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Diatoms as indicators of environmental change in ancient Lake Ohrid during the last glacial–interglacial cycle (ca. 140 ka)

The ancient lakes of the world are iconic geographical and geological features whose biota has attracted biologists for several centuries. They still garner much phycological attention and continue to surprise us with new diversity and new understandings of how these lakes and their biotas have survived and changed over the uncommonly long timeframes that the ancient lakes have existed. From Baikal to Tanganyika to Titicaca, the ancient lakes each have unique patterns of diversity but most are characterized by high diversity, high levels of endemism, and unfortunately growing risks of exploitation. It is the diatoms of Europe’s most ancient lake, Lake Ohrid, and their paleoecological interpretation over the past 140,000 years that are the subject of a recent volume in the Diatom Monographs series published by Koeltz. This edited book series has been used to publish a variety of diatom-based works ranging from floristic checklists, to bibliographic summaries of electron micrographs, to monographic revisions, and taxonomic and ecological treatments as exemplified by the current volume. Lake Ohrid is thought to be Europe’s oldest lake and is estimated at between 2 and 10 million years old. A few years ago, a major diatom flora was published on the modern diatoms of the lake (Levkov et al. 2007), treating over 500 taxa, including the descriptions of 66 new species. This added significantly to the earlier efforts by Hustedt (1945) and Jurilj (1954) to describe this lake’s amazing diatom diversity. Only recently has the historical diversity of Lake Ohrid been considered, as coring and drilling efforts have begun to recover and interpret the lengthy sediment record preserved beneath the lake. As in other ancient lake drilling efforts, the diatom record of Ohrid holds promise as a proxy for understanding climate change and impacts, diversity and evolutionary fate, and sedimentary processes. The book is organized into two main parts – a taxonomic treatment of over 130 diatom taxa found in a sediment core sequence from Lake Ohrid, followed by a paleoecological interpretation of their stratigraphy in relation to the glacial– interglacial cycles and tephra deposition. The former provides well-written taxonomic descriptions of each taxon, its modern ecological setting in Lake Ohrid, and typically a representative size series of light micrographs (LMs) organized in the book’s 49 plates. Scanning electron micrographs (SEMs) are provided for some taxa and to illustrate some of the characteristics associated with diatoms in this sediment sequence (dissolution patterns). The LMs and SEMs are of excellent contrast and quality, a testament to the continued training of great microscopists from this lab group. Two Cyclotella species, Cyclotella fottii and Cyclotella ocellata, are the dominant diatoms throughout the core and are treated in much greater detail, including the designation of morphotypes, size classes, and characteristic dissolution patterns associated with some core strata. Two new species are also formally described: Encyonema cespitosiforme Cvetkoska & Levkov and Mastogloia ohridana Cvetkoska & Levkov. The latter section of the book works to interpret the diatom record by showing the strong stratigraphic alignment of diatom assemblage zones with the known Quaternary Marine Isotope Stages, which define periods of glacial– interglacial activity. The interpretation relies heavily on the records of two Cyclotella species, for which the authors have gone to great lengths to interpret subtle morphological differences (e.g. they describe 22 morphotypes of C. ocellata), size classes, and patterns of dissolution. The response of the diatom flora to tephra deposits (from volcanic eruptions) is also explored but is shown to be subtle. The publication of a flora to accompany ecological or paleoecological studies is a welcome approach that is finally being done with greater frequency; however, the majority of applied phycological studies still do not recognize the important aspect of documenting taxonomies. A strength of this book is that it provides a toolbox for larger and deeper drilling efforts planned for Lake Ohrid, which will benefit from this careful taxonomic work and its framework for interpreting subfossil diatom communities in the lake. Unfortunately, outside of the two new taxa that were described, it was not readily apparent whether any of the material investigated in this study has been deposited in an accessible collection or herbarium. The book is well illustrated and nicely edited and organized; however, it is not written for a general scientific Phycologia (2013) Volume 52 (4), 379–380 Published 3 July 2013