AME 83:49-63 (2019)  -  DOI: https://doi.org/10.3354/ame01903

ABSTRACT: The abundances of bacteria, flagellates and ciliates were investigated over 13 mo in an unpolluted first-order stream. Four habitats on different substrates were integrated in our study: sediment, as well as the surfaces of dead wood, macrophytes, and leaf litter. Organismal biomass and secondary production in the habitats were calculated and the relative contribution to overall secondary production was estimated. We expected highest organismal densities on leaf litter in autumn and in the other 3 habitats in spring/summer. We assumed bacteria to be most abundant and ciliates to represent the highest biomass and dominate secondary production. Moreover, we hypothesized that dead wood and leaf litter would account for the largest share of total secondary production of all 4 habitats. In the stream’s sediment, protozoan abundance showed a trend towards a seasonal pattern. Annual mean abundance, biomass and secondary production by all organismal groups were highest on dead wood. Ciliates made up the highest percentage of total annual biomass in sediment and on dead wood and leaf litter, whereas on macrophytes, bacteria had the highest percentage of total annual biomass. In all habitats, ciliates had the highest share of secondary production. Total organismal secondary production during the sampled year was 660.6 µg C cm^-2, of which 71% was contributed by organisms on dead wood. The contribution of dead wood to the annual mean habitat cover ratio at the sampling site was only 9%, but it still made up 34% of total unicellular secondary production. Our study clearly showed that the unicellular secondary production on dead wood in streams has thus far been highly underestimated.

KEY WORDS: Protozoa · Bacteria · Seasonal dynamics · Sediment · Dead wood · Macrophyte · Leaf litter