Larval Biomass Research Articles

Entomotoxic action of Sambucus nigra agglutinin i in Acyrthosiphon pisum aphids and Spodoptera exigua caterpillars through caspase‐3‐like‐dependent apoptosis

In this project, the toxicity and mechanism of action of the ricin-B-related lectin SNA-I from elderberry (Sambucus nigra) in the pea aphid (Acyrthosiphon pisum) and the beet armyworm (Spodoptera exigua), two important pest insects in agriculture, were studied. SNA-I is a chimeric lectin belonging to the class of ribosome-inactivating proteins and consists of an A-chain with N-glycosidase activity and a carbohydrate-binding B-chain. Incorporation of 2 mg/ml of SNA-I in the diet of neonates and adults of A. pisum caused 40-46% mortality within 2 days, while in third instars of S. exigua, the larval biomass was significantly reduced by 12% after feeding for 3 days on a diet containing 5 mg/g of SNA-I. Interestingly, extracts of the (mid)gut of treated A. pisum and S. exigua demonstrated DNA fragmentation and this was accompanied with an increase in caspase-3-like activity. The involvement of cell death or apoptosis in the entomotoxicity of SNA-I through induction of caspase-3-like activity was also confirmed by addition of the permeable caspase-3 inhibitor III in the diet, leading to a rescue of the treated aphid neonates. Finally, similar to the chimeric lectin SNA-I, the hololectin SNA-II, consisting of two carbohydrate-binding B-chains caused high mortality to neonate A. pisum aphids with an LC₅₀ of 1.59 mg/ml, suggesting that the entomotoxic action of the lectins under study mainly relies on their carbohydrate-binding activity.

Differential effects of elevated nutrient and sediment inputs on survival, growth and biomass of a common larval fish species (Dorosoma cepedianum)

Summary1. Elevated allochthonous inputs of nutrients and sediments to aquatic ecosystems are associated with eutrophication and sedimentation. Reservoirs receive substantial subsidies of nutrients and sediments from catchments due to their large catchment : lake area ratios. We examined the effect of elevated subsidies of sediments and/or dissolved nutrients on the success (survival, growth, biomass and condition factor) of larval gizzard shad (Dorosoma cepedianum), a widespread and dominant omnivorous fish in reservoir ecosystems.2. We simulated allochthonous agricultural subsides by manipulating dissolved nutrients and sediment inputs in a 2 × 2 factorial design in experimental mesocosms. We predicted that larval fish success would be greater under elevated nutrients. However, we propose two alternative hypotheses with respect to the overall effect of allochthonous sediment inputs. If sediment inputs negatively affect larval gizzard feeding success, larval success would be highest when only nutrients are added and lowest when only sediments are added (+N > +N+S ≥ C > +S). If high turbidity enhances larval foraging activity (due to greater contrast between prey and background), we predict that larval success would be highest when both subsidy types (nutrients and sediment) are elevated, intermediate when either nutrients or sediments are added and the lowest when no subsidies are added (+N+S > +N ≥ +S > C).3. Our results indicate that elevated nutrient and sediment conditions enhanced larval gizzard shad biomass, but the overall nutrient addition effect was greater than the sediment addition effect (+N ∼ +N+S > +S > C). We observed differential effects of nutrient and sediment inputs on larval survival, growth and condition factors.4. The enhancement of fish biomass in elevated nutrients (+N, +N+S) relative to control conditions was associated with improved gizzard shad survival and not greater growth. The enhancement of fish biomass in the elevated sediment treatment (+S) relative to the control conditions was caused by an increase in survival that more than compensated for a negative effect of sediment addition on growth.5. Our findings support the recommendation that reservoir management practices must consider the links between land use practices and food web dynamics. Our results suggest that reduction of subsidies of nutrients and sediments to productive reservoirs would decrease survival of larval gizzard shad due to lower food availability.

A trophic pathway from biogenic methane supports fish biomass in a temperate lake ecosystem

Although some primary consumers such as chironomid larvae are known to exploit methane‐derived carbon via microbial consortia within aquatic food webs, few studies have traced the onward transfer of such carbon to their predators. The ruffe Gymnocephalus cernuus is a widespread benthivorous fish which feeds predominantly on chironomid larvae and is well adapted for foraging at lower depths than other percids. Therefore, any transfer of methanogenic carbon to higher trophic levels might be particularly evident in ruffe. We sampled ruffe and chironomid larvae from the littoral, sub‐littoral and profundal areas of Jyväsjärvi, Finland, a lake which has previously been shown to contain chironomid larvae exhibiting the very low stable carbon isotope ratios indicative of methane exploitation. A combination of fish gut content examination and stable isotope analysis was used to determine trophic linkages between fish and their putative prey. Irrespective of the depth from which the ruffe were caught, their diet was dominated by chironomids and pupae although the proportions of taxa changed. Zooplankton made a negligible contribution to ruffe diet. A progressive decrease in δ13C and δ15N values with increasing water column depth was observed for both chironomid larvae and ruffe, but not for other species of benthivorous fish. Furthermore, ruffe feeding at greater depths were significantly larger than those feeding in the littoral, suggesting an ontogenetic shift in habitat use, rather than diet, as chironomids remained the predominant prey item. The outputs from isotope mixing models suggested that the incorporation of methane‐derived carbon to larval chironomid biomass through feeding on methanotrophic bacteria increased at greater depth, varying from 0% in the littoral to 28% in the profundal. Using these outputs and the proportions of littoral, sub‐littoral or profundal chironomids contributing to ruffe biomass, we estimated that 17% of ruffe biomass in this lake was ultimately derived from chemoautotrophic sources. Methanogenic carbon thus supports considerable production of higher trophic levels in lakes.

Treatment with chemical coagulants at different dosing levels changes ecotoxicity of stormwater from the Tahoe basin, California, USA

In recent decades, the transport of stormwater-associated fine particles and phosphorus into Lake Tahoe has led to decreased water clarity and related ecological changes. Polyaluminum chloride coagulants (PACs) have shown great promise in removing these constituents from stormwater before it enters the lake. However, the potential risks of coagulant treatment to aquatic organisms are not well understood. This study investigated stormwater and coagulant toxicity under non-dosed, optimally-dosed, and over-dosed conditions using the US EPA 3-species test through growth of green algae (Selenastrum capricornutum), zooplankton (waterflea, Ceriodaphnia dubia) mortality and reproduction, and larval fish (fathead minnow, Pimephales promelas) mortality and biomass. Stormwater samples were collected during a 2005 spring snowmelt runoff event from three sites representing various forms of developed regions around Lake Tahoe. Samples were dosed with two different coagulants (a chitosan and a PAC) at levels optimized with a streaming current detector (SCD). Non-treated highway runoff was toxic to zooplankton and fish. Optimal coagulant dosing increased algal growth and reduced zooplankton toxicity. Overdosing at two and three times the optimal level of a PAC decreased zooplankton reproduction and increased fish mortality. PAC-related toxicity was correlated with increasing total unfiltered aluminum and decreasing alkalinity, pH, and DOC. Because of toxicity risks, we recommend keeping PAC coagulant dosing at or below optimal levels in practice.

Host Plant Quality ofTamarix ramosissimaandT. parviflorafor Three Sibling Species of the Biocontrol InsectDiorhabda elongata(Coleoptera: Chrysomelidae)

Several sibling species of the leaf beetle Diorhabda elongata (Brullé) have been introduced into North America for the biocontrol of saltcedars (Tamarix spp.), but only one, D. carinulata (Desbrochers), has been extensively used in the field. The first open releases took place in 2001, and widespread defoliation occurred at sites infested by Tamarix ramosissima, T. chinensis, and their hybrid forms. The beetles failed, however, to establish at sites where other Tamarix species are targeted for control. In this study, we compared the preference and performance of three Diorhabda sibling species using adult choice and larval performance experiments on the two formally targeted Tamarix species: T. ramosissima and T. parviflora. In the adult choice experiment, a greater proportion of D. carinulata was found on T. ramosissima than on T. parviflora. For the other two sibling species, D. elongata (Brullé) and D. carinata (Faldermann), adults were found in similar proportions on the two host plants. In the larval performance experiment, larval growth and survival did not differ between Tamarix species for any Diorhabda type; however, D. carinata larval biomass was 35-50% greater than the other beetles regardless of host species. Based on the few adults of D. carinulata found on T. parviflora in the adult choice experiment, we do not recommend introducing this beetle at sites where T. parviflora is targeted for biological control. The species D. carinata seems especially promising for future release because its larvae gained substantially more biomass than the other beetles during the same time period on both Tamarix species.

Breeding success and lutein availability in great tit ( Parus major)

The relationship among temporal variation in the availability of carotenoid-rich food, tissue carotenoid levels and breeding success are poorly known. We studied how diet quality and quantity affect the carotenoid profile and fledging success of great tit ( Parus major) nestlings along a pollution gradient. We found declining seasonal trend in lutein concentration of caterpillars, which may be the explanation for the declining trend in nestlings' lutein concentration of plasma with season, despite the increase in caterpillar biomass. This may be because the biomass of most lutein-rich caterpillars (autumnal moths) decreased and less lutein-rich caterpillars (sawflies) increased during the breeding season. The temporal difference in occurrence of different caterpillar species means that peak lutein availability does not coincide with peak caterpillar abundance. However the positive association between total larval biomass and the number of great tit fledglings may suggest that fledging success depends more on total caterpillar availability than on lutein concentration of caterpillars.

From lecithotrophy to planktotrophy: ontogeny of larval feeding in the Amazon River prawn Macrobrachium amazonicum

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 7:19-30 (2009) - DOI: https://doi.org/10.3354/ab00180 From lecithotrophy to planktotrophy: ontogeny of larval feeding in the Amazon River prawn Macrobrachium amazonicum Klaus Anger1,*, Liliam Hayd2 1Biologische Anstalt Helgoland, Alfred-Wegener-Institut für Polar- und Meeresforschung, Meeresstation, 27498 Helgoland, Germany 2Universidade Estadual de Mato Grosso do Sul, Campus de Aquidauana, 79200-000 Aquidauana, MS, Brazil *Email: klaus.anger@awi.de ABSTRACT: During downstream transport from rivers to estuaries, early larval stages of the Amazon River prawn Macrobrachium amazonicum (Heller 1862) are likely exposed to planktonic food limitation. In the laboratory, we studied the effects of presence or absence of food on larval survival, moulting and biomass (dry mass, and content of carbon, hydrogen and nitrogen). Unfed larvae developed successfully from hatching of the Zoea I (Z I) to the third zoeal stage (Z III). Complete absence of starvation effects indicated obligatory lecithotrophy in Z I, while significantly delayed moulting and reduced biomass in unfed Z II proved that this stage is facultatively lecithotrophic. Although unfed Z III did not develop any further (obligatory planktotrophy), they still showed a high endotrophic potential, surviving for up to another 10 d (in total 2 wk from hatching), and utilizing about two-thirds of their initial biomass. Dramatically decreasing C:N ratios in unfed larvae suggest an almost complete metabolic degradation of internal lipid stores (visible as fat droplets in the hepatopancreas region), but little protein mobilization. Larvae obtained from 2 different females differed significantly in biomass at hatching and, correspondingly, also in maximum survival time, delay of moulting to the Z III and average rates of biomass utilization. In conclusion, the early larval stages of M. amazonicum depend very little on food, shifting from completely non-feeding behaviour (Z I) through facultative lecithotrophy (Z II), to planktotrophy (later stages). This ontogenetic pattern may be an adaptation to initial food limitation associated with larval export from limnic to estuarine environments. KEY WORDS: Palaemonid shrimp · Larval feeding · Lecithotrophy · Starvation · Larval growth · Dry mass · CHN Full text in pdf format PreviousNextCite this article as: Anger K, Hayd L (2009) From lecithotrophy to planktotrophy: ontogeny of larval feeding in the Amazon River prawn Macrobrachium amazonicum. Aquat Biol 7:19-30. https://doi.org/10.3354/ab00180Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 7, No. 1-2. Online publication date: August 19, 2009 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2009 Inter-Research.

Variation in Endophyte–Plant Associations Influence Black Cutworm (Lepidoptera: Noctuidae) Performance and Susceptibility to the Parasitic NematodeSteinernema carpocapsae

This study examined how variability in Neotyphodium endophyte-grass associations influences black cutworm Agrotis ipsilon Hufnagel performance and susceptibility to the entomopathogenic nematode Steinernema carpocapsae (Weiser). Second-instar cutworm larvae were confined to greenhouse pots containing four different tall fescue Schedonorus phoenix (Scop.) Holub cultivars. After 1 wk, larvae were recovered from the pots, weighed, and individually exposed to 20 infective juvenile nematodes. Nematode-induced mortality was monitored for 72 h after exposure. Endophyte infection levels and ergot alkaloid concentrations varied between tall fescue cultivars, but endophyte infection level was not a significant predictor of ergot alkaloid concentrations in above-ground plant tissue. Larval survival also varied between cultivars, but neither endophyte infection level nor ergot alkaloid concentration was a significant covariate. Larval susceptibility to the entomopathogenic nematode varied between cultivars at 48 and 72 h after exposure. In all but one cultivar (Plantation), cumulative mortality at 72 h decreased significantly as ergot alkaloid concentrations increased. Neither larval biomass nor endophyte infection levels in tall fescue were significant predictors of larval susceptibility to the nematode. Results show that variation in endophyte-plant associations can influence black cutworm performance and susceptibility to entomopathogenic nematodes and that susceptibility to the nematode H. bacteriophora may be partially tied to ergot alkaloid levels in the insects' food. Findings further support the assertion that black cutworm may use certain endophyte-mediated toxins, particularly ergot alkaloids, as a form of acquired chemical defense against nematode-induced septicaemia.

High-frequency coastal upwelling events influence Octopus vulgaris larval dynamics on the NW Iberian shelf

Planktonic larval dispersal affects the structure, management, and conservation of many fish and coastal invertebrate populations. The dynamics in coastal upwelling areas favour transport of larvae to the open ocean during upwelling episodes, and concentration of larvae in coastal waters un- der upwelling relaxation or downwelling conditions. Recent work provides evidence that pelagic lar- val stages in upwelling areas are influenced by specific larval behaviour, biogeography, and life his- tory parameters among others. Nevertheless, very few of these studies have addressed these findings quantitatively. Here, we present a general approach for assessing the influence of high-frequency up- welling events on Octopus vulgaris planktonic larvae. Specifically, we analyse the rates of change in abundance and biomass of the O. vulgaris early larval phase in the NW Iberian coast, where upwelling events occur with a frequency of 10 to 20 d from April to September. Our analysis indicates that the in- crease in larval abundance and biomass is significantly correlated with the simultaneous decrease of water column integrated nitrate, ammonium and chlorophyll levels. These conditions occur during the early stage of the relaxation phase of coastal upwelling events, when nutrient salts are consumed to produce biogenic matter, which is retained in the system and transferred through the food web.

Growth and Survival of a Tropical Polyphagous Caterpillar: Effects of Host and Group Size

Abstract. An experiment at Estacion de Biologia Chamela in western Mexico addressed the consequences of social behavior on growth and survival of Hylesia lineata Druce caterpillars. Three of the primary hosts (Casearia corymbosa HBK, Thouinia paucidentata Radlk., and Erythroxylum havanense Jacq.) were used as experimental plants. Because caterpillars usually build shelters with leaves from their hosts, it was suspected that differences in leaf size, leaf form, and branching pattern among hosts could promote contrasting effects on larval performance. In addition, H. lineata caterpillar colonies usually are formed of dozens to hundreds of individuals, suggesting strong differences in larval performance because of group size and social interactions. During a period of 21 days, accumulation of larval biomass was greater on C. corymbosa than on T. paucidentata or E. havanense. Group size had a strong effect on growth of H. lineata larvae. Caterpillars accumulated more biomass when kept in larger groups than in...

Patterns of larval growth and chemical composition in the Amazon River prawn, Macrobrachium amazonicum

The Amazon River prawn, Macrobrachium amazonicum (Heller, 1862), is a target species for regional fisheries in Brazil and a candidate for aquaculture. Under controlled laboratory conditions (29 °C, 10‰), the larval phase of this species shows variability in the morphology and number of successive stages (mostly 9–10, occasionally 8 to > 12). In the most commonly observed developmental pathway (9 stages, taking approximately 20–22 days from hatching to the first juvenile stage), we studied patterns of larval growth in terms of total body length (TL), carapace length (CL), dry mass (W), and elemental composition (carbon, hydrogen, nitrogen; collectively CHN). At hatching, about 12% of late embryonic W, 15–18% of C and H, but only 7% of N were lost, indicating higher losses of lipids and/or carbohydrates than proteins. Significant variability was observed in the initial biomass and elemental composition of newly hatched larvae from 20 different egg batches. This may cause variation in the endotrophic potential of the early stages, as the zoea I of this species is a non-feeding stage, and also the zoea II may still utilize internal energy stores remaining from the egg yolk. Lacking or low larval feeding activity from hatching through stage II coincided with low initial growth. Concomitantly, the proportions of C and H (in % of W) as well as the C:N ratio decreased from hatching through stage IV, indicating a utilization of stored lipids. The percentage of N showed an opposite pattern, reflecting protein synthesis associated with morphogenesis. Size growth showed maximum increments per moult in the late zoeal stages (III–VI), followed by lower increments in the subsequent decapodid stages (VII–IX). This sigmoidal growth pattern may reflect ontogenetic changes in morphometric relationships. Biomass showed exponential patterns of increase from zoeal stage III throughout later larval development and in the first two juvenile stages. Furthermore, patterns of larval growth in M. amazonicum are characterized as linear relationships between larval W in stage n and that in stage n + 1 (Hiatt diagram), between larval size (CL) and biomass (W, C), and between W and either C or N. Using CHN data, we also provide estimates of the protein and lipid contents of larval biomass (ca. 38–46% and 10–12% of W, respectively). High survival, rapid development, and predictable patterns of larval growth support the assumption that M. amazonicum should be a suitable species for production in aquaculture.

Arthropod diversity sheltered in Thaumetopoea pityocampa (Lepidoptera: Notodontidae) larval nests

In pine ecosystems, the role of the larval nests of the Mediterranean defoliator Thaumetopoea pityocampa as shelter of other arthropods, was studied for the first time. In Portugal, Pinus stands which differed in understorey plant diversity and level of attack by T. pityocampa were compared. 2. The arthropod fauna found sheltering inside the nests consisted of 60 species, representing 12 foraging types. Both arthropod richness and abundance were positively correlated with nest size, expressed as larval biomass. Arthropod richness was further positively correlated with understorey plant diversity, while no correlation was detected between arthropod richness and nest density. 3. Spiders accounted for up to 50% of the species richness, while 80% of the individuals collected were either juveniles, or females with brood, implying that T. pityocampa nests are used for overwintering and brood care. Seventy-six per cent of the Araneae were nocturnal ground foragers and specialised cryptic hunters, demonstrating the occurrence of indirect interactions among species belonging to different communities, namely ground vegetation layers and forest pine coppice. 4. It was concluded that, in Mediterranean pine ecosystems, T. pityocampa nests (i) create habitat diversification and contribute to improve overwintering survival of a wide range of arthropod species; (ii) play a functional role in the food web of pine ecosystems, by promoting indirectly mediated interactions among species from different communi- ties; and (iii) do not contribute to create habitat for symtopic phytophagous arthropods, since contrary to literature references for different types of shelters, 98% of the associ- ated species belonged to foraging types other than T. pityocampa.

Life history and production of the riffle beetle, Stenelmis crenata (Say, 1824) (Coleoptera: Elmidae), in a tallgrass prairie stream

We examined life history dynamics and estimated production of the riffle beetle, Stenelmis crenata (Say, 1824), in a tallgrass prairie stream. Stenelmis crenata had a univoltine life cycle with larvae present year-round. Recruitment of first instars occurred from June–October, larval growth was synchronised through the winter, pupation occurred in late spring, and adults first appeared in late May. Adults were most abundant (24 individuals/m2) during summer and were present in samples through October. For larval biomass and production estimates, a body length–mass relationship (ash-free dry mass [AFDM] = 0.0079*TL2.7595) was constructed. Mean annual density and biomass of larvae were 235 individuals/m2 and 90.7 mg AFDM/m2, respectively. Annual larval production was 493 mg/m2/y, representing a total of ∼101 g AFDM for the stream reach examined. Production estimates for S. crenata in this stream were high compared to other estimates for elmids, and this species comprised an appreciable portion of total scraper (13.5%) production.

A new method to measure substrate coherent strength of Stenopsyche marmorata

We developed a method for estimating the substrate coherent strength of a net-spinning caddis larva, Stenopsyche marmorata, in the field. Plastic experimental cages (prefabricated containers with 5-mm mesh; 0.1 m high, 0.12 m wide, 0.2 m long) that enclosed gravel substrate and an objective stone (5–6 cm in diameter) were prepared. We expected the caddisflies to build a retreat(s) between the objective stone and cage substrate when submerged in a riffle channel reach for 6 days. Ten final-instar larvae (4–5 cm long) were placed in the cage and allowed to form retreats. Two treatments (cages with and without larvae) with 15 replicates each were used in two experimental trials. The vertical lift-force of objective stones associated with a retreat (coherent strength) was measured using a spring weighing scale. In 87% of 30 cages of with-larvae treatment, retreats were formed between the objective stone and cage substrate. Coherent strength ranged from 0.0 to 1.6 kg. Our approach can be used under varying flow velocities, substrate conditions, and larval biomass, all of which are normally difficult to test in flume experiments. Findings based on our field method provide unique physical properties of the caddisfly retreats in stream ecosystems.

Changes in periphyton abundance and community structure with the dispersal of a caddisfly grazer, Micrasema quadriloba

We examined the larval population densities and biomass of a caddisfly grazer, Micrasema quadriloba, and the abundance and community structures of periphyton at a segment scale (7.4 km with four study sites), along a second-to fourth-order Japanese mountain stream throughout the grazer’s life cycle. In the uppermost riffle of the study segment (site 1), periphyton abundance was kept at low levels when the larvae occurred. The larval distribution spread downstream as larvae developed from first instars in May to fifth instars in January. We performed multiple regression analyses to test the effects of environmental variables and larval biomass on periphyton abundance in both the riffle of site 1 and the study segment; the results revealed that the larval biomass was significantly negatively correlated with periphyton abundance similarly in both the riffle and the study segment. In addition, both the correlation and community analyses showed that the larval biomass was significantly negatively correlated to the relative abundance of large and/or filamentous microalgae, which appeared in the uppermost layer of the periphyton mat, and that larval biomass was significantly positively correlated to the relative abundance of small diatoms, which strongly adhered to the substrate. Thus, the present study implied that the grazing of M. quadriloba larvae would regulate the abundance of periphyton in a riffle and also regulate the abundance and community structure of periphyton at the segment scale with the expansion of their longitudinal distribution.

On the ecology of the filter-feeding Neureclipsis bimaculata (Trichoptera, Polycentropodidae) in an acid and iron rich post-mining stream

Open-pit mining of lignite in East Germany has created landscapes with extreme environmental conditions. Post-mining aquatic habitats are characterized by low biodiversity and simple food webs due to the impact of acid mine drainage. In this study, the ecology of the filter-feeding caddisfly Neureclipsis bimaculata (L.) was examined, which is abundant in the acidic Flosgraben stream (pH 2.5–3.6) in Lower Lusatia, Germany. From benthic samples, we measured larval size and biomass and estimated population dynamics. The seston drift was sampled and retention efficiency of the larvae’s nets was assessed in a field tracer experiment to evaluate diet availability. Mean annual abundance was 1,380 ind m−2 with a biomass of 1,010 mg m−2. Annual secondary production of N. bimaculata was 8,450 mg m−2. The larval microdistribution reflected the preference for in-stream wood and a limitation by low flow velocity. Morphometric factors of the larvae in the acidic stream were in the range of morphometric factors found in circumneutral streams that covered a range of trophic levels. Although coverage by iron particles reduced flow, the nets account for 63% of the mean particle retention. It is suggested that the retention efficiency and the availability of drifting organisms allowed the larvae to feed on 8.4 mg m−2 per day, which revealed a ratio of biomass production to ingested food of 60%.

Estimating larval density in cod ( Gadus morhua) first feeding tanks using measurements of feed density and larval growth rates

Due to unpredictable mortality in larval cod rearing, a reasonably accurate estimate of the larval biomass in rearing tanks is important for production management such as determination of feed doses and planning of live feed production. A good estimate of larval numbers can also give an early warning if a larval group is suffering high mortality. Because direct measurement of the larval density is difficult, a model based estimator is developed to estimate the larval density from parameters that are simpler to measure, such as feed density and larval size. The estimator is based on an extended Kalman filter using measurements to update a process model. The estimator was tested by acquiring data on feed densities and larval growth rates in a first feeding experiment on cod. Cod larvae were reared from hatching up to day 16 post hatch in nine 160 l tanks at three different densities. The larvae were fed with rotifers ( Brachionus plicatilis) from day 3 until the end of the experiment. Results show that the estimator is able to correctly detect differences in larval density.

Methane‐derived carbon flows through methane‐oxidizing bacteria to higher trophic levels in aquatic systems

Recent investigations have shown that biogenic methane can be a carbon source for macro invertebrates in freshwater food webs. Stable carbon isotopic signatures, used to infer an organism's food source, indicated that methane can play a major role in the nutrition of chironomid larvae. However, the pathway of methane-derived carbon into invertebrate biomass is still not confirmed. It has been proposed that chironomid larvae ingest methane-oxidizing bacteria (MOB), but this has not been experimentally demonstrated to date. Using (13)C-labelled methane we could show for the first time that chironomid larvae assimilate methane-derived carbon through MOB. Chironomid larval biomass was significantly (13)C-enriched after dwelling for 10 days in lake sediment enriched with labelled methane. Moreover, phospholipid fatty acids diagnostic for MOB were detected in larval tissue and were significantly (13)C-enriched, which encompasses the (13)C-uptake predicted for a methane-based nutrition. Additionally, chironomid larvae fed on sediment and water-column derived MOB biomass.

Aquatic and terrestrial invertebrate drift in southern Appalachian Mountain streams: implications for trout food resources

Summary1. We characterised aquatic and terrestrial invertebrate drift in six south‐western North Carolina streams and their implications for trout production. Streams of this region typically have low standing stock and production of trout because of low benthic productivity. However, little is known about the contribution of terrestrial invertebrates entering drift, the factors that affect these inputs (including season, diel period and riparian cover type), or the energetic contribution of drift to trout.2. Eight sites were sampled in streams with four riparian cover types. Drift samples were collected at sunrise, midday and sunset; and in spring, early summer, late summer and autumn. The importance of drift for trout production was assessed using literature estimates of annual benthic production in the southern Appalachians, ecotrophic coefficients and food conversion efficiencies.3. Abundance and biomass of terrestrial invertebrate inputs and drifting aquatic larvae were typically highest in spring and early summer. Aquatic larval abundances were greater than terrestrial invertebrates during these seasons and terrestrial invertebrate biomass was greater than aquatic larval biomass in the autumn. Drift rates of aquatic larval abundance and biomass were greatest at sunset. Inputs of terrestrial invertebrate biomass were greater than aquatic larvae at midday. Terrestrial invertebrate abundances were highest in streams with open canopies and streams adjacent to pasture with limited forest canopy.4. We estimate the combination of benthic invertebrate production and terrestrial invertebrate inputs can support 3.3–18.2 g (wet weight) m−2 year−1 of trout, which is generally lower than values considered productive [10.0–30.0 g (wet weight) m−2 year−1].5. Our results indicate terrestrial invertebrates can be an important energy source for trout in these streams, but trout production is still low. Any management activities that attempt to increase trout production should assess trout food resources and ensure their availability.

Linking stream habitats and spider distribution: spatial variations in trophic transfer across a forest–stream boundary

AbstractIn headwater streams, many aquatic insects rely on terrestrial detritus, while their emergence from streams often subsidizes riparian generalist predators. However, spatial variations in such reciprocal trophic linkages remain poorly understood. The present study, conducted in a northern Japanese stream and the surrounding forest, showed that pool–riffle structure brought about heterogeneous distributions of detritus deposits and benthic aquatic insects. The resulting variations in aquatic insect emergence influenced the distributions of riparian web‐building spiders. Pools with slow current stored greater amounts of detritus than riffles, allowing more benthic aquatic insects to develop in pools. The greater larval biomass in pools and greater tendency for riffle insects to drift into pools at metamorphosis resulted in an emergence rate of aquatic insects from pools that was some four to five times greater than from riffles. In the riparian forest, web‐building spiders (Tetragnathidae and Linyphiidae) were distributed in accordance with the emergence rates of aquatic insects, upon which both spider groups heavily depended. Consequently, the riparian strips bordering pools had a density of tetragnathid spiders that was twice as high as that of the riparian strips adjacent to riffles. Moreover, although limitations of vegetation structure prevented the aggregation of linyphiid spiders around pools, linyphiid density normalized by shrub density was higher in habitats adjacent to pools than those adjacent to riffles. The results indicated that stream geomorphology, which affects the storage of terrestrial organic material and the export of such material to riparian forests via aquatic insect emergence, plays a role in determining the strength of terrestrial–aquatic linkages in headwater ecosystems.