The dependence between bacterial production and environmental conditions in the Gulf of Gdañsk

Abstract

Bacterial production, primary production and a number of other environmentalfactors were measured during six cruises in the Gulf of Gda&#x0144;sk conducted invarious seasons from 1995 to 2001. Bacterial production (BP) in theepipelagic layer ranged from 1.5% (April) to 80% (July) of the gross primaryproduction (PP). Significant differences were observed between the BP/PPratios in estuarine and open-water areas. The highest values were recorded inthe coastal area and near the mouth of the river Vistula. It suggests thatallochthonous organic matter has a great influence on BP. The correlationsbetween particular parameters and regression analyses indicated that BP inthe Gulf of Gda&#x0144;sk depended on temperature, organic nitrogen concentration,PP, chlorophyll <i>a</i> concentration, organic phosphorus concentration, salinityand biochemical oxygen demand. Of all the independent variables, thetemperature had the greatest impact on BP (<i>R</i>² = 0.62). There was aninverse parabolic relationship between bacterial production and temperature.It appears that above a temperature of 12&#x00B0;C bacterial productiondepended on substrates to a higher degree than on temperature. The negativecorrelation between BP and concentrations of mineral nitrogen and phosphorusin the annual cycle were probably due to an indirect dependence. A multipleregression equation, which included temperature and organic phosphorusconcentrations, explained 78% of the variation in BP. Increasing BP resulted in an increasing biomass of bacterivorousnanoflagellates and of bacterivorous ciliates, which is indicativeof bottom-up control in this segment of the trophic chain.