The common tube-building polychaete
Lanice conchilega is known as a habitat structuring species and can form dense aggregations. The effects of
L. conchilega on the surrounding benthic community have received little attention, especially in subtidal areas. Therefore, the presence
of
L. conchilega in different habitats in the North Sea and its effect on the abundance, species richness, diversity and community structure
in these habitats are evaluated in the present paper, based on data from the ICES North Sea Benthos Survey of 2000.
Lanice conchilega has a wide geographical distribution and a low habitat specialization, but optimally occurs in shallow fine sands. In the
present study, the presence of
L. conchilega resulted in a density increase and a significant (positive) correlation of the benthos density with the density of
L. conchilega. Furthermore, the species richness (number of species) increased with increasing density of
L. conchilega. This trend was, however, not consistent: the number of species reached more or less an asymptotic value or even decreased
after reaching a critical density of
L. conchilega (>500–1,000 ind/m2), as observed in shallow fine sands. The same overall pattern was detected concerning the expected number
of species. The
N
1-diversity index showed similar or slightly higher values in
L. conchilega patches compared to patches without
L. conchilega. From the results of the community analysis, it can be concluded that the species, which were responsible for the increase
of the diversity, belonged to the overall species-pool of that habitat. The effects on density and diversity differed between
the four discerned habitats (shallow muddy sand, shallow fine sand, shallow medium sand and deep fine sand), and were most
pronounced in shallow fine sands. These patterns can be attributed to the habitat structuring capacity of
L. conchilega. The mechanisms responsible for the increase of the habitat quality in patches of
L. conchilega can be summarized as (1) changes in the hydrodynamics, (2) increases of the habitat stability and oxygen supply, and (3)
a creation of habitat heterogeneity in a uniform environment. In this way,
L. conchilega alters the habitat characteristics and affects other organisms, and can therefore even be considered as an ecosystem engineer.
In other words,
L. conchilega patches are responsible for an increased habitat quality in an otherwise uniform habitat, which results in a higher survival
of the surrounding benthic species.
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