TAXONOMIC COMPOSITION OF EPIPHYTIC DIATOMS FROM AREAS AFFECTED BY INVASIVE MACROALGAE CAULERPA TAXIFOLIA AND CAULERPA CYLINDRACEA (ADRIATIC SEA, CROATIA)

The present study focuses on the taxonomy of epiphytic diatoms in areas affected by invasive macroalgae representing the the genus of Caulerpa J.V. Lamouroux, 1809 on the eastern Adriatic Sea coast. Material for the study of epiphytic diatoms was collected during two years (autumn 2008 – autumn 2010) from an area influenced by Caulerpa taxifolia (Vahl) C. Agardh in the bay of Stari Grad (the Island of Hvar), and from areas influenced by Caulerpa cylindracea Sonder in Dubrovnik and on the Island of Mljet (Gonoturska Bay). In order to compare epiphyte assemblages, sampling of coexisting autochthonous brown and green algae was conducted at the same stations. The samples were acid cleaned (HCl/H2O2) prior to qualitative analysis of diatoms using light microscope (LM) (Nikon E600 microscope) under magnification of 1000x. Light and electron microscopy examinations provide for the first time the information on the general morphology and ultrastructure of taxa, and enable a determination of the taxonomy of diatoms. The seasonal dynamics were described on a fine time scale. For the first time in the Central and Southern Adriatic Sea the composition of benthic diatoms and seasonal dynamics of taxa in areas affected by invasive macroalge Caulerpa taxifolia and Caulerpa cylindracea were determined. The results of this study enable a better understanding of the functioning of ecosystems dominated by macroalgae Caulerpa spp. Knowledge of the diatom community structure in the areas impacted by Caulerpa spp. is important for studies of the toxic effects of the host.