engleski

Seasonal and vertical distribution of planktonic bacteria and heterotrophic nanoflagellates in the Middle Adriatic Sea

Temporal and spatial patterns of bacteria and heterotrophic nanoflagellates (HNF) were studied monthly from January 1997 to December 1998 in the middle Adriatic Sea. Bacterial and HNF relationships with phytoplankton biomass and temperature were analyzed to examine how relative importance of bottom up and top down factors may shift between seasons and locations. Inconsistent relationship between bacterial abundance and chlorophyll a in the coastal area, and stronger relationship between bacterial abundance and bacterial production, suggest the conditions in which other sources of substrates are more important for bacteria than substrates of phytoplankton origin. Analysis of simultaneous effect of temperature and bacterial production on bacterial abundance showed that the effect of temperature obscured the effect of bacterial production, suggesting that bacterial growth itself is highly temperature dependent. The analysis of the relationship between HNF abundance and bacterial abundance was slightly improved by the inclusion of in situ temperature, bacterial production or both parameters, as additional independent variables. About 60% of the variability in HNF abundance can be explained with bacterial abundance, bacterial production and temperature. In the open sea, tight coupling of bacteria abundance with chlorophyll a concentrations implied dominate role of this substrate supply in controlling bacterial abundance. During colder months bacterial abundance was high enough to support higher HNF abundance than observed, suggesting that predation exerted a minor depressing influence on bacterial abundance during that period. During spring-summer period, HNF controlled bacterial standing stock by direct cropping of bacterial production.

bacteria; HNF; distribution; Middle Adriatic

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