Lanice

Abstract: The competitive inter-actionis between two species of clhar-acinis (Astvanaxfisciahlus and Astyanax bimnaculaltus) wer-e investigated by studyinig their- horizonital distribution, relative abund(lanice and feeding habits in littoral and limnetic zones of Americania Reservoir, southlerni Br-azil Differences in hor-izontal distribution of the species mainily as adults led to thcir partial habitat segr-egation Most adult A bimnacidialus wer-e littoral dwellers, wher-eas A Jfasciatls adults wer-e distributed from inslhore to offshore waters, but with most in the latter region Both are facultative zooplanktivores in the reser-voir-, feedin-g mostly on plaiiktonic crustaccanis, insects (chiefly chlironiomids), some higlher plant material, detritus anid eveni fish scatles (,4 biiacullalus) Food overlap coefficients, considering adult and juveniile stages of both species are lar-ge in dry as well as wet seasons, although in the dry season the overlaps are significantly r-educed for juveniles of both species and for juveniiles of A bimnacidalius ver-sus adtults of Afascialus Both species prey mor-e on cladocerans than oni cyclopoid copepods, anid the adults selectively take lar-ger- forms (Daphiiia gessneri and A'Ioina miiicrura) in the r-eser-voir- (as in previously r-epor-ted enclosur e expei-iients)Juveiiiles prey heavily on Bosminia longirostiis These two formerly i-iverine species may reduce competition, in the reservoir, by partial halbitat segregation in older- stages, a mechalismii to avoid competition, whliich miay hlalve existedl in their- previous interactive history in rivers

Abstract: The tube-building polychaete Lanice conchilega forms intertidal mounds in association with macroalgae. This assemblage produces structures that can record tidal and seasonal cycles in the stratigraphic record. They mark low-tide levels because the assemblage occurs below neap low tide and many of the structures form when water drains off the assemblage. Mounds are created by disturbance of the sediment surface around aggregations of the assemblage and accumulation of sediments within the aggregations. The initial aggregations may be relict patches of adult worms, new clumps of juveniles or both. Juvenile worms and drift algae easily settle and survive in high-density patches, whereas predators and waves more readily disturb low-density patches. Algae and tubes extend through accumulated sediment and create a new, higher surface. Through this interactive process the high-density patches increase height rapidly while the low-density patches erode. Regardless of density, when the initial distribution is regular the surface remains flat, rising evenly or eroding evenly. Accumulation and erosion increases during spring tides and decreases during neap tides. Mound development also follows a seasonal pattern. The recruitment of juvenile worms in spring facilitates algal settlement and initiates mound buildup. The rate of tube-building and algal growth increases in early summer as the erosive forces of storms decline. This leads to the greatest development of mounds in late summer just before the macroalgae begin to die. The loss of algae coincides with autumnal storms, and causes catastrophic erosion of the mounds into relict patches of dormant tube-worms. Patches of tubes that survive the winter enhance spring recruitment and renewal of mound development. The shape of the mounds is often obscured during burial and preservation. Because of this, it may be difficult to distinguish the original form of ancient mounds without contemporaneous cementing organisms. But cycles of deposition and erosion are recorded in Lanice tubes and other biogenic structures. These structures can be used in conjunction with physical structures to define tidal height, seasonality or current regime. In general however, the presence of tube aggregations per se is not diagnostic of a specific hydraulic environment.

Abstract: The recolonization process of Lanice conchilega was studied on an intertidal sand flat in the northern Wadden Sea after an intertidal population had been wiped out during the severe winter of 1995/96. After very low recruitment in the first two years, the population fully recovered in the third year after its destruction. By then, the distribution pattern closely resembled the pattern before the severe winter with >95% of all Lanice occurring below –0.5 m mean tidal level and dominance of the density categories 6–50 individuals (ind) m–2 and 51–200 ind m–2. Lanice larvae have been observed to attach preferentially on the tubes of adults. However, the high recruitment in the third year was also seen in areas devoid of adult Lanice, indicating that settlement facilitation by adults was of little importance for the recolonization process. Instead, we suggest that the observed recruitment pattern was a consequence of a large-scale decline in the metapopulation in the tidal basin and the onshore coastal subtidal which resulted in insufficient larval supply onto the tidal flats and low recruitment in the first two years following the severe winter.

Abstract: Evaluation of the importance of different benthos communities as feeding sites for waders and waterfowl is not only fundamental for understanding feeding ecology, it also enables the prediction of the effects of habitat loss. However, detailed analyses of the importance of different benthos communities for waterbirds are scarce, particularly for the German Wadden Sea. In the early 1990s, backbarrier tidal flats of the East Frisian Wadden Sea were dominated by Lanice conchilega. To estimate the relevance of those flats for waterbirds during autumn migration 1994, number, distribution and food consumption of the 7 most abundant bird species on these flats (oystercatcher, curlew, dunlin, redshank, common gull, black-headed gull, herring gull) were investigated on 2 different types of L. conchilega dominated flats (Lanice flat, Undulating flat). Spring tide counts throughout 1994 showed maximum bird numbers during spring (maximum: 56000 birds) and autumn migration (maximum 111 000 birds). Of the 7 species examined, 4 species (oystercatcher, curlew, redshank, common gull) used both flat types in higher densities than expected. Whereas common gulls preferred the Undulating flats, oystercatchers preferred the Lanice flats. The overall number of macrozoobenthos organisms varied between 3360 and 5520 m -2 on the Undulating flat, and between 8520 and 15100 m -2 on the Lanice flat. Correspondingly, the estimated biomass ranged from 67.6 to 142.3 g AFDW m -2 and 128.4 to 337.2 g AFDW m -2 (AFDW: ash free dry weight), respectively. Therefore, biomass was higher than in most other Wadden Sea areas. The most abundant species were Heteromastus filiformis, L. conchilega, Macoma balthica and Mytilus edulis. The overall consumption of the 7 bird species studied (70% of all waterbirds present) decreased from 16.6 g AFDW m -2 in August to 12.3 g AFDW m -2 in October. Assuming a similar consumption for the remaining 30% of the birds, overall consumption would have ranged between 17.6 and 23.7 g AFDW m -2 . Due to the high biomass of the standing stock, relative consumption (5.2 to 13.7 %) was similar to other regions of the Wadden Sea. Only 3 species (oystercatcher, curlew, common gull) consumed between 78 and 93% of the overall consumption of the 7 species examined. Whereas waders mainly foraged on the accompanying fauna of the L. conchilega community, the bulk of the diet of gulls was L. conchilega itself. In general, food supply on L. conchilega dominated flats can be judged as favourable. However, the possibility that food consumption could have been a limiting factor, at least for some species (e.g. oystercatcher), cannot be ruled out.