Macrozoobenthic assemblages in littoral sediments in the enclosed Rhine-Meuse Delta

Littoral macrozoobenthos in the enclosed Rhine-Meuse Delta was investigated by taking 95 sediment samples from 17 sites between 1984 and 1990. In addition, a set of environmental parameters was determined. The aim was to identify the main assemblages and the environmental conditions under which they occur. By the use of TWINSPAN, three main littoral zoobenthic assemblages were distinguished, which were related to geographical zones and differences in sediment grain size distribution. The ‘litoral river sand’ assemblage was found in the most upstream part; it mainly consisted of ‘interstitial’ invertebrates, including the indicator speciesVejdovskiella comata, Propappus sp. andKloosia pusilla. The ‘littoral sedimentation area silt’ assemblage was dominated byGammarus tigrinus, Einfeldia dissidens andPisidium sp. It was found in several river sections and contained the indicator speciesEinfeldia dissidens, Potamopyrgus antipodarum andValvata piscinalis. The ‘littoral sandy basin’ assemblage was concentrated in the littoral fine sands of the Haringvliet and contained the indicator speciesPisidium henslowanum, P. moitessierianum, Cladotanytarsus sp. andLipiniella arenicola. These three assemblages are the reflection of an interaction between habitat, food and disturbance. Palaeoecological analysis of insect remains revealed that 14 out of the 24 insect taxa, that were formerly common in the river sand habitat, are now extinct from the Rhine. The river silt habitat seems less impoverished: two out of the 19 insect taxa found in palaeoecological analysis are now extinct from the Rhine and seven are rate. Exotic species (Corbicula fluminea, C. fluminalis andCorophium curvispinum) have recently colonized the Rhine-Meuse Delta, but their impact on the macrozoobenthos seems limited.Corbicula spp. have become abundant in the ‘littoral river sand’ assemblage only.     

Links Between Anthropogenic Perturbations and Benthic Macroinvertebrate Assemblages in Afromontane Forest Streams in Uganda

Relationships between environmental variables and benthic macroinvertebrate assemblages were investigated among several sites that varied in disturbance history in Bwindi Impenetrable National Park, an Afromontane site in East Africa. Environmental variables were correlated with the level of past catchment disturbance – logging, agricultural encroachment, and present tourism activity. For example, sites in medium and high disturbance categories had higher values of specific conductance and lower water transparency than low disturbance category sites, these environmental variables may therefore act indicators of ecological quality of rivers. Environmental variables such as conductivity and water transparency were found to be good predictors of benthic macroinvertebrate assemblages, with anthropogenically stressed sites having lower diversity than the reference sites. Impacted sites were dominated by tolerant taxa such as chironomid and leeches, while ‘clean water’ taxa such as Ephemeroptera, Plecoptera and Trichoptera dominated at minimally impacted sites. Comparison of sites with different disturbance histories provided evidence for differences in benthic macroinvertebrate communities that reflect the state of forest restoration and recovery. We recommend quarterly monitoring of water quality to act as an early warning system of deterioration and tracking ecological recovery of previously impacted sites.     

Temporal and Spatial Distribution Patterns of Larval Trichoptera in Madeiran Streams

Temporal and spatial distribution patterns of lotic larval trichopteran assemblages in relation to environmental variables were investigated in Madeiran streams using multivariate analyses. TWINSPAN classification detected distinct faunal assemblages related to spatial factors between non-polluted high altitude sites and lower lying enriched sites where tolerant taxa were predominant but showed strong seasonal shifts in species composition and abundance. The 15 TWINSPAN end groups were grouped into five arbitrary clusters based upon the seasonal and spatial changes in the trichopteran assemblages detected by the analysis. Significant differences between environmental variables (distance from source, altitude, temperature, conductivity, alkalinity and nitrate) and the trichopteran assemblages (using trichopteran based metrics) of these clusters were confirmed by the Kruskal-Wallis test (H) and Dunn’s test. Chemical classification of samples within the clusters revealed a strong association between trichopteran assemblages and water quality. Canonical Correspondence Analysis and Monte Carlo global permutation tests also identified significant associations between the larval assemblages and physicochemical variables such as temperature and conductivity along a strong physical gradient (altitude, slope) and nitrate along a weaker seasonal gradient. Analysis of functional feeding group distribution patterns clearly showed that mid to high altitude indigenous woodland sites were trophically diverse whilst the lower reaches of the islands streams are trophically impoverished with strong seasonal shifts between two feeding groups of enrichment tolerant taxa. Trichopteran shredders are exclusive to indigenous woodland sites, indicating a limited distribution associated with land use, allochthonous input and habitat destruction. The results indicate that several ‘environmental filters’ operate at different levels upon the islands trichopteran fauna, producing temporally and spatially distinct ‘subsets’ of species best able to exploit conditions and resources at a given site or time, confounding the direct comparison of these insular systems with the findings of the River Continuum Concept, traditionally associated with unaffected continental lotic systems.     

A method for prioritizing the reestablishment of river continuity in Austrian rivers

River continuity is one of the hydro-morphological elements supporting the classification of the ecological status of rivers. In order to achieve good ecological status in the continuity of rivers, the impacts of anthropogenic activities must be limited to the extent that some fish age classes may be missing and there may only be slight changes in species composition and abundance from the type specific community. The main goal of the project is to list priorities for removing obstruction to migration within 12 years to reestablish river continuity so as to allow undisturbed migration of aquatic organisms. The ecological status of the river, the cost–benefit ratio of the proposed restoration and the distance between obstructions are analysed. More than 200 obstructions in about 170 km of river were evaluated. A 1st ranking of the parameter “extension of undisturbed river length” shows significant alterations in comparison with the 2nd and 3rd ranking, where the river length is weighted over the parameters “ecological status” of the river reach and the “cost–benefit ratio” of the measure. The ecological status is classified by comparing the present versus the potential natural morphological conditions (Leitbild). The cost–benefit ratio takes into account the increase of the fish species composition and the cost of the measures in relation to local circumstances of available property and height of the drop. Examples of obstructions in the Pinka R. move back in the priority list to a maximum of −9 places and forwards to a maximum of +8 places. As a result the list of obstructions by priority for removal to be removed first at the top is analysed. The financial policy and a schedule for removal for the period 2003–2015 are based upon the results of the priority list. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: R. L. Welcomme & G. Marmulla Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries     

Changes in the population structure,growth and mortality of striped weakfish <Emphasis Type="Italic">Cynoscion guatucupa</Emphasis> (Sciaenidae,Teleostei) of southern Brazil between 1976 and 2002

Siphonophores are exclusively marine cnidaria and their predatory role in plankton food-webs is well recognised. In this study, we analyse the structure and the spatial extent of siphonophore assemblages in relation to changes in freshwater outflows and food availability in the southern Gulf of Mexico during a high (October) and a low (April) outflow periods. A total of 149 samples were collected using a 505 μm multiple closing net at 1–6 levels (0–100 m) of the water column, depending on the bathymetry. Data on siphonophore species biovolumes (ml 100 m⁻³) were treated by means of the Bray-Curtis Dissimilarity Index, and two distinctive assemblages were identified: the ‘inner’ and the ‘outer’ assemblages, located over the inner and outer shelves. Temperature, salinity, zooplankton biomass, and siphonophore species were included in a Principal Component Analysis (PCA) to identify the factors associated with each assemblage. Geographical distribution of the assemblages practically remained the same during both seasons and its cross-shelf variability was stronger than the vertical one. Seasonally, diversity values were higher in October, when the highest river discharges occur. Spatially, the lowest diversity and mean siphonophore biovolumes values were registered in the ‘inner assemblage’, where the highest and lowest salinity values were recorded. We suggest that even when extreme salinity values (>36.5 or <34) might depress siphonophore populations in the coastal area, enough food availability in the concerned areas might mitigate the negative effect of salinity, since a positive and significant (p < 0.05) relationship was found between siphonophores biovolume and zooplankton biomass. Bassia bassensis, Diphyes dispar and Enneanogum hyalinum, present in both assemblages during both seasons, were able to survive in a wide range of salinity values, following perhaps, their prey. All the 23 species here registered were found in the ‘outer assemblage’; however, Abylopsis eschscholtzi, Chelophyes appendiculata and Diphyes bojani were more associated with the ‘outer’ group according to the PCA results. Enneagonum hyalinum was the only species frequently encountered and abundant in the ‘inner assemblage’ during both seasons and, supporting previous observations, this species might be considered as an indicator of nearshore waters. Handling editor: K. Martens     

Application of the functional habitat concept to the regulated Lower Ord River,Western Australia,Part I,macroinvertebrate assemblages

This paper tests the applicability of the Functional Habitat Concept (FHC) to a lowland tropical river in Australia. The underlying tenet of the FHC is that in-stream hydrological and physical processes form distinct habitats, and where these habitats support distinct macroinvertebrate assemblages they are considered ‘functional’ habitats. This concept has been employed in the northern hemisphere as a tool for river restoration and management, especially where habitats are easier to manage than species, but the FHC has yet to be tested in Australia. This study reports the application of the FHC to the regulated Lower Ord River (LOR) in the remote far north of Western Australia. Seven ‘potential’ in-stream habitat units were identified on the basis of their physical properties. Multivariate and species preference analysis of macroinvertebrate data indicated that these habitats supported six distinct macroinvertebrate assemblages, providing six ‘functional’ habitats (gravel runs and rock rapids, sand margins, mud/silt margins, flooded riparian vegetation, emergent vegetation, and submerged macrophyte beds). Macroinvertebrate preferences for particular habitats reflected the broad ecology and life-history characteristics of the species, which in turn reflected the physical attributes of the habitats. We argue that in a region where the fauna has been little studied, and for which there is little ecological information, the FHC is a valuable approach. For a river that is facing increased water abstraction, the FHC potentially aids in the preservation of macroinvertebrate diversity as it identifies critical functional habitats for managers to maintain. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens     

Invertebrate Assemblages Associated with Root Masses of <Emphasis Type="Italic">Eichhornia crassipes</Emphasis> (Mart.) Solms-Laubach 1883 in the Alvarado Lagoonal System,Veracruz, Mexico

This paper describes the spatial and temporal variation of aquatic invertebrate assemblages associated with root masses of Eichhornia crassipes collected at 12 sites between July 2000 and June 2002 in the Alvarado Lagoonal System (ALS), Veracruz, Mexico. A total of 96 taxa were registered; acari showed the highest species richness with 15 taxa followed by decapods (14), mollusks (12), amphipods (9), and isopods (7). Freshwater organisms represented 44% of the total taxa, 53% belonged to estuarine taxa, and marine taxa 3%. The isopod Munna sp. was the dominant taxon throughout the entire study period, followed by Ephemeroptera, Hyalella azteca, Chydorus sp., Physella sp., Podura aquatica, and Fossaria sp. during the low salinity period (July–September 2001, 1.6–3.8 psu), and Neritina virginea, Cassidinidea ovalis, Macrobrachium acanthurus and Melita longisetosa during the high salinity period (March–May 2001 9.7–12.7 psu and April–May 2002, 8.2–8.9 psu). A spatial gradient of species richness and diversity was registered for the freshwater organisms. Additionally, the spatial and temporal patterns of invertebrate densities could be explained due to the movements of Eichhornia crassipes mats through the system, and the temporal variation of environmental variables such as salinity, dissolved oxygen, and turbidity.     

Methodologies for measuring and modelling change in coastal saline lagoons under historic and accelerated sea-level rise,Suffolk coast,eastern England

Thorough assessment of vulnerable coastal habitats, impacted by sea-level rise and anthropogenic pressures, requires both the accurate establishment of the evidence base for current status and scientifically-informed forward planning of expected future status. Coastal saline lagoons are transitional, ephemeral habitats of considerable conservation interest; under European legislation their status requires on-going maintenance of ‘favourable status’. Over decadal timescales, the seaward barriers that enclose saline lagoons migrate progressively landwards. Geo-referenced and digitised historic maps and aerial photographs are used to create a detailed trajectory of barrier migration and loss of lagoon area for three saline ‘broads’ on the rapidly retreating coastline of Suffolk, eastern England. The SCAPE shoreline response model is then employed to extend this trajectory, under a range of sea-level rise scenarios, to 2050 and 2095 and to predict saline lagoon ‘time to extinction’. Loss rates are likely to accelerate considerably after 2015 and a fundamental revision of UK saline lagoon creation targets is urgently required. The approach is generic and could be used to assess the evolutionary trajectories for other vulnerable coastal habitats, under a range of near-future environmental change scenarios.     

The role of land use,nutrients, and other stressors in shaping benthic invertebrate assemblages in Slovenian rivers

Studying human impacts on riverine systems is challenging due to the natural diversity and multiple stressors that are co-occurring. The term stressor(s) refers to variable(s) of anthropogenic landscape changes and local abiotic stream conditions that reflect human activities. We compared the effects of different stressors and natural (typology) factors on benthic invertebrate assemblages in Slovenian rivers. A total of 270 river sites located in four European ecoregions were sampled, covering the gradient of human perturbation ranging from (near)natural to highly degraded/polluted. Stressors commonly affecting running waters were grouped into management-relevant stressor-groups: land use (percentage of urban, intensive and non-intensive agricultural, and natural land use in the catchment and sub-catchment), eutrophication (in-stream concentrations of phosphorus and nitrogen compounds) and other stressors (e.g., organic pollution, hydromorphological alteration). We compared the effects of the stressor-groups on invertebrate assemblages using partial Canonical Correspondence Analysis and tested the explanatory power of each stressor-group using typology variables as covariates. Stressors and typology variables showed high independent effects (40–65%) on invertebrate assemblages despite considerable joint effects from land use and typology. Stressors’ pure effects accounted for 70%, and interactions among the stressor-groups made up the remaining 30% of the total explained variability. Altogether, this study gives a good perspective on the ability to separate the effects of anthropogenic stressors from natural causes, as well as to separate effects among groups of stressors. Against this background, we advocate stressor-specific analyses to provide or improve guidelines for selecting appropriate measures to enhance the river status.     

A Feasibility Study to Monitor the Macroinvertebrate Diversity of the River Nile Using Three Sampling Methods

The River Nile is one of the world’s major rivers. Its’ catchment in Egypt has a population of 75,000,000. River flow is highly regulated and there are known discharges of pollutants. 1035 km of the river downstream of the Aswan high dam was studied to test the hypothesis that representative qualitative samples can be used to estimate macroinvertebrate biodiversity. Benthic macroinvertebrates are difficult to sample in large rivers and a reliable sampling strategy is required to evaluate their ecological status. Three methods for sampling have been investigated. Ekman Grab, macrophyte sweep netting and Artificial Substrate Samplers (ASS) were used to sample 15 sites from Aswan to Cairo between September 2001 and June 2002. Organisms were identified to species level where possible. Taxon accretion curves indicated that the all taxa present at a site should be collected using either 15 grab samples, 10 macrophyte samples or 5 ASS. The best time to sample was May–June. The biodiversity of macroinvertebrates in the Nile was recorded as 50 taxa with values of 7–31 at individual bank-side sites. Mid-stream biodiversity was much lower (0–19). Lowest biodiversity occurred at sites with known pollution inputs whilst highest occurred at sites with high levels of sedimentation. A regular programme for biomonitoring is recommended which will allow current status to be confirmed and future changes detected.     

Phytoplankton dynamics in relation to connectivity,flow dynamics and resource availability—the case of a large,lowland river,the Hungarian Tisza

Large lowland rivers with sufficient hydrological storage capacity are capable of supporting primary production, but the dynamics of the advecting phytoplankton is poorly understood. Our study aimed at exploring how longitudinal versus lateral connectivity, flow dynamics versus resource availability and continuous versus discontinuous environmental gradients shaped the species composition of phytoplankton. Samples were taken from February to October 2000 along the Hungarian Tisza River (HTR) and in its main tributaries. Longitudinal and seasonal patterns were related to resources (light and nutrients) availability and flow dynamics derived from a 1D hydrodynamic model. The HTR was autotrophic during the study period, but tributary input considerably exceeded net autochtonous production. The Szamos River was the major source of both phytoplankton and nutrients in the HTR. Chryso- and euglenophytes were flushed into the main river from floodplain oxbows during high discharge. Imported algae experienced discontinuity in environmental gradients when entering the main river. The merged impact areas of two dams (IAD) that separate the two large meandering patches of the HTR disrupted the longitudinal profiles of both physico-chemical variables and attributes of algal assemblages (biomass, species composition, richness, similarity between adjacent sampling sites). Hydraulic storage along the IAD selectively favoured the recruitment of cryptophytes that, however, could not compensate for the enhanced sedimentation of diatoms in terms of biomass. Although the meandering patches presented several small-scale differences in major environmental gradients, both patches supported the growth of planktonic diatoms. Changes in algal biomass were decoupled from nutrient availability. We conclude that various measures must be applied in various lowland rivers within the same catchment to control their trophic status as a component of the ‘good ecological status’ defined in the Water Framework Directive.     

Subtle ‘boom and bust’ response of <Emphasis Type="Italic">Macquaria ambigua</Emphasis> to flooding in an Australian dryland river

The ecology of dryland rivers is driven by their highly variable hydrology, particularly flooding regimes, whereby intermittent floods typically generate ‘booms’ of primary and secondary productivity, including massive fish production. We tested these concepts in the Moonie River, Australia, using the percichthyid, Macquaria ambigua, a dryland river species known to display pronounced ‘boom and bust’ abundance patterns in response to floodplain inundation followed by extended periods of low to no channel flow. We expected that body condition (as measured by whole body lipid content) and biomass of M. ambigua would be related to prey biomass, and that these factors would all ‘spike’ following widespread flooding. Instead we found more subtle responses. There were ‘booms’ in biomass of Macrobrachium and zooplankton, two important food items, whereas M. ambigua maintained relatively low but sustained lipid and biomass levels following flooding. It appears that instead of a ‘boom’ in fish biomass, abundant invertebrate food resources and sustained lipid levels contributed to high survivorship of this species during the ‘bust’ period over cool dry months.     

Community structure and spatial distribution of benthic fauna in the Bellingshausen Sea (West Antarctica)

The structure and spatial distribution of the macrofauna community of the Bellingshausen Sea in the western sector of Antarctica was studied during the ‘BENTART–06’ oceanographic expedition. This is one of the least explored Antarctic seas. A total of 20 box cores were sampled at 11 stations ranging from 157 to 3,304 m depth, using an USNEL-type box corer (BC) dredge. Representatives of 25 higher taxa of invertebrates were collected. Deeper sampling sites were less rich in taxa (4–7 taxa), whereas the figures were higher at shallower sites (up to 17 taxa). Faunal density on the sea bottom revealed a horizontal spatial gradient from the western sites with extremely low figures (90 indiv./m²) towards the eastern ones with the highest figures (1,360 indiv./m²) close to the Antarctic Peninsula. Several abiotic factors (depth, redox, organic matter, carbonates and particle size of surficial sediments) were measured simultaneously on the sea floor to characterise the substrate preferences of the fauna. Positive correlations were found between the faunal distribution and a combination of depth, redox values, and organic matter content of sediments. This indicates decreasing availability of food in the deeper bottoms of the Bellingshausen Sea with a prevalence of depauperated bottoms dominated almost exclusively by a foraminiferans community.     

Macroinvertebrate abundance, water chemistry, and wetland characteristics affect use of wetlands by avian species in Maine

Our objective was to determine use by avian species (e.g., piscivores, marsh birds, waterfowl, selected passerines) of 29 wetlands in areas with low (<200 μeq l⁻¹) acid-neutralizing capacity (ANC) in southeastern Maine. We documented bird, pair, and brood use during 1982–1984 and in 1982 we sampled 10 wetlands with a sweep net to collect invertebrates. We related mean numbers of invertebrates per wetland to water chemistry, basin characteristics, and avian use of different wetland types. Shallow, beaver (Castor canadensis)-created wetlands with the highest phosphorus levels and abundant and varied macrophyte assemblages supported greater densities of macroinvertebrates and numbers of duck broods (88.3% of all broods) in contrast to deep, glacial type wetlands with sparse vegetation and lower invertebrate densities that supported fewer broods (11.7%). Low pH may have affected some acid-intolerant invertebrate taxa (i.e., Ephemeroptera), but high mean numbers of Insecta per wetland were recorded from wetlands with a pH of 5.51. Other Classes and Orders of invertebrates were more abundant on wetlands with pH > 5.51. All years combined use of wetlands by broods was greater on wetlands with pH ≤ 5.51 (77.4%) in contract to wetlands with pH > 5.51 that supported 21.8% of the broods. High mean brood density was associated with mean number of Insecta per wetland. For lentic wetlands created by beaver, those habitats contained vegetative structure and nutrients necessary to provide cover to support invertebrate populations that are prey of omnivore and insectivore species. The fishless status of a few wetlands may have affected use by some waterfowl species and obligate piscivores.     

Regional patterns of evolutionary turnover in Neogene coral reefs from the central Indo-West Pacific Ocean

The Indo-Pacific is an area of intense ecological interest, not least because of the region’s rich biodiversity. Important insights into the origins, evolutionary history, and maintenance of Indo-Pacific reef faunas depend upon the analysis of faunal occurrences derived from detailed stratigraphic sections. We investigated Neogene origination and extinction patterns derived from a combination of new coral occurrences and previously published records from the central Indo-West Pacific Ocean (cIWP, Indonesia, Papua New Guinea and Fiji). Two faunal turnover events were observed. In the first, an increase in generic richness of Scleractinia from the cIWP during the middle Miocene (17–14 Ma) coincided with both large-scale sea level fluctuations and the great Mid-Miocene collision event. We raise the hypothesis that Mid-Miocene origination was facilitated by habitat and population fragmentation associated with tectonism and sea level fall. The second, subsequent, turnover event was characterized by an overall lowering of generic diversity throughout the late Miocene and Pliocene (7–3 Ma), and was followed by a pronounced pulse of extinction at the Pliocene–Pleistocene boundary (~2.6 Ma). With the exception of the onset of Pleistocene sea-level cycles and the onset of northern hemisphere glaciation around 2.5 Ma, which might explain increased extinction during this time interval, there are no tectonic, eustatic, climatic or oceanographic events that neatly coincide with this second episode of Neogene coral taxonomic turnover. Our results reveal a total of 62 genera, including synonyms, from the Miocene to the Pleistocene. Neither episode of turnover among coral genera is exactly coincident with turnover in the Atlantic thus regional environmental change is found to drive Neogene reef dynamics.     

River Dan,headwater of the Jordan,an aquatic oasis of the Middle East

River Dan is the largest of the headwater rivers of the Jordan. The karstic exsurgence of the Dan has a seasonally stable output, a long stretch of strongly turbulent flow, stable temperature around 15.5°C and high oxygen saturation. A total of 156 taxa, mainly at the species level, were identified from the river. These species are almost exclusively of Palearctic origin. About half of the species are limited to the northernmost part of Israel. The faunal complex described, does not present any longitudinal zonation for the 5 kilometers of turbulent flow; neither does it present seasonal changes in species composition. River Dan is considered to be a post-Pleistocenic river which has an important function of refugium for a wide area of aquatic water-bodies in the area, including the presently drained Lake Hula. It is suggested that in the Illies scheme of stream classification, River Dan might represent a type of stream belonging to a ‘pseudorhithral’ along with other stenothermic warm water torrents of the tropical-subtropical climatic belt.