258
H. Michaelis and W.J. Wolff
Though lying close to the NW-African upwelling area, the Banc d'Arguin
water is oligotrophic and has a particularly low plankton and seston content.
An influence of the upwelling system is completely lacking (Sevrin-Reyssac
1993; Wolff et al.I993b).
At the southern North Sea coast, we investigated an intertidal area between
the East Frisian island Juist and the mainland (Fig. 12.3) situated between
53°30' and 53°41'N. This area (108km2) is part of the Wadden Sea that extends
along the Dutch, German and Danish coast and has a coherent intertidal
fringe of 4300 km 2 in total. The mean tidal range of the Juist area is 2.5 m. The
climate is oceanic within the cool-temperate zone. The seawater temperature
- measured at Norderney - shows a long-term mean maximum of 17°C in
July/August and a mean minimum of slightly less than 2°C in January (Biitje
1986). Severe winters with drift of ice occur frequently. Salinities are widely
fluctuating. Euhaline concentrations (>30) prevail during summer and polyhaline ones «30) during winter (Biitje 1986). High turbidity is a general
feature of these waters and eutrophication results in a high production of
phytoplankton (Rahmel et al. 1995).
The material from Mauritania comprises benthos and sediment samples
from 30 randomly distributed stations (Fig. 12.2). In the Juist area benthos
and sediment samples were collected from 104 stations (Fig. 12.3). Altogether,
samples, parameters and methods from both areas can be summarized as
follows:
- Surface sediment from the top layer (1-5 cm) for analyzing grain-size
distribution. Sieving of the fractions >0.06 mm, areometer measurements
of the fractions <0.06 mm.
- Macrofauna Banc d' Arguin: At 22 stations 5 core samples covering 177 cm 2
each, 25 cm deep, were taken; at another 8 stations where a patchy distribution was suspected 10 cores covering 78.7 cm 2 each, 25 cm deep, were
obtained. Sieving was carried out with 0.6 mm mesh size. The large bivalve
Anadara senilis was separately collected from 1.5 m 2 . Sorting and first-step
identification were performed in a live state. The further taxonomic and
quantitative evaluation of the conserved material (10 % formalin) was
carried out in the home laboratories. The biomass was determined as ashfree dry weight (ADW) by incineration at 485°C (bivalves <5 mm including
the shells, > 5 mm without the shells; gastropods mainly with the shells).
- Macrofauna Juist area: At 102 stations 7 core samples covering 177 cm 2
each, 25 cm deep, were taken. Samples from two shell bed stations supplied
only qualitative information. Sieving was carried out with 1.0 mm mesh
size. Examination of all samples (sorting, species identification, counting)
was performed in a live state on board or in field laboratories. Then the
material was stored in a deep freezer for later determination of biomass as
described above. Details are given in Obert and Michaelis (in prep.).
H. Michaelis and W.J. Wolff
Though lying close to the NW-African upwelling area, the Banc d'Arguin
water is oligotrophic and has a particularly low plankton and seston content.
An influence of the upwelling system is completely lacking (Sevrin-Reyssac
1993; Wolff et al.I993b).
At the southern North Sea coast, we investigated an intertidal area between
the East Frisian island Juist and the mainland (Fig. 12.3) situated between
53°30' and 53°41'N. This area (108km2) is part of the Wadden Sea that extends
along the Dutch, German and Danish coast and has a coherent intertidal
fringe of 4300 km 2 in total. The mean tidal range of the Juist area is 2.5 m. The
climate is oceanic within the cool-temperate zone. The seawater temperature
- measured at Norderney - shows a long-term mean maximum of 17°C in
July/August and a mean minimum of slightly less than 2°C in January (Biitje
1986). Severe winters with drift of ice occur frequently. Salinities are widely
fluctuating. Euhaline concentrations (>30) prevail during summer and polyhaline ones «30) during winter (Biitje 1986). High turbidity is a general
feature of these waters and eutrophication results in a high production of
phytoplankton (Rahmel et al. 1995).
The material from Mauritania comprises benthos and sediment samples
from 30 randomly distributed stations (Fig. 12.2). In the Juist area benthos
and sediment samples were collected from 104 stations (Fig. 12.3). Altogether,
samples, parameters and methods from both areas can be summarized as
follows:
- Surface sediment from the top layer (1-5 cm) for analyzing grain-size
distribution. Sieving of the fractions >0.06 mm, areometer measurements
of the fractions <0.06 mm.
- Macrofauna Banc d' Arguin: At 22 stations 5 core samples covering 177 cm 2
each, 25 cm deep, were taken; at another 8 stations where a patchy distribution was suspected 10 cores covering 78.7 cm 2 each, 25 cm deep, were
obtained. Sieving was carried out with 0.6 mm mesh size. The large bivalve
Anadara senilis was separately collected from 1.5 m 2 . Sorting and first-step
identification were performed in a live state. The further taxonomic and
quantitative evaluation of the conserved material (10 % formalin) was
carried out in the home laboratories. The biomass was determined as ashfree dry weight (ADW) by incineration at 485°C (bivalves <5 mm including
the shells, > 5 mm without the shells; gastropods mainly with the shells).
- Macrofauna Juist area: At 102 stations 7 core samples covering 177 cm 2
each, 25 cm deep, were taken. Samples from two shell bed stations supplied
only qualitative information. Sieving was carried out with 1.0 mm mesh
size. Examination of all samples (sorting, species identification, counting)
was performed in a live state on board or in field laboratories. Then the
material was stored in a deep freezer for later determination of biomass as
described above. Details are given in Obert and Michaelis (in prep.).