Deep layer cyanoprokaryota maxima in temperate and tropical lakes

Deep layer cyanoprokaryota (Cyanobium, Planktothrix rubescens, Cilindrospermopsis raciborskii, mixed assemblage) maxima were observed in Lake Stechlin (Mecklenburger Lake District, Germany) and in Lake Dom Helvecio and Lake Carioca (Rio Doce Lake District, Brazil). All three of these lakes have trophic states between oligotrophic and mesotrophic and the euphotic depth exceeds the mixing depth in each case. In terms of density gradient stratification, tropical and temperate lakes are in a similar range and the position of the deep chlorophyll maximum (DCM) in upper hypolimnion. At the level of DCM light intensities of about 1% of subsurface irradiation are characteristic and can suffice the light demand of shade adapted species. Availability of phosphate-P was higher int he hypolimnia of the investigated lakes, therefore this can be a selective advantage for DCM populations. Although upper hypolimnia are rather stable habitats that, in theory, would allow the best adapted species to exclude all others, cyanoprokaryotic DCM can be bi- or multispecific. In multispecific DCM, weather-driven irregularities in the stability of the pycnocline might maintain a multispecific DCM assemblage. Co-dominance of Cyanobium and Planktothrix in Lake Stechlin probably exhibited a stable co-existence when one of the species was limited by light and the other by the availability of P. Occurence of DCM by buoyant cyanoprokaryota is probably much more common in lakes of moderate (from ultra-oligortophy to moderate mesotrophy) trophic state independent of latitudinal differences and they may play a key role in matter and energy cycling of freshwater

Spatial and temporal pattern of development and decline of the spring diatom populations in Lake Stechlin in 1999

Integrated samples from the euphotic layer (mostly 0-25 m) were taken between January 1994 and December 2000 in the open water of Lake Stechlin. Monthly sampling was carried out in January-April 1999 and bi-weekly in May-June 1999 at depths of 0, 10, 20, 30, 40, 50 and 60 m. Phytoplankton, with special attention to diatoms, was qualitatively and quantitatively investigated. These data, together with water chemistry and zooplankton monitoring information, were used to describe spring development and decline of the phytoplankton. Results were compared to predictions of the PEG-model. i) The large variety in timing and species composition of early-season diatom growth allows one to conclude that in lakes, which can be either mono- or dimictic, it is primaliry not the trophic state that determines spring growth/composition, rather it is the presence, absence or duration of ice-cover and weather conditions during the onset of the thermocline. ii) Physical stresses (low temperatures, low light, complete turbulent mixing) upon phytoplankton in such lakes has been less severe than growth limitation set by scarcity of nutrients. Diatom growth starts soon after the complete autumnal overturn. Thermocline development, instead if initation of the spring bloom as stated in the PEG model, terminates growth since diatoms, cells sink rapidly into the hypolimnion. iii) „Life time” of unicellular planktonic centric diatoms was the longest int he stage when they turn to decaying or dormant cells. Empty frustules dissolve rather quickly. Frustules of planktonic pennatae diatoms were apparently more persistent than that if centrics. iv) Because of their low abundance, metazooplankton cannot play a significant role in the elimination of spring the phytoplankton crop. v) After the onset of thermocline, rejuvenating diatoms can be found in small numbers throughout the hypolimnion. This study demonstrates that one should be careful with using the term „vegetation period” since the bulk of growth of planktonic primary producers might occur during the isothermal period prior to onset of the thermocline. Moreover, driving forces during this period are largely determined by climatic factors or actual weather, such as the duration of the ice-cover or the onset time of the thermocline

Sinking properties of some phytoplankton shapes and the relation of form resistance to morphological diversity of plankton – an experimental study

Form resistance (Phi) is a dimensionless number expressing how much slower or faster a particle of any form sinks in a fluid medium than the sphere of equivalent volume. Form resistance factors of PVC models of phytoplankton sinking in glycerin were measured in a large aquarium (0.6 x 0.6 x 0.95 m). For cylindrical forms, a positive relationship was found between Phi and length/ width ratio. Coiling decreased Phi in filamentous forms. Form resistance of Asterionella colonies increased from single cells up to 6-celled colonies than remained nearly constant. For Fragilaria crotonensis chains, no such upper limit to Phi was observed in chains of up to 20 cells ( longer ones were not measured). The effect of symmetry on Phi was tested in 1 - 6-celled Asterionella colonies, having variable angles between the cells, and in Tetrastrum staurogeniaeforme coenobia, having different spine arrangements. In all cases, symmetric forms had considerably higher form resistance than asymmetric ones. However, for Pediastrum coenobia with symmetric/asymmetric fenestration, no difference was observed with respect to symmetry. Increasing number and length of spines on Tetrastrum coenobia substantially increased Phi. For a series of Staurastrum forms, a significant positive correlation was found between arm-length/cell-width ratio and Phi: protuberances increased form resistance. Flagellates (Rhodomonas, Gymnodinium) had a Phi 1. The highest value ( Phi = 8.1) was established for a 20-celled Fragilaria crotonensis chain. Possible origin of the so-called 'vital component' ( a factor that shows how much slower viable populations sink than morphologically similar senescent or dead ones) is discussed, as is the role of form resistance in evolution of high diversity of plankton morphologies

Internal Transcribed Spacer 2 (nu ITS2 rRNA) Sequence-Structure Phylogenetics: Towards an Automated Reconstruction of the Green Algal Tree of Life

L). Some have advocated the use of the nuclear-encoded, internal transcribed spacer two (ITS2) as an alternative to the traditional chloroplast markers. However, the ITS2 is broadly perceived to be insufficiently conserved or to be confounded by introgression or biparental inheritance patterns, precluding its broad use in phylogenetic reconstruction or as a DNA barcode. A growing body of evidence has shown that simultaneous analysis of nucleotide data with secondary structure information can overcome at least some of the limitations of ITS2. The goal of this investigation was to assess the feasibility of an automated, sequence-structure approach for analysis of IT2 data from a large sampling of phylum Chlorophyta.Sequences and secondary structures from 591 chlorophycean, 741 trebouxiophycean and 938 ulvophycean algae, all obtained from the ITS2 Database, were aligned using a sequence structure-specific scoring matrix. Phylogenetic relationships were reconstructed by Profile Neighbor-Joining coupled with a sequence structure-specific, general time reversible substitution model. Results from analyses of the ITS2 data were robust at multiple nodes and showed considerable congruence with results from published phylogenetic analyses.Our observations on the power of automated, sequence-structure analyses of ITS2 to reconstruct phylum-level phylogenies of the green algae validate this approach to assessing diversity for large sets of chlorophytan taxa. Moreover, our results indicate that objections to the use of ITS2 for DNA barcoding should be weighed against the utility of an automated, data analysis approach with demonstrated power to reconstruct evolutionary patterns for highly divergent lineages