The Role of Bioerosion for the
Production of Carbonate Sediments
„Joint Team of Geomicrobiological Calcibiocavitology“
Jürgen Schneider, Horst Torunski, Stjepko Golubic, Thérèse Le-Campion-Alsumard
Bioerosion in marine environments comprises the synergistic processes
of Biological Corrosion mostly by endolithic cyanobacteria, and Biological Abrasion by different grazing organisms (especially gastropods and
echinoderms). Epilithic, chasmo-/krypto-endolithic and eu-endolithic
cyanobacteria colonize all carbonate substrates densely together with
fungi and other microorganisms (Golubic, Friedmann & Schneider 1981).
Fig 1: More than 500.000 individuals of euendolithic
cyanobacteria per cm2 colonize the limestone
substrates at marine coasts. Dense colonization by
the euendolithic cyanobacteria species Kyrtuthrix
dalmatica and Mastigocoleus testarum (SEM photo
of a resin cast).
Fig. 2: The euendoliths penetrate the substrate
always in a direction vertical to the surface (bore
holes of the cyanobacteria Hyella sp, SEM-photo
after removing the organisms). The grains of the
rock within the bore holes and at the surface
therefore get disintegrated.
At marine carbonate coastal profiles characteristic colour zones are caused by
different cyanobacteria species depending on the distance and height above
sea level and according to the level of exposure to humidity, insolation, waves,
spray and splash water (Le Campion-Alsumard 1969, Schneider 1976). The
endolithic cyanobacteria as the pioneer colonizers on limestone coasts facilitate
settling and attack of different grazers, predominantly gastropods and
echinoderms. The grazers, searching for food, abrade the rock surfaces
mechanically with their feeding apparatus. Thereby the loosened surface grains
are scraped away together with the microorganisms.
Fig. 3: Bioerosion scheme (after
Torunski 1979, Schneider & Torunski
1983). The carbonate rock surface is
rasped away e. g. by the radula of the
marine gastropod Patella. The
grazers never overgraze their
pasture. It exists a delicate balance
between biological corrosion and
biological abrasion.
Fig. 9: Typical carbonate particle from fecal pellets
of grazing organisms (fraction 20-63µm). The hemispherical hollows of bore holes in the outline prove
the hypothesis that grain size distribution of
bioerosional sediments is predetermined by the
boring pattern of the endolithic microorganisms.
Fig. 10: Typical bioerosional particles from the
fraction 63-80 µm from sublitoral sediments. The
particle in the centre is a very characteristic „chip“
produced by the boring sponge Cliona.
Fig. 11: Bioerosion results particularly at the
extreme high water line (spring tide) of limestone coasts, where the differences in
humidity are extreme, in a highly profiled
and accentuated coastal morphology that is
called Biokarst.
Fig. 12: On every carbonate coast at the low
water line a notch can be found world wide.
This is not a surge but a biogenic notch
produced by the synergistic bioerosional
action of microorganisms, gastropods, sea
urchins, boring sponges and boring bivalves.
Fig. 4: SEM photo
of the „caterpillar“
radula of the
gastropod Patella
Fig. 5: Meandering
grazing traces of
Patella on a carbonate surface (coin
about 20 mm)
Fig. 6: The rasped carbonate particles are excreted
with fecal pellets of Patella after grazing on a white
limestone colonized by cyanobacteria (diameter of
Patella about 4 cm)
Fig. 7: „Magic circles“ of
cyanobacterial bore holes
on limestone surfaces
Fig. 8: Theoretical grain size distribution drawn
from SEM micrographs of a limestone surface
attacked by euendolithic cyanobacteria. The grain
size of fecal pellets is predetermined by the boring
pattern of the endoliths. The dotted lines
represent the form of the carbonate particles
broken away during grazing of gastropods or
echinoderms. This is independent on the size of
the grazers. Carbonate particles within fecal
pellets of all gastropods and sea urchins were
selectively collected. The average grain size
Boreholes of
distribution in fecal pellets of small and big
endolithic cyanobacteria
gastropods (Littorina, Monodonta, Patella) or
0
µm 50
sea urchins (Paracentrotus) is between 20-63 µm.
Fig. 13: At the Adriatic coast bioerosion produces 2 kg of dissolved CaCO3
from biological corrosion and 9 kg of particular CaCO3 from biological
abrasion per every meter coast line and year. The particles produced by
biological abrasion contribute up to 25% to near shore sedimentation. The
characteristic particles are clearly discernible within the size fractions of near
shore sediments. The dissolved carbonate is washed to the sea and can be
used by all carbonate skeleton building organisms in the sublitoral. Fossil
marine carbonate rocks are that way recycled back to the sea.
Bioerosion takes place at all limestone coasts as well as in the sublitoral
zones and in tropical coral reef environments, resulting in the
destruction of every carbonate substrate and the production of fine
grained sediments.
LITERATURE
Golubic, S., Friedmann I. & Schneider, J. (1981) The lithobiontic ecological niche, with special
reference to microorganisms.- J. Sediment. Petrol., 51, 475-478.
Le Campion-Alsumard, T. (1969): Contribution à l´étude des cyanophycées lithophytes des
étages supralittoral et mediolittoral (région de Marseille).- Tethys, 1, 119-172.
Schneider ; J. (1976): Biological and inorganic factors in the destruction of limestone coasts.Contrib. Sedimentol., 6, 112 p.
Torunski, H. (1979): Biological Erosion and its Significance for the Morphogenesis of Limestone
Coasts and for Nearshore Sedimentation (Northern Adriatic).- Senckenbergiana marit., 11, (3/6),
193-265.
Schneider, J. & Torunski, H. (1983): Biokarst on limestone coasts, morphogenesis and sediment
production.- Mar. Ecol., 4, 45-63.
Schneider, J. & Le Campion-Alsumard, T. (1999): Construction and destruction of carbonates by
marine and freshwater cyanobacteria.- Eur. J. Phycol., 34, 417-426.
Prof. Dr. Jürgen Schneider,
Abteilung Sedimentologie/Umweltgeologie
Geowissenschaftliches Zentrum der
Universität Göttingen
Email: jschnei@gwdg.de