A contribution to the knowledge of the infralittoral benthos along the south-western coast of the Krk island

Abstract

       Preliminary investigations of macrobenthos in the region of infralittoral along the coast of the Krk island in the Rijeka bay were carried out.

       The biocenosis of photophylic algae is developed on the shallower hard bottoms and the praecoralligenous aspect of coralligenous biocenosis on the shadow and deeper hard bottoms, the latter one with characteristic algae Halimeda tuna and Udotea petiolata. The same aspect is developed on the shadow part of the mobile bottoms with Vidalia volubilis, Rhodymenia corallicola and Rytiphloea tinctoria and also in the lower shadow layer of biocenosis of marine phanerogams.

        The biocenoses reach in various snails and shells are developed on the mobile bottoms lacking marine phanerogams: in the shalow coastal part biocenosis of fine well calibrated sands and biocenosis of sandy-muddy bot­toms. In deeper part biocenosis of coastal detritic bottom, partly mixed with ooze is developed. Vatova (1949) described the last one as zoocenosis Shizaster chiajei.

       Considering the spread of the biocenoses of marine phanerogams, there could be distinguished two main areas of the studied region: the area of the more open part of the Adriatic with Posidonia oceanica meadows, and the area of the northwestern coast, under the influence of more polluted waters from the Rijeka bay, where Posidonia is replaced by Cymodocea nodosa. If both of these marine phanerogams occur at the same station, Cymodocea nodosa occupies the shallower part closer to the coast, and Posidonia oceanica the deeper part farther off shore. A separate and really small third area is the most closed, eutrophised area, overgrown with Zosterella noltii. It may be assumed that Posidonia oceanica withdraws with the increase of sea pol­lution, and is replaced by Cymodocea nodosa.