This case study was strictly connected to the eutrophication problem in the Baltic Sea Lagoon. Eutrophication produces remarkable phytoplankton blooms and increased sedimentation of water column-derived phytal matter. As a result, bottom sediments show a substantial organic enrichment, the sedimenting phytal matter contributing substantially to it. Whether or not this enrichment is reflected in the dynamics of benthic communities has been widely debated.
In the case of the Szczecin Lagoon, the initial link in the River Odra estuarine system, the eutrophication and related processes have been in progress for a number of years. Although overall effects in the benthic communities of the estuary have been documented, information on possible couplings between phytoplankton blooms, sedimenting phytal matter, and benthic communities in the area is hardly available. Equally scarce are data documenting the biochemical nature of the sedimenting phytal material, e.g., its phytopigment profiles. Therefore an attempt was made to find out whether the meiofaunal compartment of the Lagoon's benthos would respond, on a short-term basis, to temporal and spatial changes in the phytoplankton bloom dynamics. In this context, bottom sediments were sampled monthly, within May - December 1997 at 4 hydrodynamically differing stations in the Lagoon. Spatial and temporal differences in the structure of meiobenthic communities were followed in relation to the synoptically collected data on the variability in water column phytopigment contents and in related sedimentary variables (silt/clay fraction, organic matter, and phytal pigment contents). The data showed that, regardless of the hydrodynamic differences between the stations sampled, temporal dimension of the overall variability was much more pronounced than the spatial one. The water column pigment data demonstrated a large phytoplankton bloom to have occurred in May-June, a second, much smaller peak in the phytoplankton abundance being visible in August through October. Concurrent peaks were observed in the phytopigment contents of the uppermost sediment layer, the October peak being particularly pronounced. The suite of phytal pigments present at that time, as analysed with HPLC, was dominated by ß-carotene and chlorophyll a.
The Lagoon's meiobenthos responded to the purported phytal matter sedimentation by producing abundance peaks, observed at a time lag of about 1 month (July and November) relative to the sedimentation peaks. Moreover, the meiobenthos data allow to infer a process resembling faunal succession to be operative: the first peak resulted primarily from an increase in the density of nematodes, while the second peak was due mainly to an increase in the abundance of ostracods.
It is concluded that an in-depth explanation of the pelagic-benthic couplings suggested by the data collected in the Szczecin Lagoon in 1997 requires further research on the nature of the sedimenting phytal matter on the one hand and the type of trophic relationships between the meiobenthic dominants and their purported sedimentary food resources on the other.