Flach e (96 résultats)

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Three new Albinaria species from Crete, Nomos Lasithiou (Gastropoda Pulmonata: Clausiliidae). Three new Albinaria species, viz. Albinaria wiesei spec. nov., Albinaria fulvula spec. nov. and Albinaria purpurea spec. nov., are described by E. Gittenberger, E.C. Flach and N. Reitsma, respectively. Thus the authorship is restricted to a single person for each taxon. The species have been discovered on eastern Crete while thoroughly revising the complex Albinaria fauna of that part of the island. 6 pp., 11 figs, gr. 8.…

The amphipod Corophium volutator has a patchy distribution which has been related to different factors (both physical and biological) at different sites. Experiments in the Wadden Sea, involving manipulation of the densities of the lugworm Arenicola marina and the bivalve Cerastoderma edule showed strong negative effects of these two species on the abundance of C. valutator. This result could explain the distribution pattern of C. valutator found in the Wadden Sea. The question was if this would also be the case in other geographical regions. Therefore, these experiments were repeated under different physical conditions in two shallow and almost non-tidal soft-bottom bays in Gullmarsfjorden on the Swedish west coast. Again, a significant negative density-dependent effect on Corophium was found. This effect was even stronger when A. marina and C. edule occurred together. A. marina and C. edule affected the numbers of the two sexes of C. valutator in a similar way. However, in the treatments with high densities of A. marina and C. edule the proportion of females with eggs and the mean lengths of the females were lower resulting in a lower reproductive output. Surveys of several bays along Gullmarsfjorden showed that the bay-to-bay variability in the abundance of C. volutator could not be explained by differences in abundances of A. marina, C. edule or Nereis diversicalor. Within the only two bays with locally high densities of A. marina the densities of C. volutator showed a clear negative relationship with those of A. marina. In conclusion: at a small scale the abundance of C. volutator is closely related to densities of A. marina and C. edule, but at a larger scale other factors must be of more importance. 14 pp., 11 figs, gr. 8.…

On the tidal flats in the Dutch Wadden Sea Corophium volutator is a dominant species of the upper intertidal zone; the closely related Corophium arenarium is usually found in the lower zone, but only in low densities (a few hundreds per m2). A survey in the Dutch Wadden Sea showed that this zonation pattern was only present when a muddy sediment was found in the upper zone and a sandy in the lower zone. C. arenarium was restricted to sandy sediments, C. volutator to muddy sediments. Where a sandy sediment was found in the upper intertidal zone, C. arenarium locally occurred in relatively high densities (a few thousands per m2). An aquarium experiment showed that C. arenarium actively avoided muddy sediments. Field experiments were carried out to study the influence of other macrozoobenthic species (known to affect the related C. volutator) on the abundance of C. arenarium. Within large defaunated areas small plots were stocked with different densities of the lugworm Arenicola marina and the cockle Cerastoderma edule. In small plots within a natural benthic community densities of these species were also augmented or (in A. marina) reduced. Strongly negative density-dependent effects of both A. marina and C. edule were found on the abundance of C. arenarium. In the natural situation, its densities showed A. marina to be the most important factor in determining the abundance of C. arenarium. In particular the removal of lugworms caused a strong increase in C. arenarium densities. These results agreed with the distribution of these species along a transect perpendicular to the shore of Schiermonnikoog, where a significant negative correlation was found between the densities of A. marina and C. arenarium. Aquarium experiments showed that the negative effect of cockles and lugworms must be due to migration rather than mortality in C. arenarium. 10 pp., 10 figs, gr. 8.…

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