6.2 Material and Methods
177
6.2
Material and Methods
As a disturbance, the macroalgal cover mentioned above was simulated by covering the sediment with a plastic tarpaulin. Thus, a defaunation was achieved. With
different experiments the intensity and timing (start of recolonization) of the disturbance were modified. The recolonization by small macrofauna, nematodes and
benthic diatoms was recorded. The experiments were set up on the Groninger
Plate in the backbarrier system of Spiekeroog (Fig. 3.1.4). The single treatment
plots were interspersed.
The following experiments were carried out:
• Recolonization by macrofauna in dependence of season
In 1994, a spring experiment and an autumn experiment were set up. For the
former, the plots were covered with a tarpaulin in April; for the latter in September. The cover was removed after 4 weeks in May and October, respectively. For each treatment, three plots of 4 x 5 m in size were arranged. Three
undisturbed sandtlat plots of the same size each were marked in spring and
autumn and served as controls. They were used as controls for all experiments.
All of these plots were sampled until the end of 1995.
• Recolonization by macrofauna in dependence of disturbance intensity
In 1995, three plots of 4 x 5 m in size each were covered for 4 weeks (4-week
disturbance) or one week (I-week disturbance) and uncovered simultaneously in May. Immediately after removal of the tarpaulin, the plots were raked
to counteract the compaction of the sediment which was caused by the cover.
Three further plots of 4 x 5 m in size each were raked only (mimicking a mechanical disturbance) and all cockles (Cerastoderma edule) thus appearing on
the surface were removed. As control plots, those of the previous experiments
were used.
• Recolonization by benthic diatoms and meiofauna
In 1994, a plot of 3 x 3 m in size was covered with a tarpaulin and uncovered
after six weeks in August (6-week disturbance). To study the recolonization of
nematodes in azoic sediment, sediment was frozen and washed and subsequently filled into 4 plastic containers (20 x 20 em in size and perforated)
which were implanted into the sandtlat next to the other experimental plots. The
containers were implanted simultaneously with the uncovering of the 6-week
disturbance plot in August.
In 1995, the 4-week and I-week disturbance experiments mentioned above
were sampled as well. To study the mode of recolonization by diatoms, traps
were implanted in the experimental and control plots. These traps had an opening just above the sediment surface, allowing lateral access only.
Sampling frequencies were high (daily) in the beginning of the recolonization and
slowly extended to monthly intervals. Small macrofauna was sampled with a corer
of 38.5 cm 2 surface area to 15 cm sediment depth. The samples were sieved
through 250 f.lm mesh size and sorted and identified alive. Juvenile and adult polychaetes were separated using the criteria given in Hartmann-Schroder (1971).
177
6.2
Material and Methods
As a disturbance, the macroalgal cover mentioned above was simulated by covering the sediment with a plastic tarpaulin. Thus, a defaunation was achieved. With
different experiments the intensity and timing (start of recolonization) of the disturbance were modified. The recolonization by small macrofauna, nematodes and
benthic diatoms was recorded. The experiments were set up on the Groninger
Plate in the backbarrier system of Spiekeroog (Fig. 3.1.4). The single treatment
plots were interspersed.
The following experiments were carried out:
• Recolonization by macrofauna in dependence of season
In 1994, a spring experiment and an autumn experiment were set up. For the
former, the plots were covered with a tarpaulin in April; for the latter in September. The cover was removed after 4 weeks in May and October, respectively. For each treatment, three plots of 4 x 5 m in size were arranged. Three
undisturbed sandtlat plots of the same size each were marked in spring and
autumn and served as controls. They were used as controls for all experiments.
All of these plots were sampled until the end of 1995.
• Recolonization by macrofauna in dependence of disturbance intensity
In 1995, three plots of 4 x 5 m in size each were covered for 4 weeks (4-week
disturbance) or one week (I-week disturbance) and uncovered simultaneously in May. Immediately after removal of the tarpaulin, the plots were raked
to counteract the compaction of the sediment which was caused by the cover.
Three further plots of 4 x 5 m in size each were raked only (mimicking a mechanical disturbance) and all cockles (Cerastoderma edule) thus appearing on
the surface were removed. As control plots, those of the previous experiments
were used.
• Recolonization by benthic diatoms and meiofauna
In 1994, a plot of 3 x 3 m in size was covered with a tarpaulin and uncovered
after six weeks in August (6-week disturbance). To study the recolonization of
nematodes in azoic sediment, sediment was frozen and washed and subsequently filled into 4 plastic containers (20 x 20 em in size and perforated)
which were implanted into the sandtlat next to the other experimental plots. The
containers were implanted simultaneously with the uncovering of the 6-week
disturbance plot in August.
In 1995, the 4-week and I-week disturbance experiments mentioned above
were sampled as well. To study the mode of recolonization by diatoms, traps
were implanted in the experimental and control plots. These traps had an opening just above the sediment surface, allowing lateral access only.
Sampling frequencies were high (daily) in the beginning of the recolonization and
slowly extended to monthly intervals. Small macrofauna was sampled with a corer
of 38.5 cm 2 surface area to 15 cm sediment depth. The samples were sieved
through 250 f.lm mesh size and sorted and identified alive. Juvenile and adult polychaetes were separated using the criteria given in Hartmann-Schroder (1971).