Cladophora

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Cladophora
Cladophora ruprestis

Cladophora ruprestis

Systematics
without rank: Chloroplastida
without rank: Chlorophyta
Class : Ulvophyceae
Order : Cladophorales
Family : Cladophoraceae
Genre : Cladophora
Scientific name
Cladophora
Kützing
Cells of Cladophora

Cladophora is a green algae - genus of the class of Ulvophyceae global distribution. Many species tend to mass reproduce throughman-made eutrophication of bodies of water; they can then cause economic and ecological problems. The species-rich genus includes species that are common in the sea, fresh water and brackish water. Cladophora species have few morphological featuresand are very similar to one another, many morpho species are difficult to identify, in some cases they do not match genetically distinct lines ( crypto species ). The number of species and delimitation of the genus are therefore controversial.

description

Cladophora (translated: branch carrier) forms green-colored, more or less strongly branched tufts of single-row cell threads, which are chambered by transverse walls (septa). These are anchored on substrates of the water bed (mostly hard substrates) and range from more or less upright to creeping forms. In some species such as Cladophora rupestris , filaments growing backwards seem to form multi-part axes. The anchoring is done by thread-like rhizoids or simple retaining washers. More rarely, there are free-floating or floating forms without anchoring. The rhizoids originate from the first (basal) cells of the cell cluster, secondary rhizoids do not occur. The filaments grow and branch out in several different ways. In some species, growth occurs predominantly at the tips of the filaments (apical), in many others the cells inside the filaments elongate and divide new cells (intercalary). In many species, both growth patterns occur side by side, each in different proportions. Branches are formed when a cell pushes a bud-shaped bulge outwards near its apical end, which is finally pinched off by a septum as a new cell and elongates into another cell thread. Several such branches can proceed from one cell in succession. The shape of the tuft-shaped thallus is influenced by the point at which new side threads branch off and how long they reach, the branches often decrease in length towards the tip, in other species threads of all lengths occur next to each other. Older branches are often no longer recognizable as to which side branch was, so that an apparently forked (pseudo-dichotomous) branch results.

The individual cells within the cell threads are always more or less elongated (up to a maximum of about 300 micrometers), cylindrical to barrel or club-shaped. The nucleus divisions and constriction of new cells by cell walls are not synchronized with each other, so that the cells contain many cell nuclei . Each cell contains numerous, small vacuoles and is therefore foam-like in shape. There are mostly numerous, disc-shaped chloroplasts concentrated at the edge , many of them with a single pyrenoid , so that a homogeneous green color results, the chloroplasts can be connected like a network. In a few species, Cladophora cells have a thin, but mostly a thick and stable, sometimes longitudinally streaked cell wall, which consists predominantly of cellulose (in some species a thin outer covering made of other substances has been demonstrated). In contrast to land plants, the cellulose microfibrils have a thicker and more regular crystalline structure, which makes the cellulose more dense and more difficult to break down enzymatically.

Reproduction

The asexual multiplication takes place by the formation of two- or viergeißeligen zoospores . The spore-forming cells are almost always located in the apical (terminal) sections of the cell threads. The spores are formed by numerous cell divisions within a cell and released from the cell wall through pore-shaped openings. In addition, asexual reproduction occurs via simple fragmentation of the cell threads. Outside of the growing season, small sections of prostrate cell filaments (akinetes) can overwinter and sprout again in the next year.

The sexual reproduction is effected by the merger of equal size zweigeißeliger gametes (isogamy). The alga shows an isomorphic generation change; an asexual, spore-forming generation ( sporophyte ) alternates regularly with a similarly formed, gamete-producing generation ( gametophyte ). This development cycle was mainly observed in marine representatives of the genus, at least the most widespread freshwater species Cladophora glomerata seems to reproduce purely asexually.

distribution

The genus is distributed worldwide, in marine and limnic habitats, from the tropics to arctic waters.

Way of life

The genus includes, unusually, both freshwater and marine species, but neither species occurs in both habitats. Two diverse species invade brackish water habitats, Cladophora glomerata from fresh water and Cladophora vagabunda (in the broader sense, sensu lato , in reality a complex of cryptic species) from marine habitats.

Cladophora species usually live firmly grown on solid surfaces, mostly hard substrates such as stones, rarely in dwarf forms with a holding disk on grains of sand. Almost all of the marine species live in coastal waters, in the shore zone ( littoral ) in shallow water depths. The limnic freshwater species live in both standing and flowing waters .

Cladophora -Thalli provide a rich community of, partly specialized, bacteria and microalgae species as growth ( periphyton ) habitat. Although the thalli are almost completely spurned by herbivores due to their high cellulose content, which is difficult to digest, they can structure their habitat; numerous other species find shelter and habitat in the tangle of threads. Especially in marine habitats, however, Cladophora threads themselves also form dense growth on other macroalgae or seaweeds and thus change their habitat. They were therefore called "ecosystem engineers".

Pond with algal blooms from Cladophora glomerata
Cladophora mats, with empty shells of zebra mussels, in the shoreline of Lake Michigan

The genus is strongly dominant in rivers in meso- and eutrophic brooks and rivers in summer. Oligotrophic waters are avoided. In both marine and limnic waters, the algae can form algal bloom- like mass stocks , especially when there is an increased nutrient content, which displace other species and, due to their high biomass, especially when they die off seasonally, heavily pollute their habitat. In the American Great Lakes, for example, when Cladophora developed massively, the biodiversity in the habitat was greatly reduced. Mainly affected are waters that have been eutrophied by sewage, in coastal waters with nitrogen, in limnic waters especially with phosphorus. Supplied with plenty of phosphate, Cladophora glomerata was able to increase its biomass by 60 percent daily under optimal conditions in the Great Lakes. If the phosphate content fell below 0.6 micrograms per liter of water, however, growth was no longer possible.

Phylogeny, Taxonomy and Systematics

The genus Cladophora was described by Friedrich Traugott Kützing in 1843 (the older name Annulina Link in 1820 was suppressed by a decision of the ICBN , so the name Cladophora was preserved). Type species was Conferva oligoclona , today a synonym of Cladophora rivularis (Linnaeus) Kuntze; Carl von Linné originally grouped all algae with thread-like thalli in his now-abandoned genus Conferva . The genus Cladophora traditionally comprised the branched and fixed species of the family Cladophoraceae, in today's view the only family of the order Cladophorales. The group's taxonomy has long been difficult and controversial due to the morphologically simple degree of organization with only a few usable characteristics. In Europe, for example, significantly more than 500 species have been described over time, mostly after small variations in the branching pattern, which the researcher Christiaan van den Hoek reduced to just 34 in his revision of the genus. At the same time, these species were morphologically variable and diverse, making them difficult to differentiate. This has only changed fundamentally since the species are compared on the basis of their DNA sequence ( phylogenomics ). It soon emerged that the genus Cladophora was not a monophyletic unit in its traditional description . In addition, numerous species were indistinguishable by their DNA sequence (i.e. possible synonyms ), while others split into numerous genetically different, morphologically indistinguishable lines ( cryptospecies ). The taxonomy of the genus is therefore currently in flux and will continue to change.

Van den Hoek had split the genus into a number of sub-genres, the delimitation of which is now considered dubious.

The traditional freshwater species of the genus are morphologically very difficult to distinguish from one another and, according to genetic studies, cannot be differentiated from one another. Some researchers have therefore switched to provisionally assigning all freshwater forms to a broad species, Cladophora glomerata , until the situation has been clarified . In fact, numerous species are to be expected in freshwater, especially in the so far poorly studied tropics.

In a genetic investigation of almost 100 species, the genus was found to be polyphyletic in the traditional description compared to the other genera of the Cladophorales. Obviously, branched species have evolved into unbranched species many times and free-floating species emerged from fixed ones. Therefore, some species and groups of species were removed from the genus and moved to the new or reactivated genera Willeella and Acrocladus (later renamed Lychaete for nomenclature reasons ). The newly delimited genus Cladophora can no longer be distinguished from the related genera purely on the basis of morphological features. Even today, it includes hundreds of species.

European species

Marine water species

Freshwater species

The species Cladophora aegagrophila was transferred to another genus, the correct name is now Aegagropila linnaei .

Individual evidence

  1. ↑ a b Christiaan van den Hoek (1963): Revision of the European Species of Cladophora. EJ Brill, Leiden 1963.
  2. ↑ Cladophora , in MD Guiry in Guiry, MD & Guiry, GM 2020. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. www.algaebase.org. accessed on February 15, 2020. Description of the genre follows Škaloud, P., Rindi, F., Boedeker, C. & Leliaert, F. (2018). Freshwater flora of Central Europe. Freshwater flora of central Europe. Vol 13. Chlorophyta: Ulvophyceae (Krienitz, L. ed.). pp. [i] -vii, [1] -288, 182 figs. Berlin: Springer Spectrum.
  3. ^ A b Francis Bunker, Juliet A. Brodie, Christine A. Maggs, Anne R. Bunker: Seaweeds of Britain and Ireland. Wild Nature Press, Plymouth, 2nd edition 2017. ISBN 978-0-9955673-3-7 .
  4. ↑ a b c d Shahrizim B. Zulkifly, James M. Graham, Erica B. Young, Robert J. Mayer, Michael J. Piotrowski, Izak Smith, Linda E. Graham (2012): The Genus Cladophora Kützing (Ulvophyceae) as a Globally Distributed Ecological Engineer. Jounal of Phycology 49 (1): 1-17. doi: 10.1111 / jpy.12025
  5. ↑ a b c d Christian Boedeker, Frederik Leliaert, Giuseppe C. Zuccarello (2016): Molecular phylogeny of the Cladophoraceae (Cladophorales, Ulvophyceae), with the resurrection of Acrocladus Nägeli and Willeella Børgesen, and the description of Lurbica gen. and Pseudorhizoclonium gen. nov. Journal of Phycology 52: 905-928. doi: 10.1111 / jpy.12457
  6. ↑ a b Škaloud, P., Rindi, F., Boedeker, C. & Leliaert, F. (2018). Freshwater flora of Central Europe. Freshwater flora of central Europe. Vol 13. Chlorophyta: Ulvophyceae (Krienitz, L. ed.). pp. [i] -vii, [1] -288, 182 figs. Berlin: Springer Spectrum. ISBN 978-3-662-55494-4
  7. ↑ Michael J. Wynne (2017): The reinstatement of Lychaete J. Agardh (Ulvophyceae, Cladophoraceae). Notulae algarum 31: 1-4.
  8. ^ DM John, Brian A. Whitton, Alan J. Brook: The freshwater algal flora of the British Isles: an identification guide to freshwater and terrestrial algae. Volume 1. Cambridge University Press (England) 2002. ISBN 0-521-77051-3

Web links

Commons : Cladophora  - collection of images, videos and audio files