The mysid-feeding guild of demersal fishes in the brackish zone of the Westerschelde estuary

The demersal fish fauna of the mesohaline zone of the Westerschelde estuary (south-west Netherlands) was sampled intensively in the period 1990–1992. Almost 500 beam trawl samples were taken in both subtidal (330 samples) and intertidal (144 samples) habitats. These yielded 44 fish species, mostly as juveniles. The area functioned as a nursery for several demersal fish species, and harboured large populations of hyperbenthic mysids. Three gobies, three flatfish, one clupeoid and one gadoid dominated the fish fauna, while three mysid species were important components of the holohyperbenthos. From c. 1500 stomach contents of 25 fish species, 44 prey species were identified, the most abundant of which were also common in the hyperbenthal. The demersal fish community consisted of a group that foraged subtidally on fast-moving epi-and hyperbenthic prey (for example gadoids, gobies and clupeoids) and a group that foraged on slow-moving or sessile endobenthic organisms, mainly in intertidal areas (for example most flatfish species). Mysidacea occurred in >50% stomachs analysed and were taken as prey by 19 of the 25 fish species. Mysids were most important in the diets of Pomatoschistus minutus, P. lozanoi, Trisopterus luscus and Merlangius merlangus, and were present in appreciable numbers in Pleuronectes flesus, Trigla lucerna, Clupea harengus and Pleuronectes platessa. These species fed mainly on the brackish water endemic Neomysis integer. Mesopodopsis slabberi (present in 35% of the gobiid stomachs) and Gastrosaccus spinifer(present in 25% of the gadoid stomachs) were of secondary importance. P. minutus and T. luscus showed a diet shift from calanoids (Eurytemora aYnis and Temora longicornis) to mysids at L_S of 30 and 50 mm, respectively. Only 1% of the standing stocks of the N. integer and M. slabberi populations was removed by the local demersal fish community, so top–down control of mysid populations in estuaries seems unlikely.     

First record of Synidotea laevidorsalis (Miers, 1881) (Crustacea: Isopoda) in Europe (Gironde estuary,France)

This note reports on the presence of a well established population of the isopod Synidotea laevidorsalis (Miers) in the Gironde estuary (southwestern France). This species is new for the European fauna. S. laevidorsalis is a nonendemic cool-temperate to subtropical, shallow-water species which was probably introduced into the study area from Asia. In the salinity range of 1 to 10 g 1^-1 of the Gironde the species constitutes an important component of the brackish-water hyperbenthic community. The population was already present in 1975 when it was misidentified as the native species Idotea emarginata (Fabricius).     

Isolation of a dimethylsulfide-utilizingHyphomicrobium species and its application in biofiltration of polluted air

The methylotrophic bacteriumHyphomicrobium VS was enriched and isolated, using activated sewage sludge as inoculum in mineral medium containing dimethylsulfide (DMS) at a low concentration to prevent toxicity. DMS concentrations above 1 mM proved to be growth inhibiting.Hyphomicrobium VS could use DMS, dimethylsulfoxide (DMSO), methanol, formaldehyde, formate, and methylated amines as carbon and energy source. Carbon was assimilated via the serine pathway. DMS-grown cells respired sulfide, thiosulfate, methanethiol, dimethyldisulfide and dimethyltrisulfide.To testHyphomicrobium VS for application in biofiltration of air polluted with volatile sulfur compounds two laboratory scale trickling biofilters with polyurethane and lava stone as carrier material were started up by inoculation with this bacterium. Both methanol- and DMS-grown cells could be used. Only a short adaptation period was needed. Short term experiments showed that high concentrations of DMS (1–2 µmol 1^–1) were removed very efficiently by the biofilters at space velocities up to 100 h^–1.Abbreviations VSC volatile sulfur compounds - DMS dimethylsulfide - DMDS dimethyldisulfide - DMTS dimethyltrisulfide - MT methanethiol - DMSO dimethylsulfoxide     

Linear and inverted repetitions in protein sequences

An extensive search for internal regularities in amino acid sequences has been made, using both the genetic code and the relative frequencies of amino acid alternatives in homologous proteins. The two methods give very similar results and strongly suggest the occurrence of significant linear and inverted repetitions (similar sequences of opposite polarity) in several proteins. A hypothesis is developed to explain the occurrence of such internal regularities in proteins. This hypothesis is based on a process of duplication of an ancestral loop in which a symmetrical arrangement of amino acid allows stabilization by interaction between the amino acid side chains.     

Evolution of immunoglobulins and ferredoxins and the occurrence of pseudosymmetrical sequences

The homologous relationship between the different chains and fragments of immunoglobulins has been investigated by a sensitive method. The results lend weight to theories which suggest that all the chains of immunoglobulins have evolved from a common ancestor. Moreover, the results suggest that the variable and constant parts of light chains have also a common ancestor. The occurrence of several possible internal regularities has been investigated. The results suggest that immunoglobulins and ferredoxins derive from the repetition of a primordial (pseudo)symmetrical peptide. The significance of the results is discussed.This work was carried out under the association contract 016-61-10 ABIB between Euratom and the University of Brussels.     

Taxonomic Review of the Orders Mysida and Stygiomysida (Crustacea,Peracarida)

The order Mysida (2 families, 178 genera, 1132 species) contains species across a broad range of habitats, such as subterranean, fresh, brackish, coastal, and surface to deep-sea habitats. The Stygiomysida (2 families, 2 genera, 16 species), however, are found primarily in subterranean waters, but always in waters with a marine influence. The Mysida and Stygiomysida body is divided into three main regions: cephalon, thorax, and abdomen. They are shrimp-like in appearance, containing morphological features earlier referred to as defining a "caridoid facies". The shrimp-like morphology was to some extent diagnostic for the historic Decapod taxon Schizopoda, containing the Nebalia, Mysida, Lophogastrida, and Euphausiacea. In 1904 the concept of Schizopoda was abandoned, and the Mysidacea (Mysida and Lophogastrida) along with Cumacea, Amphipoda, Isopoda, and Tanaidacea were placed in a new taxon, the Peracarida. Later discoveries of groundwater mysids led to the establishment of Stygiomysida, but placement to either Lophogastrida or Mysida remained unclear. The presence of oostegites and absence of podobranchiae, coupled with non-statocyst bearing uropods have been used to classify the Stygiomysida as a primitive Mysida family, comparable to Petalophthalmidae. On the other hand, equally suggestive characters, but for a Lophogastrida affiliation, was suggested for the archaic foregut characters and again, non-statocyst bearing uropods. With the inclusion of DNA sequence data of ribosomal genes, sister group relationships between Stygiomysida, Lophogastrida, and Mictacea within the Peracarida are observed, which supports a classification of the Stygiomysida as a separate order removed from the Mysida.     

Sediment cores from Lake Urmia (Iran) suggest the inhabitation by parthenogenetic Artemia around 5,000?years ago

In Lake Urmia area, northwestern Iran, parthenogenetic Artemia and the bisexual Artemia urmiana Günther 1890 are found to occupy different ecological niches determined by salinity. Given the fluctuations of the lake over geological times, we thus hypothesized that species identification of Artemia cysts, buried in the sediments, can provide information on lake conditions in the past. Therefore, encysted embryos of Artemia were recovered from lake sediments by augering at a site near the present shoreline. Cysts and associated plant remains from two studied levels yielded radiocarbon ages in the range 5,000–6,700 YBP. For determination of the type of Artemia, the constant synonym mutation in exon-7 of the Na/K ATPase gene was verified, and the diameter of the recovered cysts was compared with that of modern cysts from the Lake Urmia region. The results show that the cysts represent a parthenogenetic type of Artemia, whose cyst diameter is somewhat different from that of present-day local parthenogenetic Artemia. The present study firstly confirms the stability of DNA in ancient Artemia cysts for molecular analysis. Moreover, it suggests variation in Lake Urmia’s conditions over time, and based on comparison with salinity preferences of contemporary Artemia populations, it more specifically suggests that Lake Urmia was a brackish lake dominated by a parthenogenetic Artemia population in the geological period sampled. It finally illustrates how, like in the study of freshwater propagule banks, paleogenetic analysis of Artemia DNA recovered from sediment cores can be used as a tool in the paleoecological study of generally highly fluctuating saline habitats.     

Curvature facilitates prey fixation in predatory insect claws

Insects show a large variety in prey capture strategies, with a correspondingly large diversity in predatory adaptations. We studied a specific type of predatory claws, these can for example be found in praying mantis species. The claw is closeable over its entire length and the prey is fixed between the femur (upper arm) and the tibia (lower arm) of the insect leg. The morphology of these predatory claws is diverse. Some species have straight claws covered with spines, while other species have smooth, curved claws. We have studied the mechanics of this femur-tibia type of predatory insect claws, by making a physical model, eventually trying to explain why in some insect species the claws are curved instead of straight. The main results are (1) when comparing curved claws to straight claws, curvature leads to a strong reduction of forces driving the prey away from the pivoting point, thereby reducing the need for friction generating structures. (2) In the curved claw model a position exists where the resulting force on the prey is exactly zero. This is because the normal forces on the femur and tibia are opposed, and in line. At this position the prey is perfectly clamped and not driven out of the claw. This feature does not exist in straight claws. (3) In the curved claw, the prey cannot be placed at a position further than a certain maximum distance from the pivoting point. Near this maximum position, the resulting force on the prey reaches high values because moment arms are near zero. (4) Between the zero position and the maximum position the resulting force is directed toward the pivoting point, which stabilizes prey fixation.     

Temperature and salinity effects on post-marsupial growth of Neomysis integer (Crustacea: Mysidacea)

There has been an increasing interest in using the brackish water mysid Neomysis integer as a toxicological test species for Western European estuarine systems. In this respect, more data on growth, moulting and development in this species is needed. The influence of prevailing environmental variables (e.g. temperature, salinity) and age on these processes as well as their optimal range have to be known in order to develop optimal laboratory cultures and to differentiate between chemically induced variability and natural variability in toxicity testing. Individual post-marsupial growth (size, intermoult period, growth factor) was studied from first day neonates until adulthood at eight environmentally relevant temperature-salinity conditions. Three salinities (5, 15 and 30 psu) were tested at 15 and 20 °C, and two more extreme temperatures (8 and 25 °C) were tested at a salinity of 5 psu.Survival and growth of N. integer were detected within the whole range tested, but sexual maturation was only possible in the narrower range of 15-25 °C and 5-15 psu. The size at maturity of N. integer increased with decreasing temperature and increasing salinity. Salinity seems to have a stronger effect than temperature on the duration of maturation. The sigmoid von Bertalanffy growth model was fitted to the individual and pooled data, except for the 8 °C experiment where growth was linear. Estimates from pooled data were comparable with individually based estimates, but generally underestimated the asymptotic length. Temperature was negatively correlated with the asymptotic length and positively correlated with the growth constant K. Higher temperatures caused smaller intermoult periods but had no effect on the growth increment, while salinity effects were less straightforward and dependent on the water temperature. A tool is provided to estimate the age, moult number, intermoult period, growth factor and growth rate from the body standard length of N. integer. Experimentally derived von Bertalanffy parameter estimates resulted in a higher growth performance index compared with field-based estimates for the Schelde estuary and Galgenweel populations of N. integer.