158
5 SpalIaI and Temporal DistnhutHlIl Patterns
(Zuhlke et a!. 1998). At both study areas, the Groninger Plate and the Oornumer
Nacken, benthos abundances were significantly enhanced within the Lanicepatches at all sampling dates (Fig. 5.5.1). Juvenile bivalves (Mya arenaria, Mytilus
edulis, Macoma halthica) were more frequent in patches with Lanice than without
and settled especially on the tentacle crown of the worm tubes. Polychaetes, which
made up the majority of the benthos, occurred with more species and individuals
in Lanice-patches. In particular, abundances of predatory polychaetes (Eteone
tonga, Nephthys homhergii, Nereis diversicolor) were higher. Independent of the
Lanice density, the commensal polychaete Malmgreniella lunulata was more
abundant with than without Lanice. Higher numbers of spionids (especially Pygospio elegans) were only recorded in the Lanice site at the Oornumer Nacken. Seasonal and annual variations of polychaete abundances were, however, common
(see above). Multidimensional scaling (MOS) of the benthos associations revealed
distinct faunal groups at the sampling sites in each year. Samples taken in February 1996, straight after the ice winter, had a very different benthos composition
from all other dates in the MOS. In the course of the recolonization of Lanice in
the summer of 1996, a benthos association comparable to the previous years developed. Only the commensal polychaete M. lunulata and predatory polychaetes
did not yet achieve densities as before. Contrary to the previous years, abundances
of Polydora cornuta and Phyllodoce mucosa were enhanced in the Lanice-patches.
The meiofauna distribution was also affected by Lanice. Studies on the smallscale distribution of copepods showed that two species (Harpacticus ohscurus and
Halectinosoma gothieeps) were restricted in their occurrence to the Laniee-patches
(Sach & van Bernem 1996). Modelling their small-scale distribution with a modified Thomas-process (a two-phase stochastic point process relating spatial distributions of so-called parent and daughter points, Pfeifer et al. 1996) confirmed that
these species aggregate around the tubes of Laniee and only few individuals occur
in the space between the worm tubes. A cluster analysis indicated a greater similarity of the copepod fauna among sites with Lanice than among sites without.
Copepods could use the biogenic structure provided by Laniee as a shelter from
high current velocities. Their aggregation around the tubes could, however, also be
related to their reproductive cycle, as many of the copepods found near the worm
tubes were in pre-copula (Sach & van Bernem 1996).
Nematodes were three times as abundant at the worm tubes than at 1.5~5 cm
distance (Zuhlke et al. 1998). The majority of the nematodes close to the Laniee
tubes were DOM (dissolved organic matter)-feeders, following the classification
of trophic groups given in Giere (1993). At 2 cm distance from the worm tubes,
diatom-feeders dominated amongst the nematodes. A relation between small-scale
distributions of food sources and nematodes was also confirmed with multicorer
data, where nematodes of the same trophic group had similar small-scale distributions (Blome et a!. 1999). In total, 72 nematode species of 25 families were recorded in Lanice-patches out of 235 nematode species known from the East
Frisian Wadden Sea and adjacent estuaries (Blome 1996).
The colony-forming benthic diatom Amphipleura rutilans was more abundant
within the Laniee patches. This species was absent in the spring of 1996 after the
ice winter CRamm pers. comm.).
5 SpalIaI and Temporal DistnhutHlIl Patterns
(Zuhlke et a!. 1998). At both study areas, the Groninger Plate and the Oornumer
Nacken, benthos abundances were significantly enhanced within the Lanicepatches at all sampling dates (Fig. 5.5.1). Juvenile bivalves (Mya arenaria, Mytilus
edulis, Macoma halthica) were more frequent in patches with Lanice than without
and settled especially on the tentacle crown of the worm tubes. Polychaetes, which
made up the majority of the benthos, occurred with more species and individuals
in Lanice-patches. In particular, abundances of predatory polychaetes (Eteone
tonga, Nephthys homhergii, Nereis diversicolor) were higher. Independent of the
Lanice density, the commensal polychaete Malmgreniella lunulata was more
abundant with than without Lanice. Higher numbers of spionids (especially Pygospio elegans) were only recorded in the Lanice site at the Oornumer Nacken. Seasonal and annual variations of polychaete abundances were, however, common
(see above). Multidimensional scaling (MOS) of the benthos associations revealed
distinct faunal groups at the sampling sites in each year. Samples taken in February 1996, straight after the ice winter, had a very different benthos composition
from all other dates in the MOS. In the course of the recolonization of Lanice in
the summer of 1996, a benthos association comparable to the previous years developed. Only the commensal polychaete M. lunulata and predatory polychaetes
did not yet achieve densities as before. Contrary to the previous years, abundances
of Polydora cornuta and Phyllodoce mucosa were enhanced in the Lanice-patches.
The meiofauna distribution was also affected by Lanice. Studies on the smallscale distribution of copepods showed that two species (Harpacticus ohscurus and
Halectinosoma gothieeps) were restricted in their occurrence to the Laniee-patches
(Sach & van Bernem 1996). Modelling their small-scale distribution with a modified Thomas-process (a two-phase stochastic point process relating spatial distributions of so-called parent and daughter points, Pfeifer et al. 1996) confirmed that
these species aggregate around the tubes of Laniee and only few individuals occur
in the space between the worm tubes. A cluster analysis indicated a greater similarity of the copepod fauna among sites with Lanice than among sites without.
Copepods could use the biogenic structure provided by Laniee as a shelter from
high current velocities. Their aggregation around the tubes could, however, also be
related to their reproductive cycle, as many of the copepods found near the worm
tubes were in pre-copula (Sach & van Bernem 1996).
Nematodes were three times as abundant at the worm tubes than at 1.5~5 cm
distance (Zuhlke et al. 1998). The majority of the nematodes close to the Laniee
tubes were DOM (dissolved organic matter)-feeders, following the classification
of trophic groups given in Giere (1993). At 2 cm distance from the worm tubes,
diatom-feeders dominated amongst the nematodes. A relation between small-scale
distributions of food sources and nematodes was also confirmed with multicorer
data, where nematodes of the same trophic group had similar small-scale distributions (Blome et a!. 1999). In total, 72 nematode species of 25 families were recorded in Lanice-patches out of 235 nematode species known from the East
Frisian Wadden Sea and adjacent estuaries (Blome 1996).
The colony-forming benthic diatom Amphipleura rutilans was more abundant
within the Laniee patches. This species was absent in the spring of 1996 after the
ice winter CRamm pers. comm.).