Cladoceran and diatom evidence of lake-level fluctuations from a Finnish lake and the effect of acquatic-moss layers on microfossil assemblages

We studied Holocene lake-level fluctuations from a small lake, Iso Lehmälampi, southern Finland, utilizing cladoceran and diatom analyses. We report data from a sediment core (A) taken from the deepest part of the lake (8.1 m) where two layers of moss, mixed with gyttja, were found. These layers were formed in situ during the early Holocene (1. ca. 8100-7900, 2. ca. 7300 BP). Lake-level fluctuations were inferred also from another core C, which did not have moss layers. According to the ratio of planktonic/littoral Cladocera, the water level was high around 9000 BP and started to fall before 8000 BP. The lowering continued until 7000 BP and the moss layers were formed during this lowering. Water level was high again ca. 6000 BP and lowered towards ca. 4000 BP. The late Holocene is characterized by several rapid fluctuations of lake-level. The ratio of planktonic/littoral Cladocera and the diatom species composition in core A showed drastic changes between the moss layers and the non-moss gyttja sections of the core. We suggest that they reflect changes in sedimentary facies between the local moss environment and the pelagic bottom. Thus, cores which contain moss layers may lead to erroneous interpretations of lake-level fluctuations.     

Zooplankton Community Structure of Çavuşcu and Eber Lakes in Central Anatolia Struktur von Zooplankton-Gemeinschaften im Çavuşcu Lake und im Eber Lake in Zentralanatolien

This research has been undertaken to determine the zooplanktonic fauna (Rotatoria, Crustacea) and their seasonal distribution in two lakes with different characters. Çavu?cu lake has a surface area of 1000 ha with a maximum depth of 4 m and is classified as an oligo-mesotrophic lake. Eber lake has a surface area of 5200…17000 ha with a maximum depth of 2.5 m and is classified as an eutrophic lake. Zooplankton samples have been collected seasonally between the period of 1990 to 1993 from three stations with a zooplankton net of 44 μm mesh size. From Çavu?cu lake totally 50 Rotifera, 2 Copepoda, and 7 Cladocera species; 49 phytoplankton genera and 5 macrophytes have been identified while, 37 Rotifera, 3 Copepoda, 5 Cladocera; 45 phytoplankton genera and 6 macrophytes have been identified from Eber lake. 13 new rotifer records for the Turkey were found, which were Brachionus diversicornis, Macrochaetus collinsi, Lecane stichaeta, Cephalodella sterea, Cephalodella auriculata, Trichocerca iernis, Encentrum saundersiae. Pompholyx complanata, Floscularia ringens, Conochilus natans, Filinia pejleri, Rotaria rotatoria, and Philodina megalotrocha.     

An annual fossil record of production,planktivory and piscivory during whole-lake manipulations

Annual and subannual paleolimnological records of pigments and zooplankton were used to analyze three whole-lake manipulations. The relative abundance of cladoceran remains in recent seasonal laminae was significantly correlated with the relative abundance of species in the plankton (r ²=0.59,P<0.001). Comparison of food-web structure after piscivore introduction showed that there are multiple outcomes of predation and that final food-web structure depended on the strength of interaction between piscivorous and planktivorous fish. Intense predation on cyprinids (Phoxinus eos, P. neogaeus, Umbra limi) by largemouth bass (Micropterus salmoides) allowed large herbivores (Daphnia pulex) and invertebrate predators (Chaoborus punctipennis) to dominate. Analysis of fossil invertebrate morphology suggested that small grazers (Bosmina longirostris, Diaphanosoma birgei) were eliminated by invertebrate predators. Under moderate predation by rainbow trout (Oncorhynchus mykiss), cyprinids remained, only intermediate-size herbivores (D. rosea) increased in abundance, andBosmina persisted. In contrast to food-web manipulations, increased algal abundance resulting from watershed disturbance (road construction) did not alter the species composition or size-structure of fossil Cladocera.     

Palaeolimnological Development of Lake Njargajavri, Northern Finnish Lapland, in a Changing Holocene Climate and Environment

This study used palaeolimnological approaches to determine how Holocene climatic and environmental changes affected aquatic assemblages in a subarctic lake. Sediments of the small Lake Njargajavri, in northern Finnish Lapland above the present treeline, were studied using multi-proxy methods. The palaeolimnological development of the lake was assessed by analyses of chironomids, Cladocera and diatoms. The lake was formed in the early Holocene and was characterized by prominent erosion and leaching from poorly developed soils before the establishment of birch forests, resulting in a high pH and trophic state. The lake level started to lower as early as ca. 10,200 cal. BP. In the resulting shallow basin, rich in aquatic mosses, pH decreased and a diverse cladoceran and chironomid assemblage developed. It is likely that there was a slight rise in the water level ca. 8000 cal. BP. Later, during the mid-Holocene characterized by low effective moisture detected elsewhere in Fennoscandia, the lake probably completely dried out; this is manifest as a hiatus in the stratigraphy. The sediment record continues from ca. 5000 cal. BP onwards as the lake formed again due to increased effective moisture. The new lake was characterized by very low pH. The possible spread of pine to the catchment and the development of heath community may have contributed to the unusually steep (for northern Fennoscandia) decline in pH via change in soils, together with the natural decrease in leaching of base cations. Furthermore, the change in pH may have been driven by cooling climate, affecting the balance of dissolved inorganic carbon in the lake.     

A new and simple method for qualitative sampling of meiobenthos-communities

The introduced collecting method is based on a common entomologist exhauster, which is specified for the fieldwork in aquatic systems with a sieve-inset and a bottom-lid. The living organisms are collected visually from the sampled debris and no further extraction is needed. The apparatus is designed for qualitative sampling of microcrustaceans (e.g. Cladocera, Copepoda, Ostracoda) and minimises disturbance at the sampling site.     

Does the zooplankton prey availability limit the larval habitats of pike in the Baltic Sea?

The objectives of this study were to (1) investigate whether the availability of suitable zooplankton prey limits the distribution of the coastal larval areas of pike (Esox lucius) in two archipelago areas of the northern Baltic Sea and (2) compare the availability of zooplankton prey in spring between different types of coastal littoral habitat. According to the results, reed belt habitats formed by Phragmites australis constitute hot spots for zooplankton prey in the coastal ecosystem. During the spring, reed-covered shores of the inner archipelago maintained more than 10 times higher densities of copepods and cladocerans, the preferred prey for larval pike, compared to the other studied shores. Temperature conditions were also most favourable in the reed belt habitat. Thus, the reed belts of the inner and middle archipelago were shown to form the best habitat for larval pike in the coastal area of the northern Baltic Sea, and this was also the only habitat where pike larvae were found. Our results suggest that the poor survival and recruitment of pike in the outer archipelago, however, cannot exclusively be explained by sub-optimal feeding conditions of the larvae. There are also other important factors, presumably connected to the exposure to the open sea, that affect the distribution of the pike larvae. Our results, however, highlight the importance of sheltered coastal reed belt shores as reproduction habitat for spring-spawning fish in the northern Baltic Sea. Further, this study disproves the assumption that the seaweed bladder wrack (Fucus vesiculosus) forms a reproduction habitat for pike in the coastal area.     

The late-glacial and early-Holocene palaeoecology of cladoceran microfossil assemblages at Kråkenes, western Norway, with a quantitative reconstruction of temperature changes

Cladoceran microfossil remains were analysed from a sediment core taken from a lake basin at Kråkenes, western Norway. The sequence included immediate post-glacial conditions (ca. 12,300 ¹⁴C BP), the Allerod, Younger Dryas, and early Holocene to approximately 8,500 ¹⁴C BP. The interpretation of changes in the cladoceran assemblages is based on the known ecology of the taxa, the documented environmental history of the study sequence, the variations in the organic content of the sediment, the radiocarbon dates, and the results of analyses of other biotic groups, including diatoms, macrophytes, and chironomids. In addition, a quantitative reconstruction of changes in air temperature is presented for the study period. This reconstruction is based on transfer functions developed from a separate Swiss surface-sediment cladoceran data set.The cladoceran assemblages throughout the sequence are dominated by littoral chydorid taxa. Bosmina, Daphnia, and Simocephalus represent the open-water component of the zooplankton. Chydorus piger and Daphnia were the only immediate post-glacial pioneer taxa. A rapid proliferation of the open-water and littoral cladoceran taxa began with the onset of the Allerod and persisted for approximately 1,000 yrs. At the start of the Younger Dryas a local glacier formed and drained into the lake, causing a sudden decline in chydorid diversity, with only Chydorus sphaericus and Acroperus harpae persisting throughout this period. Chydorid diversity started to recover in the upper Younger Dryas and continued in the early Holocene. Progressive acidification and oligotrophication are also discernible from the cladoceran assemblages present in the Holocene.The reconstructed mean summer air temperature was from 8-21 °C, with prediction errors of 1.8-2.5 °C. The Allerod was only slightly warmer than the Younger Dryas period, but a progressive increase in temperature is apparent during the early Holocene. In conclusion, the results of this study provide a further demonstration of the value of cladocera as indicators of a variety of palaeoenvironmental parameters, including temperature.     

Reinvestigation of the classic late‐glacial Bølling Sø sequence,Denmark: chronology,macrofossils, Cladocera and chydorid ephippia

The late‐glacial Bølling period was first identified by Johs. Iversen on the basis of pollen results from Lake Bølling Sø in Denmark. Because there were no radiocarbon dates from the sequence the Bølling Chronozone (12 000–13 000 ¹⁴C yr BP) was later established on the basis of dates from other sites. A new project is reinvestigating the sediments from the Bølling Sø sequence with AMS radiocarbon dating and multiproxy analyses. Here we present results of AMS radiocarbon dating, macrofossil analyses, cladoceran analyses (Cladocera concentrations and chydorid ephippia) and Pediastrum analyses (concentrations). The AMS dates on land plant remains show that the lower part of the sequence is around 12 500 ¹⁴C yr BP, and thus clearly pre‐dates the Allerød chronozone. However, construction of a chronology for the sequence was problematic, partly because of reworking of macroscopic plant remains. The climate ameliorated after glacial conditions to such an extent that growth of plants could begin at ca. 12 500 ¹⁴C yr BP, but the results of multiproxy analyses show little evidence for a further warming period during the pre‐Allerød part of the sequence. Lake productivity was low, and tree birch rare or maybe absent. This may reflect widespread occurrence of dead ice, unstable soils, heavy in‐wash of minerogenic matter to the lake, resulting in turbid water and rapid sedimentation. The early pioneer vegetation was characterised by Salix polaris and Dryas octopetala, and by herbs. The Allerød Chronozone, and especially its initial part, appears to have been relatively warm but reduced cladoceran concentrations and increased proportion of chydorid ephippia suggest that climate cooled in the middle Allerød and that the late Allerød was colder than the early part. The early Younger Dryas was probably colder than the late Younger Dryas. Clear warming is apparent at the beginning of the Holocene, where the first macrofossil evidence of trees (Betula pubescens, Populus tremula) is found. Copyright © 2004 John Wiley & Sons, Ltd.     

Interactions between the rotifer Euchlanis dilatata and the cladocerans Alona glabra and Macrothrix triserialis in relation to diet type

We studied, separately, the effect of the cladocerans Alona glabra and Macrothrix triserialis on the population growth of the rotifer Euchlanis dilatata using three different food types (Chlorella and Scenedesmus, live or dead, offered on a comparable dry weight basis, 3.16 μg C ml⁻¹). Regardless of the presence or absence of competition, E. dilatata cultured using Chlorella (live or dead) showed a higher population growth as compared to Scenedesmus. Compared to heat-killed C. vulgaris, E. dilatata cultured alone and fed on live algae reached higher abundances. Both cladoceran species had an adverse effect on the population growth of Euchlanis, but did not eliminate the rotifers. Of the two cladocerans, M. triserialis had a far more adverse effect on the population densities of E. dilatata as compared to A. glabra. E. dilatata also influenced the population growth of A. glabra and M. triserialis, the former being more adversely affected than the latter. When the egg ratios of E. dilatata were plotted as a function of population density, a significantly inverse relation was obtained only in treatments containing Chlorella but not for other treatments. Statistically the rate of population increase (r) per day of E. dilatata was adversely affected by the diet type and the presence of competing species. The interaction of diet type X competition was also significant. For A. glabra, the presence of E. dilatata and the diet type, but not their interaction, significantly influenced the r. On the other hand for M. triserialis, only the diet type was significant. Our results suggest that the competitive outcome between rotifers and cladocerans was dependent on diet type.     

Distribution of benthic microcrustaceans along a water depth gradient in an Austrian Alpine lake - Sedimentary evidence for niche separation

Distribution of benthic microcrustacean (Crustacea: Cladocera) was investigated with paleolimnological approach by using their fossil surface sediment assemblages within a thermally extreme lake in the Niedere Tauern, Austrian Alps. The results from 20 surface sediment samples suggested that the spatial distribution of chydorids is clearly heterogeneous along the water depth gradient (1.8-6.1 m); Alona quadrangularis dominated in shallow (warm, minerogenic) habitats, Chydorus sphaericus-type succeeded at intermediate depths, and Alona affinis dominated in deep (cold, organic) sites. Apparently, these benthic cladocerans exhibit clear habitat and resource segregation. The distributional patterns revealed local community thresholds at approximately 2.5 and 4.5 m water depths and these thresholds were likely to be forced by variances in habitat quality (minerogenic-organic), food resources (periphyton/detritus), thermal properties (warm-cold), and UV-exposure (high-low). The results emphasize the usability of the paleolimnological approach in distributional investigations and its applicability in providing information on species-environmental relationships for environmental change evaluations and paleoecological interpretations.