Influence of water quality,local knowledge and river–floodplain connectivity on commercial wild crayfish harvesting in the Atchafalaya River Basin

Water quality and river connectivity influence fisheries, but their role is not understood in wild crayfish harvest, or how water quality and river connectivity are incorporated into crayfish harvest strategies. In Louisiana, wild harvesting practices were evaluated with field observations and interviews with individual harvesters. Field observations included trap locations, water quality, water stable isotopes (2016) and habitat components over two seasons (2015 and 2016). Traps were set in less turbid water (NTU < 69.4), in depths from 1 to 3 m or 3 to 3.6 m and in locations associated with river water inputs. Harvester interviews indicated the importance of tradition (35%‐47% respondents), depth (88% respondents) and water colour (>40% respondents; a surrogate for turbidity and connectivity) in harvesting initiation and trap locations. Harvesters appeared to follow lateral water movements onto and within the floodplain, likely based on local environmental knowledge.     

Disentangling the trophic interactions between American bullfrogs and native anurans: Complications resulting from post‐metamorphic ontogenetic niche shifts

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Trophic structure of a landlocked Arctic char Salvelinus alpinus population from southern Baffin Island, Canada

Gallagher CP, Dick TA. Trophic structure of a landlocked Arctic char Salvelinus alpinus population from southern Baffin Island, Canada. Ecology of Freshwater Fish 2010: 19: 39–50. © 2009 John Wiley & Sons A/S
Abstract –  Stable isotopes, diet and parasites were used to investigate the trophic structure of landlocked Arctic char ( Salvelinus alpinus ) from a small Canadian Arctic lake. Two trophic levels of char were identified. The lower trophic level comprised smaller char that consumed mainly invertebrates and harboured low numbers of the cestode plerocercoid Diphyllobothrium spp. while the higher trophic level char were larger, mainly piscivorous and had high numbers of plerocercoids. Procercoids of Diphyllobothrium spp. in copepods are eaten by char where the parasite then differentiates into a plerocercoid. Plerocercoids from smaller fish are transmitted to larger fish by piscivory where they encyst again as plerocercoids until the fish is eaten by a gull. These plerocercoids are a good indicator of trophic level as their numbers accumulate over time in larger fish. The three variables together provided a better resolution of trophic structure than applied separately. For example, plerocercoid numbers plus diet were better predictors of trophic status than stable isotopes in 4–7 year olds, but for char ≥8 years all three variables were complementary. Some char (≥10 years old) were placed in the lower trophic level based on their stable isotope values and had low Diphyllobothrium spp. abundance but were piscivorous and/or cannibalistic. The absence of sexually mature char in the higher trophic group was associated with high numbers of Diphyllobothrium spp. plerocercoids.     

南昌市大气硫沉降的空间变化和来源

[目的]探讨苔藓组织硫含量和雨水硫酸根浓度的相关性及南昌市大气硫的来源。[方法]在南昌市南昌大学北区、南昌大学前湖校区、电厂、梅岭4个采样点采集石生细叶小羽藓[Bryohaplocladium microphyllum（Hedw.）R.Watanabe et Iwats]样品29个,并在南昌电厂采集煤样9个,然后测定苔藓组织和煤的硫含量和硫同位素值。[结果]南昌大学北区苔藓组织硫含量（0.45%±0.059%）高于南昌大学苔藓组织硫含量（0.26%±0.002%）,能反映南昌市雨水硫酸根浓度变化规律。南昌市苔藓硫同位素的变化范围是-0.64‰～9.71‰,其中南昌市市郊梅岭苔藓组织硫同位素值最高（4.02‰～9.71‰）,明显高于南昌大学前湖校区（0.55‰～0.56‰）和电厂苔藓组织硫同位素值（-0.64‰～0.45‰）。[结论]对苔藓组织硫含量和硫同位素值相关性的研究表明,南昌市大气硫源主要受到中国北方远距离传输硫和生物成因硫的共同影响。     

Seasonality of energy sources of Colossoma macropomum in a floodplain lake in the Amazon – lake Camaleão, Amazonas, Brazil

Abstract  Stomach content and stable isotopes of tambaqui, Colossoma macropomum (Cuvier), were use to determine seasonality of energy sources in a floodplain lake in the central Amazon. The turnover time of carbon in young tambaqui was fast enough to detect a broad seasonal variation both in stomach content and tissue isotopic signal of carbon and nitrogen. The relative importance of food items varied with water level. C₃ plants (seeds and fruits) contributed between 55% and 95% of the biomass fraction of tambaqui. Zooplankton contributed a minimum of 26% of the nitrogen fraction during periods of flooding, and a maximum of 67% in the dry season. C₄ plants (macrophyte leaves and roots) contributed a maximum of 26% of the biomass fraction and 13% of the N fraction mainly during the flooding period. The feeding habits and behaviour of tambaqui are complex and linked to the flood pulse.     

放牧强度对内蒙古荒漠草原土壤碳氮及其稳定同位素的影响

为了探究不同放牧强度对荒漠草原土壤碳氮元素的影响,选取内蒙古希拉穆仁荒漠草原为研究对象,分析3种放牧强度(无牧、轻度放牧、重度放牧)对0～50 cm 土壤有机碳(Soil organic carbon,SOC)、全氮(Total nitrogen,TN)、稳定碳、氮同位素(δ13C,δ15N)的影响.结果表明:随着放牧...     

Do postlarval amphidromous fishes transport marine‐derived nutrients and pollutants to Caribbean streams?

Diadromous fishes are known biotransport vectors that can move nutrients, energy and contaminants in an upstream direction in lotic ecosystems. This function has been demonstrated repeatedly in anadromous salmonids, but the role of other diadromous species, especially tropical taxa, as biotransport vectors is less studied. Amphidromous fish species exhibit potential to act as upstream vectors of nutrients and contaminants in their postlarval and juvenile stages, but this role is largely unknown because of limited understanding of larval growth habitats. Moreover, because some species are harvested in artisanal fisheries as postlarvae, and postlarvae are consumed by riverine and estuarine predators, heavy contaminant loads may present a human or wildlife health concern. This research incorporates stable isotope and contaminant analyses to infer larval habitats and contaminant accumulation of amphidromous fishes on the Caribbean island of Puerto Rico. The isotopic signatures of postlarval amphidromous fishes indicated marine basal sources and food web components, rather than those from riverine habitats. Additionally, postlarvae did not contain concentrations of anthropogenic pollutants that would be of ecological or human health concern. These findings are the first and strongest evidence that amphidromous fish postlarvae function as biotransport vectors of marine nutrients into and up river ecosystems without posing a health threat to the receiving food web or human consumers.     

Latitudinal variation in growth and otolith‐inferred field metabolic rates of Canadian young‐of‐the‐year Arctic charr

Countergradient variation (CGV) is defined as genetic variation that counteracts the negative influences of the physical environment, minimising phenotypic variability along an environmental gradient. CGV is thought to have relevance in predicting the response of organisms to climate variability and change. To test the hypothesis that growth rate increased with latitude, consistent with CGV, young‐of‐the‐year (YOY) Arctic charr, Salvelinus alpinus, were examined along a ~27° latitudinal gradient in central and eastern Canada. Growth rates were estimated from fork lengths standardised by the thermal opportunity for growth based on experienced water temperatures derived using otolith oxygen stable isotopes. Results demonstrated patterns consistent with CGV, where northern populations demonstrated faster growth rates. A secondary aim was to test for similar geographical patterns in otolith‐inferred metabolic rates, which reflect the energetic costs of standard metabolic rate (SMR) and other processes such as feeding, locomotion, thermoregulation, reproduction and growth. Results demonstrated a significant, positive relationship between otolith‐inferred metabolic rate and latitude, which may reflect an increase in one, or a combination, of the above‐noted physiological processes. The similar latitudinal pattern in growth and otolith‐inferred metabolic rates suggests greater intake of food per unit of time by northern fish. The phenotypic variation in physiological traits observed here demonstrates the significant adaptability of Arctic charr to different thermal regimes with different growing season lengths. Determining the relative contributions of phenotypic plasticity and genetic variation to the observed latitudinal variation will be critical to predicting the responses of Arctic charr to climate change more accurately.     

Dynamics of C natural abundance in wood decomposing fungi and their ecophysiological implications

Factors that affect the δ¹³C values of fungi need to be analyzed for the progress of isotope-based studies of food-chain or organic matter dynamics in soils. To analyze the factors that control δ¹³C values of the fungal body, basidiomycete and ascomycete species were grown on a beechwood substrate (six species) and in glucose medium (nine species), and the δ¹³C value of produced fungal body was compared to that of the carbon source. The ¹³C enrichment (Δδ¹³C) in the fungal aggregates compared to the decomposed wood varied from 1.2 to 6.3‰ among six species. In the glucose substrate experiment, the degree of ¹³C enrichment in the hyphal mat was relatively small and varied from −0.1 to 2.8‰ among nine basidiomycetes species depending on their growth stage. Calculated δ¹³C values of the respired CO₂ were lower than those of the hyphal mat, organic metabolites and the glucose used. The degree of ¹³C enrichment was affected by fungal species, substrate and growth stage. Fungal internal metabolic processes are the plausible mechanism for the observed isotopic discrimination between fungal bodies and substrates. Especially, dark fixation of ambient CO₂ and kinetic isotope fractionation during assimilation and dissimilation reactions could well explain Δδ¹³C dynamics in our experiments. Through the analysis of field Δδ¹³C, we could know undisturbed fungal status about starvation, aeration and type of decomposition.