Benthic Particulate Organic Matter Research Articles

Determinants of chironomid species richness in mid-European temperate rivers – Environmental factors, regional influences, diversity, and seasons

Multiscale determinants of riverine chironomid species richness were assessed in seven rivers in Central Poland, an area representative of the European temperate climatic zone. The impact of environmental factors, seasonality, as well as the concepts of gamma diversity, i.e. habitat species richness (HSR), alpha diversity, i.e. local species richness (LSR), and the relationships between these, i.e. beta diversity, were studied.One site in each river was defined as a habitat and monthly LSR time series data were obtained at each site over a full annual cycle for analysis. No strong trend in the time series was detected. The autocorrelation function (ACF) indicated that the time series were uncorrelated white noise.A stepwise forward regression model with no HSR indicated that depth, Substrate Index (SI), velocity and dissolved oxygen were significant factors of LSR values in the studied area, explaining together with summer (as a dummy variable) 67.01% of LSR variance (R2adj = 0.66). Seasonality was noticeable in the impact of summer on increase in species richness. When HSR was included in a similar model then it explained, together with benthic particulate organic matter (BPOM), SI, depth, and velocity, 70.90% of variability in LSR variance (R2adj = 0.69), HSR alone accounting for 58.95% in LSR variance (R2adj = 0.59).In both the annual cycle and in given seasons, HSR strongly positively correlated with the minimum, maximum, and mean LSR values, and there was no saturation of the rivers by chironomid species, i.e. other chironomid species were still able to inhabit the rivers beside the present ones. HSR did not correlate with beta diversity when measured by two widely used setwise beta diversity indices, or by three pairwise beta diversity indices. The exception was in autumn, where one setwise and two pairwise beta diversity measures correlated with both alpha and gamma diversity measures, which suggests a greater stability of larval chironomid assemblages in that season. This larval stability was not associated with greater stability of environmental factors in autumn, hence the stability seems to be related to undisclosed biotic mechanisms.Seasonality was also a strong factor in predicting the exchange of species. Turnover index between seasons ranged from 0.133 (spring vs summer) to 0.261 (autumn vs winter) and UPGMA clustering determined least chironomid similarity between winter and other seasons.

Modelling of physical drivers of a large feeding aggregation of killer whales (Orcinus orca) in the western Great Australian Bight, Australia

Every year >100 killer whales accumulate on the continental slope near Bremer Bay in the western Great Australian Bight from late austral spring to early autumn (January–April), which can be regarded as a natural wonder. For unknown reasons, the whales tend to feed in the same confined region over a seafloor plateau near the head of the Hood Canyon, where the total water depth is ~800–1000 m. The hypothesis behind this work is that the killer-whale aggregation is the signature of a localized marine food web originating from flow-induced upwelling and concentration of benthic particulate organic matter (POM). To test this hypothesis a hydrodynamic model is applied to analyse the pathways of virtual suspended particles released near the seafloor in three large submarine canyons that exist in the region. Here we show that, due to its shape and positioning on the continental slope, the Hood Canyon operates to funnel significantly more benthic particles onto the ambient continental slope than the adjacent Bremer Canyon and the Whale Canyon. Moreover, findings suggest that smaller-scale topographic undulations within the Hood Canyon are the cause of this slope upwelling of POM. This transport mechanism of POM may explain the ecological uniqueness of the region.

Structural and functional changes in the macroinvertebrate community in Alpine stream networks fed by shrinking glaciers

The status of glaciers is alarming globally with still unknown effects on freshwater ecosystems. Thegeneral aim of this study was to investigate the structural and functional changes in the macroinvertebrate communityin stream networks fed by shrinking glaciers in relation to environmental variables. Feeding glaciers haddifferent surface areas and retreating rates. We selected 10 study sites in the Italian Alps, spanning five kryal, twoglacio-rhithral, two krenal and one proglacial pond, sampled twice in summer 2018. Eight of these sites weresampled previously between 1996 and 2014. In all, in 2018, > 15,000 individuals (73 taxa) were collected, of which82 % were chironomids (Diptera Chironomidae) (33 taxa). Diamesa zernyi gr. (Chironomidae Diamesinae) wasthe most frequent and abundant taxon, followed by Oligochaeta and Chironomidae Orthocladiinae. Taxonomical(Shannon index) and functional (based on functional feeding groups) diversity both increased with decreasingglacial influence (estimated as glacial index, GI, based on distance from the glacier snout of each site and glacierarea), from kryal to glacio-rhithral and krenal habitats. Taxa distribution was explained mainly by GI, maximumwater temperature, substrate stability, silica, epilithic chlorophyll-a, and benthic particulate organic matter. Thesame variables explained temporal differences in the community structure for the eight sites re-sampled in the lasttwo decades. Among the taxa best associated with high GI was the chironomid Diamesa steinboecki, that in 2018was exclusive of the kryal sites with GCC (% glacier cover in the catchment, expressed in a range from 0 %–100 %)> 50 % and maximum temperature < 5 °C. This species was absent only in the kryal site C0 (GCC = 33 %), whereit was dominant in 1996 –1997. This site was still fed by ice melt in 2018, but resembled a glacio-rhithral site inhabitat features (e.g. maximum temperature > 6 °C) and biota (e.g. % Diamesa spp. < 30 %). In C0, it was evidentthat in the last 22 years, the macroinvertebrate community changed remarkably. This change was due to upstreammigration of generalist insect species to sites once exclusive for kryal species with consequent changes in food webstructure and loss of strictly kryal species, first D. steinboecki that we propose as the “flagship” species of the kryalin the Alps. The site C0 represents a “tipping point”, showing us the effects of climate change on alpine biodiversityin a relatively short period; unfortunately, there are many such sites in the Italian Alps.

Stable isotope ratios of emergent adult aquatic insects can be used as indicators of water pollution in the hyporheic food web

Bio-assessment protocols for the subsurface domain of river channels (i.e. hyporheic zone) are scarce despite of the known importance of its ecological function in river ecosystems. The larvae of the Alloperla ishikariana Plecoptera species inhabit the hyporheic zone. Therefore, we examined whether emergent adult A. ishikariana could serve as proxy indicators of the effects of pollution in the hyporheic food web. The study site comprised a 15-km stretch of a gravel bed river in Hokkaido, Japan, from which all invertebrates were collected from the riverbed at a depth of 30–50 cm, and emergent A. ishikariana adults were sampled in riparian zones. Water quality changed gradually along the river owing to the effects of a wastewater treatment plant and surrounding land uses. Nitrogen and carbon stable isotope ratios (SIRs) of epilithic biofilms, hyporheic particulate organic matter (POM), benthic POM, and invertebrates were used to determine the major basal carbon sources, the effects of water pollution on the hyporheic zone, and the trophic positions of dominant invertebrates. Generalized linear (mixed) models were used for statistical testing and modeling. Amphipoda and the larvae of A. ishikariana were considered as top predators and secondary consumers in the hyporheic food web, respectively. The observed similarity in water quality between the hyporheic and surface water suggested a large degree of hydrological exchange between the two zones, and resulted in positive increases in the nitrogen SIRs of hyporheic invertebrates, including A. ishikariana larvae, in proportion to nitrate levels in the surface water. The nitrogen SIRs of A. ishikariana adults were significantly correlated with the nitrogen SIRs of their larvae within the same location (adjusted R2 = 0.78), indicating that emerged adults can provide information on the longitudinal variability of the effects of synthetic nitrogen. In contrast, the carbon SIRs of adults did not predict those of their larvae, possibly reflecting the diverse feeding habitats of larvae. Overall, we demonstrated that adult aquatic insects emerging from the hyporheic zone can be used as indirect indicators of pollution-associated nutrient assimilation as well as the spatial heterogeneity of dietary carbon resources in hyporheic food web.

Relationship between bacterial compartment and particulate organic matter (POM) in coastal systems: An assessment using fatty acids and stable isotopes

Particulate organic matter (POM) in coastal systems is a mixture of different organic matter (OM) sources originating from land and sea. Among sources, bacterial biomass plays a large role in OM processing and carbon recycling in the ocean and is often neglected as a source in common approaches. The present study proposes to use elemental and isotopic ratio of carbon and nitrogen (C:N, δ13C, δ15N) and fatty acids to investigate the relationship between bacteria and surface water POM composition of three systems with different characteristics (two marine and one estuarine) over an annual cycle. Overall, our results highlight a positive relationship between bacterial contribution and continental degraded or undergoing degradation POM for all the studied systems and an inverse relationship with pelagic primary producers. At multisystem scale, high bacterial contribution is linked to high proportion of refractory terrestrial material characterizing estuarine stations whereas in marine systems, the occurrence of bacteria is mainly linked to river POM. Over the annual cycle, bacterial markers are more abundant during the winter period characterized by larger river and/or benthic POM contribution. This seasonal pattern is mainly driven by changes in river flows and resuspension. This study highlights the importance of bacterial compartment as a component of coastal and estuarine POM. Even though these results remains semi-quantitative, similar studies in other types of systems can help to understand microbial role in OM dynamic and to better estimate bacterial source in carbon budgets and food web studies.

Characteristics of consumer trophic resources for Waikato shallow lake food webs

ABSTRACTWe characterised the quantity (mass per unit area or volume), quality (cabon:nitrogen ratio) and enrichment (δ15N) of basal food resources and benthic macroinvertebrates in six shallow lakes in the Waikato region, New Zealand, to elucidate patterns related to lake type (peat, riverine), habitat (littoral, mid-lake) and enrichment status (Trophic Level Index >6 or ≤5). Total seston dry mass was dominated by fine material that was correlated with chlorophyll a concentration. Seston was a higher quality food resource than benthic particulate organic matter which had higher biomass overall in littoral than in mid-lake habitats. Biomass of Chironomidae was highest in the less-enriched peat lakes, possibly due to clearer water supporting benthic algae in shallow littoral areas. Our results highlight the potential role of multiple bottom-up influences on shallow lake food webs. The more abundant and higher quality pelagic food resources in highly enriched lakes may have implications for resilience to non-indigenous fish invasion.

Relationships between depth and δ15N of Arctic benthos vary among regions and trophic functional groups

Stable isotope ratios of nitrogen (δ15N) of benthic primary consumers are often significantly related to water depth. This relationship is commonly attributed to preferential uptake of 14N from sinking particulate organic matter (POM) by microbes, and suggests that relationships between δ15N and water depth may be affected by local POM sources and flux dynamics. We examined the relationships between δ15N and water depth (20–500 m) for six trophic functional groups using a mixed effects modelling approach, and compared relationships between two contiguous Arctic marine ecosystems with different POM sources and sinking export dynamics: the Canadian Beaufort Sea and Amundsen Gulf. We demonstrate for the first time in the Arctic that δ15N values of mobile epifaunal carnivores increased as a function of depth when considered separately from benthopelagic and infaunal carnivores, which contrarily did not exhibit increasing δ15N with depth. The δ15N of suspension/filter feeders, infaunal deposit feeders and bulk sediment also increased with water depth, and the slopes of the relationships were steeper in the Amundsen Gulf than in the Beaufort Sea. We propose that regional differences in slopes reflect differences in POM sources exported to the benthos. In the Beaufort Sea, terrestrial POM discharged from the Mackenzie River quantitatively dominates the sedimentary organic matter across the continental shelf and slope, dampening change in δ15N of benthic POM with depth. In the Amundsen Gulf, we attribute a faster rate of change in δ15N of POM with increasing depth to larger contributions of marine-derived POM to the benthic sedimentary pool, which had likely undergone extensive biological transformation in the productive offshore pelagic zone. Differences in POM input regimes among regions should be considered when comparing food webs using stable isotopes, as such differences may impact the rate at which consumer δ15N changes with depth.

Resource partitioning between Pacific walruses and bearded seals in the Alaska Arctic and sub-Arctic.

Climate-mediated changes in the phenology of Arctic sea ice and primary production may alter benthic food webs that sustain populations of Pacific walruses (Odobenus rosmarus divergens) and bearded seals (Erignathus barbatus). Interspecific resource competition could place an additional strain on ice-associated marine mammals already facing loss of sea ice habitat. Using fatty acid (FA) profiles, FA trophic markers, and FA stable carbon isotope analyses, we found that walruses and bearded seals partitioned food resources in 2009-2011. Interspecific differences in FA profiles were largely driven by variation in non-methylene FAs, which are markers of benthic invertebrate prey taxa, indicating varying consumption of specific benthic prey. We used Bayesian multi-source FA stable isotope mixing models to estimate the proportional contributions of particulate organic matter (POM) from sympagic (ice algal), pelagic, and benthic sources to these apex predators. Proportional contributions of FAs to walruses and bearded seals from benthic POM sources were high [44 (17-67)% and 62 (38-83)%, respectively] relative to other sources of POM. Walruses also obtained considerable contributions of FAs from pelagic POM sources [51 (32-73)%]. Comparison of δ13C values of algal FAs from walruses and bearded seals to those from benthic prey from different feeding groups from the Chukchi and Bering seas revealed that different trophic pathways sustained walruses and bearded seals. Our findings suggest that (1) resource partitioning may mitigate interspecific competition, and (2) climate change impacts on Arctic food webs may elicit species-specific responses in these high trophic level consumers.

Dynamics of particulate organic matter composition in coastal systems: A spatio-temporal study at multi-systems scale

In coastal systems, the multiplicity of sources fueling the pool of particulate organic matter (POM) leads to divergent estimations of POM composition. Eleven systems (two littoral systems, eight embayments and semi-enclosed systems and one estuary) distributed along the three maritime façades of France were studied for two to eight years in order to quantify the relative contribution of organic matter sources to the surface-water POM pool in coastal systems. This study was based on carbon and nitrogen elemental and isotopic ratios, used for running mixing models.The POM of the estuary is dominated by terrestrial material (93% on average), whereas the POM of the other systems is dominated by phytoplankton (84% on average). Nevertheless, for the latter systems, the POM composition varies in space, with (1) systems where POM is highly composed of phytoplankton (≥93%), (2) systems characterized by a non-negligible contribution of benthic (8–19%) and/or river (7–19%) POM sources, and (3) the Mediterranean systems characterized by the contribution of diazotroph organisms (ca. 14%). A continent-to-ocean gradient of river and/or benthic POM contribution is observed. Finally, time series reveal (1) seasonal variations of POM composition, (2) differences in seasonality between systems, and (3) an inshore-offshore gradient of seasonality within each system that were sampled at several stations.Spatial and seasonal patterns of POM composition are mainly due to local to regional processes such as hydrodynamics and sedimentary hydrodynamic (e.g. resuspension processes, changes in river flows, wind patterns influencing along-shore currents) but also due to the geomorphology of the systems (depth of the water column, distance to the shore). Future studies investigating the link between these forcings and POM composition would help to better understand the dynamics of POM composition in coastal systems.

The annual and seasonal variability of the carbonate system in the Bay of Brest (Northwest Atlantic Shelf, 2008–2014)

From 2008 to 2014, the MAREL-Iroise buoy, located in the Bay of Brest, collected high-frequency measurements of partial pressure of CO2 (pCO2) and ancillary hydrographic parameters, in conjunction with a comprehensive sampling regime of two additional carbonate system variables total alkalinity (AT), and dissolved inorganic carbon (DIC). Biological processes drive variations in AT and DIC throughout the year, except in winter, when primary production is negligible and large freshwater inputs occur. Annually, the Bay of Brest generally behaves as a source of CO2 to the atmosphere (0.14±0.20molCm−2yr−1), showing inter-annual variability significantly linked to annual net community production (NCP). The presence of a large community of benthic filter feeders leads to high levels of particulate organic matter (POM) and opal deposition during the spring diatom bloom. Over the following few months, benthic POM remineralisation reduces the spring CO2 deficit relative to the atmosphere, and remineralisation of biogenic silica supplies further late spring primary production. The result is an inverse spring NCP – air-sea CO2 flux relationship, whereby greater NCP in early spring results in lower fluxes of CO2 into the Bay in late spring. This recycling mechanism, or silicic acid pump, also links the spring and summer NCP values, which are both determined by the peak wintertime nutrient concentrations. The carbonate system is further affected by the benthic community in winter, when CaCO3 dissolution is evident from notable deviations in the ΔAT:ΔDIC ratio. This study highlights the necessity of individual study of coastal, temperate ecosystems and contributes to a better understanding of what determines coastal areas as sinks or sources of CO2 to the atmosphere.

Effect of reservoir‐derived plankton released from dams on particulate organic matter composition in a tailwater river (Uji River, Japan): source partitioning using stable isotopes of carbon and nitrogen

ABSTRACTWe estimated the contribution of reservoir‐derived plankton released from an upstream dam to particulate organic matter (POM) relative to terrestrial allochthonous (fallen leaves) and instream autochthonous (downstream epilithic algae) sources in the Uji River, Japan, to investigate the influence of the reservoir plankton on downstream POM composition. Four types of POM such as suspended fine, suspended coarse, benthic fine and benthic coarse POM were collected and then analyzed using two types of mixing models combining δ13C–δ15N: a standard linear model (SLM) and a concentration‐weighted model (CWM), which are compared with the microscopic examination. Results demonstrate that the three trophic sources were isotopically distinct, and all POM samples are plotted inside the mixing triangle defined by the three end members in the δ13C–δ15N biplot. SLM underestimated the terrestrial source contribution and overestimated that of the reservoir plankton, suggesting that despite popular application of the SLM method, CWM was more appropriate for the source partitioning of riverine POM particularly in the case where large differences in source concentrations of C and N are present. Reservoir plankton contribution was highest in suspended fine POM (S‐FPOM), accounting for 47%. Nitrogen in S‐FPOM was found to be supplied mostly by the reservoir plankton (68%). These results collectively suggest that reservoir plankton from dams can greatly influence downstream S‐FPOM composition and play a role in supplying nitrogen to tailwater ecosystems. Our findings on the riverine POM source partitioning in a tailwater channel should be useful in assessing downstream heterotrophic food webs and nutrient transport in response to the plankton‐derived POM originating from upstream reservoirs. Copyright © 2013 John Wiley & Sons, Ltd.

Size-related and seasonal diet of the manila clam (Ruditapes philippinarum), as determined using dual stable isotopes

Stable isotope ratios of lab-cultured Manila clams (Ruditapes philippinarum) and those from natural tidal flats of Seonjae Island in Korea were investigated in terms of their dietary uptake patterns in relation to body size and season. The smallest size group of wild Manila clams revealed significantly depleted δ15N based on the results of a one-way ANOVA. There was significant seasonal change in the proportional contribution of food sources, especially in winter, from benthic particulate organic matter (BPOM) to pelagic particulate organic matter (POM). Laboratory-cultured Manila clams showed growth rates of 6.02–37.75 mm/yr, and smaller-sized clams did not fully utilise the microalgal diets that were provided constantly. Instead, they derived most of their energy from detritus or dead microalgae that had settled on the bottom. Bigger clams, however, exhibited well-balanced source contributions, converting the microalgal diets into biomass. This demonstrates intra-specific differences in the growth rates and preferred diet uptakes of Manila clams, even under similar environmental conditions.

Rotational vegetation burning effects on peatland stream ecosystems

Summary Rotational vegetation burning in peatlands is undertaken predominantly to increase habitat suitability and food availability for red grouse Lagopus lagopus (Linnaeus). Red grouse shooting contributes to the upland economy and is seen as a traditional leisure activity. However, there is concern that burning can have detrimental effects on peatland terrestrial and freshwater ecosystems. This study examined spatial and seasonal dynamics of stream physicochemistry and benthic macroinvertebrates from peatland sites that are managed via rotational vegetation burning and compared these with intact sites with no recent history of burning. Streams draining burned catchments were characterized by higher fine benthic particulate organic matter (FPOM), suspended sediment concentration (SSC), aluminium, iron and dissolved organic carbon than unburnt intact catchments. Anion concentrations were higher in intact catchments. There were significant differences in benthic macroinvertebrate richness, diversity and dominance, and community composition and functional feeding groups between burned and intact catchments, suggesting that land management had an effect on aquatic ecosystems. Higher SSC and FPOM in burned catchments were associated with lower abundance of some mayflies, stoneflies and caddis‐flies and elevated abundance of some Diptera (Chironomidae and Simuliidae) larvae. Synthesis and applications. This study suggests that some aspects of peatland stream ecosystems are altered in catchments with rotational vegetation burning. Currently, there is much emphasis on the effects of rotational burning on peat carbon stores, but this study is the first to document the impacts on stream biota. Agencies with a remit covering upland freshwater ecosystem management might need to consider ways of reducing the extent of rotational vegetation burning to prevent effects on lotic ecosystems, and monitor whether macroinvertebrate assemblages subsequently shift back to a status similar to those in intact peatland streams. Fire occurs commonly on peatlands throughout the world, and our results suggest that trade‐offs are needed to satisfy both economic and ecological facets of the combined social–ecological systems in such areas, especially where fire is implemented as a management tool.

Spatial and Temporal Pattern of Caddisfly Distribution at a Mesohabitat Scale in two Patagonian Mountain Streams Subjected to Pastoral Use

AbstractSubstrate, flow type, nutrients, aquatic vegetation, organic matter, and caddisfly community structure were studied at two low order streams (Glyn and Nant y Fall) subjected to pastoral use in the Patagonian mountains. At both sites, we examined the effect of habitat type (boulder‐pebble with and without filamentous algae, cobble‐pebble, gravel‐sand, leaf‐pack, the submerged macrophytes Myriophyllum quitense and Isoetes savatieri) and season (high and low water period) on caddisfly assemblages. Benthic particulate organic matter (BPOM) ranged between 4.6 and 472 g m–2, all allochtonous detrital fractions were significantly higher at leaf‐packs at Glyn, whereas M. quitense habitats supported more BPOM and macrophytes biomass at Nant y Fall. As expected, boulder‐pebble sustained higher Trichoptera richness than M. quitense and gravel‐sand, moreover all habitats showed higher density than M. quitense at Nant y Fall. According to our results at least nine caddisfly species exhibited some habitat preference with boulder‐pebble and cobble‐pebble the most selected habitat. These particular habitats sustained more than 68% of the total caddisfly species. Multidimensional scaling ordination highlighted differences in composition per habitat for both sites showing a clear distinction among depositional and erosional habitats. Substrate, flow type, detritus biomass were important predictors defining assemblages. Based upon our findings, those anthropogenic actions or stressors that change hydraulic as well substrate attributes in mountain streams such as stock trampling, dredging, clearing of riparian areas, will reduce caddisfly richness. These results are relevant for outline management and conservation biomonitoring and schemes in headwater Patagonian streams as well as other similar environments worldwide (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Food Web Structure of the Alaskan Nearshore Shelf and Estuarine Lagoons of the Beaufort Sea

The eastern Alaska Beaufort Sea coast is characterized by numerous shallow (2–5 m) estuarine lagoons, fed by streams and small rivers that drain northward from the Brooks Range through the arctic coastal plain, and bounded seaward by barrier islands and shoals. Millions of birds from six continents nest and forage during the summer period in this region using the river deltas, lagoons, and shoreline along with several species of anadromous and marine fish. We examined biogeochemical processes linking the benthic community to the overall food web structure of these poorly studied but pristine estuaries, which are largely covered by 1.8 m of ice for 10 months annually. In summer, these lagoons are relatively warm with brackish salinities (5–10°C, S = 10–25) compared to more open coastal waters (0–5°C, S > 27). The stable isotopic composition of organic materials in sediments (i.e., benthic particulate organic matter) and water column suspended particulate organic matter from both streams and lagoons are largely indistinguishable and reflect strong terrestrial contributions, based upon δ13C and δ15N values (−25.6‰ to −27.4‰ and 1.4‰ to 3.3‰, respectively). By comparison, shifts toward more heavy isotope-enriched organic materials reflecting marine influence are observed on the adjacent coastal shelf (−24.8‰ to −25.4‰ and 3.4‰ to 5.3‰, respectively). The isotopic composition of lagoon fauna is consistent with a food web dominated by omnivorous detritovores strongly dependent on microbial processing of terrestrial sources of carbon. Biomagnification of 15N in benthic organisms indicate that the benthic food web in lagoons support up to four trophic levels, with carnivorous gastropod predators and benthic fishes (δ15N values up to 14.4‰) at the apex.

The temporal and spatial distribution of krill (Meganyctiphanes norvegica) at the deep seabed of the Faroe–Shetland Channel, UK: A potential mechanism for rapid carbon flux to deep sea communities

The temporal and spatial distribution of Meganyctiphanes norvegica near the seabed (<5 m above the seafloor) was investigated using remotely operated vehicle (ROV) video footage from eight sites in the Faroe–Shetland Channel. Meganyctiphanes norvegica was most abundant near the seabed at 400–600 m depth, which corresponds to a temperature transitional region between shallower warmer water and deeper cold water. Densities of M. norvegica were significantly lower in the warm water, and no krill were detected at 900–1500 m depth in the cold water. Meganyctiphanes norvegica densities declined at night owing to daily vertical migrations. Time-series analysis showed higher krill densities at 06:00–09:00 and 18:00–21:00 at a depth of 400–480 m and at 12:00–15:00 at a depth of 600 m. A great reduction in krill abundance in winter was detected from both ROV surveys and continuous plankton recorder records. Meganyctiphanes norvegica was observed feeding on benthic particulate organic matter on the seafloor and being consumed by benthic and epibenthic predators. The maximum density of M. norvegica at 480 m depth was 596 ± 261 individuals m–3. This represents a standing stock of 12.8 ± 5.6 g C m–3 with an egestion rate of 0.63 ± 0.28 g C m–3 day–1. Meganyctiphanes norvegica potentially provides an important source of carbon for communities in the deep waters of the Faroe–Shetland Channel.

Bidirectional exchanges of benthic invertebrates in a large river–floodplain system (Paraná River, Argentina)

The flood pulse regime and the hydrological connectivity determine the lateral bidirectional exchanges of water, chemical compounds, and biota between the river and the floodplain habitats. The primary goal of the present research was to analyze the effect of water flow on macroinvertebrates in two water levels in a lateral connectivity gradient, from the main channel through a connection channel to a permanently connected lake. We tested the hypothesis that the water flow from the main channel to the floodplain habitats during high water level causes a decrease in beta diversity between the sites, increasing similarity in the system. To test this hypothesis, we sampled a river–floodplain–lake system of the Middle Parana River during two water levels, and analyzed the spatial and temporal turnover of species between sites and habitats. Local physical characteristics, such as depth, benthic particulate organic matter, and grain size of bottom sediments influenced assemblage composition. Taxa richness, density, and Shannon diversity differed among habitats within the river–lake system, but did not show significant differences between water levels. Richness, density, and diversity were higher in the lake and the connection channel than in the Parana River bank. Beta diversity was significantly higher during high water period. During low water period, benthic assemblage composition was homogenized, as reflected by the lower values of species turnover between the sites situated in the main channel–lake corridor during this phase. The lateral bidirectional exchanges among the habitats are essential for maintaining the specific invertebrate diversity of large river corridors.

Stable isotope variations in benthic filter feeders across a large depth gradient on the continental shelf

Spatial variations in carbon and nitrogen stable isotopes (δ 13C and δ 15N) of benthic filter feeders were investigated on an inshore-offshore gradient (0–250 km) along the continental shelf of the northern Bay of Biscay (NE Atlantic Ocean). δ 13C and δ 15N values were measured in muscle tissues of four filter-feeding mollusc species (epifaunal: Pecten maximus, Aequipecten opercularis; infaunal: Glycymeris glycymeris, Venus casina) and in benthic particulate organic matter along a corresponding water-depth gradient from 6 to 220 m. All four species showed a decreasing pattern of muscle δ 13C and δ 15N values with increasing depth. At the Ushant front (∼130 m water depth), where there is a decrease in both bottom water chlorophyll a and suspended particulate matter, muscle δ 13C and δ 15N values decreased in all species. Although δ 13C values of infaunal clams initially decreased at 30 m depth, δ 13C values of epifaunal scallops decreased around 120 m depth, far below the expected depth reduction in microphytobenthic production suggesting that carbon isotopes might not simply track microphytobenthic utilization. The difference between infaunal and epifaunal bivalve stable isotope values may reflect differences in feeding strategies. Muscle δ 15N values at the deepest stations (∼2‰) were lower than expected considering the typical trophic enrichment value of 3–4‰ between prey and consumers. These low δ 15N values may result from low metabolic rates and suggest the classic trophic enrichment may not hold true in species inhabiting deep waters. Stable isotopes in benthic filter feeders can reveal much information regarding their ecology and environment, but are not straightforward recorders of stable isotope baseline variations as is often assumed.

Catchment‐scale peatland restoration benefits stream ecosystem biodiversity

Summary1. Drainage of peat‐dominated catchments across the world has caused widespread degradation of peat and freshwater ecosystem services. In the UK, an estimated £500 million has been spent over the last decade blocking drains to reverse these changes. The practice raises water‐tables to induce rewetting and promote peat aggradation. However, the potential benefits for impacted ecosystems such as streams remain unknown.2. This study examined stream physicochemistry and benthic macroinvertebrates across peatland catchments with artificial drainage networks, or drains that have recently been blocked, and compared these with intact peatland sites having no history of drainage.3. Streams in artificially drained catchments were characterised by more benthic fine particulate organic matter (FPOM), higher suspended sediment concentrations and finer bed sediments (D50) than in drain‐blocked and intact catchments.4. Drained sites had higher abundance of Diptera (Simuliidae and Chironomidae) larvae, and lower abundance of Ephemeroptera, Plecoptera and Trichoptera larvae, than drain‐blocked sites. In contrast, streams in drain‐blocked catchments had macroinvertebrate communities broadly similar to intact sites in terms of taxon richness, overall species composition and community structure. These changes were associated with lower suspended sediment and benthic FPOM concentrations following drain‐blocking.5. Synthesis and applications. This study has shown changes in the structure of stream benthic macroinvertebrate assemblages linked to increases in benthic particulate organic matter and suspended sediment following peatland drainage. However, these effects seem to be reversible following catchment‐scale restoration by drain‐blocking. Drain‐blocking therefore appears to benefit not only peatland soil, vegetation and hydrological ecosystem services but also stream water quality and biodiversity. The numerous agencies undertaking peatland restoration should consider implementing detailed pre‐ and post‐blocking monitoring of streams to further improve our understanding of the mechanisms through which peatland management affects stream biodiversity and biological recovery dynamics, refine drain‐blocking practices, and inform aquatic conservation and management strategies.

Life cycle phenology, secondary production, and trophic guilds of caddisfly species in a lake-outlet stream of Patagonia

Lake-outlets are transitional areas recognized as highly productive ecosystems in terms of density and biomass of aquatic insects. Life cycle, secondary production, trophic guilds and environmental constraints of caddisfly assemblages were investigated on a natural lake-outlet stream (Nant y Fall) in Patagonia, Argentina. We investigated the site monthly from May 2007 to April 2008 by recording environmental data and sampling caddis larvae using a Surber sampler at riffle areas (n = 36). Mastigoptila longicornuta, Smicridea annulicornis, Smicridea frequens, Brachysetodes quadrifidus and Parasericostoma ovale displayed well synchronized univoltine life cycles, while Neoatopsyche brevispina, Neopsilochorema tricarinatum, showed an asynchronous development pattern, although most of them had an extended recruitment, similar to those reported for non lake-outlet streams in the area. Annual secondary production per species varied from 8.22 (B. quadrifidus) to 3568.83 mg m−2 y−1 (P. ovale), with overall caddisfly production amounting to 4.8 g m−2 y−1. Shredder/collector-filterer ratio was 3.3/1 suggesting that the system was detrital based. Redundancy analysis indicated that seasonally dynamic variables such as discharge, benthic particulate organic matter and temperature were the main predictors of seasonal caddisfly assemblage variation. We propose that the variety of food resources and the significant spatial heterogeneity at lake-outlet streams contribute to sustain a rich caddisfly community.