engleski

Species composition and abundance of diatom flora inhabiting thalli of Caulerpa racemosa and C. taxifolia (Adriatic Sea coast, Croatia)

This study focused on the diatom species associated with exotic seaweeds on the coast of the Croatian Adriatic Sea. The macroalgae are Caulerpa racemosa (Island of Mljet, Island of Lokrum near Dubrovnik, Southern Adriatic) and C. taxifolia (Bay of Stari Grad, Island of Hvar, Middle Adriatic). Fresh and processed material was studied by means of light (LM) and electron microscopy (SEM and TEM). Our examination of both unprocessed and processed (hydrogen peroxide treated) samples revealed an abundant and species-rich diatom flora. Examination of unprocessed material demonstrated an attached diatom flora, not incorporated into bioaggregates. A total of ca. 150 taxa have been identified. The difference in species composition between the seaweed taxa was significant, as only 26 taxa occurred on both host plants. We have identified 69 diatom taxa, representing 26 genera, associated with C. racemosa and 131 taxa, representing 32 genera, with C. taxifolia. Mode of attachment of the epiphytes differed between the two host algae. On C. racemosa surface-adhered Cocconeis or tube dwelling Mastogloia species were dominant. On C. taxifolia tube-dwelling taxa dominated. In the case of C. racemosa, the most abundant species were Cocconeis spp., while in C. taxifolia, Mastogloia spp. were most abundant. The most species rich genus included Mastogloia with 14 taxa on C. racemosa and 25 taxa on C. taxifolia. A variety of tube patterns of Mastogloia spp. were observed on thalli of both seaweed species. This was independent from preservation state of the thalli (i.e. fresh versus decaying). The abundant taxa are well known as epiphytes. Included in this group are representatives of Berkeleya, Cocconeis, Licmophora, Mastogloia and Navicula.

Diatom; Caulerpa; Adriatic Sea

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