[Schwalb] Bündelantrag: "Scientific Collaboration On Past Speciation Conditions in Ohrid (SCOPSCO)": Recent and fossil Ostracodes from Lake Ohrid as indicators of past environments: A coupled ecological and molecular genetic approach with deep-time perspective
German Title: Bündelantrag: "Scientific Collaboration On Past Speciation Conditions in Ohrid (SCOPSCO)": Recent and fossil Ostracodes from Lake Ohrid as indicators of past environments: A coupled ecological and molecular genetic approach with deep-time perspective
Current Status: completed
Main Applicant:Prof. Dr. Antje Schwalb
Dr. Julia Lorenschat
Dr. Finn Viehberg
Ancient Lake Ohrid, located on the southern Balkan Peninsula in Macedonia and Albania is characterized by a high degree of endemism and is considered to be the oldest lake in Europe. Its exact age (between one and ten million years) and its origin are still a matter of debate. To unravel these uncertainties the International Continental Scientific Drilling Program (ICDP) drilling project “Scientific Collaboration On Past Speciation Conditions” (SCOPSCO) started in April 2013. In advance of ICDP-SCOPSCO, we improved the use of ostracodes, small crustaceans, as indicators of environmental change. Within the framework of one PhD-, three Diploma- and one BSc-thesis, ostracodes and a multiplicity of environmental data were collected in Lake Ohrid and its adjacent waters during four field campaigns to (1) compile a state-of-the-art inventory of ostracodes, to (2) identify species preferences and tolerances and to (3) interpret environmental changes during the last 136,000 years using fossil assemblages from sediment cores. A total of 47 ostracode species were detected in the lake and in water bodies of its catchment, out of which 32 were found alive and 12 were endemic to Lake Ohrid. Multivariate statistics identified water depth, salinity, conductivity, pH, and dissolved oxygen as main determining factors for ostracode distribution in the entire study area. In Lake Ohrid, the distribution was mainly controlled by water depth, water temperature, and pH. The presence of the ostracode genus Amnicythere points to a marine origin of the lake. The specialized endemic ostracode fauna shows highest abundances and the greatest spatial distribution in Lake Ohrid. Eight cosmopolitan and holarctic species were found for the first time in the lake. They inhabited mainly the northern part of the lake, where two cities are located and industry and agriculture play a major role. These species were limited to water depths above 50 m, providing evidence for an increasing anthropogenic pressure that causes a replacement of endemic species to deeper waters. A multi-proxy study using short sediment cores unraveled the inception of perceptible human impact on Lake Ohrid. A strong and abrupt decrease in ostracode abundance and a concomitant increase in heavy metal concentrations suggest that anthropogenic pollution began to impact the aquatic ecosystem significantly at about 1895 AD. Between the early 1920’s and the late 1980’s lake productivity was relatively low. Geochemical proxies and ostracode abundance point to an increasing productivity since the late 1980’s in both the southeastern and in the northern part of the lake. Since the early 1990’s, increasing productivity and relatively high concentrations of arsenic, iron, and nickel correspond to a decreasing number of ostracodes especially in the northern part of the lake, despite the bringing into service of sewage treatment plants. This demonstrates that living conditions have become less favorable for the endemic ostracode fauna at least in the northern part of the lake close to the cities. Climate change is expressed in fluctuations in ostracode assemblages and abundances archived in three sediment cores, spanning approximately the past 400, 39,500 and 136,000 years. Between Marine Isotope Stage (MIS) 6 and MIS 2 the ostracode abundance was very low or valves were absent. This corresponds to low lake productivity, low carbonate content, and low lake level. Abundance and diversity increased markedly during the transitions from glacial to interglacial for both the Eemian and the Holocene in response to climate warming leading to higher productivity and higher carbonate contents. The Holocene is characterized by a higher degree of diversity compared to the Eemian, even before the onset of human impact. During the Little Ice Age (LIA), ostracode abundance decreased, and species with preferences for warmer waters disappeared. Overall, new indicator species for important environmental variables such as water temperature and water depth were identified. They will allow the quantitative reconstruction of paleo-water depths and paleo-temperatures from fossil assemblages just in time for the application on the newly recovered sediment sequences by ICDP-SCOPSCO that are crucial for the generation of high-resolution long-term paleoenvironmental data of global importance in paleoclimate research.