Short-term variability of abundance, diversity and activity of estuarine bacterioneuston and bacterioplankton

Abstract

Short-term variability in abundance, heterotrophic activity and structural diversity of bacterioneuston and bacterioplankton were assessed over 24-h cycles at a fixed point in the estuarine system of Ria de Aveiro (Portugal). Lipase activity was the only descriptor of bacterial activity significantly different in samples collected during the day and the night (up to 40% higher during the night) at equivalent tidal conditions. The lack of diel patterns in other microbiological parameters indicates uncoupling of estuarine bacteria from primary production, pointing to the relevance of allochthonous nutrient sources for heterotrophic bacteria in this mesotrophic system. Occurrence of strong positive correlations between the values of microbiological parameters (total bacterial abundance, chlorophyll a concentration, leucine-aminopeptidase, lipase, phosphatase, sulphatase and acetate and glucose incorporation) in bacterioneuston and bacterioplankton suggests that the surface community may originate from the underlying waters (UWs) concentrating at the surface through upward passive transport, and that bacterioneuston and bacterioplankton are subjected to similar environmental regulation. The results also indicate that the microbial enrichment of the surface microlayer relative to the UW is highly variable during the day, pointing to the importance of the sampling time for the outcome of comparative analyses of bacterioneuston and bacterioplankton dynamics.