Connectivity and complexity of floodplain habitats govern zooplankton dynamics in a large temperate river system

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Just add water: sources of chironomid drift in a large river floodplain

Although seasonal floodplains represent one of the most dynamic and productive of aquatic ecosystems, the sources of this productivity are poorly understood. We examined composition and sources of chironomid drift in the Yolo Bypass, the primary floodplain of the Sacramento River. We found that invertebrate drift during winter floodplain inundation is dominated by a single species, the newly identified chironomid Hydrobaenus saetheri (Diptera: Chironomidae). In order to determine sources of chironomids in the Yolo Bypass, invertebrates were sampled from several potential sources prior to and during initial floodplain inundation. Rehydration of dried floodplain sediments from several locations showed that H. saetheri dominated insect emergence from this colonization pathway. By contrast, H. saetheri was not a substantial component of inundated floodplain ponds or of tributary inputs to the floodplain. We conclude that the initial pulse of invertebrate abundance in Yolo Bypass floodwaters is dominated by chironomid emergence from sediments in multiple regions of the floodplain. Handling editor: S. Declerck     

Ecology of invertebrate predators in a Coastal Plain stream

1. The spatial and temporal abundance patterns, production and feeding habits of invertebrate predators were determined in a sand-bottomed, headwater stream in Virginia, U.S.A. 2. Annual mean density and biomass of predators in debris dams were 3897 individuals m^?2 and 2.5 g dry mass m^?2, respectively, but only 711 individuals m^?2 and 0.2 gm^?2 on the sediment. Predator production was 8.36 gm^?2yr^?1 in debris dams compared to 1.52 gm^?2yr^?1 on the sediment. Annual predator production, weighted by habitat availability, was 1.73gm^?2yr^?1. 3. The predominant taxa in terms of production were the chironomids Thienemannimyia spp, complex, Ablabesmyia parajanta, Zavrelimyia sp., and the odonate Cordulegaster maculata. Chironomidae and Odonata together comprised 77% of the production of the predator guild. 4. Based on gut content analysis and calculations of the trophic basis of production, estimated predator production was supported mostly by Chironomidae (38%), detritus (20%), unidentifiable insects (14%), and Ephemeroptera (11%). Total food ingestion by predators was 9.8 gm^?2yr^?1, 63% of which was detritus and 37% of which was animal material on an areal basis. The predator guild consumed an estimated 94% of primary invertebrate consumer production on the channel surface of the stream.     

How to survive six months in a flooded soil: Strategies in Chilopoda and Symphyla from Central Amazonian floodplains∗

Annual, long‐term inundation of flood waters for 5–7 months has led to the development of survival strategies in terrestrial invertebrates of Central Amazonian floodplains. Strategies observed are given for terricolous and arboricolous species and include migrants and non‐migrants. Subadult and advanced juvenile stages of the symphylan Ribauliella amazonica Scheller pass inundation in a dormant state inside tree roots in the flooded soil. Reproduction in this univoltine species is restricted to the non‐inundation period. R. amazonica represents the terricolous non‐migrating invertebrate guild with dormant stages in naturally available retreats under water during annual inundation. The undescribed parthenogenetic centipede Lamyctes sp. is found to hatch from flood‐resistant eggs at the beginning of non‐inundation periods. Development is fast, with the first hemi‐edaphic post‐larvae being captured 6–8 weeks after the floods have receded. Their surface structure does not protect the strongly elevated stigmata from lethal inundation. Lamyctes sp. represents the terricolous non‐migrating invertebrate guild, with dormant egg stages under water during annual inundation.     

The relation between invertebrate drift and two primary controls,discharge and benthic densities,in a large regulated river

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Invertebrate seedbanks: rehydration of soil from an unregulated river floodplain in the south-eastern U.S.

1. We investigated the responsiveness of aquatic invertebrates to rehydration of floodplain soil in a south‐eastern U.S. river floodplain. Non‐inundated soil divots containing invertebrate seedbanks were collected from three floodplain elevations with different inundation histories (inundated for 2, 38, and 78% of a year), and subjected to rehydration (experimental inundation) in aquaria for 10 weeks. 2. Before rehydration, samples were collected to assess the initial density and composition of invertebrates in non‐inundated soil at each elevation. After rehydration, benthic samples were collected biweekly and emergence of aquatic insects was collected weekly from aquaria. 3. The surviving invertebrates were classified as aquatic, semi‐aquatic and terrestrial. Some aquatic invertebrates survived the non‐inundated period in an active state (e.g. Chironomidae and Ceratopogonidae), while others appeared to be dormant (e.g. Heptageniidae, microcrustaceans and Chironomidae). The response for several invertebrates (e.g. Chironominae, Oligochaeta, Collembola and terrestrial invertebrates) depended on the length of rehydration and inundation history. 4. The capacity of aquatic invertebrates to survive and recover was greatest at the most frequently inundated site. Despite variation in floodplain environments, both active and dormant invertebrates persisting in non‐inundated floodplain soil contributed to the floodplain assemblage during flooding. Thus, maintaining the connection between river and floodplain appears to be important in sustaining the invertebrate seedbank and its capacity to recover during inundation. River channelisation and regulation that severs this connection may result in a loss of diversity and abundance.     

The food and daily food consumption of lacustrine 0+ perch, Perca fluviatilis L.

SUMMARY.

• 1 The diet and daily food consumption (C_t) of 0+ perch were investigated in two shallow Scottish lakes.
• 2 The first food comprised the rotifer Keratella sp., Volvox sp., copepod nauplii and stage I copepodites of Cyclops strenuus abyssorum Sars. Larger copepodites and adults of C. s. abyssorum and Diaptomus gracilis Sars were consumed as larvae grew and cladocerans were also eaten by larvae >11 mm. The diet of juveniles included a wider range of cladocerans and benthic invertebrates. Cannibalism was not observed among 0+ perch.
• 3 The range of food items taken by larvae increased with length, and the size of food particles ingested was governed by jaw gape which was linearly related to fish length.
• 4 Larvae fed during daylight hours with feeding maxima in midmorning and the evening.
• 5 The arithmetic (constant) rate of evacuation R of the digestive tract of larvae was 0.59—1.16% of body weight h^?1 and exponential R was 0.21–0.33% h^?1. Daily C_t calculated using an arithmetic model was 14.2–23.4% body weight at water temperatures of 12.5–18.2°C, and 23.9–40.3% utilizing an exponential method. For larvae of 9 mm. this was 46 μg dry weight day^?1 and 148 by an exponential model. Food conversion efficiency was 37–72% (arithmetic model) and 21–45% (exponential model).

     

The relative contributions of refugium types to the persistence of benthic invertebrates in a seasonal snowmelt flood

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What predicts the use by brook trout (Salvelinus fontinalis) of terrestrial invertebrate subsidies in headwater streams?

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A vegetation-based hierarchical classification for seasonally pulsed floodplains in the Okavango Delta,Botswana

A classification scheme is presented for seasonal floodplains of the Boro-Xudum distributary of the Okavango Delta, Botswana. This distributary is subject to an annual flood-pulse, the inundated area varying from a mean low of 3 600 km² to a mean high of 5 400 km² between 2000 and 2006. A stratified random sample of 30 sites was surveyed for species composition and abundance in March–June 2007, using multiple quadrats along transects orthogonal to the floodplain long axis. A combination of indicator species analysis and ordination was used to derive a hierarchical classification system for floodplains, based on species assemblages. Indicator species analysis was used to identify ecologically meaningful levels of division, at four and nine classes. The four main classes of floodplain were: (1) Dry Floodplain Grassland (main indicators Urochloa mosambicensis, Ipomoea coptica, Chloris virgata and Pechuel-Loeschea leubnitziae); (2) Seasonally Flooded Grassland (Nicolasia costata, Eragrostis lappula, Cyperus sphaerospermus and Setaria sphacelata); (3) Seasonally Flooded Sedgeland (Eleocharis dulcis, Leersia hexandra, Oryza longistaminata and Cyperus articulatus); and (4) Seasonal Aquatic Communities (Sacciolepis typhura, Eleocharis variegata, Fuirena pubescens and Cycnium tubulosum). The resultant dendrogram provides an objective routine for classifying floodplains in the Boro-Xudum distributary in an ecologically meaningful way. This classification will assist in monitoring changes in vegetation resulting from hydrological change.     

Spatial variations of microinvertebrates across different microhabitats of temporary floodplains of lower Okavango Delta,Botswana

Temporary floodplains of the Okavango Delta have been suggested as important nursery sites for juvenile fish. Fish production in the Delta is dependent on how well temporary floodplains are maintained. A study was conducted to understand how floodplains function so as to put measures in place that will sustain temporary floodplains in a high productive state. During high floods, distinct microhabitats (open water, sedges and inundated terrestrial grasses) develop in which microinvertebrate community structure was assessed across such habitats during the 2009–2010 flooding season. Depth was highest (ANOVA, P < 0.05) in the open‐water microhabitat and lowest within inundated grasses. Conductivity, total phosphorus and chlorophyll a were all highest (ANOVA, P < 0.05) within inundated grasses than in other microhabitats. A total of 46 microinvertebrate taxa were identified, and they were most diverse within the sedges. The abundance of microinvertebrates was highest (ANOVA, P < 0.05) within the inundated grasses and lowest within the open‐water zone. Given that microinvertebrates are an important food source for juvenile fish, their presence in high densities within inundated terrestrial grasses is a key determinant of fish production. This suggests the need for serious consideration of the importance of temporary floodplains when formulating conservation strategies for the Okavango Delta.     

Habitat alters the effect of false starts on seasonal‐wetland invertebrates

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Growth,lipid content,productivity, and fatty acid composition of tropical microalgae for scale‐up production

Biomass and lipid productivity, lipid content, and quantitative and qualitative lipid composition are critical parameters in selecting microalgal species for commercial scale‐up production. This study compares lipid content and composition, and lipid and biomass productivity during logarithmic, late logarithmic, and stationary phase of Nannochloropsis sp., Isochrysis sp., Tetraselmis sp., and Rhodomonas sp. grown in L1‐, f/2‐, and K‐medium. Of the tested species, Tetraselmis sp. exhibited a lipid productivity of 3.9–4.8 g m^?2 day^?1 in any media type, with comparable lipid productivity by Nannochloropsis sp. and Isochrysis sp. when grown in L1‐medium. The dry biomass productivity of Tetraselmis sp. (33.1–45.0 g m^?2 day^?1) exceeded that of the other species by a factor 2–10. Of the organisms studied, Tetraselmis sp. had the best dry biomass and/or lipid production profile in large‐scale cultures. The present study provides a practical benchmark, which allows comparison of microalgal production systems with different footprints, as well as terrestrial systems. Biotechnol. Bioeng. 2010;107: 245–257. © 2010 Wiley Periodicals, Inc.     

Fish mediate high food web connectivity in the lower reaches of a tropical floodplain river

High levels of hydrological connectivity during seasonal flooding provide significant opportunities for movements of fish between rivers and their floodplains, estuaries and the sea, possibly mediating food web subsidies among habitats. To determine the degree of utilisation of food sources from different habitats in a tropical river with a short floodplain inundation duration (~2 months), stable isotope ratios in fishes and their available food were measured from three habitats (inundated floodplain, dry season freshwater, coastal marine) in the lower reaches of the Mitchell River, Queensland (Australia). Floodplain food sources constituted the majority of the diet of large-bodied fishes (barramundi Lates calcarifer, catfish Neoarius graeffei) captured on the floodplain in the wet season and for gonadal tissues of a common herbivorous fish (gizzard shad Nematalosa come), the latter suggesting that critical reproductive phases are fuelled by floodplain production. Floodplain food sources also subsidised barramundi from the recreational fishery in adjacent coastal and estuarine areas, and the broader fish community from a freshwater lagoon. These findings highlight the importance of the floodplain in supporting the production of large fishes in spite of the episodic nature and relatively short duration of inundation compared to large river floodplains of humid tropical regions. They also illustrate the high degree of food web connectivity mediated by mobile fish in this system in the absence of human modification, and point to the potential consequences of water resource development that may reduce or eliminate hydrological connectivity between the river and its floodplain.     

Food web quantification using secondary production analysis: predaceous invertebrates of the snag habitat in a subtropical river

1. Secondary production was estimated for Plecoptera, Odonata and Megaloptera (mostly large predators) occurring on the snag habitat of a subtropical blackwater river in the southeastern U.S.A. Coastal Plain for 2 years. Production estimates and gut analyses were used in estimating species‐specific ingestion to construct a quantitative food web of the predator portion of the invertebrate assemblage. Neither basal resources (e.g. detritus) nor predaceous vertebrates (e.g. fishes) were considered in this analysis. A discharge‐specific model of snag‐habitat availability was used to convert values per m² of snag surface to values per m² of river bed.
2. These three orders included the major large predators on the snag habitat, as well as two detritivorous stoneflies. The major predators were the hellgrammite (Corydaluscornutus), five perlid stoneflies (Paragnetinakansensis, Perlestaplacida, Neoperlaclymene, Acroneuriaevoluta and Acroneuriaabnormis) and two dragonflies (Neurocorduliamolesta and Boyeriavinosa). The detritivores were Pteronarcysdorsata and Taeniopteryxlita.
3. Total predator production was high, but varied from only 7.1 to 7.4 g dry mass (DM) m^?2 y^?1 of snag surface (2.4–2.7 g DM m^?2 y^?1 of river bed) over two years. Corydalus was the largest predator and had the highest production (2.8–3.1 g DM m^?2 of snag surface). The most productive stoneflies were Perlesta (0.7–1.0 g DM m^?2 of snag surface) and Paragnetina (1.0–1.3 g DM m^?2 of snag surface). The most productive dragonfly was Neurocordulia (0.7–1.9 g DM m^?2 of snag surface). Production of the non‐predaceous stoneflies was 1.0–2.3 g DM m^?2 of snag surface. Production values per m² of river bed were 2–3.5 times lower than the values per m² snag surface.
4. Measurement of ingestion fluxes within the predator portion of the food web showed that predaceous invertebrates were primarily supported by chironomid and mayfly prey. However, the greatest consumption of chironomids and mayflies was by omnivorous hydropsychid caddisflies, which had a considerably higher production than the larger predators. There was a hierarchy of feeding with Corydalus as top predator consuming all other groups, followed in order by dragonflies, stoneflies and hydropsychids. Although the feeding hierarchy suggested the presence of four predatory trophic levels within the invertebrate assemblage, calculations of trophic position indicated there were less than two. With primary consumers (e.g. midges) having a trophic position of 2, Corydalus had a trophic position of only 3.5.
5. A relatively high fraction of invertebrate production was consumed by predaceous invertebrates, ranging from 9 to >100% for various primary consumer groups, with total consumption representing 52% of total production. Because these estimates do not include vertebrate consumption or emergence, it means that a high fraction of larval mortality is due to predation.     

Biology of the rainbowfish,Glossolepis multisquamatus (Melanotaeniidae), from the Sepik River floodplains,Papua New Guinea

Synopsis G. multisquamatus is abundant in the Sepik River, preferring floodplain lakes and marginal areas of floodplain with moderate turbidity. It is the only rainbowfish documented to inhabit river floodplains. Migrations onto and off the floodplain occur in response to changes in flood conditions. Seasonality is evident in reproduction, condition factor and fat deposit and stomach fullness indices; all increasing in the flood season. Fecundity is high compared with stream dwelling rainbowfish species mainly due to decreased egg size. The reproductive strategy ofG. multisquamatus is interpreted as a response to increased adult mortalities encountered on floodplains in comparison to more stable stream habitats occupied by related species.G. multisquamatus is carnivorous, its diet being similar to other rainbowfishes, consisting of a variety of small invertebrates taken from mid-water or the water surface. The ecology and behaviour ofG. multisquamatus is explained as a partial colonisation of newly developed floodplains in this river.     

Production estimates of the benthic invertebrate community in a small Danish stream

Quantitative samples were used to investigate density, biomass and annual production of the benthic invertebrate fauna in a small Danish stream. Forty-eight taxa were found and the total invertebrate densities varied from 3 810 m^?2 in July to 20 040 m^?2 in December. The total mean annual biomass of the invertebrate fauna was 6.1 g ash-free dry wt m^?2. The annual production of the invertebrates was estimated from their mean annual biomass and their annual P/B ratio. Production of the primary consumers (herbivores and detritivores) was 21.4 g ash-free dry wt m^?2 y^?1 and of secondary consumers (carnivores) 1.1 g m^?2 y^?1. The amount of invertebrate production available to the trout population and the importance of the species as food for trout are discussed.     

Secondary production of chironomid communities in insecticide-treated and untreated headwater streams

SUMMARY.

• 1 Production of chironomid communities of three first order, Appalachian Mountain streams was estimated and the effects of an insecticide-induced disturbance on chironomid production was examined.
• 2 Annual production of non-Tanypodinae chironomids in the streams during the first study year (no treatment) ranged from 1366 to 3636 mg m^?2, while production of Tanypodinae chironomids ranged from 48 to 116 mg m ^?2. Production/biomass ratios ranged between 19 and 23 for non-Tanypodinae and from 6 to 7 for Tanypodinae chironomids.
• 3 Insecticide applications resulted in significantly lower chironomid densities and biomass in the treated stream relative to the pretreatment year and reference stream. Annual production of non-Tanypodinae (703 mg m^?2) and Tanypodinae (32 mg m ^?2) chironomids in the treated stream decreased by 64% and 67%, respectively, compared with the pretreatment year. In contrast, production of non-Tanypodinae (2084 mg m^?2) increased by 34% and production of Tanypodinae (96 mg m^?2) by 57% in the reference stream.

     

Lateral hydrological connectivity differentially affects the community characteristics of multiple groups of aquatic invertebrates in tropical wetland pans in South Africa

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Vegetation,invertebrate, and fish community response to past and current flow regulation in floodplains of the Savannah River,Southeastern USA

In 2005 and 2006, the United States Army Corps of Engineers released experimental flows to mimic natural spring flooding on the highly regulated lower Savannah River in the Southeastern US. We used vegetation, invertebrate, and fish communities to assess how past regulation and current experimental releases were affecting the ecological conditions on floodplains. The nearby Altamaha River, of similar size but retaining near-natural spring pulses, served as a reference. We did not find that past flow regulation of the Savannah River had significantly altered floodplain forest structure. However, numbers of tree seedlings in bottomland hardwood forests were higher during a year with an artificial pulse than one without. Analyses of invertebrate and fish communities suggested some limited differences in floodplain community structure between rivers, with differences being most pronounced for predaceous Dytiscidae beetles and Esox spp. fishes. Artificial re-creation of small spring flood pulses down the Savannah River in 2005 and 2006 elicited some responses from fish and invertebrates, but did not shift species assemblages towards those occurring on Altamaha River floodplains.