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.

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 Biolo-gical 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.

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. 4: SEM photo of the „caterpillar“ radula of the gastropod Patella

Fig. 5: Meandering grazing traces of Patella on a carbo-nate 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 distribution in fecal pellets of small and big gastropods (Littorina, Monodonta, Patella) or sea urchins (Paracentrotus) is between 20-63 µm.

Fig. 9: Typical carbonate particle from fecal pellets of grazing organisms (fraction 20-63µm). The hemi-spherical 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 lime-stone 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.

LITERATUREGolubic, 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/UmweltgeologieGeowissenschaftliches Zentrum der Universität Göttingen Email: jschnei@gwdg.de

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.

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Boreholes of endolithic cyanobacteria