Freshwater Ostracod Assemblages and Their Relationship to Environmental Variables in Waters from Northeast Germany
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Hydrobiologia (2006) 571:213–224 Ó Springer 2006 DOI 10.1007/s10750-006-0241-x Primary Research Paper Freshwater ostracod assemblages and their relationship to environmental variables in waters from northeast Germany Finn A. Viehberg Institut fu¨r Geographie und Geologie, Universita¨t Greifswald, Friedrich-Ludwig-Jahn-Str. 17a, D-17487, Greifswald, Germany Present Address: Laboratoire de pale´olimnologie et de pale´oe´cologie, Centre d’E´tudes Nordiques, Pavilion Abitibi-Price, Universite´ Laval, Sainte-Foy, Que´bec, G1K 7P4, Canada (E-mail: fi[email protected]) Received 16 June 2005; in revised form 22 March 2006; accepted 28 April 2006; published online 13 July 2006 Key words: ostracoda, calibration dataset, canonical correspondence analysis, phenology, water temperature, Mecklenburg-Vorpommern Abstract An ecological calibration dataset for freshwater ostracods from 33 localities throughout West-Pomerania (Mecklenburg-Vorpommern, Germany) was evaluated using multivariate statistical methods. A total of 47 freshwater ostracod species were identified. Nine species were rediscovered after 100 years since the last published record and Candonopsis scourfieldi and Pseudocandona sucki was recorded for the first time in the study area. Special emphasis is put on the phenology of each species to gain information on the water characteristics at the time of their last moult. Canonical correspondence analysis (CCA) revealed that the ecological variables such as water temperature, Ca, Mg, and lake area were statistically most significant (p < 0.005; n = 72) in explaining variation in the distribution of ostracod assemblages. In addition, a transfer function was developed for paleolimnological approaches, based on a weighted-averaging (WA) model to calculate water temperature from the relative abundances of 22 selected ostracod species. This model was successfully applied to infer lake water temperature from subfossil ostracod assemblages col- lected from lacustrine deposits in northeast Germany (Lake Krakower See). Introduction nological interest as preserved ostracod valves store valuable paleoenvironmental information for Research on freshwater ostracods started in Eur- reconstruction purposes in Quaternary science. In ope in the late 18th century (i.e., O.F. Mu¨ ller, this context, the use of ostracod analysis increased 1772). These small bivalved microcrustaceans were significantly over the past years and has been subject to numerous monographs of taxonomy successfully applied to identifying changes in lake and systematics, while initially only little attention paleohydrology and reconstructing trophic status was paid to ecological aspects. Redeke (1936) was (e.g., Namiotko et al., 1993; Scharf, 1998), water one of the first who emphasized the ecology of level (e.g., Colman et al., 1994; Viehberg, 2004), single ostracod species. Recently, Meisch (2000) water temperature (e.g., Colman et al., 1990; summarized new and already published ecological Forester, 1991), salinity (e.g., Gell et al., 1994; data of Western and Central-European species Boomer et al., 1996), and ion-composition (e.g., and it became apparent that the understanding of Forester, 1991; Smith et al., 1992). the fundamental or realized ecological niche for Nevertheless, some authors regret that the use some ostracods still needs further investigation. of ostracods as paleo-proxies remained more This ecological knowledge is of great paleolim- descriptive than precise over decades compared to 214 other zoological indicators (e.g., Holmes, 2003). Du¨ gel, 2004), but an European equivalent is still Due to this imprecision, subfossil ostracod valves missing. It is one task of this paper to initiate such are often used as a calcite source for analysis of an ecologically orientated database for northeast stable isotopes (18O and 13C) or trace elements Germany and to present paleotemperature esti- (Ca, Mg, Sr, and Mn) (e.g., Holmes & Chivas, mates inferred with the developed quantitative 2002; Schwalb, 2003), rather than quantitative transfer function. paleoindicators themselves. Quantitative transfer functions need to be Materials and Methods developed upon modern calibration datasets to fulfill the requirements of modern paleolimnolog- The study area is situated in West Pomerania and ical approaches. Some encouraging results have covers 8,633 km2 in the northeast of Germany. been published for North America (Alin & Cohen, A total of 33 lakes were sampled at 10-weeks 2003), South America (Mourguiart et al., 1998), intervals from 19.02.2002 to 24.08.2003 for living and the Eastern Mediterranean (Ku¨ lko¨ ylu¨ oglu & Ostracoda (Fig. 1; Table 1). Figure 1. Study area (8,633 km2). Rural districts: DM = Demmin, NVP = North – Vorpommern, OVP = East – Vorpommern, RU¨ G=Ru¨ gen district, UER = Uecker- Randow district; Cities: HGW = Greifswald, HST = Stralsund, NB = Neubrandenburg; Numbered squares = sampled lakes (1–33; coordinates, see Table 1); K3 = core KOS III (see text). 215 Table 1. Localities for calibration dataset. Listed from North continental elements. In addition, the Baltic Sea to South with annotations to lake area and mean water depth influences a 10–30 km wide strip along the coast max. min. mean STDS (Duphorn et al., 1995). The annual mean daily temperature recorded at Stralsund and Neubran- Area (104m2) 3,255.8 6.2 234.9 662.6 denburg respectively is + 8.5 °C and + 7.9 °C, Depth (m) 32.3 1.6 4.2 3.1 representing a transect through the study area. The annual mean annual precipitation for the area is 552 mm. Water temperature (°C) 23.5 1.6 14.5 6.0 ) Ca (mg dm 3) 228.0 2.1 81.1 36.3 Sampling and laboratory techniques Mg (mg dm)3) 85.5 1.6 19.3 17.1 Winter (1.12. – 29.2.) The surface sediment was sampled randomly in the Water temperature (°C) 5.9 1.6 3.5 1.69 littoral zone of each lake with a simplified Kajak- ) Ca (mg dm 3) 106.1 62.7 83.5 18.5 corer (diameter 5.38 cm). The top 2 cm were ) Mg (mg dm 3) 33.4 12.8 20.2 8.1 placed into a white bowl with the overlying water. Spring (1.3. – 31.5.) All ostracods were collected alive in the field with a Water temperature (°C) 15.7 5.4 10.8 2.8 water exhauster (Viehberg, 2002). Special care was ) Ca (mg dm 3) 228.0 2.1 80.4 44.0 taken to assure representative results. First, all ) Mg (mg dm 3) 83.7 1.6 19.8 19.3 swimming and fast moving species were collected Summer (1.6. – 31.8.) to concentrate more easily on slow crawling spe- Water temperature (°C) 23.5 15.9 21.5 1.6 cies, which were also sucked by the exhauster. ) Ca (mg dm 3) 153.1 15.8 79.4 31.3 Finally, the bowl was tilted gently in all directions ) Mg (mg dm 3) 85.5 3.4 18.7 16.32 several times, so part of the sample was exposed to Autumn (1.9. – 30.11.) the air and submerged by the next counter move- Water temperature (°C) 18.2 5.0 12.7 3.7 ment with suppositious water. Thus, remaining ) Ca (mg dm 3) 136.0 15.3 84.1 31.3 ostracods stuck to the water surface due to their ) Mg (mg dm 3) 71.5 3.1 19.0 15.7 hydrophobic valve surface characteristic. A species–area curve is calculated based on the Jaccard-coefficient. Therefore, 20 samples were The lake basins of this study are situated north taken from a species-rich lake in the study area of the Pomeranian terminal moraine lobe (stage (Lake Kummerower See, Fig. 1: 20), in which 12 WII sensu Mu¨ ller et al., 1995) in the till plains of different species were identified at that time. To the north eastern lowland. It is considered that optimize the sampling procedure in terms of most lakes were ice-free and recolonized by biota treatment, time consumption due to collection in at the latest by 14,000 a BP when the buried dead the field, and picking the individuals in the labo- ice finally melted (Kaiser, 2001). ratory, we restricted our sampling to eight short Today, the landscape is mainly characterized cores (total of 182 cm2) at each locality. Following by intensive agriculture, which is reflected by the this compromise, approx. 95 % of the expected generally increased nutrient load in surface water. species were still caught based on limited trials Additionally, the carbonate concentration is high (Fig. 2), and all live samples of one field day could due to the soluble CaCO3 content of the underly- be treated within 48 hours. One exhauster was ing moraines (Table 2). Most lakes are shallow used for each lake. (mean depth: 4.2 m; Table 1 + 2) and are not In the laboratory, living individuals were sorted thermally stratified during the summer period and enumerated under a stereo-microscope. Iden- (UM-MV, 1998). tifications and taxonomy was adopted from In addition, water bodies close to the Baltic Sea Meisch (2000). Single specimens were prepared shoreline revealed an increased conductivity and the soft parts mounted on microscopic slides ) (>1000 lScm1), caused either by brackish in HydroMatrixÒ, while the analogous valves were groundwater inflow or occasional water exchange. stored in CelkaÒ-slides where necessary. All other The climate of the study area is influenced by ostracods were stored in small glass vials filled both temperate North Atlantic as well as extreme with 70% ethanol. 216 Table 2. Summary of selected environmental data for the investigated lakes which are included in the CCA Loc.Nr. key Lake (closest municipality) Coordinates Mean water Lake area (Potsdam date) depth (m) (104m2) 1 Nonnensee (Bergen) 54° 26¢ 00.2¢¢ N13° 25¢ 13.3¢¢ E 1.6 81.8 2 Ossen (Bergen) 54° 26¢ 38.8¢¢ N13° 28¢ 10.0¢¢ E 1.5 34.6 3 Schmachter See (Binz) 54° 24¢ 02.7¢¢ N13° 35¢ 17.7¢¢ E 2.3 119.8 4 Speicher Prohn (Prohn) 54° 23¢ 00.3¢¢ N13° 02¢