Morphological evolution from a unicellular to multicellular state provides greater opportunities for organisms to attain larger and more complex living forms. As the most common freshwater cyanobacterial genus, Microcystis is a unicellular microorganism, with high phenotypic plasticity, which forms colonies and blooms in lakes and reservoirs worldwide. We conducted a systematic review of field studies from the 1990s to 2017 where Microcystis was dominant. Microcystis was detected as the dominant genus in waterbodies from temperate to subtropical and tropical zones. Unicellular Microcystis spp. can be induced to form colonies by adjusting biotic and abiotic factors in laboratory. Colony formation by cell division has been induced by zooplankton filtrate, high Pb2+ concentration, the presence of another cyanobacterium (Cylindrospermopsis raciborskii), heterotrophic bacteria, and by low temperature and light intensity. Colony formation by cell adhesion can be induced by zooplankton grazing, high Ca2+ concentration, and microcystins. We hypothesise that single cells of all Microcystis morphospecies initially form colonies with a similar morphology to those found in the early spring. These colonies gradually change their morphology to that of M. ichthyoblabe, M. wesenbergii and M. aeruginosa with changing environmental conditions. Colony formation provides Microcystis with many ecological advantages, including adaption to varying light, sustained growth under poor nutrient supply, protection from chemical stressors and protection from grazing. These benefits represent passive tactics responding to environmental stress. Microcystis colonies form at the cost of decreased specific growth rates compared with a unicellular habit. Large colony size allows Microcystis to attain rapid floating velocities (maximum recorded for a single colony, ∼ 10.08 m h-1 ) that enable them to develop and maintain a large biomass near the surface of eutrophic lakes, where they may shade and inhibit the growth of less-buoyant species in deeper layers. Over time, accompanying species may fail to maintain viable populations, allowing Microcystis to dominate. Microcystis blooms can be controlled by artificial mixing. Microcystis colonies and non-buoyant phytoplankton will be exposed to identical light conditions if they are evenly distributed over the water column. In that case, green algae and diatoms, which generally have a higher growth rate than Microcystis, will be more successful. Under such mixing conditions, other phytoplankton taxa could recover and the dominance of Microcystis would be reduced. This review advances our understanding of the factors and mechanisms affecting Microcystis colony formation and size in the field and laboratory through synthesis of current knowledge. The main transition pathways of morphological changes in Microcystis provide an example of the phenotypic plasticity of organisms during morphological evolution from a unicellular to multicellular state. We emphasise that the mechanisms and factors influencing competition among various close morphospecies are sometimes paradoxical because these morphospecies are potentially a single species. Further work is required to clarify the colony-forming process in different Microcystis morphospecies and the seasonal variation in this process. This will allow researchers to grow laboratory cultures that more closely reflect field morphologies and to optimise artificial mixing to manage blooms more effectively.

Colony formation in the cyanobacterium Microcystis

Bridging the Rubicon: Phylogenetic analysis reveals repeated colonizations of marine and fresh waters by thalassiosiroid diatoms

Similar to the increased number of studies on invasive plants and animals in terrestrial and aquatic ecosystems, many reports were recently published on the invasion of Nostocales (cyanobacteria) to freshwater environments worldwide. Invasion and proliferation of Nostocales in new habitats have the potential to significantly alter the structure of the native community and to modify ecosystem functioning. But most importantly, they influence the water quality due to a variety of toxic compounds that some species produce. Therefore a special attention was given to the invasion and persistence of toxic cyanobacteria in many aquatic ecosystems. Here we summarize the currently published records on the invasion of two Nostocales genera, Cylindrospermopsis and Aphanizomenon, to lakes and water reservoirs in subtropical and temperate zones. These invading species possess traits thought to be common to many invasive organisms: high growth rate, high resource utilization efficiency and overall superior competitive abilities over native species when local conditions vary. Assuming that dispersion routes of cyanobacteria have not been changed much in recent decades, their recent establishment and proliferation in new habitats indicate changes in the environment under which they can exploit their physiological advantage over the native phytoplankton population. In many cases, global warming was identified as the major driving force for the invasion of Nostocales. Due to this uncontrollable trend, invasive Nostocales species are expected to maintain their presence in new habitats and further expand to new environments. In other cases, regional changes in nutrient loads and in biotic conditions were attributed to the invasion events.

/pdf/invasion-of-nostocales-cyanobacteria-to-subtropical-and-1tvta26w3r.pdf

Invasion of Nostocales (cyanobacteria) to Subtropical and Temperate Freshwater Lakes - Physiological, Regional, and Global Driving Forces.

A review of the phylogeny, ecology and toxin production of bloom-forming Aphanizomenon spp. and related species within the Nostocales (cyanobacteria).

Lake phytoplankton studies outnumber studies on lake periphyton by an order of magnitude, and most periphyton research has been done in streams. Most benthic algal taxa found in lakes also can be found in lotic systems, but assemblages and taxa differ in a number of ways. The ecological characteristics of some lake benthic algae reflect habitat coupling. Littoral zones (benthic areas above the light compensation depth) are areas of high productivity and biodiversity. The proportion of benthic and planktonic primary production (autotrophic structure) is a key ecosystem property. The distribution of lake benthic algae is markedly influenced by the depth gradient and substratum, and assemblages change with depth from epilithic and epiphytic rheobionts to epipsammic and epipelic limnobionts. At shallow depths, periphyton must cope with the effects of high radiation, water-level fluctuations, wave action (e.g., desiccation, ultraviolet radiation exposure, shear stress), and seasonal shifts in temperatu...

https://www.jstor.org/stable/10.1086/676140

Lake benthic algae: toward an understanding of their ecology

The valve morphology and ultrastructure of the the so-called “stelligeroid” taxa of the genus Cyclotella (Kutzing) Brebisson (Bacillariophyceae) are discussed. These taxa have marginal mltoportulae and the rimoportula(e) positioned between costae. As this and other discussed characters do not fit the current description of the genus Cyclotella (Kutzing) Brebisson nom. cons., the formal transfer of these taxa into a new genus, Discostella gen. nov., is proposed.

The stelligeroid taxa of the genus cyclotella (kützing) brébisson (bacillariophyceae) and their transfer into the new genus discostella gen. nov.

The invasion and spread of non-native species of many different kinds of organisms is of increasing interest to researchers. Invasions by microscopic organisms, however, are poorly understood, and their impact on the environment is probably underestimated. We collected available data on non-native and invasive/expansive algae and cyanobacteria in the Czech Republic; we mapped their distribution and assessed their impact on local species and other real or potential risks resulting from their spread. The list of alien species in the Czech Republic contains 10 species of cyanobacteria, 9 species of Bacillariophyceae, 1 species of Dinophyta, 1 species of Ulvophyceae, 2 species of Chlorophyceae, and 1 species complex of Zygnematopyceae. The literature on the worldwide occurrence of these taxa is also reviewed.

http://rybarstvi.eu/pub%20rybari/2010%20kastovsky.pdf

A review of the alien and expansive species of freshwater cyanobacteria and algae in the Czech Republic

Several morphotypes of the “Orthoseira roeseana” complex from different localities have been examined and their appreciable morphological variability is illustrated and discussed. The shape of girdle-bands of “spiral” forms is described and depicted in SEM. The occurrence of valves with a ring of wall attenuations at the margin was observed in two different morphological groups. Moreover it seems that J. D. Moller's type slides of Liparogyra dendroteres Ehr. and Orthosira roeseana Rabh. treated here are derived respectively from Ehrenberg and Rabenhorst type material.

Some morphotypes in the Orthoseira roeseana' complex

A new stelligeroid Cyclotella (Bacillariophyceae), Cyclotella mascarenica KLEE, HOUK et BIELSA nov. spec., from a pond on Reunion Island (France) is described here on the basis of LM and SEM studies. This species is strongly reminiscent of Cyclotella stelligera (CLEVE et GRUNOW) VAN HEURCK, however, it differs from it by thicker ribs, by the fact that inside, each rib is typically forked to a finger-like structure near the valve margin and that the marginal fultoportula is inserted on a rib where this forking begins. Une nouvelle espece de Cyclotella (Bacillariophyceae), Cyclotella mascarenica KLEE, HOUK et BIELSA nov. spec., provenant de l'ile de la Reunion (France) est decrite a partir d'observations au microscope optique et au microscope electronique a balayage. Cette espece est tres proche de Cyclotella stelligera (CLEVE et GRUNOW) VAN HEURCK; elle en differe par des cotes plus epaisses qui se caracterisent interieurement par des extremites bifurquees au voisinage du bord de la valve et par la position de la fultoportula marginale, placee au depart de la bifurcation.

Václav Houk

Papers

The stelligeroid taxa of the genus cyclotella (kützing) brébisson (bacillariophyceae) and their transfer into the new genus discostella gen. nov.

A review of the alien and expansive species of freshwater cyanobacteria and algae in the Czech Republic

Some morphotypes in the Orthoseira roeseana' complex

Cyclotella mascarenica nov. spec., a new stelligeroid Cyclotella (bacillariophyceae) from a pond of the Réunion Island (France)

Morphology and Ultrastructure of Cyclotella woltereckii HUSTEDT (Bacillariophyceae)