126
.5 Spatial and Temporal DlstnhutlOll Patterns
Modifications of the organic and inorganic sediment composition entail certain
distribution patterns of the benthos. The polychaete Capitella capitata is a typical
representative of polluted coastal regions and an indicator for increased concentrations of organic matter (Weston 1990; Alongi & Tenore 1985). During the investigations on the Swinnplate, Capitella spp. occurred with higher abundances in the
old mussel bed and the biodeposit-enriched sediments (Table 5.2.3). Probably, the
natural habitat of this species-complex is POC-enriched sediment. Also the capitellid polychaete Heteromastus filiformis occurred more frequently at the edge of
the mussel bed than in the sandtlat. Thiermann et al. (1996) found a distribution of
macrofauna which was related to the variation of the corresponding sulphide regllne.
A classification of benthos into trophic groups revealed a modified composition
of macrofauna assemblages along the transect. In the mussel bed on the
Swinnplate, subsurface deposit-feeders were more frequent than in the sandtlat.
Predatory polychaetes were almost absent in the biodeposit-enriched sediments. A
similar distribution of trophic groups was described by Dittmann (1990) as a functional interaction ("trophic group amelioration").
In the biodeposits of the mussel bed, bioturbation was strongly reduced, because
no deep-dwelling macrofauna occurred here. Their abundance increased with increasing distance to the mussel bed. In the sandflat (reference site SP6) for example, Arenicola marina fulfils an important role as bioturbator (Reichert 1988).
Almost half way between the centre of the mussel bed and the reference site in the
sandtlat, the conditions seemed to be most favourable for the macrofauna. These
areas contained species- and individual-rich meio- and macrobenthic infauna with
a dominance of polychaetes. Probably both the supply with organic matter as well
as oxygen availability for aerobic respiration were sufficient here.
During the investigations on the Swinnplate, the content of organic matter
turned out as an important factor for the distribution of macrofauna. However,
together with the production of biodeposits, several other sediment characteristics
changed (see Dahlbiick & Gunnarsson 1981). In the case of the biodeposits which
were transported by the ebb current away from the mussel bed, changes in the
content of organic matter were correlated with the proportion of fine-grained
sediment material. Grain size distribution of the sediment itself can also influence
the distribution of macrofauna. as it was shown e.g. for tubificoid oligochaetes
(Giere & Pfannkuche 1982). Oligochaetes also dominated the infauna in mussel
beds studied by Dittmann (1990) and Krbncke (1996).
However, not only the quantity, but also the quality of organic matter determines infaunal distributions. The availability of organic matter for macroorganisms can be roughly determined by leaching experiments (e.g. sum of the easily
extractable macromolecules of the POC, Relexans et al. 1992). This labile organic
substance represents the potentially availahle food for benthic consumers, however
it usually makes up only a small part (less than 10 %) of the total carbon pool.
Bulk parameters such as the content of organic carbon (POC), total nitrogen or the
ClN-ratio are not enough to assess the quality of the organic matter. Furthermore,
the traditional biogeochemical division of organic matter into big groups (protein,
carbohydrates, fatty acids) is not sufficient as an indicator for the quality and
availability of organic matter for macroorganisms (Dauwe 1999). A more precise
.5 Spatial and Temporal DlstnhutlOll Patterns
Modifications of the organic and inorganic sediment composition entail certain
distribution patterns of the benthos. The polychaete Capitella capitata is a typical
representative of polluted coastal regions and an indicator for increased concentrations of organic matter (Weston 1990; Alongi & Tenore 1985). During the investigations on the Swinnplate, Capitella spp. occurred with higher abundances in the
old mussel bed and the biodeposit-enriched sediments (Table 5.2.3). Probably, the
natural habitat of this species-complex is POC-enriched sediment. Also the capitellid polychaete Heteromastus filiformis occurred more frequently at the edge of
the mussel bed than in the sandtlat. Thiermann et al. (1996) found a distribution of
macrofauna which was related to the variation of the corresponding sulphide regllne.
A classification of benthos into trophic groups revealed a modified composition
of macrofauna assemblages along the transect. In the mussel bed on the
Swinnplate, subsurface deposit-feeders were more frequent than in the sandtlat.
Predatory polychaetes were almost absent in the biodeposit-enriched sediments. A
similar distribution of trophic groups was described by Dittmann (1990) as a functional interaction ("trophic group amelioration").
In the biodeposits of the mussel bed, bioturbation was strongly reduced, because
no deep-dwelling macrofauna occurred here. Their abundance increased with increasing distance to the mussel bed. In the sandflat (reference site SP6) for example, Arenicola marina fulfils an important role as bioturbator (Reichert 1988).
Almost half way between the centre of the mussel bed and the reference site in the
sandtlat, the conditions seemed to be most favourable for the macrofauna. These
areas contained species- and individual-rich meio- and macrobenthic infauna with
a dominance of polychaetes. Probably both the supply with organic matter as well
as oxygen availability for aerobic respiration were sufficient here.
During the investigations on the Swinnplate, the content of organic matter
turned out as an important factor for the distribution of macrofauna. However,
together with the production of biodeposits, several other sediment characteristics
changed (see Dahlbiick & Gunnarsson 1981). In the case of the biodeposits which
were transported by the ebb current away from the mussel bed, changes in the
content of organic matter were correlated with the proportion of fine-grained
sediment material. Grain size distribution of the sediment itself can also influence
the distribution of macrofauna. as it was shown e.g. for tubificoid oligochaetes
(Giere & Pfannkuche 1982). Oligochaetes also dominated the infauna in mussel
beds studied by Dittmann (1990) and Krbncke (1996).
However, not only the quantity, but also the quality of organic matter determines infaunal distributions. The availability of organic matter for macroorganisms can be roughly determined by leaching experiments (e.g. sum of the easily
extractable macromolecules of the POC, Relexans et al. 1992). This labile organic
substance represents the potentially availahle food for benthic consumers, however
it usually makes up only a small part (less than 10 %) of the total carbon pool.
Bulk parameters such as the content of organic carbon (POC), total nitrogen or the
ClN-ratio are not enough to assess the quality of the organic matter. Furthermore,
the traditional biogeochemical division of organic matter into big groups (protein,
carbohydrates, fatty acids) is not sufficient as an indicator for the quality and
availability of organic matter for macroorganisms (Dauwe 1999). A more precise