154
5 SpatIal and TemJloral Dlstnbul!oll Patterns
5.5.2
Methods
The benthic fauna in the sandtlats and especially in Lanice-patches was studied
with several approaches in ELA W AT. Each study had a specific question which
required respective methods. These are briefly outlined below with respect to their
relevance for this chapter. The main study areas were the Groninger Plate and
Dornumer Nacken in the backbarrier tidal tlats of the islands of Spiekeroog and
Langeoog (see Chap. 3.1). Especially two sampling sites at the Groninger Plate
with different Lallice densities (Table 5.5.2) are often referred to in the text (GPI
and GP2, see Fig. 3.1.4).
I. Spatial distribution: Macrobenthos was sampled with a corer of 100 cm
2
surface
area and penetration depth of 20 cm. To assess small-scale distributions, a 5x5
multicorer of 25 corers with 100 cm
2
surface area each was used in addition.
The samples were sieved through I mm mesh. To assess the smaller sized infauna, a corer of 32 cm
2
surface area was used to 10 cm sediment depth. These
samples were sieved through 0.5 mm mesh. The fauna was sorted from unpreserved samples, determined to the lowest possible taxonomic unit and counted.
See Zuhlke et al. (1998) for details. Spatial patterns of harpacticoid copepods
were assessed with 50 corers of 2x2 cm
2
each arranged to a transect of I m
length (Sach & van Bernem 1996). Nematodes in the vicinity of Lanice-tubes
were sampled with corers of 0.2 cm
2
surface area to a depth of 5 cm. The corers
were inserted in a row up to 2 cm distance from the tubes and additional samples were taken in 5 and 10 cm distance (Zuhlke et al. 1998).
2. Short-term variability: Macrobenthos samples were taken daily during sampling
campaigns on the Groninger Plate each spring and autumn from 1994 to 1996
(Steuwer, unpubl.). The benthos was sampled with a corer of 177 cm 2 surface
area to 30 cm sediment depth and sieved through 0.5 mm mesh. The samples
were treated alive. In addition, driftnets (after Armonies 1992) were installed in
the vicinity of the grid to assess dispersal of benthic fauna. These nets (opening
diameter 20 cm, 0.5 mm mesh) were set up 20 cm above the sediment surface
and could rotate with the tide.
3. Experiments: To test for the effect of the tube structures as such, worm tubes
were experimentally simulated by inserting metal sticks of about the same size
as real Lallice-tubes into the sediment (Zuhlke et al. 1998). In six experimental
treatments, 1000 of these metal sticks (4 mm wide, 25 cm long) were implanted
in each of the I m
2
sized plots, protruding 2-3 cm above the sediment surface.
In three additional treatments, the same number of metal sticks was implanted,
but level with the sediment surface. These plots served as controls for a possible effect of the metal on benthic organisms. Seven reference plots of I m 2 size
were left totally untreated. The sites for the three treatments were arranged at
random in the field.
5 SpatIal and TemJloral Dlstnbul!oll Patterns
5.5.2
Methods
The benthic fauna in the sandtlats and especially in Lanice-patches was studied
with several approaches in ELA W AT. Each study had a specific question which
required respective methods. These are briefly outlined below with respect to their
relevance for this chapter. The main study areas were the Groninger Plate and
Dornumer Nacken in the backbarrier tidal tlats of the islands of Spiekeroog and
Langeoog (see Chap. 3.1). Especially two sampling sites at the Groninger Plate
with different Lallice densities (Table 5.5.2) are often referred to in the text (GPI
and GP2, see Fig. 3.1.4).
I. Spatial distribution: Macrobenthos was sampled with a corer of 100 cm
2
surface
area and penetration depth of 20 cm. To assess small-scale distributions, a 5x5
multicorer of 25 corers with 100 cm
2
surface area each was used in addition.
The samples were sieved through I mm mesh. To assess the smaller sized infauna, a corer of 32 cm
2
surface area was used to 10 cm sediment depth. These
samples were sieved through 0.5 mm mesh. The fauna was sorted from unpreserved samples, determined to the lowest possible taxonomic unit and counted.
See Zuhlke et al. (1998) for details. Spatial patterns of harpacticoid copepods
were assessed with 50 corers of 2x2 cm
2
each arranged to a transect of I m
length (Sach & van Bernem 1996). Nematodes in the vicinity of Lanice-tubes
were sampled with corers of 0.2 cm
2
surface area to a depth of 5 cm. The corers
were inserted in a row up to 2 cm distance from the tubes and additional samples were taken in 5 and 10 cm distance (Zuhlke et al. 1998).
2. Short-term variability: Macrobenthos samples were taken daily during sampling
campaigns on the Groninger Plate each spring and autumn from 1994 to 1996
(Steuwer, unpubl.). The benthos was sampled with a corer of 177 cm 2 surface
area to 30 cm sediment depth and sieved through 0.5 mm mesh. The samples
were treated alive. In addition, driftnets (after Armonies 1992) were installed in
the vicinity of the grid to assess dispersal of benthic fauna. These nets (opening
diameter 20 cm, 0.5 mm mesh) were set up 20 cm above the sediment surface
and could rotate with the tide.
3. Experiments: To test for the effect of the tube structures as such, worm tubes
were experimentally simulated by inserting metal sticks of about the same size
as real Lallice-tubes into the sediment (Zuhlke et al. 1998). In six experimental
treatments, 1000 of these metal sticks (4 mm wide, 25 cm long) were implanted
in each of the I m
2
sized plots, protruding 2-3 cm above the sediment surface.
In three additional treatments, the same number of metal sticks was implanted,
but level with the sediment surface. These plots served as controls for a possible effect of the metal on benthic organisms. Seven reference plots of I m 2 size
were left totally untreated. The sites for the three treatments were arranged at
random in the field.