In
0 Recolol1lzatiofl of Tidal Flats Alter Disturhance
Nematode samples were taken with a corer of 2 cm 2 surface area to 2 cm sediment
depth. The samples were pickled in 4 % buffered formalin and the nematodes
were extracted using the McIntyre method (63 flm mesh size), followed by a microscopic classification of the species (see Blome 1983). For benthic diatoms,
samples were taken with a multicorer of 5 x 5 cm (single corer size 1 cm 2 ). In
addition, 25 subsamples of I cm 3 each were taken at random in an area of 0.25 m 2 ,
divided into 625 fields. 10 of the latter samples were sorted alive and the remaining samples were stored in 4 % buffered formalin for later analysis.
Sulphide was measured in the defaunation experiments using both a pore water
sampler and a diffusion sampler (Langner 1997).
Benthic recolonization after the ice winter was studied in a plot of 100 x 100 m
on the Groninger Plate. Sampling was carried out as in the preceding years.
6.3
Recolonization After Experimental Disturbances
In the experimental plots that were covered with a tarpaulin, the sediment was
compacted by this cover and thus the sediment surface was lowered by about 0.52 cm compared to the surrounding ambient sediment. The tarpaulin had interrupted gas exchange and thus the anoxic sediment horizon reached to the sediment
surface by the time the tarpaulin was removed. But within a few days after the
removal, a thin (mm) oxidized sediment layer developed in the experimental plots
and reached I cm thickness after 5 (experiments 1995) or 11 weeks (experiments
1994). Straight after removing the tarpaulin, sulphide concentrations of 33.8 mmol dm) were measured. In the course of the experiment, the sediment layer
with the highest sulphide concentrations shifted further into greater sediment
depths. No free sulphide was measured in the control plots (Langner, Oelschlager,
unpub!. data).
All experimental plots were recolonized. The recolonization was faster in the
spring than autumn and faster in the I-week than the 4-week disturbance. Microphytobenthos and meiofauna reached background values within days, whereas the
macrofauna required several weeks.
6.3.1
The Course of Recolonization
M icrophyto/Jcf1thos
Benthic diatoms appeared as quick colonizers (Keuker-Rudiger, un pub!, data).
Within a few days after the plots were opened for recolonization, species number
reached background values (9 days after 6-week disturbance in 1994 and 7 days
after 4-week disturbance in 1995, Fig. 6.3.1 a, c). Abundance increased 20-fold in
the first week of recolonization after the 6-week disturbance, but did not reach
background values. After the 4-week disturbance in 1995, the abundances of diatoms in the experimental plots were as high as control values after 7 days
(Fig. 6.3.1 b, d). Some sessile diatoms survived the experimental disturbance;
0 Recolol1lzatiofl of Tidal Flats Alter Disturhance
Nematode samples were taken with a corer of 2 cm 2 surface area to 2 cm sediment
depth. The samples were pickled in 4 % buffered formalin and the nematodes
were extracted using the McIntyre method (63 flm mesh size), followed by a microscopic classification of the species (see Blome 1983). For benthic diatoms,
samples were taken with a multicorer of 5 x 5 cm (single corer size 1 cm 2 ). In
addition, 25 subsamples of I cm 3 each were taken at random in an area of 0.25 m 2 ,
divided into 625 fields. 10 of the latter samples were sorted alive and the remaining samples were stored in 4 % buffered formalin for later analysis.
Sulphide was measured in the defaunation experiments using both a pore water
sampler and a diffusion sampler (Langner 1997).
Benthic recolonization after the ice winter was studied in a plot of 100 x 100 m
on the Groninger Plate. Sampling was carried out as in the preceding years.
6.3
Recolonization After Experimental Disturbances
In the experimental plots that were covered with a tarpaulin, the sediment was
compacted by this cover and thus the sediment surface was lowered by about 0.52 cm compared to the surrounding ambient sediment. The tarpaulin had interrupted gas exchange and thus the anoxic sediment horizon reached to the sediment
surface by the time the tarpaulin was removed. But within a few days after the
removal, a thin (mm) oxidized sediment layer developed in the experimental plots
and reached I cm thickness after 5 (experiments 1995) or 11 weeks (experiments
1994). Straight after removing the tarpaulin, sulphide concentrations of 33.8 mmol dm) were measured. In the course of the experiment, the sediment layer
with the highest sulphide concentrations shifted further into greater sediment
depths. No free sulphide was measured in the control plots (Langner, Oelschlager,
unpub!. data).
All experimental plots were recolonized. The recolonization was faster in the
spring than autumn and faster in the I-week than the 4-week disturbance. Microphytobenthos and meiofauna reached background values within days, whereas the
macrofauna required several weeks.
6.3.1
The Course of Recolonization
M icrophyto/Jcf1thos
Benthic diatoms appeared as quick colonizers (Keuker-Rudiger, un pub!, data).
Within a few days after the plots were opened for recolonization, species number
reached background values (9 days after 6-week disturbance in 1994 and 7 days
after 4-week disturbance in 1995, Fig. 6.3.1 a, c). Abundance increased 20-fold in
the first week of recolonization after the 6-week disturbance, but did not reach
background values. After the 4-week disturbance in 1995, the abundances of diatoms in the experimental plots were as high as control values after 7 days
(Fig. 6.3.1 b, d). Some sessile diatoms survived the experimental disturbance;