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PHYTOPLANKTON COMPOSITION AT THE FISH AND SHELLFISH FARM IN THE KALDONTA BAY (CRES ISLAND)
2004, 62 (4) p. 127-142
Abstract
The Kaldonta Bay is situated at the south–western coast of the Cres island in the Lošinj channel, rather protected from larger influence of general sea water current. In the Bay there are installed 44 floating cages of 5 by 10 m dimensions. The cages are used for the culture of about 70 tons of sea water fish: gilthead sea bream (Sparus aurata), sea bass (Dicentrarchus labrax), sharp–snouted sparus (Diplodus puntazzo) and dentex (Dentex dentex). Besides some physico–chemical parameters (sea water temperature, transparence and salinity), special attention has been paid to the qualitative composition of net phytoplankton. Investigations were performed in the period of May, September and December 2003 and February 2004 at five locations in the Kaldonta Bay (Figure 1) at the depths of 0.5 m, 5 m, 10 m and 1 m from the bottom. According to the physico–chemical parameters, sea water temperature was influenced by the temperature of the environment, and the transparence suggested to the oligotrophic situation in the investigated aquatorium. Qualitative composition of net phytoplankton comprised 161 microphytic species belonging to the systematic compartments of Cyanobacteria, Chrysophyta and Dinophyta (Table 1). The most numerous algal group were diatoms or Bacillarophyceae (98 species or 61%), with relative frequencies of species from 1 to 7. Taxonomic composition of diatoms showed Chaetoceros–Rhizosolenia (Proboscia) to be the dominant community. Diatom species was the most abundant in late autumn period (beginning of December). The second most important comparatment were Dinophyta (55 species or 34.1%), with the dominant genera Ceratium and Protoperidinium. During the investigation, the representatives of Dinophyta did not show large variety of species in the water column. Relative frequency of the species was 1, rarely 2 and 3. Dinophyts were the most abundant in September. From Cyanobacteria (5 species or 3.1%) only filamentous algae were determined, with relative frequency from 1 to 3. Qualitative composition of net phytoplankton suggests the similarity of species composition in the water column at all the investigated locations. From all characteristics of net phytoplankton that were obtained conclusion can be made that all the investigated locations represent stable ecosystems.