The environmental and evolutionary history of Lake Ohrid (FYROM/Albania): Interim results from the SCOPSCO deep drilling project

Abstract

<p><strong>Abstract.</strong> This study reviews and synthesises existing information generated within the SCOPSCO ("Scientific Collaboration on Past Speciation Conditions in Lake Ohrid") deep drilling project. The four main aims of the project are to infer (i) the age and origin of Lake Ohrid (Former Yugoslav Republic of Macedonia/Republic of Albania), (ii) its regional seismotectonic history, (iii) volcanic activity and climate change in the central northern Mediterranean region, and (iv) the drivers of biodiversity and endemism. The Ohrid basin formed by transtension during the Miocene, opened during the Pliocene and Pleistocene, and the lake established de novo in the still relatively narrow valley between 1.9 and 1.3 Myr ago. The lake history is recorded in a 584 m long sediment sequence, which was recovered within the framework of the International Continental Scientific Drilling Program (ICDP) from the central part (DEEP site) of the lake in spring 2013. To date, 50 tephra and crypto-tephra horizons have been found in the upper 460 m of this sequence. Tephrochronology and tuning biogeochemical proxy data to orbital parameters revealed that the upper 247.8 m represent the last 637 kyr. The multi-proxy dataset covering these 637 kyr indicates long-term variability, with a change from cooler and wetter to drier and warmer glacial and interglacial periods around 300 ka. Short-term environmental change caused, for example, by tephra deposition or the climatic impact of millennial-scale Dansgaard-Oeschger and Heinrich events are superimposed on the long-term trends. Evolutionary studies on the extant fauna indicate that Lake Ohrid was not a refugial area for regional freshwater animals. This differs from the surrounding catchment, where the mountainous setting with relatively high water availability provided a refugial area for temperate and montane trees during the relatively cold and dry glacial periods. Although Lake Ohrid experienced significant environmental change over the last 637 kyr, preliminary molecular data from extant microgastropod species do not indicate significant changes in diversification rate during this period. The reasons for this constant rate remain largely unknown, but a possible lack of environmentally induced extinction events in Lake Ohrid and/or the high resilience of the ecosystems may have played a role.</p>

Diatoms do radiate: evidence for a freshwater species flock

“…However, such a scenario does not necessarily invalidate the definition of a species flock (see Schön & Martens, ). Estimated divergence times for the ‘ stroesei ’ group suggest that this clade most likely evolved in situ (MRCA mean age: 0.81 Myr; 95% highest posterior density, HPD: 0.23, 1.53 Myr), given that the lake originated 1.3–1.9 Myr ago (Wagner et al ., ). This rapid in situ speciation is also reflected by short branch lengths within the clade (Fig.…”

“…In conclusion, neontological and palaeontological data in combination with biogeographical information suggest that the Aneumastus ‘ stroesei ’ group occurring in Lake Ohrid forms a species flock. Both molecular and fossil data indicate that these endemic species rapidly evolved after the lake reached deep‐water conditions (see Wagner et al ., ). The appearance of these conditions and the associated emergence of novel habitats may thus have promoted both in situ speciation and reduced competition (i.e.…”

“…380 mcd). Moreover, it also yielded a continuous and well‐preserved diatom record (Wagner et al ., ).…”

“…With an age of c . 1.3–1.9 million years (Myr) (Wagner et al ., ), Lake Ohrid is the oldest freshwater lake in Europe and a biodiversity hot spot for several taxonomic groups such as diatoms, gastropods and crustaceans (see Föller et al ., ). The SCOPSCO campaign recovered the entire lacustrine history of the lake (584 m composite depth, mcd), including the initiation phase ( c .…”

“…In Lake Ohrid, the opportunity to study such processes has been enabled by the international continental scientific drilling project SCOPSCO. With an age of c. 1.3-1.9 million years (Myr) (Wagner et al, 2017), Lake Ohrid is the oldest freshwater lake in Europe and a biodiversity hot spot for several taxonomic groups such as diatoms, gastropods and crustaceans (see F€ oller et al, 2015). The SCOPSCO campaign recovered the entire lacustrine history of the lake (584 m composite depth, mcd), including the initiation phase (c. 450 mcd) and the onset of deep-water conditions (c. 380 mcd).…”