Download PhD thesis of Mgr. Kateřina Kopalová `Taxonomy, ecology and

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.