engleski

Structure of microbial community in estuary areas along the eastern Adriatic coast

The structure of the microbial food web was studied in six estuary areas along the eastern Adriatic coast during March, July and October 2012. Heterotrophic bacteria and autotrophic picoplankton (APP), particularly picoeukaryotes and Synechococcus, reached marked abundance and biomass, and thus play an important role in the microbial food web. Similarity analysis, based on abundances of all studied picoplankton and nanoplankton groups, showed clear separation of the two northernmost estuaries in March and October, and the southernmost estuary in July. However, the studied estuaries showed many more similarities than differences. High nitrogen/phosphorus ratio was a common feature for all of them, suggesting phosphorus-limited environments. Some characteristics of the microbial food web could be associated with oligotrophic environments (heterotrophic/autotrophic ratio > 1, high contribution of low nucleic acid (LNA) bacteria), and others with more eutrophic environments (domination of picoeukaryote biomass within the APP community, as well as domination of Synechococcus over Prochlorococcus biomass). On the other hand, relationships within the picoplankton community, as well as domination of bottom-up vs. top-down control of bacteria, varied on a spatial and temporal scale. Stable viruses (virus-like particles) abundance was found in all estuaries, and they showed strong correlation with bacteria, and occasionally with all APP groups (picoeukaryotes, Synechococcus and Prochlorococcus). LNA bacteria were abundant in all estuaries and these bacteria could be described as a form of adaptation to environmental conditions rather than metabolically inactive bacteria. This paper highlights the potential importance of the picoplankton community not only in the open Adriatic Sea, but also in coastal/estuarine environments.

Microbial community; Estuary areas; Adriatc Sea; Food web

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