Studies on primary pelagic bioproduction in the Gulf of Trieste (North Adriatic)

Abstract

       In July 1979 a study of primary pelagic bioproduction in the Eastern part of the Gulf of Trieste (North Adriatic) using the ¹⁴C technique in situ started. These studies were performed at two fixed sampling points (K-1 in the Bay of Koper and MA in the Bay of Piran) monthly, both having the maximal depth of 16 m. For each depth one light and one dark bottle were inoculated with ¹⁴C and then incubated at the place of sampling in horizontal position for 4 hours. The light bottle uptake of radiocarbon on the filter was corrected by subtraction of dark bottles.

         The primary production rates varied from 1.3 - 23.1 mgCm^-2h^-1 at both stations. The values observed were somewhat lower than those in the North Adriatic offshore of Rovinj but comparing the data it should be considered the shorter sea water column the Gulf of Trieste. The highest values were observed in October 1979 at both stations and the minimum in March 1980. Higher values observed in July 1979 were probably in correlation with favourable temperature and particulary light conditions. The annual primary bio­production was estimated by integration of the area under the annual production curve and it coresponds to some 42 gCm^-2y^-1 at both stations. The value obtained indicates relatively low primary production in the Gulf of Trieste.

         Phytoplankton standing crop expressed as the chlorophyll a concentrations varied from 2.6 - 46.9 mgm^-2. Its seasonal dynamics showed autumn and winter maximum in correlation with the primary production dynamics. Assi­milation rations were mostly less than 1 indicating low growth rates of phyto­plankton.