The Distribution of Hydrobiids and the Effects of Sediment Characteristics on the Population Dynamics of Hydrobia ventrosa in a Coastal Region of the Southern Baltic

The composition of the hydrobiid fauna in a coastal water of the southern Baltic was studied in 1990/91 at three stations with different sediment characteristics (grain size, organic content). Four species were found (Hydrobia ventrosa, H. ulvae, H. neglecta and Potamopyrgus jenkinsi). H. ventrosa was dominant at all stations. The mean hydrobiid abundances were 4,000 (stn. C), 18,000 (stn. B) and 40,000 (stn. A) ind./m² respectively. Abundance was found to correlate with the organic content of the sediment. The reproduction and growth of H. ventrosa was studied. Two reproduction phases were observed, one in summer and the other in late autumn. The autumn reproduction peaks were staggered owing to the different growth rates at the various stations. Possible correlations between the differences in shell size of H. ventrosa at the various stations and both sediment characteristics and abundance are discussed.     

Diversity and species composition of peracarids (Crustacea: Malacostraca) on the South Greenland shelf: spatial and temporal variation

The interannual variability in peracarid (Crustacea: Malacostraca; Amphipoda, Isopoda, Cumacea, Tanaidacea) species composition and diversity on the South Greenland shelf was studied at four stations over a sampling period of 3 years (2001, 2002 and 2004), using a Rauschert sled at depths of about 160 m. The South Greenland peracarids were relatively stable over the 3 years with respect to evenness and diversity. Moderate changes in temperature and salinity had negligible effects on the species composition, while sediment structure was found to be the most important environmental variable shaping the peracarid fauna.     

象山港大型底栖动物生物多样性现状

2006年7月至2008年8月对象山港13个站位进行了8个航次的大型底栖动物采样调查.研究了该海域大型底栖动物群落的优势种组成, 大型底栖动物的丰度、生物量、次级生产力和P/B值,并采用物种丰富度指数、物种均匀度指数和物种多样性指数分析大型底栖动物物种的多样性.调查共获得大型底栖动物123种,其中软体动物48种,甲壳类33种,鱼类和环节动物多毛类各12种,棘皮动物8种,还包括一些腔肠动物、线虫等.群落中优势种较为集中,且优势度指数较高.该海域大型底栖生物年次级生产力平均值为16.70 ·m^-2·a^-1,平均P/B值为0.60.对物种丰富度指数(d)、均匀度指数( J )、辛普森多样性指数(D)和香农多样性指数(H)进行双因素方差分析表明,不同站位之间4种指数的差异均高度显著(P<0.01),周年之间4种指数的差异除均匀度指数不显著外(P>0.05),均高度显著(P<0.01).     

The effect of wind exposure and filamentous algae on the distribution of surf zone macroinvertebrates in Lake Esrom,Denmark

Distribution and composition of the epilithic macroinvertebrate fauna was studied on 21 different sites situated in the surf zone of Lake Esrom. A relative degree-of-exposure (windinduced wave activity) was calculated for each station from the specific number of wind days, wind velocity and a measured wind fetch. Macroinvertebrate abundance averaged 20 200 ind. m^–2 stone bottom, and was composed primarily of six taxa (70% of the mean densities). The distribution patterns of the 48 most common taxa were compared to exposure, the amount of filamentous algae and shore slope, by regression, cluster analysis and ordination analysis (PCA and RDA). The abundance of 25 taxa was significantly correlated to the amount of filamentous algae, and a protectional effect of algae growth was suggested for the exposed sites. Seventeen taxa showed significant difference in abundance between sheltered western stations and exposed eastern stations. Stations with a gentle slope were characterised by sand covered stones and a fauna that qualitatively was similar to the fauna at greater depth in the littoral. Redundancy analysis (RDA) showed filamentous algae and slope to be the most important factors controlling the species distribution, whereas the gradient of exposure in Lake Esrom was too short to explain the species tolerance range.     

A survey of the fauna of streams on Mount Elgon, East Africa, with special reference to the Simuliidae (Diptera)

The stream fauna of Mt Elgon is described from collections taken during a 6-week visit. Collections were mainly made on the cultivated slopes below the belt of montane forest, and although stations were concentrated on the western sides of the mountain sufficient were worked elsewhere to show that there was little or no geographical variation of the fauna. The streams are physically diverse but faunistically rather uniform, with a few genera dominating the fauna throughout the entire range of altitude investigated. Most of the other taxa showed evidence of altitudinal limitation which may be attri-buted to the pronounced temperature gradients of the mountain's streams. As the species of Simuliidae and adult Elminthidae could be reliably distinguished their distributions were studied in greater detail. The Simuliidae showed a pronounced zonation of species, the majority being confined to narrow ranges of altitude below the forest margin. Factors considered to influence their distribution were principally altitude (temperature), current speed and, to a lesser extent, stream size. The influence of these factors on the distribution of adult Elminthids was less marked, although all species showed at least an upper or a lower limit of altitude, and more than half the commoner species a preference for a particular stream type. Taxonomic knowledge of African freshwater faunas allows few groups to be identified beyond the genus, and with this limitation the Elgon stream fauna is found to differ in only minor respects from the faunas of other highland areas in Central Africa.     

Variations in the intertidal and subtidal macrofauna and sediments along a salinity gradient in the upper forth estuary

The intertidal and subtidal soft-sediment macrofauna of the upper Forth estuary, eastern Scotland, UK has been examined. The intertidal fauna was sampled in 1977, and again in 1988/89, at up to twelve stations along the salinity gradient. The subtidal fauna was sampled in 1982 and in 1988/89 at up to 15 stations. The stations span the region of the freshwater-seawater interface, and area of the turbidity maximum. Large spatial and temporal variations in macrofaunal abundance and species composition were observed. Sites at the head of the estuary with low salinity were dominated by oligochaetes, but more saline areas were characterised by a depauparate estuarine fauna. The area has historically received large quantities of organic waste both from sewage and industrial discharges which supported very high abundances of oligochaetes of up to 500,000 m⁻² in the upper reaches of the estuary. Reductions in the organic inflow to the area since the early-1980's have begun to cause reductions in oligochaete populations and also allowed the further penetration intertidally of non-oligochaete species into the upper and middle reaches of the estuary. No comparable upstream penetration by the non-oligochaete subtidal fauna has been observed, possibly on account of the greater sediment instability in the estuary's main channel.     

Response of invertebrates to lotic disturbance: is the hyporheic zone a patchy refugium?

1. Natural experiments, in the form of disturbance from spates, were used to study the resistance and resilience of interstitial communities. Investigations were conducted in a by-passed section of the Rhône River characterized by an artificial hydrology with frequent spates separated by regular minimum discharge of 30 m³ s^–1. 2. Three areas of a bar were studied, upwellings at the head of the bar (stations 1 and 2), and downwelling at the tail of the bar (station 3). In the head of the bar the substratum was characterized by stable cobbles, while mobile gravels dominated in the tail of the bar. At each station, samples were derived from four depths (0.5, 1.0, 1.5 and 2.0 m below the surface of the substratum). Fifteen spates occurred during the study period whose peak discharge ranged from 50 to 1640 m³ s^–1. Temporal variations of the fauna were studied by comparing the spate effect observed 1 day (resistance), 7 days (resilience) and 17 days after the spate. Within-class correspondence analysis was used to compare the temporal variability of the fauna within each class {station/depth}. 3. The fauna differed markedly between the three stations, and the relative density of stygobionts (i.e. hypogean fauna) decreased from 55% at station 1 to 4% at station 3. The spatio-temporal variability increased dramatically from station 1 to station 3. 4. The results suggest that the hyporheic zone acts as a patchy refugium: the stations were more or less active refugial zones, depending on hydrology (upwelling or downwelling), substratum stability and spate amplitude. 5. The downwelling station was the main refugium area for benthic taxa. Important migrations of benthic groups (e.g. Gammarus, Cladocera) or hyporheic taxa (e.g. Cyclopoida and Harpacticoida) were observed deep into the sediment (2 m). Vertical movements of stygobionts (Niphargus, Niphargopsis) were also observed at high amplitude spates. These movements were very important (great numbers of individuals migrated) at low and medium magnitude spates, but were unimportant at high discharge, when the threshold of sediment instability was exceeded. In this case the substratum became mobile and induced drift of benthic organisms. 6. Conversely, in the upwelling stable stations, accumulation was less important (lower number of species and lower densities) but more constant with increasing discharge, suggesting that substratum stability is also a key factor. 7. Generally recovery was rapid at all stations (within 7 days) but no relationships were found between resilience (rate of recovery) and the amplitude of spates.     

Bathymetric distribution and diversity of deep water polychaetous annelids in the Sigsbee Basin, northwestern Gulf of Mexico

The deep water polychaete fauna is analyzed in this study particularly regarding its composition and variations with depth in the Sigsbee Basin, northwestern region of the Gulf of Mexico. Samples were taken at 10 stations along a bathymetric gradient with depth ranges from 200 to 3760 m with a USNEL (0.25 m²) corer. A total of 287 individuals were identified, from 21 families and 65 species. The most important families, both in terms of abundance and species richness, were: Paraonidae (65.4 ind./0.25 m², 9 spp.), Cirratulidae (28.93 ind./0.25 m², 7 spp.) and Spionidae (18.07 ind./0.25 m², 7 spp.). In general, density tended to decrease with depth with minima at around 2000 m, although two abundance peaks were detected at 3700 and 3760 m, making the pattern seem an inverted parabolic curve. The Shannon-Wiener diversity values varied from 0.54–0.92 at around 2000 m to 3.39 at 3620 m and 3.34 at 3760 m. These results contrast with what is already reported from the North Atlantic and the Tropical Pacific deep benthic communities, where highest diversities are found at 2000 m. Faunal changes evaluated through Beta Diversity (0.08–0.1) and the low similarity found between the stations, emphasized the high variability in the composition of the fauna in the Sigsee Basin, meaning that the faunal composition is practically different at all the sampling stations. Ten species are newly recorded for the Mexican fauna.     

Spatial distribution patterns of the hyporheic invertebrate communities in a polluted river in Romania

The purpose of this study was to examine the sensitivity, in a field situation, of the hyporheic fauna to pollution by heavy metals and also to test the use of oxidative stress enzymes produced by this fauna as a sensitive indicator of oxidative stress generated by chemical contamination. This was done by surveying the patterns of distribution, structure, and composition of hyporheic invertebrate communities in one of the most polluted rivers in Romania. Twelve permanent sampling stations with differing water qualities were established along a 180 km transect of the Arie? River. Data on hyporheic invertebrate abundance and richness, chemistry of the surface and hyporheic water and interstitial suspended particles were analyzed via multifactorial analyses. In the downstream, more polluted stations, epigean species were less abundant and hyporheic communities, especially macrocrustaceans and oligochetes, became dominant. The higher levels of hyporheic invertebrate biodiversity in the moderately polluted stations compared to highly polluted, and the increase of the number of some hyporheos (especially macrocrustaceans) in the moderately polluted stations, suggested that the hyporheic fauna was more tolerant of heavy metal pollution than the surface water fauna of the area. However, the different richness and abundance of hyporheic fauna in sites of similar water chemistry suggested that additional factors, such as sediment structure are shaping the spatial distribution of hyporheic fauna. Strong correlations between superoxide dismutase (SOD) activity in pooled tissues extracts and some chemical parameters suggest that oxidative stress enzymes may prove to be sensitive indicators of chemical pollution in hyporheic zones.     

Algae-associated marine molluscs in the Azores

The raolluscan fauna of a special habitat, the high intertidal algal turf, was studied at four stations on the island of Sao Miguel, Azores. The number of species found ranged from 13 to 23. However, a small group of only six species (the bivalve Lasaea adansoni and the gastropods Pisinna punctulum, Omalogyra atomus, Fossarus ambiguus, Skeneopsis planorbis and Alvania postrema) accounted for more than 80% of all the specimens collected. Mollusc density reached values of 20000 specimens per 100 g algal dry weight. The abundance and number of species of molluscs was comparable with those reported for algal zones lower on the Azorean shores.
Wave exposure and seasonality effects were found to be small, presumably because of the relatively mild abiotic conditions and the protective role of the turf. The algal substrata influenced the phytal molluscan community in two ways. First, the abundance of molluscs was significantly correlated with algal dry weight. Secondly, molluscan abundance and diversity were influenced by the algal composition of the turf. A rich algal composition, with several species of branched fleshy and coralline algae, was associated with a rich molluscan fauna. The dominance of coralline algae resulted in a abundant but species-poor fauna, while an almost monospecific turf of Gigartina was poor in both species and number of molluscan fauna.     

中街山列岛岩相潮间带大型底栖动物的群落格局

于2006年9月和2007年7月在中街山列岛4个有居民海岛岩相潮间带设立8个断面,对大型底栖动物的群落结构进行了调查。共获得大型底栖动物34种,其中腔肠动物1种,环节动物3种,甲壳动物10种,软体动物20种。优势种有日本笠藤壶(Tetraclita japonica)、紫贻贝(Mytilus edulis)和节蝾螺(Turb articulatus)等4种。以季节和站位为因子对多样性指数进行双因素方差分析,结果表明只有夏、秋季丰富度指数(P=0.028)存在显著差异,其他指数的方差分析没有显著差异(P>0.05)。3个潮带4个岛屿共12个站位的聚类分析和MDS标序分析表明,12个群落可分为3组(Ⅰ、Ⅱ和Ⅲ组)。大型底栖动物ABC曲线分析表明底栖动物群落尚未受到干扰。     

Spatio-temporal variability of faunal and floral assemblages in Mediterranean temporary wetlands

Six temporary wetlands in the region of Sejenane (Mogods, NW Tunisia) were studied in order to characterize the aquatic flora and fauna and to quantify their spatio-temporal variability. Samplings of aquatic fauna, phytosociological relevés, and measurements of the physicochemical parameters of water were taken during four different field visits carried out during the four seasons of the year (November 2009–July 2010). Despite the strong anthropic pressures on them, these temporary wetlands are home to rich and diversified biodiversity, including rare and endangered species. Spatial and temporal variations affect fauna and flora differently, as temporal variability influences the fauna rather more than the plants, which are relatively more dependent on spatial factors. These results demonstrate the interest of small water bodies for maintaining biodiversity at the regional level, and thus underscore the conservation issues of Mediterranean temporary wetlands that are declining on an ongoing basis currently.     

Répartition transversale des macroinvertébrés benthiques dans un bras du Rhône

While the downstream distribution of benthic macrofauna has been studied in many rivers, its transverse distribution remains rather unknown. The present work concerns this problem in a semi-regulated arm of the Rhône. The characteristics of this arm are: width 80 m, depth 0.5 to 1 m in the section studied, pebble substrate, rocky banks, discharge regulated at 30 m³. s^-1 except for floods up to 1 000 m³. s^-1. The substrate was sampled with a Hess cylinder which collects the fauna present on 0.125 m². Eight stations were located across the river, and 22 samples were collected. Correspondence analysis was applied to the Taxa X Samples matrix, and the results were studied by analysis of inertia, canonical correlation and variance analysis. A close correlation appears between the faunistic structures and the stations. Two main units are revealed. The first one includes a ten meters band along each bank, the other covers the main part of the bed, between these two bands. The two units differ in their taxonomic richness and abundance, many taxa being only present along the banks. A symmetrical gradient of density appears between the channel and the banks. Moreover, the fifth factor of the correspondence analysis reveals that the fauna of one side is not identical to that of the other. The cause of these structures remains uncertain. Among the different parameters, the distance from the banks seems to be the most significant. The existence of a gradient may be due to a dissemination of the fauna from the banks towards the channel. This study suggests the importance of the banks in the dynamics of the benthic fauna of large, fast-flowing rivers, especially in connection with the floods. This must be taken into account when sampling in such rivers.     

Variation of the epifauna on pier-pilings between 1980 and 1992 near the city of Tromsø, Northern Norway

The epifaunas of pier-pilings at six localities were investigated during two periods: 1980 and 1991-1992. The sampling stations were spatially distributed to determine if there were qualitative and/or quantitative differences between the fauna near the city of Tromsø and that closer to the open ocean. The results from both periods suggest that organic effluents from the urbanised areas of Tromsø have moderate and local effects on the fauna. Additionally, large increases, both in the number of taxa and the abundance of conspicuous organisms, took place from 1980 to 1991/1992. Possible reasons for these temporal changes are discussed.     

The effects of trawling on the benthic fauna of the Gulf of Nicoya, Costa Rica

Four van Veen grab replicates where collected to sample macrofauna (organism retained on a 500 micron mesh sieve) at four stations in the Gulf of Nicoya, during October 24, 1997, January 16 and April 30, 1998. This information was used to search for any effects of trawling on the benthic fauna. Two stations where located in a trawled area, and two stations where in a protected area. Diversity (H') varied from 2.01 to 3.52 in the trawled area and from 2.13 to 2.78 in the protected area. Diversity was generally higher in the trawled area, and this was in contradiction to what we would have expected from other studies where the trend has been that trawling reduces diversity. Brittlestars and lancelets seemed to be the groups mostly harmed by the trawling, while amphipods where more abundant in trawled areas. The multivariate analyses did not reveal the patterns of faunal change as well as we hoped. This is surely because of our lack of more replicate samples. The multivariate analyses are easily confounded when few sites are analyzed. We have found differences in the type of fauna found in trawled and protected areas and, considering the differences in environmental variables in our stations and our lack of replication, this indicates that there are differences and a larger investigation is in order to reveal its magnitude.     

<Emphasis Type="Italic">Boreogadus saida</Emphasis> (Lepechin) (Gadidae): a review of its metazoan parasite fauna from Greenland,eastern Canada,Alaska and the Russian Arctic

The metazoan parasite fauna of 50 specimens of Boreogadus saida (Lepechin) (Gadidae) from eastern Greenland is very similar to those of previous studies of the parasite fauna of B. saida from Greenland, eastern Canada, Alaska and the Russian Arctic. The digeneans Hemiurus levinseni, Derogenes varicus and Lecithaster gibbosus and cestode larvae were found at most stations. Single specimens of the nematode larvae Anisakis simplex were found at four stations. A comparison of the distribution of the larvae of Contracaecum sp. and Hysterothylacium sp. is difficult due to a possible confusion of the two genera. Most of the metazoan parasites of B. saida are generalist species found in several fish families. Boreogadus saida acquires most of its endoparasites by eating pelagic crustaceans, mainly copepods and amphipods. It plays an important role in the arctic ecosystem and its parasites are transferred to predatory fish, birds and mammals through the food web.     

Chironomids as water quality indicators in the River Mignone (Central Italy)

Chironomids of the River Mignone (Central Italy) were studied in order to examine their community structure and their relationship to some common biological indices (Biotic Score, Extended Biotic Index, Indice Biotique de Qualité Générale) utilizing the total macroinvertebrate fauna (chironomids generally at family level) for water quality assessment in rivers.A total of 36 taxa belonging to Tanypodinae (2 taxa), Orthocladiinae (22 taxa) and Chironominae (12 taxa) was collected at seven stations four times during a year. The results support the importance of the chironomid identification in water quality assessment studies in rivers, and demonstrate the usefulness of the factorial correspondence analysis as ordination technique based on both qualitative and quantitative chironomid data to determine environmental quality gradients.The value as bioindicator of some taxa was discussed, and chironomid assemblages were related to biological water quality of the river according to functional feeding groups.This study forms part of a larger Research project supported by MPI and CNR grants and is aimed at the biological water quality assessment of the river and at the analysis of the total macrobenthic community.     

Effects of spates on the vertical distribution of the interstitial community

The effect of hydrological variations on the vertical distribution of interstitial organisms was studied in a by-passed channel of the Rhône River(France) in terms of the distortion and recovery of community structure over a 480-day period that included 9 spates. The hypogean and epigean components of the interstitial assemblages were studied, the latter at four depths (50, 100, 150 and 200 cm) within the substratum, during a succession of artificially regulated spates and periods of low flow. Interstitial fauna were obtained with a Bou-Rouch sampler through permanent standpipes at intervals of one, seven and seventeen days after each spate. A strong relationship was demonstrated between disturbance intensity (amplitude and duration of spates) and the magnitude of changes in the vertical distribution of the fauna. Both hypogean and epigean organisms were displaced vertically after each spate, resulting in an increase in the numbers of epigean organisms in interstitial layers. Recovery of vertical distribution of the interstitial fauna to pre-spate conditions, consisted of a decrease of epigean and an increase of hypogean fauna with the substratum, mainly at intermediate sampling depths (100, 150 cm). The effect of spates on community structure and rate of recovery varied in relation to 1) the combination of spate amplitude and duration (i.e. the shape of the discharge pattern), 2) the disturbance regime (i.e. the recent hydrological past) and 3) season (temperature and biological cycle).     

Mountain streams of the barberton area,eastern transvaal. Part II,the effect of vegetational shading and direct illumination on the distribution of stream fauna

Summary During the survey reported in Part I, it became apparent that vegetational shading affected the incidences of certain species. The extent to which the distribution of stream fauna is influenced by direct or indirect consequences of shade or illumination was examined and an attempt was made to determine which species or groups are affected.Three pairs of comparable sampling stations (stickles) were selected on the basis of their physical similarity, one of each pair being shaded and the other illuminated. Samples taken from these stations were compared and species found predominantly in shaded or exposed reaches were assessed.Although certain species appeared influenced in their distribution, it appears that the population density is minimally affected and there is no overall effect on any group or family.     

Analysis of the demersal community of fish and cephalopods on the Agulhas Bank, South Africa

The demersal fish and cephalopod communities of the continental shelf and upper slope from 17 to 395m deep were studied during five annual cruises between Cape Agulhas and Port Alfred, South Africa. The cruises showed a consistent pattern of an inshore community (<100m), a shelf community ( c . 90–190m) and a shelf-edge/upper slope fauna (>200m). These groups were identified by dendrograms and multidimensional scaling cluster analysis, which supported on-board observations of catch variation with depth. Although the boundaries are not clearly defined, examination of physical features at the clustered stations suggests that depth, temperature and, to a lesser extent, oxygen concentration are important in the grouping. Occasional, apparently anomalous associations of inshore stations suggested that water temperature and oxygen may over-ride the normal depth distributions of the species groups. This intimates that patterns offish and cephalopod distribution may be dynamic and in part related to the physical parameters of the water body.