streaks, organic matter, and

some bioturbation.8–19 Mud, brownish grey, with a few silty streaks, more bioturbate.20–40 Mud as above, with worm tubes.40–400 Clay, brownish grey to dark greenish grey, silty to very fine grained

(40–100 cm, 280–330 cm), with H2S smell and fissures; higher organicmatter content between 40–90 cm, 160–280 cm and 320–400 cm; sporad-ic dropstones to 1 cm diameter present throughout; shells frequent below380 cm.

400–420 Clay, as above, very sandy, with Macoma baltica, Cardium edule, Nassa-rius reticulus, and Mytilus edule; Transgressional contact.

420–452 Marl to lake marl, laminated, with abundant diatoms.452–476 Peat, very muddy, (457–474 cm, 8 540 ± 120 a BP conventional 14C-age).476–500 Postglacial sands and gravels, not sorted.

30 samples of 2–4 g fresh sediment were taken from the 15–485 cm sediment section.

3.4.1. Chironomidae

At 475 cm and 485 cm no chironomids were found. The remaining 28 samples from the15–465 cm section provided 243 head capsules. The number of head capsules per sampleranged from 1 to 25 with a mean value of 8.7 specimens per sample. In spite of this limit-ed numerical basis a clear distribution pattern appeared which divided the profile into twoclearly distinguished sections (Fig. 8).

There were 69 specimens from 21 taxa in the 425–465 cm section with a mean densityof 4.9 head capsules per gram sediment (range: 1.3–8.0 specimens/g). Microtendipes (17%),Glyptotendipes (14%), and Tanytarsus spp. (13%) were the most frequent taxa.

At 405 cm and 415 cm 2.5 and 3.5 specimens/g were found, respectively, and in the15–395 cm section mean density decreased to 0.8 specimens/g (range: 0.3–1.6 speci-mens/g). Furthermore, a total change in the composition of the chironomid assemblageoccurred. From 0–405 cm three taxa, Chironomus salinarius (56%), Cricotopus/Halocladi-us (31%), and Clunio marinus (30%) accounted for 96% of the chironomid material(n = 160) while only six head capsules from other taxa were found. The 415 cm samplerepresents a transitional position as Chironomus salinarius occurred together with someChironomus gr. plumosus, Endochironomus albipennis, and Glyptotendipes.



Figu

re8.

Kie

l Fj

ord

core

14

855–

1 –

Chi

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frac

tion

>20

0 µm

): t

otal

chi

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ost

freq

uent

tax

a (n

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sed

imen

t) (

for

abbr

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ig.2

).


Figu

re9.

Kie

l Fj

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core

148

55–

1 –

Fora

min

ifer

a, C

lado

cera

, an

d B

osm

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spec

ies

(num

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/g w

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ent)

; B

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as p

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tot

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n);

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orid

spe

cies

div

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ty i

ndex

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t ca

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ated

for

the

15

–40

5cm

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tion)

; pe

rcen

tage

s of

chy

dori

d sp

e-ie

s (+

+ i

ndic

ates

occ

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nces

) (f

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ions

see

Fig

.2).


In the 425–465 cm section mean cladoceran density was 1,340 specimens/g (range:700–2,272 specimens/g). It decreased to 288 specimens/g at 415 cm and from 405 cm to thetop mean density further decreased to 11 specimens/g (range: 0–32 specimens/g) (Fig. 9).

In this core, only one Bosmina species, B. longirostris, was present. At 445 cm and455 cm it accounted for 13–14% of the total cladocerans. This proportion rapidly decrea-sed to about 1% at 415 cm and 425 cm. Maximum densities occurred at 445 cm (140 spec-imens/g) and 455 cm (237 specimens/g). From 0–415 cm only a few specimens were foundin five samples.

In total 22 chydorid species were present in this core with maximum densities of650–2,200 specimens/g in the 425–455 cm section. In the 415 cm sample density was 284specimens/g and above this horizon densities were approximately 10 specimens/g (range:0–32 specimens/g).

Percentage compositions of the chydorid assemblages were only calculated for the415–455 cm section. The data indicate a compositional change within this zone. From435–455 cm several species had proportions >5% in at least two of the samples: Eurycer-cus lamellatus, Alona rectangula, Alona affinis, Graptoleberis testudinaria, Alonella nana,Pleuroxus trigonellus, and Chydorus sphaericus. These seven most frequently found speciesaccounted for 71.8%–82.6% of the total chydorids. At 415 and 425 cm a shift to almostexclusive predominance of Chydorus sphaericus occurred which made up 79.8% (425 cm)and 66.2% (415 cm) of the material. At 415 cm only two species, Camptocercus rectirostrisand Alona rectangula, had percentages > 5% and at 425 cm none of the other species reach-ed a proportion of 5%.

In this case, cluster analysis separated the 415, 425, and 465 cm samples which have highpercentages of Chydorus sphaericus from the 435–455 cm section where proportions of thisspecies were lower, and percentages of Alonella nana, Alona affinis, and Graptoleberistestudinaria were higher.

The high predominance of Chydorus sphaericus lowered species diversity. Thus this indexwas lower (range: 1.40–2.03) at 415, 425, and 465 cm than in the 435–455 cm section(range: 3.14–3.66).

Foraminifers were found to increase towards the top of the sediment core. In the405–435 cm section density was very low (range: 0–3 specimens/g). Above 405 cm meandensity was 18 specimens/g (range: 3–43 specimens/g) with peak values at 75 cm (32 spec-imens/g), 215 cm (40 specimens/g), and 315 cm (43 specimens/g).

4. Discussion

4.1. The Late Glacial Period

Sediments from the Younger Dryas were analyzed in the cores 15391 (Vejsnaes) and15342 (Neustadt Bay). The most extensive chiromomid material from this period exists fromcore 15391. A predominating taxon of the diverse fauna was Microtendipes, which seemsto be a characteristic element of late glacial lake fauna, although the species of this genusare not generally considered as cold-stenothermous. Microtendipes was also abundantlyfound in Older Dryas, Alleröd and Younger Dryas layers of north German lakes and in theOldest Dryas from a Swiss lake (HOFMANN, 1971b, 1978, 1983a, 1983b). Some taxa wererestricted to the late glacial section which are considered to be cold-stenothermous and aretherefore related to a cold climate: Monodiamesa, Heterotrissocladius, Orthocladius conso-brinus, Paracladius, Paracladopelma nigritula, Stictochironomus, Corynocera ambigua,


Micropsectra. Under the climatic conditions of the Younger Dryas they might have occur-red in the littoral zone (HOFMANN, 1983b, 1986a, 1988; WALKER et al., 1991a, 1991b;OLANDER et al., 1997).

In contrast, the Younger Dryas chironomid assemblage from core 15342 was relativelypoor, and of the elements which can be considered as related to that climatic period onlyCorynocera ambigua was present and a predominating taxon. However, this is based onrestricted material from only two samples.

The late glacial chydorid assemblages of core 15391 are clearly subdividable into twounits of which the assemblage of the lowermost part (180 and 190 cm) was characterized by the predominance of Monospilus dispar, Acroperus elongatus, Rhynchotalona falcata,and so far varies from late glacial assemblages found in different European regions (FREY,1958; GOULDEN, 1964; HARMSWORTH, 1968; WHITESIDE, 1970; HOFMANN, 1978, 1983a,1986b). The prevailing species of this association are typical of oligotrophic conditions andobviously reflect the existence of extensive sand areas in the littoral zone (FLÖSSNER, 1972).A fauna in which Acroperus harpae, Alonella nana, and Chydorus sphaericus predominat-ed which is typical of the late glacial period (HOFMANN, 1987b) replaced this assemblage.This fauna has also been characterized as an early Holocene pioneering assemblage (KOR-HOLA, 1992). At the present time these species occur in high frequencies in arctic and sub-arctic regions (HARMSWORTH, 1968; KORHOLA, in press). At the end of this period, a shiftoccurred which resulted in a slight decrease in Alonella nana and increases in Chydoruspiger and Monospilus dispar.

The Younger Dryas section of the Neustadt Bay core 15342 was also characterized bythe predominance of the above mentioned taxa Acroperus harpae, Alonella nana, and Chy-dorus sphaericus. Eurycercus lamellatus had percentages >10%. This can also be consider-ed a typical subarctic association.

In both cores, Bosmina longirostris and Bosmina longispina occurred during the YoungerDryas the former being more abundant.

The present investigations of the faunal associations in the cores did not exhibit any affi-nities to support either marine incursions or nearness to a marine environment for thewesternmost Baltic area during this period.

4.2. The Holocene Section below the Transgression Horizon

Because of their marginal positions in the Mecklenburg Bay where erosion and reworkinghad taken place (WINN et al., 1983) or in the channels where strong currents could producenondepositional phases, we have not found any indications of the marine/brackish precur-sors of the main Littorina Transgression reported in the Great Belt (WINN, 1974), or fromthe main Mecklenburg Bay (KOLP, 1964; ERONEN et al., 1990).

The chironomid assemblage of this period (Preboreal to Boreal) in core 15391 clearly dif-fered from the late glacial association due to the disappearance of the cold-stenothermousand oligotrophic elements, a decrease in the number of taxa, and a shift to a predominanceof Dicrotendipes and Chironomus gr. plumosus. The chironomid fauna reflected more eutro-phic conditions.

In contrast, in core 15432 the assemblage of the Holocene sediments (Atlantic) was clear-ly more diverse than the late glacial fauna indicating a great diversity of littoral habitats.Furthermore, there were some taxa indicative of oligotrophic conditions (Protanypus, Mon-odiamesa, and Corynocera ambigua).

In the dated part of core 15386 (Boreal 2) the chironomid fauna resembles that of core15391 particularly with respect to the predominance of Chironomus gr. plumosus. The undat-ed layer below where Microtendipes predominated and considerable numbers of Corynoceraambigua and Tanytarsus gr. chinyensis were found may originate from the Late-Glacial period.


The restricted material from the section below the transgression horizon from the undat-ed core 14855 indicates that it represents a littoral fauna of a former freshwater lake.

The chydorid assemblage of this period appears in core 15391 as a well-separated unitcharacterized by the lack of species that are typical of oligotrophic conditions, by high abun-dance of Alona rectangula, by high percentages of species occurring in submerged vegeta-tion (Eurycercus lamellatus, Acroperus harpae) and low percentages of mud dwellers (Pleu-roxus trigonellus, Leydigia). It reflects a diverse littoral environment of a mesotrophic/eutrophic lake.

In the Neustadt Bay core 15342 the chydorid association is highly diverse and includestaxa typical of oligotrophic conditions and sandy habitats (Chydorus piger, Monospilusdispar, Rhynchotalona falcata).

Similarly, the Mecklenburg core 15386 indicates the presence of an oligotrophic lake dueto the occurrence of Acroperus elongatus, Chydorus piger, Monospilus dispar, and Rhyn-chotalona falcata. The separation of the 60 cm and 53 cm samples brought about by a shiftin percentages from Alonella nana to Alonella excisa reflects there is a change within theassemblage. Alonella excisa frequently occurs in bogs at low pH conditions (FLÖSSNER,1972) and is considered as acidobiontic (KRAUSE-DELLIN and STEINBERG, 1987). Here, how-ever, the sediment consists of lake marl (WINN et al., 1983) which is inconsistent with acidconditions.

In the Kiel Fjord core the association is characterized by the high abundance of Alonarectangula, the considerable number of mud dwellers (Pleuroxus trigonellus, Leydigia), andby the lack of species typical of sand habitats. It represents an assemblage, which would beexpected in the littoral zone of a eutrophic lake.

In the cores from Neustadt and Mecklenburg Bay three Bosmina taxa were co-occurring:B. longirostris, B. longispina, and B. longicornis kessleri. This coincides with the situationin larger north German lakes from the Boreal to the Subatlantic 1 (HOFMANN, 1978, 1984)and implies that a large water body exists (HOFMANN, 1987b). On the other hand, maximumpercentages of Bosmina species relative to total cladocerans were 37% (15342) and 40%(15386). This so-called planktonic/littoral ratio (ALHONEN, 1970) is rather low when com-pared to Holstein lakes and thus indicates inshore sites (MUELLER, 1964; HOFMANN, 1986,1998).

The occurrence of B. longispina indicates oligotrophic/mesotrophic conditions. This spe-cies is not found in eutrophic lakes and disappeared from north German lakes due to eutro-phication in the late Holocene period (HOFMANN, 1984, 1986b). In contrast, in the Kiel Fjordsite 14855 only Bosmina longirostris was present which is indicative of a small shallow lake(HOFMANN, 1983a, 1987b).

At all the sites, rich chironomid and cladoceran faunas were found below the horizon oftransgression. With respect to species composition and species diversity, they do not differfrom subfossil assemblages recorded from diverse lake sediments (FREY, 1958; GOULDEN,1964, HARMSWORTH, 1968; WHITESIDE, 1970; HOFMANN, 1971b, 1978, 1986b, 1987b, 1988)and thus provides evidence of a former freshwater situation.

4.3. The Holocene Section above the Transgression Horizon

In the Vejsnaes core15391, the Neustadt Bay core 15342 as well as in the Kiel Fjord core14855 the chironomid assemblage of this period was characterized by the predominance andthe almost exclusive occurrence of the taxa Clunio marinus, Chironomus salinarius, and Cri-cotopus/Halocladius. In core 15386 the only sample from this zone contained two speci-mens of Clunio marinus.

Clunio marinus is a marine species that occurs in the Baltic Sea under brackish water con-ditions (CRANSTON et al., 1983). Chironomus salinarius is typical of brackish waters and has


a tolerance range for salinity from 3–18‰ (MOLLER PILLOT, 1984). These species indicatethe existence of brackish water conditions. Therefore, the Cricotopus/Halocladius specimenspresumably belonged to the brackish water taxon Halocladius or to euryhaline or halobi-ontic Cricotopus species. In the genus Cricotopus several euryhaline species from differentspecies groups exist while the species of the caducus-group are considered to be halobiontic(HIRVENOJA, 1973).

In this period, the Chydoridae almost completely disappeared and were only representedby single findings. In the cases of the Neustadt Bay core 15342 and the Kiel Fjord core14855 the lowermost samples of this period were characterized by extremely high percent-ages of Chydorus sphaericus and high numbers of Alona rectangula. These assemblagesresemble the chydorid fauna found in the sediments of the brackish water pond Silkteich(Untere Trave) and may indicate a transitional phase of moderately increasing salinity (HOF-MANN, 1985). A momentary rise in salinity has been documented to cause a pronouncedC. sphaericus expansion by KORHOLA (1995). SPITTLER and SCHILLER (1984) reported astrain of Chydorus sphaericus from boddens south of Darss-Zingst, which occurred at a sali-nity of 8‰ and was not able to reproduce in freshwater. In core 15342 this horizon was alsocharacterized by a decrease in chironomid taxa and a strong predominance of Chironomusgr. plumosus and Dicrotendipes.

In all the sites under discussion the genus Bosmina was found in extremely low numbers.In Vejsnaes 15391 and Mecklenburg 15386 (but not in 15342) B. longispina was slightlymore abundant than B. longirostris.

The sediments from the section above the transgression horizon were also characterizedby the occurrence of Foraminifera which were found in all the sites and which were partic-ularly abundant in cores 15342 and 15391. They also indicate brackish/marine conditions(LUTZE, 1965).

5. Conclusions

The four sites situated in different areas of the present Western Baltic were inhabited byfreshwater midges and cladocerans during the early Holocene and Younger Dryas (twosites). In each of the cores a dramatic change in the fauna occurred at the transgression hori-zon as determined by sedimentological characters (WINN et al., 1982, 1983; WINN and AVER-DIECK, 1984; SIMANOWSKY, 1985). The freshwater taxa disappeared and were replaced byforaminifers and chironomid species adapted to brackish/marine conditions.

In the case of the Neustadt core 15342 the cladoceran and chironomid results differ fromthe data presented by MATTHIESSEN and BRENNER (1995) who found that subfossil dinoflag-ellate cysts and green algae indicate a salinity of about 10‰, i.e., mesohaline conditions,below the sedimentological clay gyttja/clay boundary at 340 cm. The diverse freshwatercladoceran and chironomid fauna present at that time should, however, exclude the existen-ce of mesohaline conditions. REMANE (1971) stated that the “rich fauna of the Cladocera isof no importance in the marine oligohalinikum”, i.e., in the salinity range of 0.5–5‰.

In contrast to the situation in sediment cores from the Central Baltic (HOFMANN, 1987a),the abundance of chironomid and cladoceran remains in the early Holocene layers from thewestern Baltic was higher and the faunal change forced by the transgression was more dra-matic and more clearly defined. Furthermore, there were marine/brackish water speciesamong the chironomids, which characterized the situation after the transgression. Thesespecies are obviously restricted to near shore areas and their remains were therefore notfound in sediments from the Central Baltic.

The subfossil assemblages in different cores from the Baltic Proper which were from fardistant sites (Bornholm Basin, Gdansk Bay) were rather similar giving the impression of a


uniform paleo-environment, whereas the associations of both cladocerans and chironomidsfrom the different coring sites of the Western Baltic show individual characteristics, henceindicating origins from isolated water bodies.

The development in the chironomid and cladoceran fauna reflects the Late Glacial andHolocene development of this area in concordance with SAURAMO (1958). Before the Litto-rina Transgression the sites under discussion were separate freshwater bodies which nevercame under marine or brackish influence, although WINN (1974) mentioned that the area ofthe Great Belt was possibly connected with the sea in the early Boreal period. KOLP (1964)on the basis of a diatom analysis stated there was a brackish water lake in the Younger Dryasand Preboreal in the area of the Mecklenburg Bay. This was not indicated by faunal remains,however the sediment cores under discussion did not represent continuous series but wererather incomplete.

As Cladocera and Chironomidae turned out to be reliable indicators of freshwater andbrackish/marine conditions, it would be desirable to analyze in detail the faunal changes ina continuous profile through a transgression horizon. This would permit a direct observationof the progress of transgression and its ecological effects

6. References

ALHONEN, P., 1970: On the significance of the planktonic/littoral ratio in the cladoceran stratigraphy oflake sediments. – Soc. Scient. Fenn. Comment. Biol. 35: 1–9.

BJÖRK, S., 1995: A review of the history of the Baltic Sea, 13.0–8.0 ka BP. – Quat. Int. 27: 19–40.CRANSTON, P. S., D. R. OLIVER and O. A. SAETHER, 1983: The larvae of Orthocladiinae(Diptera: Chiro-

nomidae) of the Holarctic region – Keys and diagnoses. – Ent. scand. Suppl. 19: 149–291.DIETRICH, G. and R. KÖSTER, 1974: Geschichte der Ostsee. – In: MAGAARD, L. and G. RHEINHEIMER

(eds.): Meereskunde der Ostsee, Springer, Berlin, Heidelberg, New York: 5–18.ERONEN, M., O. RISTANIEMI and D. LANGE, 1990: Analysis of a sediment core from the Mecklenburg

Bay, with a discussion on the early Holocene history of the southern Baltic Sea. – Geol. För. Stock-holm Förh. 112: 1–8.

FLÖSSNER, D., 1972: Kiemen- und Blattfüßer, Branchipoda; Fischläuse, Branchiura. – In: DAHL, M. andF. PEUS (eds.): Die Tierwelt Deutschlands 60: 1–499.

FREY, D. G., 1958: The late glacial cladoceran fauna of a small lake. – Arch. Hydrobiol. 54: 209–275.FREY, D. G., 1986: Cladocera analysis. – In: BERGLUND, B. E. (ed.): Handbook of Holocene Palaeoe-

cology and Palaeohydrology, John Wiley and Sons, Chichester: 667–692.GOULDEN, C. E., 1964: The history of the cladoceran fauna of Esthwaite Water (England) and its lim-

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Manuscript received November 5th, 1998; revised July 12th, 1999; accepted September 25th, 1999


the littorina transgression in the western baltic sea as indicated by subfossil chironomidae...

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