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Species composition and abundance of epiphytic diatoms from an area influenced by “killer” seaweed Caulerpa taxifolia (the island of Hvar, adriatic sea): summer/autumn aspect

This study focuses on the taxonomy of epiphytic diatoms in areas of invasive macroalgae of the genus Caulerpa sp. on the eastern Adriatic Sea coast. Material was collected during two years (autumn 2008 – autumn 2010) from an area influenced by Caulerpa taxifolia in the bay of Stari Grad (the Island of Hvar). In order to compare epiphyte assemblages, sampling of coexisting autochthonous brown and green algae was conducted on the same station. Light and electron microscopy provide the information on the general morphology and ultrastructure of species, and enable a determination of the taxonomy of diatoms. The diatom assemblage was characterized by high abundances of genera Cocconeis, Mastogloia, Nitzschia, Navicula, Amphora, Hyalosynedra, Diploneis and Licmophora. The highest number of taxa was in summer (85 in July 2009, 102 in August 2009 and 74 in July 2010) and the lowest in the end of autumn/winter (eg. 32 in November 2008 and 25 in November 2009). Althought, the number of taxa within the genera Cocconeis is quite low (15), species of the genus Cocconeis, dominated the epiphytic diatom flora. The diatom assemblage was characterized by the abundance of a new species of Cocconeis, tiny Cocconeis caulerpacola Witkowski, Car et Dobosz, particularly during summer and autumn (eg. 63% in October 2009 and 40% in October 2010). Periods of higher abundance of C. caulerpacola appear to coincide with maximum toxicities observed for C. taxifolia in summer and autumn, while the minimum abundance is observed in winter and spring. The seasonal dynamics will be described on a fine time scale. Knowledge of the diatom community structure in the areas of Caulerpa spp. is important for studies of the toxic effects of the host.

epiphytic diatoms; Caulerpa taxifolia; summer; autumn

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