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Ongoing environmental change across the Arctic is affecting many freshwater ecosystems, including small thaw ponds that support macroinvertebrates, thus potentially affecting important forage for fish and bird species. To accurately predict how fish and wildlife that depend on these macroinvertebrates will be affected by ecosystem change at high latitudes, understanding proximate factors that influence macroinvertebrate abundance is critical.To better understand factors that affect spatial and seasonal (i.e. phenology) patterns in abundance, we collected macroinvertebrates throughout the growing season of a single year from 33 thaw ponds on the Arctic Coastal Plain in northern Alaska. We used hierarchical N‐mixture models to provide detection‐corrected estimates of abundance (of the population exposed to sampling) in relation to pond type and seasonal patterns in environmental variables (i.e., cumulative water temperature, nutrient levels) for five taxonomic groups representing key food items for birds and fish—Anostraca (Arthropoda: Branchiopoda), Chironomidae (Insecta: Diptera), Cladocera (Arthropoda: Branchiopoda), Limnephilidae (Insecta: Trichoptera), and Physidae (Mollusca: Gastropoda).For three of five taxa (Anostraca, Cladocera, Limnephilidae), abundance varied across pond types and was lower in pond types where water temperatures increased more rapidly. Further, seasonal temperature profiles in ponds affected phenology, suggesting that seasonal patterns in abundance were influenced by changes in water temperature.These findings suggest that increases in water temperature in northern areas could alter macroinvertebrate phenology, possibly with consequences for upper level predators if availability of macroinvertebrate prey is reduced or shifted seasonally. Our results will facilitate improved predictions of how changing abiotic conditions could affect inland waters in northern areas, a critical need for conservation of Arctic wildlife and ecosystems. [ABSTRACT FROM AUTHOR]

Invertebrate drift is a key process in riverine ecosystems controlling aquatic invertebrate distribution and availability to fish as prey. However, accurately quantifying drifting invertebrates of all sizes is difficult because the fine-mesh nets required to capture the smallest specimens clog easily, which reduces filtration efficiency and measurement accuracy. To address this problem, we developed a gas-powered pump system that delivers 20 m3/hour of river water through nested 80- and 750-μm-mesh nets suspended in the air. We compared 17 pumped samples with those obtained by adjacent, conventional deployment of a 250-μm drift net in a clear-water Alaskan river during both low and high flows. Our drift pump system sampled a geometric mean drift concentration of 467 invertebrates m−3 (maximum 5637 m−3) – eleven times the mean concentration of 42 m−3 estimated using the drift net. Invertebrates ≤ 3 mm long, primarily chironomids, comprised the entire difference between methods. Investigators for whom the drift of 0.5–3 mm invertebrates might be relevant (e.g., those applying foraging models for juvenile drift-feeding fishes) should consider using a pump or similar aerial filtration method to quantify small invertebrate drift, lest they underestimate it by an order of magnitude. [ABSTRACT FROM AUTHOR]

Fluxes of materials or organisms across ecological boundaries, often termed "resource subsidies," directly affect recipient food webs. Few studies have addressed how such direct responses in one ecosystem may, in turn, influence the fluxes of materials or organisms to other habitats or the potential for feedback relationships to occur among ecosystems. As part of a large-scale, multi-year experiment, we evaluated the hypothesis that the input of a marine-derived subsidy results in a complex array of resource exchanges (i.e., inputs, outputs, feedbacks) between stream and riparian ecosystems as responses disperse across ecological boundaries. Moreover, we evaluated how the physical properties of resource subsidies mediated complex responses by contrasting carcasses with a pelletized salmon treatment. We found that salmon carcasses altered stream–riparian food webs by directly subsidizing multiple aquatic and terrestrial organisms (e.g., benthic insect larvae, fishes, and terrestrial flies). Such responses further influenced food webs along indirect pathways, some of which spanned land and water (e.g., subsidized fishes reduced aquatic insect emergence, with consequences for spiders and bats). Subsidy-mediated feedbacks manifested when carcasses were removed to riparian habitats where they were colonized by carrion flies, some of which fell into the stream and acted as another prey subsidy for fishes. As the effects of salmon subsidies propagated through the stream–riparian food web, the sign of consumer responses was not always positive and appeared to be determined by the outcome of trophic interactions, such that localized trophic interactions within one ecosystem mediated the export of organisms to others. [ABSTRACT FROM AUTHOR]

Abstract: This study examined the fluvial transport of invertebrates (aquatic and terrestrial) and coarse organic detritus from forested headwaters in alternatives-to-clearcutting (ATC) harvest units to aquatic habitats downstream in the coastal mountains of southeastern Alaska. Fifty small streams (mean discharge 2.7Ls−1, range 0.1–128.1Ls−1) representing three geographic areas (ATC installations) throughout southeastern Alaska were sampled with 250μm nets three times per year (April, July, September). Samples were used to assess the subsidy of energy from fishless headwaters to downstream systems containing or potentially containing fish, and to obtain preharvest data on streams for the ATC study. Invertebrates of both aquatic and terrestrial origin were captured, with aquatic taxa averaging roughly 3/4 of the total individuals sampled. Invertebrates and detritus were transported from headwaters during all sampling periods, averaging 163mg invertebrate dry mass stream−1 day−1 (1.7mgm−3 water) and 10g detritus stream−1 day−1 (0.05gm−3 water), respectively. Based on the frequency of headwater streams in the watersheds studied, and the average amount of food delivered to downstream habitats by these streams, every kilometer of salmonid-bearing stream could receive enough energy from fishless headwaters to support 100–2000 young-of-the-year salmonids. These results illustrate that headwaters are source areas of aquatic and terrestrial invertebrates and detritus, linking upland ecosystems with habitats lower in the catchment. ATC activities are predicted to have variable effects on headwater stream productivity, and subsequent food resources for downstream salmonids. Partial canopy removal is expected to increase solar penetration to the stream and primary and secondary production within these partially harvested sites, and full canopy removal will likely reduce allochthonous inputs of leaf litter into the streams, and reduce stream invertebrate abundance. [Copyright &y& Elsevier]

1. We examined the export of invertebrates (aquatic and terrestrial) and coarse organic detritus from forested headwaters to aquatic habitats downstream in the coastal mountains of southeast Alaska, U.S.A. Fifty-two small streams (mean discharge range: 1.2–3.6 L s-1 ), representing a geographic range throughout southeast Alaska, were sampled with 250-μm nets either seasonally (April, July, September) or every 2 weeks throughout the year. Samples were used to assess the potential subsidy of energy from fishless headwaters to downstream systems containing fish. 2. Invertebrates of aquatic and terrestrial origin were both captured, with aquatic taxa making up 65–92% of the total. Baetidae, Chironomidae and Ostracoda were most numerous of the aquatic taxa (34, 16 and 8%, respectively), although Coleoptera (mostly Amphizoidae) contributed the greatest biomass (30%). Mites (Acarina) were the most numerous terrestrial taxon, while terrestrial Coleoptera accounted for most of the terrestrial invertebrate biomass. 3. Invertebrates and detritus were exported from headwaters throughout the year, averaging 163 mg invertebrate dry mass stream-1 day-1 and 10.4 g detritus stream-1 day-1 , respectively. The amount of export was highly variable among streams and seasons (5–6000 individuals stream-1 day-1 and <1–22 individuals m-3 water; <1–286 g detritus stream-1 day-1 and <0.1–1.7 g detritus m-3 water). Delivery of invertebrates from headwaters to habitats with fish was estimated at 0.44 g dry mass m-2 year-1 . We estimate that every kilometre of salmonid-bearing stream could receive enough energy (prey and detritus) from fishless headwaters to support 100–2000 young-of-the-year (YOY) salmonids. These results illustrate that headwaters are source areas of aquatic and terrestrial... [ABSTRACT FROM AUTHOR]