Sea Fi.sheriei. fumrute Gdymi;, !.',iJ..md The paper presents results of long•term investigations on primary production and chlorophyll a concentrations at two stationsin. the Southern Baltic (in the Gdansk Deep and il"' the Bomholm Deep). The data show increasing trends in the anrcual primary production and mean chlorophyll a contents. A mean increase in the annual primary production within the recent years is estimated at 1-2% per year.
Sell Fisheries hmti!te Gd}'llia. Pol.!md The paper presents data on primary production and chloro phyll a concentrations at two stations located in the Gulf of Gdaiisk (Baltic Sea). The primary production in 1987 was much higher than the mean values for the region, observed in other years when the production was 125-200 g C/m 2 a. Our observations show the primary production in the Puck Bay to be approximately two times that in offshore waters of the Gdaiisk Deep. The chloro phyll contents decrease along the Vistula estuary-Gdaiisk Deep transect.
The paper presents data on Secchi depth in the Southern Baltic waters. The mean annual Secchi depth is 8.2 m in the Gdansk Deep, 9.6 m in the Bomholm Deep, 9.9 m in the southern part of the Gotland Deep, and 5.7 m in the Gulf of Gdansk. The Secchi depth is subject to seasonal fluctuations, their amplitude being approximately 35% of the mean annual value. A trigono• metric polynomial was applied to describe periodic intra-annual changes of Secchi depth in the Baltic. The largest water trans parency was observed in winter, the transparency being lowest in summer. Effects of chlorophyll a concentrations on water transparency are presented in a graphic form.
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