AME 13:37-46 (1997)  -  doi:10.3354/ame013037

In 1995, an extensive investigation was carried out in the Elbe Estuary in Germany between Cuxhaven and Geesthacht. Special attention was paid to microorganisms, including bacteria, amoebae, ciliates and flagellates, which were dispersed in the water column and associated firmly or loosely with different types of aggregates. The abundance, size and colonization by microorganisms of the aggregates varied in the limnetic, brackish and marine environments. There were differences in the locations of occurrence and abundance at each site, attributable to differences in the physical and chemical conditions. The composition of the aggregates mainly reflected the structure of the plankton community and also the benthic environment. In the upper estuary, aggregates were composed mainly of organic material, and most of the associated material consisted of remnants of the plankton. About 85% of the particles were colonized by bacteria, and 25% by protozoans. Abundances of dispersed bacteria varied between 0.6 × 10⁹ and 25.5 × 10⁹ bacteria l^-1, and dispersed protozoan abundance ranged between 241 × 10³ and 8778 × 10³ l^-1. Attached bacteria reached concentrations between 0.3 × 10⁶ and 22.5 × 10⁶ bacteria l^-1, while attached protozoans numbered from 98 to 22500 l^-1. Attached bacterial density accounted for about 75% of total bacterial density during the year. About 90% of the total bacterioplankton in the upper estuary were tightly attached to aggregates; only 40% were similarly attached in the lower estuary. During the whole year, aggregates in the lower parts of the estuary were dominated by mineral particles, and they were not as densely colonized as in the upper part. Dispersed and attached organisms in the Elbe Estuary showed an annual seasonal succession.

Elbe · Estuary · Aggregate · Colonization · Attached organisms · Particles · Protozoa · Bacteria