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Transcript
PhD thesis of Mgr. Kateřina Kopalová ‘Taxonomy, ecology and biogeography of aquatic and limno-terrestrial diatoms (Bacillariophyta) in the Maritime Antarctic Region’. Charles University in Prague, Faculty of Science Evaluation by Dr. Ingrid Jüttner, National Museum of Wales, Cardiff, U.K. The thesis on the diatom flora from Livingston Island (LIV), South Shetland Islands, and James Ross Island (JRI), located on the western and eastern side of the Antarctic Peninsula, is a valuable contribution to the expanding knowledge of diatoms in the Antarctic region. The data provided on their taxonomy and diversity, as well as ecological and biogeographical patterns were a result of extensive and well performed investigations. They are essential for further meaningful studies in ecology and paleoecology. Chapter 1 A brief introduction on diatoms followed by a description of the study areas and review of existing literature on Antarctic diatoms gave sufficient background to place the present study into context. Chapter 2 Detailed descriptions are provided for five species in the genus Luticola. This genus is a typical and common constituent of terrestrial diatom assemblages in the Antarctic region. Detailed taxonomic data as presented here are an essential prerequisite for biogeographical studies. The descriptions are correctly based on investigations using both light- and electron microscopy. Useful comparisons are provided between the new and similar previouslyknown taxa. In addition information on habitat, ecology and species distributions are given. Such data are necessary for further ecological and monitoring studies. Chapter 3 Six taxa from freshwater habitats on LIV, Deception Island and JRI belonging to a number of small-sized naviculoid genera are investigated; taxa in these genera are difficult to identify and have been insufficiently studied. Prior to this study, the six taxa studied here were most likely unrecognized and incorrectly identified. As a result of this study, four are described as new species and one new combination is made. Detailed descriptions are followed by data on ecology and distribution. The taxonomic positions are discussed and comparisons made with the most similar species from other geographical areas including Europe, the Americas and the Antarctic. The morphological variability of populations within the Antarctic region is also documented. The new data allow a more effective use of these difficult taxa in paleoecological, ecological and biogeographical studies. Chapter 4 The diatom floras of streams and seepage habitats on JRI are investigated. The ecology and distribution of Antarctic species are described. This is particularly important as it underpins several ecological hypotheses with respect to large-scale pattern of species richness and distribution. An analysis of the diatom assemblages in this poorly studied area confirms that there is a high level of endemism, with characteristic floras on the Antarctic Continent, the Antarctic Peninsula and the Subantarctic islands in the southern Atlantic Ocean, and islands in the southern Indian Ocean. The results also support the hypothesis of decreasing species richness with increasing latitude. Chapter 5 The study on diatom assemblages collected mainly from lakes and pools on the Byers Peninsula, LIV, related for the first time in this area species distribution to water chemistry using a detailed taxonomic resolution and appropriate numerical methods. It reveals that ion concentration related to a salinity gradient and nutrients are important factors. The recognition of a much larger number of species compared to previous studies, as a result of better species recognition, and insight into species distribution along chemical gradients provides necessary data for applied studies, such as the construction of transfer functions and reconstruction of historical trends in chemical conditions in lakes. A comparison with previous studies in the same area highlights the importance of detailed taxonomic investigations for adequate assessments of diatom diversity. Certain groups of taxa (for example in the genera Gomphonema and Nitzschia) remained unresolved and will require further work following the excellent examples of taxonomic studies on other genera such as Luticola and Pinnularia. In the appendix a useful list of species with their main geographical occurrences in the Antarctic region is provided. Chapter 6 This first ecological study on the freshwater diatoms of JRI revealed important environmental information on diatoms in a location at the boundary between Maritime and Continental Antarctica. A transfer function was established for conductivity that can be used to reconstruct historical changes across different lake types. The required statistical analyses were performed carefully using well established methods. Conductivity is an important determinant for the existing diatom assemblages. In the future a better understanding of its variability over time might lead to a better understanding of climate-driven change in an area of Antarctica that has recently experienced considerable environmental change. The occurrence of certain species typically found in Continental Antarctica confirms the transitional position of JRI in contrast to the other study area on LIV. JRI might therefore be an interesting location for further studies on diatom dispersal. The comparison of assemblages from different habitats including lakes, seepage and streams provides interesting data on differences in species-richness patterns which apparently do not hold across different taxonomic groups. This poses the question as to why evolutionarily older organisms such as cyanobacteria appear to be more diverse in less stable habitats such as streams and seepages. This study also highlights the lack of investigations on seepage assemblages in polar regions which would be required for cross-comparisons of richness and assemblage composition. Such studies would be highly desirable because this habitat is very species-rich and particularly affected by changes in temperature. Chapter 7 The diatom flora living on bryophytes, which has rarely been studied in the Antarctic region, is investigated on LIV and JRI. Although comparison between both islands must be made cautiously due to the low number of samples from JRI the data suggest that the epiphytic diatom flora on mosses is dominated by different genera in each area, probably as a result of differences in climate and water availability. Although no clear difference between assemblages on different moss species were found, a more detailed analysis of host preference using a specially designed study might be interesting. Chapter 8 A concluding discussion summarizes the results of the individual investigations and places the distribution of the lake diatom flora into a wider context. The presumed geographical distribution of the recorded taxa emphasizes the distinct floristic composition on LIV and JRI, particularly with respect to the known floras of the Subantarctic islands and to other areas on the Antarctic Continent. This observation is also reinforced by the much smaller contribution of cosmopolitan species to the overall species composition. It would, however, be interesting to review this distribution of ‘Antarctic’ species after further comparison with floras from similar habitats in arctic and alpine areas of the northern Hemisphere. Interestingly the presented abundance data reveal that some of the most common and abundant taxa belong to the species complexes in the genera Nitzschia and Fragilaria that are yet to be resolved taxonomically. Despite the location of both islands in Maritime Antarctica, the combined analyses of all samples document clearly the difference in assemblage composition between geographical areas on the western and eastern side of the Antarctic Peninsula. Similarly collections from JRI demonstrate the importance of different habitats for overall species diversity, but further investigations in other areas and of microhabitats within the selected aquatic ecosystems are needed before these patterns can be confirmed as generally applicable. An ordination of assemblages performed at the species- and genus-level convincingly demonstrates a high degree of separation of diatom assemblage composition between the three Antarctic regions – Maritime Antarctica, Continental Antarctica and Sub-Antarctica, a pattern previously shown for other biota. However, uncertainty about the true biogeographical pattern in diatoms of the Antarctic region remains, due to the nature of the currently applied species-concepts and the largely unexplored cryptic diversity revealed by molecular phylogenetic analysis elsewhere. These questions will provide ample opportunities for further studies extending the already impressive knowledge on diatoms from this geographical region assembled by the team of researchers involved in the presented work. In general the thesis is a well-written and thorough piece of work, supported by extensive study of the relevant scientific literature. It is particularly commendable because some of the work in the field was conducted under challenging environmental conditions that would deter and defeat many scientists.The methods applied are appropriate and correctly applied, leading to interesting and new results and achieving the objectives set for this study. The thesis is therefore suitable for the defence, and the quality of the taxonomic and ecological analyses fulfil the criteria necessary for obtaining a Ph.D. degree. I would like to congratulate the candidate Kateřina Kopalová on her impressive work and wish her success in her future scientific undertakings.