engleski

Periphytic algae development in the upper reach of the Zrmanja Estuary (eastern Adriatic coast)

Diatom composition and abundance in biofilm that formed on artificial sub¬ ; ; strates exposed at several depths in July 2000 were investigated at two stations in Croatia's oligotrophic and highly-stratified Zrmanja Estuary. Chlorophyll a ranged from 2.27 to 92.81 mg m^-2. HPLC analysis provided evidence of diatom dominance, while green algae and cyanobacteria contributed less than 1 %. Of 57 diatom species, two genera, Navicula and Nitzschia, dominated. After 2 weeks of exposure, diatom abundance was 2.3 x 10^7 cells cm^-2 and species richness was 41 ; after 4 weeks, abundance doubled and richness increased to 50. Periphyton was composed mostly of Amphora coffeaeformis and Navicula veneta (> 91 % of samples, average abundance 106-10^7 cells cm^-2) after 2 weeks ; after 4 weeks, Melosira moniliformis was co-dominant (91 % and 2.3-8.6 x 10^6 cells cm^-2). Maximum diatom abundance was at 0.5 m after 2 weeks and 1.5 m after 4 weeks. Shannon's diversity index ranged between 0.87 and 2.08 at the upper estuary station and between 1.1 and 2.7 at the other. Amphora coffeaeformis and Navicula veneta contributed more than 80 % to abundance at both stations, averaging 10^6-1.8 x 10^7 cells cm^-2.

periphytic algae; diatoms; artificial substrate; salinity; estuary; Adriatic Sea

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