Soft-bottom macrobenthic faunal associations and factors affecting species distributions in an Arctic glacial fjord (Kongsfjord,Spitsbergen)

The Kongsfjord (west Spitsbergen) hosts the most active glacier on the island. Therefore the glacial impact on the marine ecosystem is very pronounced and easily recognisable. The study examines the influence of the steep glacier-derived environmental gradients on dominant macrofaunal species distributions and faunal associations in the fjord. The macrobenthic fauna was sampled by van Veen grab at 30 stations situated throughout the fjord (at depths 38–380 m). Two major communities were recognised. An inner basin receives the outflows from three glaciers and is occupied by a Glacial Bay Community dominated by small, surface detritus-feeders, with Chone paucibranchiata and a set of thyasirid and nuculanid bivalves (Thyasira dunbari, Yoldiella solidula, Y. lenticula) as characteristic species. An outer basin of the fjord is characterised by a common set of dominant species, including Heteromastus filiformis, Maldane sarsi, Levinsenia gracilis, Lumbrineris sp. and Leitoscoloplos sp. Three associations may be distinguished within the Outer Basin Community. Association TRANS is of transitional character, with Nuculoma tenuis and Terebellides stroemi. Association CENTR is the most typical for the community. It is dominated by tube-dwelling Prionospio sp., Clymenura polaris, Galathowenia oculata and Spiochaetopterus typicus. Association ENTR contains shelf benthos elements, e.g. Ophiura robusta and Lepeta caeca. An opportunistic eurytopic Chaetozone group is present throughout the fjord and its density and dominance increase with proximity to the glaciers. Dominant species distribution is discussed in relation to environmental factors, of which sediment stability, inorganic particle concentration, sedimentation rate and amount of organic matter in sediments are considered to be most important in structuring the communities.     

The distribution of juvenile benthic invertebrates in an arctic glacial fjord

The distribution of juvenile benthic invertebrates with respect to their abiotic environment was investigated at four locations along a gradient in Kongsfjorden (79°N, 12°E), Spitsbergen, in September 1997. Heavy discharge of inorganic sediments released by the three glaciers was expected to be one of the main structuring factors of benthic communities in the fjord. Juveniles of 76 species/families are identified. Total abundance increases with distance from the fjord head due to the dominance of opportunistic polychaetes, while diversity is highest close to the glacier. Juvenile polychaetes are the most abundant taxon over all stations (92%), followed by bivalves, crustaceans and others. Polychaetes also provide most species (55%) and are the dominant taxon at every station. Their abundance is highly correlated with total organic carbon, indicating that most of them are deposit feeders. Young crustaceans rapidly decrease towards the fjord mouth, probably due to stronger bottom currents. Even though young oligochaetes are exclusively found near the glacier, no species seem to be well adapted to the high sedimentation rate close to the glacier. Juvenile suspension-feeding bivalves seem to be less disturbed by glacial discharge but appear to be more vulnerable to currents on the more exposed sites. The importance of deposit feeders and carnivores increases towards the outer stations. Non-metric multidimensional scaling confirms the distinct gradient in community composition along the fjord. Coupling the biotic data to abiotic factors (depth, bottom-water salinity, bottom-water temperature, sediment grain size and sedimentation rate) using canonical correspondence analysis revealed that hydrographic factors are more responsible for the structuring of the benthic juvenile community at the shallow stations close to the glacier (except the station directly at the glacier). At the outer deeper stations, sediment grain size and related properties may play a more important role.     

Meiofaunal distribution in Hornsund fjord,Spitsbergen

The meiofaunal community structure at 32 stations in Hornsund fjord (77°N) was investigated, and results were compared with data from another Spitsbergen fjord, Kongsfjorden (79°N). Steep environmental gradients of sedimentation, organic matter content, and salinity from the inner to the outer basin of the fjord are present due to intensive glacial discharges of meltwater and ice. As the natural environmental disturbances were described for macrofauna benthic communities before, we aimed to check whether the same pattern occurs among meiofauna. A total of 12 higher meiofaunal taxa were recorded, with nematodes predominating at all stations. Non-parametric multivariate analyses demonstrated clear differences in meiofaunal abundance and composition between stations in the glacial bay and in the outer part of the fjord. Meiofaunal abundance increased with increasing distance from the source of disturbance, which in our study is tidal glaciers. Therefore, the current study demonstrates that the spatial structure of meiofauna is affected by the natural environmental disturbance, and analysis of meiofaunal assemblages can be used to assess the effect of such disturbances.     

Distribution patterns of polychaete fauna in an Arctic fjord (Hornsund, Spitsbergen)

Polychaetes are one of the most important groups of benthic organisms in marine ecosystems. They dominate on the Arctic shelf and play an important role in ecosystem functioning. This study focuses on the polychaete biodiversity and their distribution patterns in Hornsund, an open glacial fjord, in western Spitsbergen and provides important baseline data for future studies of temporal fluctuations in benthic fauna. The main aim of this study was to assess how the polychaete abundance, biomass, diversity, community structure, and function vary along the Hornsund fjord’s axis, in relation to the environmental factors. Eighty-eight polychaete taxa were identified; an average density was 457 ind. m^?2 ± 237.5 SD. Three assemblages were distinguished (INNER, MIDDLE, and OUTER) along the fjord axis, reflecting the intensity of glacial disturbance. A clear division between the highly disturbed inner part of the fjord (Brepollen) and the less impacted middle and outer parts was observed. Continuous gradients in abundance, biomass, and diversity were found with all those values diminishing toward the inner region of the fjord. The polychaete assemblages' indices were significantly correlated with bottom temperature, sediment characteristics (grain size), and distance to the glacier (longitude). No significant correlations were found with depth or total organic carbon content. Carnivore and motile surface deposit feeding polychaete species dominated in the areas close to the glaciers, while the OUTER community was dominated by carnivores and surface sessile and discretely motile species, and had more complex trophic structure, with multiple species representing different functional groups including carnivores, sessile, discretely motile, and motile surface deposit feeders and motile burrowers.     

Decadal change in macrobenthic soft-bottom community structure in a high Arctic fjord (Kongsfjorden, Svalbard)

Marine benthic macrofauna communities are considered a good indicator of subtle environmental long-term changes in an ecosystem. In 1997/1998 and 2006, soft-bottom fauna of an Arctic glacial fjord Kongsfjorden was extensively sampled and major communities were identified along the fjord axis, which were related to the diminishing influence of glacial activity. Spatial patterns in community structure and species diversity were significantly different in the central basin of Kongsfjorden between periods while there was no change in the inner part of the fjord. In 1997/98, three faunal associations were distinguished with significant differences in species richness and diversity (H′) while in 2006 only two faunal associations were identified and there were no differences any more between the two formerly distinct associations in the central fjord. The increased input of Atlantic water due to a stronger West Spitsbergen Current may be the reason for unification of previous clear faunal division. The faunal association in the inner, well separated glacial part of the fjord, characterized by strong glacier influence, was protected from Atlantic water inflow and, hence, the macrobenthic fauna essentially remained unaffected. Reduced abundance of species typical for glacial bays in the central part of the fjord in 2006 may result from the decreasing effect of Blomstrandbreen glacier, strong increase of input of Atlantic water into the fjord and increased temperature of West Spitsbergen Current. Higher values of POC in 2006 than in 1998 are likely the effect of increased primary production resulting from warmer water temperatures.     

Macrozoobenthic community structure in a high-arctic East Greenland fjord

A macrozoobenthic community study was conducted in an East Greenlandic fjord (Young Sound, 74°18′N; 20°15′W) during the ice-free period from July to August in 1996. Grab samples as well as underwater photography were used for quantifying the macrozoobenthos at water depths between 20 and 85 m. Abundance decreased with depth from 2700 ind. · m⁻² at 20 m to 900 ind. · m⁻² at 85 m. At a time series station at 35 m, abundance increased from 700 ind. · m⁻² in mid-July to 1400 ind. · m⁻² in mid-August. Polychaetes dominated in grab samples but bivalves constituted an important part of the benthic fauna, especially at the shallow part of the depth gradient. Photographs revealed high abundances of large epifaunal species, especially brittle stars. Diversity was generally high, with around 45 species per 201 individuals, as calculated by Hurlbert's rarefaction term. A gradual change in community structure with depth was observed, which could be related to variation in sediment composition and disturbance intensity. Accepted: 20 May 2000     

Temporal patterns of benthic community development in an Arctic fjord (Kongsfjorden, Svalbard): results of a 24-year manipulation study

We investigated temporal patterns of recolonisation and disturbance in a benthic hard bottom community in high-arctic Kongsfjorden from 1980 to 2003 through annual photographic surveys. A manipulative sampling design was applied, where half of the study area (treatment areas) was cleared at the beginning of the study. Twenty-three different taxa and groups of benthic epifauna were found in the photographs. The benthic community structures of treatments and controls converged within the first decade, but significant differences prevailed until ≤13 years after the start of the study. We could distinguish between three different time intervals with increased inter-annual changes. While the observed differences during the first two intervals could be attributed to recolonisation and succession, the changes in interval 3 were mostly due to increased external forcing and characterised by low inter-group and high inter-annual differences. During this interval, brown algae (mainly Desmarestia) and the sea urchin Strongylocentrotus droebachiensis emerged in high densities, while sea anemone populations declined. Different recolonisation patterns for individual species were related to life span, rate of maturity, predators and larval settlement. We could not find a climax stage in the succession for the benthic community at Kvadehuken, presumably due to the constant level of disturbances at the site.     

Intertidal meiofauna of a high-latitude glacial Arctic fjord (Kongsfjorden, Svalbard) with emphasis on the structure of free-living nematode communities

Meiofauna communities of four intertidal sites, two sheltered and two more exposed, in Kongsfjorden (Svalbard) were investigated in summer 2001 at two different tidal levels (i.e. the low-water line and close below the driftline, referred to as mid-water (MW) level). A total of seven meiofaunal higher taxa were recorded with nematodes, oligochaetes and turbellarians being numerically dominant. Mean total meiofaunal densities ranged between 50 ind. 10 cm⁻² and 903 ind. 10 cm⁻². Our data showed a clear decrease in total meiofaunal densities with increasing coarseness of the sediment. Total meiofaunal biomass varied from 0.2 g dwt m⁻² to 2 g dwt m⁻² and, in general, was high even at low meiofaunal densities, i.e. larger interstitial spaces in coarser sediments supported larger meiofauna, especially turbellarians. The results on the vertical distribution of meiofauna contrasted sharply with typical meiobenthic depth profiles on other beaches, probably in response to ice-scouring and concomitant salinity fluctuations. Oligochaetes were the most abundant taxon, with a peak density of 641 ind. 10 cm⁻² at Breoyane Island. They were mainly comprised of juvenile Enchytraeidae, which prohibited identification to species/genus level. Nematode densities ranged between 4 ind. 10 cm⁻² and 327 ind. 10 cm⁻². Nematodes were identified up to genus level and assigned to trophic guilds. In total, 28 nematode genera were identified. Oncholaimus and Theristus were the most abundant genera. The composition of the nematode community and a dominance of predators and deposit feeders were in agreement with results from other arctic and temperate beaches. Nematode genus diversity was higher at the more sheltered beaches than at the more exposed ones. Low-water level stations also tended to harbour a more diverse nematode communities than stations at the MW level. Differences in nematode community structure between low- and MW stations of single beaches were more pronounced than community differences between different beaches and were mainly related to resources quality and availability.     

Distribution of Calanus species in Kongsfjorden, a glacial fjord in Svalbard

The distribution of Calanus species was investigated in Kongsfjordenin summer of 1996 and 1997. In both years Calanus finmarchicusand Calanus glacialis dominated, although the boreal C. finmarchicuswas more abundant than the Arctic C. glacialis in 1997. Thiscoincided with a 2°C higher water temperature at 50 m in1997, indicating stronger influence of Atlantic origin waterthat year. Advected Calanus finmarchicus occurred in deep andsubsurface layers of the outer fjord in 1996 (200 ind. m^-3,mainly CIII). A less abundant local population aggregated insurface layers of the inner fjord (100 ind. m^-3). Similarly,advected C. finmarchicus occurred in subsurface layers in 1997(446 ind. m^-3, mainly CIII and CIV) and a local population insurface layers (183 ind. m^-3, mainly CI). Calanus glacialisin 1996 aggregated as CII and CIII in the deep layers of theouter fjord (272 ind. m^-3), whereas CIII–CV were abundant(216 ind. m^-3) in cold surface waters of the inner fjord. In1997 C. glacialis (mostly CIII–CV) was more abundant inthe outer than in the inner part of the fjord (40 and 192 ind.m^-3, respectively). Within Kongsfjorden, Calanus finmarchicusneeds one year to complete its life cycle, whereas Calanus glacialisneeds two. Calanus hyperboreus seems to be an expatriate inthe fjord system.     

Comparison of productivity and phytoplankton in a warm (Kongsfjorden) and a cold (Hornsund) Spitsbergen fjord in mid-summer 2002

Kongsfjorden and Hornsund are two glacial fjords without sills on the West Spitsbergen coast. Both sites are under the influence of relatively warm Atlantic-derived water, although Hornsund is more influenced by cold water from the Barents Sea. In this study, we compared the impacts of cold Arctic and warmer Atlantic waters on the pelagic ecosystems of Kongsfjorden and Hornsund. Both fjords were strongly influenced by Atlantic-derived waters during summer (2002). Diatoms were the most substantial contributors to phytoplankton biomass, especially in outer basins of both fjords, whereas the second most important contributors were autotrophic dinoflagellates in Kongsfjorden and nanoflagellates in Hornsund. Total phytoplankton biomass was highest in Hornsund. Primary production rates were an order of magnitude lower in Kongsfjorden than in Hornsund, and increased from inner to outer fjord (from 2.47 to 4.48 mg C m⁻² h⁻¹ in Kongsfjorden and from 14.00 to 86.65 mg C m⁻² h⁻¹ in Hornsund). Chlorophyll-a concentration was also substantially lower in Kongsfjorden. Zooplankton was dominated by omnivorous species in Kongsfjorden and herbivorous in Hornsund. Observed differences between the fjords may originate from (1) advection of different waters into the fjords; (2) differences in freshwater runoff and turbidity, and (3) timing of the phytoplankton bloom. Climate warming will likely increase the Atlantic water influence, and result in reduced production of diatoms and increase in flagellates.     

Free-living nematodes and macrobenthos in a high-latitude glacial fjord

Kongsfjord is an open glacial fjord on the west coast of Svalbard, where the influence of the West Spitzbergen current ameliorates the effects of high latitude (79°N). The fjord is heavily influenced by glacial discharges of meltwater, ice and till, and related environmental gradients in sediments from the glaciers to the open sea include sediment deposition, organic content and disturbance. Other factors, such as the formation and break up of sea ice, also affect benthic communities. In this study spatial patterns in nematode and macrofaunal communities, in samples collected using box-corers and van Veen grabs during a cruise in September 1997, are described, compared and contrasted. Non-parametric multivariate analyses demonstrate that there were clear differences in community structure between stations in both macrofaunal and nematode assemblages. At stations where macrofauna were sampled using both box-cores and grabs there were also significant differences between samples collected by different methods, although there is evidence that these were influenced in part by slight differences in sampling location. Some evidence of disturbance to macrofaunal assemblages in the centre of the fjord is apparent. Macrofaunal community composition varied most closely with a combination of depth and sediment C : N ratio, whereas that of nematodes varied most closely with C : N alone. Proportions of feeding groups of nematodes showed little variation along the fjord. There is no evidence of a specialised nematode assemblage inhabiting the part of the fjord subject to the heaviest deposition of sediment. The taxonomic distinctness of nematodes decreased with increasing distance from the source of disturbance. This is in contrast to studies showing that the taxonomic distinctness of nematodes tends to decrease with increasing anthropogenic stress.     

Dynamics of coexisting Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus populations in a high-Arctic fjord

We studied the population dynamics of Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus in Billefjorden, Svalbard (78°40N). All three species reproduced in the fjord with different timing. The maximum abundance of Calanus spp. copepodite stages peaked on the 11th of July (29,000 ind m^–2). C. glacialis was the dominant species accounting for 60–80% of the total Calanus abundance. C. finmarchicus appear to thrive in the fjord despite the low temperatures (–1.86°C to 5°C) and accounted for 20–30% of the total population. C. hyperboreus contributed less to the total abundance (5–20%). A 1-year life cycle is suggested for C. finmarchicus and C. hyperboreus in the fjord, C. glacialis has a 1- to 2-year life cycle. Highest mortality rates were observed for copepodite stage CV in C. finmarchicus and C. glacialis (0.09 and 0.075 d^–1, respectively) and for females in C. hyperboreus (0.149 d^–1). Mortality of copepodite stages was substantially lower in C. glacialis than in the other species. This is particularly obvious in the early and numerous copepodite stages (CI + CII) during the period of recruitment to these stages. This suggests that differences in secondary production in Arctic pelagic ecosystems are controlled partly by population loss rates.     

Structure of bryozoan communities in an Antarctic glacial fjord (Admiralty Bay,South Shetlands)

Bryozoans are among the most important groups of the Southern Ocean benthic macrofauna, both in terms of species richness and abundance. However, there is a considerable lack of ecological research focused on their distribution patterns and species richness on smaller scale, especially in the soft bottom habitats of Antarctic glacial fjords. The aim of this study was to describe those patterns in the Admiralty Bay. Forty-nine Van Veen grab samples were collected at the depth range from 15 to 265 m, in the summer season of 1979/1980, at three sites distributed along the main axis of the fjord. Among 53 identified species of bryozoans, 32 were recorded in the Admiralty Bay for the first time. The most common and abundant species were Himantozoum antarcticum, Inversiula nutrix and Nematoflustra flagellata. Genera such as Arachnopusia, Cellarinella and Osthimosia were the most speciose taxa. It was demonstrated that depth was important for the distribution of the bryozoans. More than half of the recorded species were found only below 70 m. An influence of glacial disturbance was reflected in the dominance structure of colony growth-forms. The inner region of the fjord was dominated almost entirely by encrusting species, while the diversity of bryozoan growth-forms in less disturbed areas was much higher. In those sites the highest percentage of branched, tuft like species represented by buguliform and flustriform zoaria was observed.     

Variation in Serripes groenlandicus (Bivalvia) growth in a Norwegian high-Arctic fjord: evidence for local- and large-scale climatic forcing

We examined the growth rate of the circumpolar Greenland Cockle ( Serripes groenlandicus ) over a period of 20 years (1983–2002) from Rijpfjord, a high-Arctic fjord in northeast Svalbard (80°10'N, 22°15'E). This period encompassed different phases of large-scale climatic oscillations with accompanying variations in local physical variables (temperature, atmospheric pressure, precipitation, sea ice cover), allowing us to analyze the linkage between growth rate, climatic oscillations, and their local physical and biological manifestations. Standard growth index (SGI), an ontogenetically adjusted measure of annual growth, ranged from a low of 0.27 in 2002 up to 2.46 in 1996. Interannual variation in growth corresponded to the Arctic climate regime index (ACRI), with high growth rates during the positive ACRI phase characterized by cyclonic ocean circulation and a warmer and wetter climate. Growth rates were influenced by local manifestations of the ACRI: positively correlated with precipitation and to a lesser extent negatively correlated with atmospheric pressure. A multiple regression model explains 65% of the variability in growth rate by the ACRI and precipitation at the nearest meteorological station. There were, however, complexities in the relationship between growth and physical variables, including an apparent 1 year lag between physical forcing changes and biological response. Also, when the last 4 years of poor growth are excluded, there is a very strong negative correlation with ice cover on a pan-arctic scale. Our results suggest that bivalves, as sentinels of climate change on multi-decadal scales, are sensitive to environmental variations associated with large-scale changes in climate, but that the effects will be determined by changes in environmental parameters regulating marine production and food availability on a local scale.     

Seasonal variability of meio- and macrobenthic standing stocks and diversity in an Arctic fjord (Adventfjorden, Spitsbergen)

Strong environmental seasonality is a basic feature of the Arctic system, still there are few published records of the seasonal variability of the Arctic marine biota. This study examined the year-round seasonal changes of soft bottom macro- and meiobenthic standing stocks and diversity on a station located in an Arctic fjord (Adventfjorden, Spitsbergen). The seasonality observed in benthic biota was related to the pelagic processes, primarily the seasonal fluxes of organic and inorganic particles. The highest abundance, biomass and richness of benthic fauna occurred in the spring after the phytoplankton bloom. During the summer, when a high load of glacial mineral material was transported to the fiord, the number of both meio- and macrobenthic individuals decreased remarkably. The strong inorganic sedimentation in summer was accompanied by a decline in macrobenthic species richness, but had no effects on evenness. Redundancy analysis (RDA) pointed to granulometric composition of sediments (depended on mineral sedimentation) and organic fluxes as factors best related to meio- and macrobenthic taxonomic composition, but no clear seasonal trend could be observed on the nMDS plots based on meiobenthic higher taxa or macrobenthic species abundances in the samples. This study addresses the possible effects of changes in the winter ice cover on the fjordic benthic systems because it was performed in a year with no ice cover on the fjord.     

Prediction of benthic community structure from environmental variables in a soft-sediment tidal basin (North Sea)

The relationship between benthos data and environmental data in 308 samples collected from the intertidal zone of the H?rnum tidal basin (German Wadden Sea) was analyzed. The environmental variables were current velocity, wave action, emersion time (all of which were obtained from a 2-year simulation with a numerical model) and four sediment grain-size parameters. A grouping of sample stations into five benthos clusters showed a large-scale (>1?km) zoning of benthic assemblages on the tidal flats. The zoning varied with the distance from the shore. Three sample applications were examined to test the predictability of the benthic community structure based on environmental variables. In each application, the dataset was spatially partitioned into a training set and a test set. Predictions of benthic community structure in the test sets were attempted using a multinomial logistic regression model. Applying hydrodynamic predictors, the model performed significantly better than it did when sediment predictors were applied. The accuracy of model predictions, given by Cohen’s kappa, varied between 0.14 and 0.49. The model results were consistent with independently attained evidence of the important role of physical factors in Wadden Sea tidal flat ecology.     

Microbial community structure in moraine lakes and glacial meltwaters, Mount Everest

The bacterial diversity and abundance in two moraine lakes and two glacial meltwaters (5140, 5152, 5800 and 6350 m above sea level, respectively) in the remote Mount Everest region were examined through 16S rRNA gene clone library and flow cytometry approaches. In total, 247 clones were screened by RFLP and 60 16S rRNA gene sequences were obtained, belonging to the following groups: Proteobacteria (8% alpha subdivision, 21% beta subdivision, and 1% gamma subdivision), Cytophaga-Flavobacteria-Bacteroides (CFB) (54%), Actinobacteria (4%), Planctomycetes (2%), Verrucomicrobia (2%), Fibrobacteres (1%) and Eukaryotic chroloplast (3%), respectively. The high dominance of CFB distinguished the Mount Everest waters from other mountain lakes. The highest bacterial abundance and diversity occurred in the open moraine lake at 5152 m, and the lowest in the glacial meltwater at 6350 m. Low temperature at high altitude is considered to be critical for component dominancy. At the same altitude, nutrient availability plays a role in regulating population structure. Our results also show that the bacteria in Mount Everest may be derived from different sources.     

Interpreting long-term changes in benthic community structure: a new protocol

Documentation of long-term change in benthic ecosystems is important for assessing and managing the effects of such change on: 1) secondary production, particularly leading to commercially important food webs, 2) pollutant transfer within the food web, 3) the ability of the new assemblage to metabolically burn-off labile detritus that might otherwise accumulate, contributing to long-term hypoxia, and 4) recyling of nutrients from the seafloor back to primary producers.Organism-sediment relationships which accompany benthic disturbances have predictable features. Although participating species may vary regionally or seasonally, their life-history attributes and functional relationships to the associated sediment appear to be universal. Pioneering seres are near-surface dwelling, productive, and are readily available to demersal predators. However, these taxa may be potential pollutant vectors. Dense tube mats may promote the deposition and retention of high BOD organic matter. Late successional stage seres are represented by deeply bioturbating head-down deposit feeders. The deep cryptic infaunal habitat of these species may make them less important as prey for epifaunal predators. Sediments populated by these equilibrium assemblages are characteristically low in labile organic matter, sedimentary sulphides, and oxygen demand. Nutrients (N, P, Si) are returned to primary producers by biogenic irrigation of sediment pore water.Mapping of successional mosaics is important for documenting major long-term change in benthic community structure and associated biogenic processes. Our mapping tool consists of a vessel-deployed sediment-profile camera; organism-sediment relationships can be imaged in situ with this instrument. Such a mapping protocol is not intended to replace traditional sampling. Rather, the successional maps are used to efficiently detect change in a system, design a cost-efficient sampling grid for obtaining geochemical and biological ground-truth samples, and to construct hypotheses about how the change might answer the four outlined management questions.     

Macroinvertebrate community structure in relation to environmental variables in a Swiss glacial stream

1. Benthic macroinvertebrate distribution was examined in relation to channel characteristics (including stability), substratum, hydraulic variables, primary production (chlorophyll a ) and coarse particular organic matter (CPOM) in an alpine glacial stream, the Mutt (Upper Rhône valley, Switzerland). Co-inertia analysis and canonical correspondence analysis were used to identify the major environmental gradients influencing community variations.
2. The Mutt (length: 3.6 km, altitudinal range: 1800–3099 m a.s.l.) exhibited typical characteristics of a kryal stream. Average summer temperature remained below 2 °C immediately downstream from the snout but was on average 5 °C higher 1700 m downstream. Seasonal variations in water sources were evidenced by the high late-summer (September) contribution of groundwater with increased conductivity.
3. Sixty-six taxa were recorded from the five reaches sampled at three periods (snowmelt, ice melt and low water in late summer) in 1996 and 1997, of which 29 were Chironomidae. Three taxa of Diamesinae were the first colonizers of the stream below the glacier, but 16 taxa, including Ephemeroptera, Plecoptera and Trichoptera, were already recorded 200 m downstream. Water depth, channel slope and Pfankuch's Index of channel stability were strongly correlated with the longitudinal faunal gradient. Maximum temperature, current velocity and water conductivity were also correlated, but to a lesser extent.
4. The rapid incorporation of non-chironomid taxa into the stream community represented a departure from Milner & Petts's (1994) conceptual model of invertebrate succession downstream of glacial margins. The results confirmed that glacial stream communities are primarily driven by physical determinants.     

Assessing scales of variability in benthic diatom community structure

Sources of variability such as sampling method, sample preparation, and sample analysis (taxonomy) might affect our ability to measure differences in community structure between sites in environmental effects studies. It is therefore important to ensure that changes in community structure related to the physical or chemical differences between sites are not hidden by other sources of variability within a site. The goal of this study was to quantify the amount of variability in benthic diatom community structure related to sampling and laboratory procedures. Our results showed that variability in community structure was minimal among replicate microscope slides (< 1%) and among samples collected within a site (1.8%). Variability in community structure was substantially higher between sites located in one stream (16.6%), and highest across streams (59.6%). This suggests that field sampling and laboratory methods do not contribute a large amount of variation into our analyses of benthic diatom community structure across sites.