Descriptions of the most abundant organisms
Cyanobacteria, algae, protonemata and soil particles were differently aggregated in the plots. On the
surface only bryophytes, lichens and some Nostoc spheres were visible macroscopically. Bryophytes
not only occurred on the top of the substrate, but also in the soil under the surface with their
protonemata, whereas lichens grew relatively loose on the top. Only Collema was tightly attached to
the surface.
Organisms which were closely aggregated with the soil particles were Microcoleus and Zygogonium.
Sometimes Nostoc colonies were also woven in. Litter particles were also colonized by some
organisms or only stuck to the sand grains.
Moreover, the darkest parts of the crusts were the parts with the highest proportion of organisms;
lighter parts showed fewer organisms. Mostly the dark colour results from cyanobacteria or
protonemata. The parts with a higher bryophyte cover are characterized by fewer cyanobacteria and
algae. Only in bryophyte layers were different Bacillariophyceae present. some organisms like
Microcoleus and Zygogonium were detected in all parts and depths of the crust, whereas coccal
cyanobacteria and algae only occurred in the upper millimetres or at the highest accumulations.
Lyngbya and Gloeocapsa were often also detected under larger sand grains.
In
water
samples
which
were
withdrawn,
many
Bacillariophyceae,
Synechococcus,
Chloridella/Pleurochloris and a few Cylindrocystis, Oscillatoria and Zygogonium were detected.
Furthermore, various spores of fungi were visible but could not be identified further.
1 Cyanobacteria
(a) Gloeocapsa compacta
Microscopic colonies, gelatinous, irregular, with many cells, composed of several sub-colonies with
two to four cells. Cells spherical, 2.6 µm in diameter with individual envelopes and unified with
envelopes from other generations. Mucilaginous envelopes wide, at first colourless, later intensely
violet.
(b) Chroococcus pallidus
Microscopic gelatinous colonies; colonies often consisting of two cells (sometimes four). Cells
spherical, 7.5 µm in diameter without envelopes, pale blue-green coloured.
(c) Sychenococcus cf. sciophilus
Cells elliptical or cylindrical (straight, ends rounded), 3.0-5.0 µm broad, 7.0-15.0 µm long, pale bluegreen, cells solitary or two together after division.
(d) Tolypothrix fasciculata
Filaments aggregating in erect fascicles, false branches (raised from below a heterocyst), sheath firm,
narrowed, at first without colour, yellow to brown with increasing age. Cells blue-green, cylindrical,
7.6 µm broad, longer than broad. One heterocyst, sometimes two, one behind the other.
(e) Nostoc commune
Macroscopic thalli (up to 2 cm) often detected in the field after moist periods. Colonies in dry
conditions thin, almost black, after rewetting they swell up. Colonies at first spherical, later spread out
flat on the surface, gelatinous, crumpled, often green-brown or yellow-brown, with a solid outside.
Trichomes densely entangled, cells almost spherical 5.1 µm in diameter, sometimes shorter or longer
than broad, olive green. Heterocysts almost spherical 7.0 µm in diameter. Heterocysts intercalarly, in
germinating hormogones terminal.
(f) Nostoc microscopicum
Thalli spherical or elliptical, on agar smaller than N. commune (often up to 3-5 mm), with a solid
outside, olive-green. Trichomes loosely entangled, cells 5.1 µm in diameter, intensely blue-green.
Heterocysts almost spherical, 7.0 µm in diameter.
(g) Nostoc cf. minutum
Thallus small (<1 mm), first spherical, later spread out, with a solid outside. Trichomes dense
entangled, cells cylindrical 2.6 µm, heterocysts 5.0 µm.
(h) Oscillatoria
Individual trichomes without sheaths, but often with crawling movement. Trichomes cylindrical,
straight or slightly waved. With or without constrictions at the cross-walls (taxon-dependent). Cells
short, shorter than wide. Hormogones are common in cultures and soil substrate.
(i) Phormidium sp.
Filaments solitary or in colonies. Trichomes pale blue-green, with morphologically identical ends,
straight, sometimes slight curved, motile, 3.0 µm wide. Sheaths present, thin, narrow and colourless.
(j) Lynbya sp.
Filaments straight, solitary, sheaths thin and colourless. Trichomes cylindrical, not constricted at
cross-walls. Cells shorts, shorter than wide, without calyptra.
(k) Microcoleus vaginatus (Plate III a)
Filaments solitary, often forming an almost black thallus. Sheaths colourless, often wrapped rope-like
around each other, containing numerous, densely entangled or parallel trichomes. Cells bright blue,
3.0-5.0 µm wide (sometimes broader) and 3.0 µm long (sometimes longer), granulations at the not
constricted cross-walls. Apical cell capitate, with a conical calyptra.
(l) Microcoleus cf. paludosus
Filaments solitary or forming a back blue-green thallus. Filaments dark blue-green, unbranched,
sometimes divided at the ends, sheath slightly mucilaginous and colourless, containing many
trichomes either straight in parallel or sometimes twisted like a rope. Trichomes without granulations
at the cross-walls and without constrictions, 5.0-7.0 µm wide and 4.0-7.6µm long. Apical cell not
capitate, conical.
2 Algae
(a) Chloridella/Pleurochloris sp.
Cells spherical, sometimes a bit irregular, with a slight size increase. Cell wall soft, sometimes tough,
several chloroplasts. Cells mostly 5.1 µm in diameter, in individual cases 3.0-4.0 or 8-10 µm.
(b) Chlorococcum cf. infusionum
Cells solitary, sometimes an irregular cluster of cells was recorded. Young cells elliptical, older forms
spherical, cell wall thin. Chloroplast solid, in older forms often cut in ribbons. Cells 10 up to 23.0 µm
in diameter (sometimes only 8.0 µm). In old cultures individuals often golden coloured.
(c) Chlorella cf. vulgaris
Individual cells, spherical, cell wall thin without structure, large vacuole. Cells mostly 10.0 µm.
(d) Elliptochloris cf. subspherica
Individual cells, young ones cylindrical with rounded ends, older ones elliptical or almost spherical.
The size of the chloroplast is almost the half of the cell size. Cells 5.0-6.0 µm broad, up to 10.2 µm
long, spherical individuals up to 15.0 µm in diameter.
(e) Gloeocystis cf. vesiculosa
Many subcolonies forming a large colony. Subcolonies spherical or oval, with concentric stacked jelly,
1-8 cells oval or spherical, cells 5.1 µm (sometimes up to 7.7 µm), subcolonies 15.0-23.0 µm.
(f) Cylindrocystis cf. brebissonii
Cells cylindrical, ends wide rounded. In every half cell one axial, asteroid chloroplast. Cells 16.017.9 µm broad and 34.4-38.3 µm long.
(g) Scenedesmus acututs
Four cells forming a colony. Cells arranged in parallel in a single row, in contact with one another
over up to half of their sides, poles are slightly narrowed. Cells inside the colonies straight, outer cells
show concave ends. Cells 2.6 µm broad and 10.2 µm long.
(h) Bracteacoccus cf. minor
Coenoblasts spherical, 7.6 µm in diameter, containing several chloroplasts. Cell walls thin, smooth
without structure.
(i) Chlamydomonas cf. reinhardtii
Cells spherical to elliptical, motile. Cell wall soft, chloroplast solid (pot-shaped), Stigma present. Cells
7.6 µm broad, 10.2 µm long (or smaller).
(j) Zygogonium ericetorum
Filaments cylindrical, with regular thick cell walls and solid chloroplasts. In unfavourable conditions
cell walls often thick, chloroplasts flattened. Cells often 10.2 µm broad (sometimes 7.6 or >10.2 µm).
(k) Stichococcus bacillaris
Cells cylindrical and almost straight, poles rounded. Chloroplasts fill up to 2/3 of the whole cell. Cells
2.6 µm (or broader) and up to 10.2 µm long. Sometimes two cells one behind the other.
(l) Klebsormidium cf. crenulatum
Young filaments with soft cell walls, in older ones thick, rough and warty. Many cell fragments
(reproduction). Cells 10.2-12.8 µm broad, length less than or equal to breadth.
(m) Klebsormidium cf. dissectum
Filaments consisting of 4-15 cells, often curved. Often disintegrating into smaller pieces. Cells 5.1 µm
broad and 7.6 µm long.
(n) Klebsormidium flaccidum
Often forming thick layers (visible also in the field). On agar develops dense loops of parallel
filaments. Cells cylindrical, 7.6 µm broad and 12.8-17.9 µm long.
(o) Klebsormidium cf. klebsii
Cells cylindrical, without constrictions on the cell walls. Forms long filaments like those of
Klebsormidium flaccidum. Cells 5.1 µm broad and 5.1-10.2 µm (sometimes 12.8 µm) long.
(p) Coccomyxa cf. confluens
Macroscopic colonies, adhering to the substrate, often up to one centimetre in size, mucilaginous,
green. Cells almost elliptical, irregularly distributed in the jelly. Cells 5.1 µm broad and 7.6 µm long.
(q) cf. Chlorosarcinopsis sp.
Cells 8.0-10.2 µm in diameter, cell walls soft, flatten against each other, occurring in cell stacks.