The inner German Bight — an ecologically sensitive area as indicated by the bottom fauna

The muddy sediments of the sublittoral area of the inner German Bight are inhabited by a specialized macrofauna with few species. Long-term investigations on community and population dynamics have shown that the majority of this fauna are very susceptible to environmental stress (e. g. oxygen deficiency), and that the impoverishment trend recorded in 1977 has continued. The special hydrographic conditions of the inner German Bight, especially a long flushing time and the possibility of thermohaline stratifications, together with its function as a sediment trap are discussed. It is proposed that such areas should be considered as sensitive, and hence be protected from avoidable additional stress, e. g. introduction of wastes. This proposal is discussed with regard to the dangers arising from the view that muddy areas enriched with organic matter are inhabited by organisms preadapted to the decomposition of additional waste matter.     

The association between the caprellid Pariambus typicus Krøyer (Crustacea,Amphipoda) and ophiuroids

The work of Kazutsugu Hirayama over the past 25 yearspromoted the wide use of the marine rotifer Brachionusplicatilis as an experimental model in zooplanktonecology. His reports about the nature of geneticvariation in the B. plicatilis complex stimulated usto investigate how mate recognition maintains speciesboundaries. For the past several years, we haveexamined chemical communication between female andmale B. plicatilis. Here we report on the comparativebinding of polyclonal antibody against the materecognition pheromone (MRP) to three B. plicatilisstrains and three B. rotundiformis strains.Quantification of anti-MRP binding permitsinvestigation of how the female mating signal differsamong closely related Brachionus species and strains.Antibody binding reflects differentiation independentof the male receptor which has been describedelsewhere. Anti-MRP bound to females of all sixstrains and was localized in the corona. Antibodybinding greatly reduced mating in all three B. plicatilis strains. However, antibody bindingsignificantly reduced mating in only one of the B. rotundiformis strains. The MRP of both species has asimilar molecular weight, but the differential bindingsuggests that the mate recognition pheromone onfemales has differentiated in B. plicatilis and B. rotundiformis.     

Das de Mansche Organ der Oncholaimidae,eine genito-intestinale Verbindung bei Nematoden

The different types of the de Manian system are described and compared in 10 genera (for the first time in Viscosia and Oncholainmllus). By tracing a morphological sequence the organ is interpreted as a more or less segregated appendix of the female genital tube (duplication theory). The organ, which has distally an ingrowth of intestinal tissue, functions as a seminal receptacle.

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Hauptteil einer Dissertation zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Hamburg, angenommen am 16.4. 1969. Der Teil Systematische Bemerkungen zur Familie der Oncho laimidae wird in den Veröffentlichungen des Instituts für Meeresforschung in Bremerhaven erscheinen (Rachor, 1970). Die Untersuchungen wurden mit Unterstützung der Deutschen Forschungsgemeinschaft durchgeführt.     

BIODIVERSITY RESEARCH: Turning up the heat: the impacts of Andropogon gayanus (gamba grass) invasion on fire behaviour in northern Australian savannas

Aim This study aimed to quantify changes in fire severity resulting from the invasion of Australia’s tropical savannas by the African grass Andropogon gayanus Kunth. (gamba grass). Location Mesic savannas of the Northern Territory, Australia. Method Byram’s fire‐line intensity (I_f), fuel load and architecture, and two post‐fire indicators of fire intensity – scorch height (SH) and char height (CH) of woody vegetation – were determined for fires in native grass savanna and A. gayanus invaded savanna. Leaf scorch is the height at which the fire’s radiant heat browns leaf tissue, and leaf char is the height that radiant heat blackens or consumes leaf tissue and provides an indirect measure of flame height. These data, and 5 years of similar data collected from the Kapalga Fire Project in Kakadu National Park, were used to develop empirical relationships between I_f and the post‐fire indices of fire intensity. Results A relationship between A. gayanus I_f and SH could not be developed because complete canopy scorch occurred in most A. gayanus fires, even at low I_f. In contrast, A. gayanus I_f was strongly correlated with CH. This empirical relationship was substantially different from that for native grass fires. For a given I_f, there was a significantly greater CH in invaded sites. This increase in radiant heat is attributable to the increased biomass (mean 3.6 t ha^?1 in native grasses compared to 11.6 t ha^?1 in A. gayanus) and height (approximately 0.5 m in native grasses compared to 4 m in A. gayanus) of the standing fine fuel. Main conclusion Andropogon gayanus invasion resulted in substantial changes in fire behaviour. This has important regional implications owing to the current (10,000–15,000 km²) and predicted (380,000 km²) area of invasion and the negative consequences for the native savanna biota that has evolved with frequent but relatively low‐intensity fire.     

Faunenverarmung in einem Schlickgebiet in der Nähe Helgolands

Variations in abundance and species composition of macro-zoobenthos were studied at a sublittoral muddy-bottom station in the inner part of the German Bight from 1969 to 1976. The fauna of this area can be included in the classicalAbra alba community. A total of 98 species were found in 62 samples. Of these, only 4 species occurred in all samples:Nucula nitidosa, Diastylic rathkei, Ophiura texturata andNephtys hombergii. Species richness has declined since 1969. Populations of several species disappeared in the investigated area and its surroundings. Other populations are shown to exhibit remarkable fluctuations in abundance with sometimes heavy spatfalls or sudden breakdowns in population density, mainly during late summer. The long-term trend of impoverishment of the fauna is attributed to the development of anaerobic conditions in the muddy sediment. Such conditions are favoured by stable, thermohaline strafications of the water during summer, resulting in low oxygen levels and, probably, enrichment of hydrogen sulfide even in near-bottom water. Moreover, both continuou influx into the area of Elbe water, rich in suspended matter and nutrients and dumping of sewage sludge about 8 km east of the investigated area are considered to have increased the strees on the bottom fauna.     

A seafloor crater in the German Bight and its effects on the benthos

 In 1963 a deep crater was formed about 65 m below sea level in the western part of the German Bight, due to a gas eruption caused by drilling carried out from the platform ’Mr. Louie’. The study area is situated in a sandy to muddy bottom area inhabited by an Amphiura filiformis association (sensu Salzwedel et al. 1985). The crater, sometimes called ’Figge-Maar’, functions as a sediment trap, concentrating particles and organisms from the water column, thus leading to extreme sedimentation rates of about 50 cm, on average, per year. Crater stations, compared with stations situated in the vicinity, show enrichments of juveniles. Echinoderms, especially the subsurface-dwelling heart urchin Echinocardium cordatum and ophiuroids are responsive to enrichment. Other species that are typical of the Amphiura filiformis association are shown to be unable to cope with the special conditions in the crater. Received: 12 June 1998 / Accepted:16 September 1998     

Red List of macrofaunal benthic invertebrates of the Wadden Sea

Parasites were observed in medium- and small-sized fish taken from the discards of a commercial shrimper during seven different cruises in the tidal channels of the North Frisian Wadden Sea (Süderaue, North Sea) from April to September 1991. In total, 442 fish comprising four species (Sprattus sprattus, Hyperoplus lanceolatus, Ammodytes tobianus, Pomatoschistus minutus) were investigated. The parasite fauna consisted of 22 species. The parasite community structure of the 4 hosts was compared. The diet of the hosts seemed to be the main factor determining the structure of the parasite community. Other factors could not be assessed. Eight species of parasites occurred as larval stages. This indicated that fish were intermediate or paratenic hosts in their life cycle. The nematodeHysterothylacium sp. (Anisakidae) and the digeneanCryptocotyle lingua (Heterophyidea) were the dominant parasites, reaching their highest prevalence and density in sprat and sand eel. Sprat and sand eel play a very important role in parasite transmission to predacious fish and seabirds.     

An annotated checklist of macrozoobenthic species in German waters of the North and Baltic Seas

The present compilation is the first attempt to generate a comprehensive list of all macrozoobenthic species recorded at least once in the German regions of the North Sea and Baltic Sea including non-indigenous species and freshwater species which occurred in brackish waters (estuaries, bays, fjords etc.). Based on the data of several research institutes and consultancies, the macrozoobenthic species inventory comprises a total of 1.866 species belonging to 16 phyla including 193 threatened species. The most common groups were: malacostracan crustaceans (21%), Polychaeta (19%), and Gastropoda (12%). Even though the two major marine regions are separated by only 50 km of land, the composition of the respective communities was different. The two seas shared only 36.6% of the recorded species which should have profound and far-reaching consequences for conservation purposes. Considering all macroinvertebrates listed 96 species, or the equivalent of 5.2%, were introduced mainly during the last two centuries. Both seas are heavily affected by human activities and are sensitive to climate change displayed by effects on the faunal compositions. The present checklist is an important step to document these changes scientifically and may act as a base for political and management decisions.     

Chemical defence against predators in a sub-Arctic fjord

The development of chemical defences in marine organisms is supposed to be driven by intense pressure of predation and competition. While benthic communities in tropical and also Antarctic regions are thought to be mainly structured by intra- and interspecific interactions, these factors are proposed to be less important in northern high latitudes. Consequently, selective pressure for chemical defence should be low in these regions. To investigate the incidence of chemical defence against predation in northern high latitudes, crude extracts of 18 abundant sessile or slow-moving invertebrate species (4 sponges, 3 actinians, 1 soft coral, 4 bryozoans, 3 ascidians and the egg mass of a gastropod) from Kongsfjord (Spitsbergen) were tested for feeding deterrent activity. Laboratory assays were performed by offering artificial food with extracts to two different predators, the amphipod Anonyx nugax which is a common species in Kongsfjord, and the starfish Asterias rubens from the North Sea. Of the 18 extracts tested, 2 (Haliclona viscosa, Hormathia nodosa) exhibited significant feeding deterrent effects in the amphipod assay. Furthermore, 6 extracts had a significantly stimulating effect on the amphipod feeding, and 10 extracts did not affect consumption. In the starfish assay, only the crude extract of H. viscosa was significantly rejected. For H. viscosa, feeding deterrence could be established for two pure compounds, and for H. nodosa for one fraction. The present data show that feeding deterrent compounds are present in sub-Arctic marine invertebrates from Kongsfjord but are less abundant than in temperate, tropical and Antarctic species.     

Benthic macrofauna communities of the submersed Pleistocene Elbe valley in the southern North Sea

Macrozoobenthic community structure was studied in two surveys along a transect of 13 stations following the submersed Pleistocene Elbe valley in the south-eastern North Sea during May to June 2000 and March 2001. Two replicates of bottom samples were taken with a van Veen grab of 0.1 m² sampling size. In order to analyse the benthic macrofauna communities, the animals obtained were identified and counted, and MDS and cluster analysis were performed. Out of 200 taxa identified, 84 were polychaetes, 46 molluscs, 40 crustaceans, 15 echinoderms, and 15 belonged to other groups. Mean abundance was 4,860 individuals per m², mean biomass 32.9 g ash free dry mass per m². Mean diversity was 1.76 and mean evenness 0.54. The macrofauna of the Pleistocene Elbe valley is composed of three associations according to the cluster analysis. Each association is described by a combination of characterizing and discriminating species. An Amphiura-brachiata―Tellimya-ferruginosa-association was found in the south-eastern part of the depression, whereas a transitional association with elements of both assemblages lead to an Amphiura-filiformis―Galathowenia-oculata―Nuculoma-tenuis-association in the north-western part of the valley. In the context of the entire southern North Sea, both associations are small-scale substructures, and as such are contained in the Nucula-nitidosa-community and the Amphiura-filiformis-community, respectively. A north-westward shift of the community of the southern Elbe valley was found and discussed as a possible consequence of warm winters of the last decades.