5.5 Biotic Interactions in a Lanier-Tidal Flat
153
5.5
Biotic Interactions in a Lanice conchilega-Dominated
Tidal Flat
Sabine Dittmann
Abstract: The tube-dwelling polychaete Lanice conchilega provides a biogenic
structure in the sandflats of the Wadden Sea, which has direct or indirect effects
on other benthic organisms. In order to separate the effect of the tube-worm from
mere effects of the tubes, experiments were carried out using artificial tubes. Both
patches with living L. conchilega as well as patches with artifial tubes showed
increased abundances and species numbers of benthic organisms compared to
ambient sediment without this biogenic structure. In both cases (natural and artifical tubes) an increased settlement of juvenile mussels occurred on the tubes.
Predatory polychaetes were also more numerous in both types of tube fields. Spionid polychaetes were more numerous in patches with a high density of
L. conchilega. However, the only true commensalistic association found was between L. conchilega and the polychaete Malmgreniella lunulata, living in the
worm tubes. The density and distribution of L. conchilega varied throughout the
study period. The tube-worms formed localized patches of 1-2 m in size with a
high density of L. conchilega. Over time, the individual numbers declined following the severe ice winter of 1995/96.
5.5.1
Introduction
Biogenic structures of polychaete tubes can affect the distribution pattern of benthic organisms by modifying the sediment (Eckman et al. 1981; Carey 1987) and
hydrographic parameters (Eckman 1983; Friedrichs 1996), or by interactions between species (Woodin 1978). The interaction between the tube-dwelling polychaete Lania conchilega (in the following text referred to as Lanice) and the
benthos were studied by Zuhlke et al. (1998) in a sandflat of the East Frisian Wadden Sea, the Groninger Plate (Chaps. 3.1 and 3.6.2). To investigate the interactions
with other fauna, the benthic associations of sandflats with different Lanice densities were analysed. Therefore, additional samples were taken on the Dornumer
Nacken, a backbarrier tidal flat behind the island of Langeoog, where Lanice attained densities twice as high as on the Groninger Plate. Furthermore, experiments
were set up with artificial tubes to study the effect of the tube structure as such
(Zuhlke et al. 1998). The Lanice-community was studied over the entire duration
of ELA W AT, allowing an assessment of natural variations in the density of this
polychaete and its effects on associated fauna. The investigations, carried out by a
number of teams in ELA WAT, are summarized in this chapter.
153
5.5
Biotic Interactions in a Lanice conchilega-Dominated
Tidal Flat
Sabine Dittmann
Abstract: The tube-dwelling polychaete Lanice conchilega provides a biogenic
structure in the sandflats of the Wadden Sea, which has direct or indirect effects
on other benthic organisms. In order to separate the effect of the tube-worm from
mere effects of the tubes, experiments were carried out using artificial tubes. Both
patches with living L. conchilega as well as patches with artifial tubes showed
increased abundances and species numbers of benthic organisms compared to
ambient sediment without this biogenic structure. In both cases (natural and artifical tubes) an increased settlement of juvenile mussels occurred on the tubes.
Predatory polychaetes were also more numerous in both types of tube fields. Spionid polychaetes were more numerous in patches with a high density of
L. conchilega. However, the only true commensalistic association found was between L. conchilega and the polychaete Malmgreniella lunulata, living in the
worm tubes. The density and distribution of L. conchilega varied throughout the
study period. The tube-worms formed localized patches of 1-2 m in size with a
high density of L. conchilega. Over time, the individual numbers declined following the severe ice winter of 1995/96.
5.5.1
Introduction
Biogenic structures of polychaete tubes can affect the distribution pattern of benthic organisms by modifying the sediment (Eckman et al. 1981; Carey 1987) and
hydrographic parameters (Eckman 1983; Friedrichs 1996), or by interactions between species (Woodin 1978). The interaction between the tube-dwelling polychaete Lania conchilega (in the following text referred to as Lanice) and the
benthos were studied by Zuhlke et al. (1998) in a sandflat of the East Frisian Wadden Sea, the Groninger Plate (Chaps. 3.1 and 3.6.2). To investigate the interactions
with other fauna, the benthic associations of sandflats with different Lanice densities were analysed. Therefore, additional samples were taken on the Dornumer
Nacken, a backbarrier tidal flat behind the island of Langeoog, where Lanice attained densities twice as high as on the Groninger Plate. Furthermore, experiments
were set up with artificial tubes to study the effect of the tube structure as such
(Zuhlke et al. 1998). The Lanice-community was studied over the entire duration
of ELA W AT, allowing an assessment of natural variations in the density of this
polychaete and its effects on associated fauna. The investigations, carried out by a
number of teams in ELA WAT, are summarized in this chapter.