2l)0
13 SUlllmary
I °C colder than the long term mean. The winter of 1995/1996 classified as a
strong winter with 49 days of ice cover, which was the longest period of ice
cover in 33 years.
• The Swinnplate was subject to seasonal morphological changes, characterized
by sediment dislodgements over the winter months and increased biodeposition
by blue mussels over the summer. After the ice winter it took 6 months until
general morphological features were re-established. The relief and location of
the Groninger Plate remained unchanged over a longer time frame.
• Eight distinct types of biofacies were distinguished in the backbarrier area of
Spiekeroog. In the central parts of the Swinnplate, sandy tidal flats prevailed
which were colonized by the lugworm Arenicola marina, the tube worm Lanice
conchilega and the blue mussel Mytilus edulis. It was estimated that blue mussels have occurred on the Swinnplate for the past 50 years. However, the mussel
beds were subject to annual change in their location and density. Sandtlats with
A. marina and L. cOllchilega in varying densities occurred in the central parts of
the Groninger Plate.
• With the seasonal input of biodeposits, the mud- and POC-content as well as
other biogeochemical properties of the sediment changed in the direction of the
ebb current away from the mussel bed on the Swinnplate. The chemical composition of the sediment was closely coupled to the grain size distribution and not
affected by the activity of the mussels. The input and subsequent decay of phytoplankton blooms and macroalgal cover could be followed with specific biomarkers. The quality of organic matter was decisive for further biotic activities.
Organic components of high quality (photosynthetic pigments, amino acids,
lipids) decreased in concentration with increasing distance from the mussel bed.
Microbial biomass and activity was tightly linked to the availability of fresh organic matter and decreased further away from the mussel bed. The distribution
of macrobenthic assemblages also differed along a gradient of decreasing
biodeposits. In the mussel bed, small opportunistic polychaetes dominated the
assemblage. Species and individual numbers as well as biomass of benthic organisms decreased from the fringe of the mussel bed to the sandtlat.
• The carrying capacity of the sediment chemistry was studied on the Groninger
Plate. Monthly samples of pore water contents revealed a high variability, both
along vertical depth profiles and with time in dependence of the activity of microbial remineralization. Experimental additions of organic matter caused the
appearance of anoxic spots on the sediment surface which took more than one
year to regenerate, depending on the amount of organic matter added.
• In the water column, high temporal and spatial variabilities were recorded for
concentrations of dissolved nutrients as well as for abundances and species
compositions of phyto- and zooplankton on the scale of tidal cycles and years.
Not all phytoplankton species were able to reproduce in the Wadden Sea.
Mainly benthic microalgal species had their habitat here. Out of 66 genera (162
species) of diatoms, 44 % lived exclusively benthic, 14 % exclusively in the
water column and 42 % occurred both in the water column and sediment. The
zooplankton recordings revealed an export out of the Wadden Sea over the
summer months of larvae of the mud snail Hydrobia ulvae, spionid polychaetes
and cirripedia. The timing and intensity of phytoplankton blooms affected the
occurrence of meroplanktonic larvae.
13 SUlllmary
I °C colder than the long term mean. The winter of 1995/1996 classified as a
strong winter with 49 days of ice cover, which was the longest period of ice
cover in 33 years.
• The Swinnplate was subject to seasonal morphological changes, characterized
by sediment dislodgements over the winter months and increased biodeposition
by blue mussels over the summer. After the ice winter it took 6 months until
general morphological features were re-established. The relief and location of
the Groninger Plate remained unchanged over a longer time frame.
• Eight distinct types of biofacies were distinguished in the backbarrier area of
Spiekeroog. In the central parts of the Swinnplate, sandy tidal flats prevailed
which were colonized by the lugworm Arenicola marina, the tube worm Lanice
conchilega and the blue mussel Mytilus edulis. It was estimated that blue mussels have occurred on the Swinnplate for the past 50 years. However, the mussel
beds were subject to annual change in their location and density. Sandtlats with
A. marina and L. cOllchilega in varying densities occurred in the central parts of
the Groninger Plate.
• With the seasonal input of biodeposits, the mud- and POC-content as well as
other biogeochemical properties of the sediment changed in the direction of the
ebb current away from the mussel bed on the Swinnplate. The chemical composition of the sediment was closely coupled to the grain size distribution and not
affected by the activity of the mussels. The input and subsequent decay of phytoplankton blooms and macroalgal cover could be followed with specific biomarkers. The quality of organic matter was decisive for further biotic activities.
Organic components of high quality (photosynthetic pigments, amino acids,
lipids) decreased in concentration with increasing distance from the mussel bed.
Microbial biomass and activity was tightly linked to the availability of fresh organic matter and decreased further away from the mussel bed. The distribution
of macrobenthic assemblages also differed along a gradient of decreasing
biodeposits. In the mussel bed, small opportunistic polychaetes dominated the
assemblage. Species and individual numbers as well as biomass of benthic organisms decreased from the fringe of the mussel bed to the sandtlat.
• The carrying capacity of the sediment chemistry was studied on the Groninger
Plate. Monthly samples of pore water contents revealed a high variability, both
along vertical depth profiles and with time in dependence of the activity of microbial remineralization. Experimental additions of organic matter caused the
appearance of anoxic spots on the sediment surface which took more than one
year to regenerate, depending on the amount of organic matter added.
• In the water column, high temporal and spatial variabilities were recorded for
concentrations of dissolved nutrients as well as for abundances and species
compositions of phyto- and zooplankton on the scale of tidal cycles and years.
Not all phytoplankton species were able to reproduce in the Wadden Sea.
Mainly benthic microalgal species had their habitat here. Out of 66 genera (162
species) of diatoms, 44 % lived exclusively benthic, 14 % exclusively in the
water column and 42 % occurred both in the water column and sediment. The
zooplankton recordings revealed an export out of the Wadden Sea over the
summer months of larvae of the mud snail Hydrobia ulvae, spionid polychaetes
and cirripedia. The timing and intensity of phytoplankton blooms affected the
occurrence of meroplanktonic larvae.