Biokarst on Limestone Coasts, Morphogenesis and Sediment Production

Biokarst-forms on limestone coasts are developed and arranged  according to the bionomic zonation. The development of biokarst is  the result of bioerosion,  a synergistic effect  of biological corrosion by endoliths and biological abrasion by grazers. The cumulative  effect of biogenic carbonate destruction leads to coastal  destruction with a resulting highly profiled  morphology on the limestone surfaces along the coastal profile. Under the influence of environmental factors a zonation of organisms develops which brings in turn a zonation of erosion rates (0.1-1.1 mm . a-I) resulting in biokarst-forms such as rock holes, rock pools and notches. Products of bioerosion on limestone coasts are dissolved carbonate  (by biological corrosion, 10-30 % of the  decomposed  limestone)  and particulate carbonate (by biological abrasion, 70-90 % of the decomposed  limestone) both of which contribute  directly or indirectly to nearshore sedimen- tation. Size and shape of the  bioerosional  grains are  determined by the boring pattern of the endoliths. The fine-grained  sediments (maximum  within the fraction 20-63 pm) contribute 3-25 % to the nearshore sediments. Drastic changes in the biological zonation (like the mass invasion of the sea urchin Paracentrotus lividus in the Northern Adriatic since 1972 which eliminated  nearly the entire macrophyte zone) due to unknown factors or pollution  can have a profound effect on the bioerosion  rates, altering them by as much as a  factor of te