Amorphous Detritus Research Articles

Temporal Dynamics of Production and Its Trophic Basis in Two Caddisflies (Hydropsyche sp. and Neureclipsis sp.) in Hujiaxi Stream, a Second-Order Stream in Middle China

ABSTRACT During the period of April 2006 to March 2007, we conducted an investigation on life cycle, annual production, and trophic basis of two dominant caddisfly species, Hydropsyche sp. and Neureclipsis sp., in a second order river (Hujiaxi Stream) of the Qingjiang River basin. The two caddisflies both appeared to develop two generations per year, and there was a little overlap in the two generations. The annual production and P/B (production/biomass) ratio were 8.54 g/m2 and 11.44 for Hydropsyche sp. and 0.35 g/m2 and 7.65 for Neureclipsis sp. Foregut content analysis revealed that amorphous detritus constituted the bulk of the diet. The annual average percentage composition was 92.3% for Hydropsyche sp. and 81.1 % for Neureciipsis sp. Animal material, vascular plant detritus, and algae constituted the remainder.

Life History, Secondary Production, and Trophic Basis of Four Dominant Mayflies in a Second Order Stream, Tanqigou Stream, China

ABSTRACT Mayflies were investigated in a second-order montane stream of the Qingjiang River basin, among which Electrogena sp., Indobaetis sp., Choroterpes sp., and Caenis sp. were the dominant species, contributing 92.4% to the total mayfly standing stock. Electrogena sp., Choroterpes sp., and Caenis sp. all developed two generations per year, and there was little overlap with the two generations in each species. Indobaetis sp. had three generations a year. The average annual production of Electrogena sp., estimated by the size-frequency method, was 15.8 g (dry weight)/m2. Indobaetis sp. was 8.8 g/m2, Choroterpes sp. was 1.6 g/m2, and Caenis sp. was 0.9 g/m2. By foregut content analysis, we found that amorphous detritus was the most important food type, accounting for 77.8%-84. 4% of their diets and 62.0%-74.7% of their annual ingestion.

Spatial variability in organic material sinking export in the Hudson Bay system, Canada, during fall

Spatial variations in the sinking export of organic material were assessed within the Hudson Bay system (i.e., Hudson Bay, Hudson Strait and Foxe Basin) during the second oceanographic expedition of ArcticNet, on board the CCGS Amundsen in early fall 2005. Sinking fluxes of particulate organic material were measured using short-term free-drifting particle interceptor traps deployed at 50, 100 and 150 m for 8–20 h at eight stations. Measurements of chlorophyll a (chl a), pheopigments (pheo), particulate organic carbon (POC), biogenic silica (BioSi), protists, fecal pellets and bacteria were performed on the collected material. In parallel, sea surface salinity and temperature were determined at 121 stations in the Hudson Bay system. Three hydrographic regions presenting different sedimentation patterns were identified based on average surface salinity and temperature. Hudson Strait was characterized by a marine signature, with high salinity (average=32.3) and low temperature (average=2.1 °C). Eastern Hudson Bay was strongly influenced by river runoff and showed the lowest average salinity (26.6) and highest average temperature (7.6 °C) of the three regions. Western Hudson Bay showed intermediate salinity (average=29.4) and temperature (average=4.4 °C). Sinking fluxes of total pigments (chl a+pheo: 3.37 mg m −2 d −1), diatom-associated carbon (19.8 mg m −2 d −1) and BioSi (50.2 mg m −2 d −1) at 50 m were highest in Hudson Strait. Eastern Hudson Bay showed higher sinking fluxes of total pigments (0.52 mg m −2 d −1), diatom-associated carbon (3.29 mg m −2 d −1) and BioSi (36.6 mg m −2 d −1) compared to western Hudson Bay (0.19, 0.05 and 7.76 mg m −2 d −1, respectively). POC sinking fluxes at 50 m were low and relatively uniform throughout the Hudson Bay system (50.0–76.8 mg C m −2 d −1), but spatial variations in the composition of the sinking organic material were observed. A large part (37–78%) of the total sinking POC was unidentifiable by microscopic observation and was qualified as amorphous detritus. Considering only the identifiable material, the major contributors to the POC sinking flux were intact protist cells in Hudson Strait (28%), fecal pellets in eastern Hudson Bay (52%) and bacteria in western Hudson Bay (17%). A significant depth-related attenuation of the POC sinking fluxes (average loss between 50 and 150 m=32%) and a significant increase in the BioSi:POC ratio (average increase between 50 and 150 m=76%) were observed in Hudson Strait and eastern Hudson Bay. For all other sinking fluxes and composition ratios, we found no statistically significant difference with depth. These results show that during fall, the sinking export of total POC from the euphotic zone remained fairly constant throughout the Hudson Bay system, whereas other components of the organic sinking material (e.g., chl a, BioSi, fecal pellets, protist cells) showed strong spatial variations.

POPULATION DYNAMICS,LIFE CYCLES,SECONDARY PRODUCTION AND TROPHIC BASIS ANALYSIS OF TWO MAYFLIES IN HEIZHUCHONG STREAM

Mayfly plays an important role in material cycle and energy flow in riverine ecosystem.During June 2003 to June 2004,an investigation on production and its trophic basis of dominant species of mayfly was carried out in a second-order river of the Hanjiang River Basin.There were six types of habitats to sample.Station 1(S1) was in the middle of the stream with big round rocks in the upper reach of the stream,station 2(S2) in the inner part of a weir with cobble substratum,station 3(S3) in the middle of a peacefully flowing section with gravel-sand bottom,station 4(S4) at the side of the riparian with aquatic macrophytes and snags,station 5(S5) in the middle of the riffle and station 6(S6) at the lower reach with a sewage outlet ca 100 meters upper.At each station,two quantitative samples were taken with a 167μm D-frame kick net or a Surber net,and the samples were sieved with a 167μm net,sorted in a dish with naked eye,fixed in 10% formalin for later processing.The life cycle of Leptophlebia sp.and Ephemera sp.was analyzed by the monthly size frequency method,and then cohorts and annual production were estimated.The results showed that Leptophlebia sp.and Ephemera sp.both developed two generations per year.The pupation of Leptophlebia sp.mainly occurred in fall and winter;while pupation of Ephemera sp.mainly in summer and winter;the abundance and biomass of the Leptophlebia sp.reached their highest peaks(913 ind/m2,0.9920g/m2) in October and August,respectively,while the abundance and biomass of the Ephemera sp reached theirs(107ind/m2,2.3639g/m2) in June and March.The cohort production and cohort P/B ratio of the Leptophlebia sp.population were 19.0181 g/m2·a and 5.7,the annual production and P/B ratio were 38.0362 g/m2·a and 11.4.The cohort production and cohort P/B ratio of the Ephemera sp.population were 38.0159g/m2·a and 5.9,the annual production and P/B ratio were 76.0318g/m2·a and 11.8.Gut content analyses showed that both Leptophlebia sp.and Ephemera sp.consumed a large portion of amorphous detritus,constituting 81.7% and 94.6% of their diets and contributing 59.2% and 84.9% to the secondary production.Diatoms were the second important food type of Leptophlebia sp.,averaging 16.8% of the mass and contributing 36.4% to its production,while diatoms merely comprised 1.5% of the diet of Ephemera sp.and contributed 4.1% to the production.

Food Web Structure of Benthic Macrolnvertebrates in a Second Order Stream of the Hanjiang River Basin in Middle China

ABSTRACT Because few detailed invertebrate food webs on riverine ecosystems have been reported in Asia, we undertook a dietary study on Heizhuchong Stream, a second order stream in Hubei Province, China. Dietary information was obtained from foregut content analysis of the dominant benthic macroinvertebrates from June 2003 to June 2004. Allochthonous inputs were the most important food sources for the macroinvertebrate community; amorphous detritus comprised 38.3–98.8% of their diets.

Influence of the Mackenzie River plume on the sinking export of particulate material on the shelf

We examined the influence of the Mackenzie River plume on sinking fluxes of particulate organic and inorganic material on the Mackenzie Shelf, Canadian Arctic. Short-term particle interceptor traps were deployed under the halocline at 3 stations across the shelf during fall 2002 and at 3 stations along the shelf edge during summer 2004. During the two sampling periods, the horizontal patterns in sinking fluxes of particulate organic carbon (POC) and chlorophyll a (chl a) paralleled those in chl a biomass within the plume. Highest sinking fluxes of particulate organic material occurred at stations strongly influenced by the river plume (maximum POC sinking fluxes at 25 m of 98 mg C m − 2 d − 1 and 197 mg C m − 2 d − 1 in 2002 and 2004, respectively). The biogeochemical composition of the sinking material varied seasonally with phytoplankton and fecal pellets contributing considerably to the sinking flux in summer, while amorphous detritus dominated in the fall. Also, the sinking phytoplankton assemblage showed a seasonal succession from a dominance of diatoms in summer to flagellates and dinoflagellates in the fall. The presence of the freshwater diatom Eunotia sp. in the sinking assemblage directly underneath the river plume indicates the contribution of a phytoplankton community carried by the plume to the sinking export of organic material. Yet, increasing chl a and BioSi sinking fluxes with depth indicated an export of phytoplankton from the water column below the river plume during summer and fall. Grazing activity, mostly by copepods, and to a lesser extent by appendicularians, appeared to occur in a well-defined stratum underneath the river plume, particularly during summer. These results show that the Mackenzie River influences the magnitude and composition of the sinking material on the shelf in summer and fall, but does not constitute the only source of material sinking to depth at stations influenced by the river plume.

NUTRIENT ENRICHMENT REDUCES CONSTRAINTS ON MATERIAL FLOWS IN A DETRITUS-BASED FOOD WEB

Most aquatic and terrestrial ecosystems are experiencing increased nutrient availability, which is affecting their structure and function. By altering community composition and productivity of consumers, enrichment can indirectly cause changes in the pathways and magnitude of material flows in food webs. These changes, in turn, have major consequences for material storage and cycling in the ecosystem. Understanding mechanisms and predicting consequences of nutrient-induced changes in material flows requires a quantitative food web approach that combines information on consumer energetics and consumer-resource stoichiometry. We examined effects of a whole-system experimental nutrient enrichment on the trophic basis of production and the magnitude and pathways of carbon (C), nitrogen (N), and phosphorus (P) flows in a detritus-based stream food web. We compared the response of the treated stream to an adjacent reference stream throughout the study. Dietary composition and elemental flows varied considerably among invertebrate functional feeding groups. During nutrient enrichment, increased flows of leaf litter and amorphous detritus to shredders and gatherers accounted for most of the altered flows of C from basal resources to consumers. Nutrient enrichment had little effect on patterns of material flows but had large positive effects on the magnitude of C, N, and P flows to consumers (mean increase of 97% for all elements). Nutrient-specific food webs revealed similar flows of N and P to multiple functional groups despite an order of magnitude difference among groups in consumption of C. Secondary production was more strongly related to consumption of nutrients than C, and increased material flows were positively related to the degree of consumer-resource C:P and C:N imbalances. Nutrient enrichment resulted in an increased proportion of detrital C inputs consumed by primary consumers (from -15% to 35%) and a decreased proportion of invertebrate prey consumed by predators (from -80% to 55%). Our results demonstrate that nutrient enrichment of detritus-based systems may reduce stoichiometric constraints on material flows, increase the contribution of consumers to C, N, and P cycling, alter the proportion of C inputs metabolized by consumers, and potentially lead to reduced ecosystem-level storage of C.

Temporal dynamics of production and ingestion of the dominant mayflies in a subtropical stream in China

We investigated temporal dynamics of secondary production and trophic basis for four dominant mayfly species in a second-order river of the Hanjiang River basin in Middle China from June 2003 to June 2004. The secondary production of the dominant four mayfly species, comprising nearly 90% of the total density of mayflies, was 14.45 g m−2 per year for Ephemera sp., 9.15 g m−2 per year for E. sinensis, 7.23 g m−2 per year for Leptophlebia sp. and 1.55 g m−2 per year for C. nigropunctata. C. nigropunctata and Ephemera sp. had most of their production in winter (from January to March), while E. sinensis and Leptophlebia sp. produced in two intervals, from June to September (summer) and from December of the first year to March of the next year (winter). Overlap in temporal distribution of production among the four mayflies was generally high (>0.60), especially those of C. nigropunctata, Ephemera sp. and Leptophlebia sp. Overlap of Leptophlebia sp. and Ephemera sp. was >0.85. Patterns of the four food types (amorphous detritus, vascular plant detritus, fungi, and diatoms) for each mayfly varied significantly (P < 0.01) over time, and patterns of food ingestion between the four mayflies were also significantly different (P < 0.05–0.01). Among the four main food types, all mayflies used amorphous detritus the most, which constituted 53–96% of their diets and contributed 54–97% to their production. Thus, temporal changes in the food web for mayflies in Heizhuchong stream are quantitative rather than qualitative.

Circadian Changes in Feeding Activity and Diet of Hydropsyche saxonica (Trichoptera)

AbstractCircadian changes in feeding activity and diet of instar IV and V larvae of Hydropsyche saxonica were studied in the Vrbovecký brook (Czech Republic). The larvae were hand‐picked at 6‐hour intervals. The ratio maximum foregut diameter/head capsule width was used to determine gut fullness and the contents of larval foreguts were analyzed using a millipore filter technique. One‐way ANOVA revealed significant differences in gut fullness among instar V larvae collected at different times. Guts were fuller in the larvae collected at dusk and at dawn, indicating high crepuscular activity. No significant temporal differences in gut fullness were recorded for instar IV larvae. There were no significant differences in foregut contents among instar V or among instar IV larvae collected at different times. However, the difference between foregut contents of instar V and IV larvae was significant. Amorphous detritus was the most important food source for instars IV, whereas instars V fed mainly on animal food and cellular detritus. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Production dynamics and life cycle of dominant chironomids (diptera, chironomidae) in a subtropical stream in China: adaptation to variable flow conditions in summer and autumn

The production dynamics and trophic basis of 7 dominant species of chironomids were investigated in the area of a second-order river of the Hanjiang River basin, in central China from June 2003 to June 2004. The results showed that Tvetenia discoloripes was by far the most abundant chironomid, dominating the overall standing stock of the taxa. In terms of lif ecycle, Chaetocladius sp., Eukiefferiella potthasti and T. discoloripes developed 1 generation a year, whereas Microtendipes sp. and Pagastia sp. developed two, while Pentaneura sp. and Polypedilum sp. developed three. T. discoloripes was the most productive chironomid with 120.305 8 g/m2. a, Pentaneura sp. and E. potthasti had relatively high production values of >17 g/m2.a, and the rest were 0.5), especially for filter-collectors Microtendipes sp., Chaetocladius sp., Chaetocladius sp., T. discoloripes and Pagastia sp. All species except Pentaneura sp. consumed a large portion of amorphous detritus, constituting more than 90% of their diets, and contributing nearly 90% to their secondary production. All the 7 chironomids represent obvious adaptation to local highly variable climate in summer and autumn in life cycle pattern, production dynamics, and food type.

Abundance, Life Cycle, Production Dynamics and Trophic Basis of a Dominant Caddisfly (Hydropsyche carbonaria McLachlan) in a Subtropical Stream in China

ABSTRACT During the period of June 2003 to June 2004, we investigated the population dynamics, life cycle, and secondary production and its trophic basis of larvae of a dominant caddisfly Hydropsyche carbonaria McLachlan in a second order stream in the Hanjiang River basin of China. The caddisfly completed two generations in one year and attained its standing stock peaks in January and again in June. The annual secondary production (dry weight) and P/B ratio of the larva estimated by the size-frequency method, were 53.49g/m2 and 9.8, respectively, and most of the production occurred in the winter. The main food types found in the foregut were animal materials and amorphous detritus, comprising of 40.5% and 38.3% of its ingestion, and contributing 64.4% and 23.5% to its production, respectively.

Life history, secondary production and trophic basis of two dominant mayflies in a subtropical stream of China

Mayflies constitute a major part of macroinvertebrate biomass and production in lotic ecosystems, and play an important role in material cycle and energy flow. There are more than 250 species of mayflies in rivers and streams of China. In order to learn their ecological functions, an investigation on life cycle, production and trophic basis of dominant species of mayflies in a second-order branch of Hanjiang River basin, Hubei, China was carried out during June 2003 to June 2004. The results showed that the dominant mayfly species Epeorus sp. and Caenis sp. developed two generations per year; in term of Epeorus sp., putation mainly occurred in spring and then from late summer to early autumn, while Caenis sp. pupated in spring and autumn. The abundance and biomass of the Epeorus sp. population peaked twice (1 226 ind/m2, 3.142 5g/m2) in April and June. Caenis sp. also had two peaks (307ind/m2, 1.590 g/m2), but in February and June. Cohort production and cohort P/B ratio of Epeorus sp. were 161.009 g/m2 wet weight and 7.7, respectively, and annual production and P/B ratio were 267.46g/m2.a wet weight and 15.4, respectively; cohort production and P/B ratio of Caenis sp. were 26.7995g/m2 wet weight and 4.7, its annual production and P/B ratio were 53.60 g/m2.a wet weight and 9.4, respectively. For Epeorus sp., the proportions contributing to secondary production of the main food types were: amorphous detritus, 33.46%; fungi, 10.83%; vascular plant detritus, 1.80%; diatoms, 53.90%; for Caenis sp., the proportions were 70.79%, 6.90%, 3.52% and 18.77%, respectively.

Production Dynamics and Trophic Basis of Dominant Chironomids (Diptera: Chironomidae) in a Subtropical Stream in China

ABSTRACT During the period of June 2003 to June 2004, we investigated production dynamics and trophic basis of seven dominant species of chironomids in a second-order river of the Hanjiang River basin in China. Tvetenia discoloripes was by far the most abundant chironomid, and it was the most productive species, with an estimated annual production of 24.06g • m−2. Pentaneura sp. and Eukieferiella potthasti had production values >3.50 g•m−2, and all other species had values <2.00g • m−2. Temporal distribution patterns of production tended to follow biomass patterns. Tvetenia discoloripes, Chaetocladius sp., and Pagastia sp. concentrated most production in winter, while E. potthasti, Pentaneura sp. and Polypedilum sp. had relatively high production throughout the year. Overlap in temporal distribution of production among the chironomid species was generally high (>0.5), especially for the filter-collectors Microtendipes sp., Chaetocladius sp., T. discoloripes, and Pagastia sp. All species except Pentaneura sp. consumed a large portion of amorphous detritus, constituting more than 90% of their diets and contributing nearly 90% to their secondary production.

Dams and Flow in the Cotter River, Australia: Effects on Instream Trophic Structure and Benthic Metabolism

This study assessed benthic macroinvertebrates and periphyton and its responses to managed river-flows, in riffles downstream of three dams on the Cotter River, Australian Capital Territory. Benthic macroinvertebrates and periphyton were also assessed in adjacent tributaries of the river, as well as in a nearby unregulated river and its tributaries. Food sources of four macroinvertebrate taxa (Leptophlebiidae, Elmidae, Glossosomatidae and Orthocladiinae) were determined by stable isotope analysis of the invertebrates and their potential food, in conjunction with examination of the gut contents of individual invertebrates. Components of benthic periphyton were the main food source for the selected taxa. Orthocladiinae consumed primarily amorphous detritus, while Elmidae, Glossosomatidae and Leptophlebiidae consumed diatoms. Enclosed benthic chambers were used to measure the response of benthic metabolism to monthly flow spikes released from one of the dams. The balance of benthic metabolism as measured by the Production/Respiration ratio (P/R) showed a shift towards production after the release of flow spikes. At sites downstream of the dams, there was more periphyton chlorophyll-a in the form of filamentous green algae than at sites in the unregulated river and the tributaries, and macroinvertebrate taxa using periphyton as a food resource were missing or reduced in abundance relative to sites without dams. However, the site downstream of the dam with environmental flow releases had more macroinvertebrate taxa and less periphyton cholorophyll-a content than sites downstream of dams without managed environmental flows, suggesting that a more suitable food supply resulting from environmental flow releases shifted macroinvertebrate communities towards those of unregulated streams.

Secondary Production and Its Trophic Basis of Two Mayflies (Leptophlebia sp. and Ephemera sp.) in Heizhuchong Stream, Hubei, China

ABSTRACT In a second-order montane stream of the Hanjiang River basin, Leptophlebia sp.and Ephemera sp. appeared to develop two generations per year, and there was little overlap with the two generations in either species. Leptophlebia sp. pupated in autumn and winter, while Ephemera sp. did so in summer and winter. Annual production of Leptophlebia sp., estimated by the size-frequency method, was 7.23 g (dry weight)/m2. The annual production of Ephemera sp. was 14.45 g/m2. The principal food type and major contributor to this production in both mayflies was amorphous detritus (59.2%), while diatoms contributed 36.4% to the production.

Sedimentation following the spring bloom in Disko Bay, West Greenland, with special emphasis on the role of copepods

The sedimentation of particulate organic material was investigated in Disko Bay, West Greenland, during June 2001. Post spring-bloom conditions were encountered, with seasonally decreasing phytoplankton biomass associated with the pycnocline. Calanus finmarchicus, C. glacialis, and C. hyperboreus dominated the zooplankton community, comprising up to 88% of the copepod biomass. Faecal pellet production by C. finmarchicus and C. glacialis was positively correlated to the available food (chlorophyll a > 10 mu m). Results from short-term sediment trap deployments (6 h) showed that particulate organic carbon (POC) sedimentation from the euphotic zone was, on average, 628 mg C m(-2) d(-1), with copepod faecal pellets contributing, on average, 29% of this amount. The faecal pellet contribution to the vertical sinking export of POC was equivalent to that of phytoplankton and amorphous detritus. Yet, on average, 35% of the copepod faecal pellet production was retained within the euphotic zone. The POC: PON (particulate organic nitrogen) ratio of the suspended material in the euphotic zone (8.1 +/- 0.4) was comparable to that of the material collected in the sediment traps just below the euphotic zone (8.0 +/- 0.9). In addition, the daily loss rates of POC and PON within each sampling depth were similar, and the carbon to nitrogen ratio in the sediment traps did not change with depth. These results indicate that the pelagic system had a low retention efficiency of nitrogen just after the spring bloom.

Secondary Production and Its Trophic Basis of Two Mayfly Species in a Subtropical Stream of China

During June 2003 to June 2004, an investigation on life cycle, production and trophic basis of two species of mayfly in a second-order river of Hanjiang River Basin, Hubei, China was conducted. The results showed Epeorus sinensis UMLER and Caenis nigropunctata WU both developed two generations a year. The mean annual production and P/B ratio of E. sinensis were 9.154 g m ‐2 a ‐1 dry weight and 16.0, and those of C. nigropunctata were 1.554 g m ‐2 a ‐1 and 9.6, respectively. For E. sinensis, the proportions contributing to secondary production of the main food types were: amorphous detritus 33.46%, fungi 10.8%, vascular plant detritus 1.8%, diatoms 53.9%; for C. nigropunctata, the proportions were 70.8%, 6.90%, 3.5% and 18.8%, respectively. Compared with those species reported in North America and Europe, although land use mode and local climate were greatly different in China, life history and trophic basis of the mayflies seemed roughly similar, yet secondary production appeared to be much higher.

Secondary production and trophic basis of sinopotamon teritisum in Heizhuchong Stream, Hanjiang Catchment

Macrozoobenthos community plays an important role in material cycle and energy flow in riverine ecosystem. During the period of June, 2003 to June 2004, an investigation on the life cycle and production of the dominant species of macrozoobenthos community in a second-order river of Hanjiang River Basin was carried out. From the upper to the lower reach of Heizhuchong stream, we chose six types of habitats to collect quantitative samples. Station 1 (S1) lied in the middle of the stream with big round rocks in the upper reach, station 2 (S2) was in the inner part of a weir with cobble substratum, station 3 (S3) in the middle of a peacefully flowing section with gravel-sand bottom, station 4 (S4) at the side of the riparian with aquatic macrophytes and snags, station 5 (S5) in the middle of the riffle, station 6 (S6) at the lower reach with a sewage outlet ca 100 meters uppstream. At each station, four quantitative samples were taken with a 167μm D-frame kick net or a Surber net, and the samples were sieved with a 167μm net, sorted in a porcelain dish with naked eye. The specimens were kept in 10% formalin for later processing. The life cycle of the S. teritisum Dai et al. population was analysed by the monthly size-class frequency distribution, the cohort and annual production were estimated by size frequency method. The results showed that S. teritisum completed one generation for nearly 4 years, the reproduction mainly occurred in from middle August to middle October, and most of the senescent individuals died in February. The abundance of the population varied greatly during the year, probably due to the relatively smaller sampling area compared with the strong activity of motion of S. teritisum. Whereas, the variation of the biomass followed the same pattern of the abundance. The a-bundance attained its peak in September with 35 ind/m2, and biomass reached its highest level in June at 41. 7 g/ m2. The estimated cohort production and cohort P/B ratio by size-frequency method were 605.2g/(m2·a) (wet wt) and 5. 5, respectively; the annual production and P/B ratio were 151. 3g/(m2·a) ( wet wt) and 1.4. The reason why the annual production of the animal in Heizhuchong Stream was the relatively higher was because of its high density. By analyzing its stomach content, the proportions of amorphous detritus, caridina, aquatic insect larvae, gastropods and vascular tissues were 45.4% , 10.9% , 35.6% , 5.7% , 8. 1% . Therefore, the contribution rates of the above types of food to production were 10.84% , 18.21% , 59.49% , 9.52% , and 1.94% , respectively.

Secondary production and its trophic basis of five dominant chironomids in Heizhuchong Stream, Hanjiang River Basin

2003年6月至2004年6月间对汉江流域2级河流—黑竹冲河大型底栖动物群落优势种类的生产力进行为期-周年的调查研究,其中主要优势摇蚊中粗腹摇蚊(Pentaneura sp.)和多足摇蚊(Polypedilum sp.)的生活史为-年三代, 小摇蚊(Microtendipes sp.)和帕摇蚊(Pagastia sp.)为-年两代,刺突摇蚊(Chaetocladius sp.)为-年-代.粗腹摇蚊种群生物量和多度在-年中出现两次峰值,多足摇蚊则出现三次,小摇蚊在6月份达到最大峰值,刺突摇蚊在1月份达到最大峰值,帕摇蚊在10月份和次年1月份分别达到次峰值和主峰值.采用龄期频率法(instar-frequency method)测算的周年生产量(鲜重)分别为:粗腹摇蚊,19.9233g/(m²·a),P/B为8.7;多足摇蚊,7.2177g/(m²·a),P/B为8.1;小摇蚊, 0.8996g/(m²·a),P/B为6.0;刺突摇蚊,3.2533 g/(m²·a),P/B为3.4;帕摇蚊,8.5132g/(m²·a),P/B为8.4.除粗腹摇蚊外,其它四种摇蚊的前肠内含物中无形态碎屑所占比例均高于90%,对生产量的贡献率达到77%-96%;粗腹摇蚊的动物性食物所占比例达到14.73%,其对生产量的贡献率高达46.04%.;Macrozoobenthos community plays an important role in material cycle and energy flow in riverine ecosystem. During the period of June, 2003 to.Tune 2004, an investigation on the life cycle and production of the domipant species of macrozoobenthos community in a second-grade river of Hanjiang River Basin was carried out. From the upper reach to the lower reach of Heizhuchong stream, we chose six types of habitats to sample. At each station, two quantitative samples were taken with a 167μm D-frame kick net or a Surber net, and the samples were sieved with a 167μm net, sorted in a porcelain dish with naked eye. The specimens were kept in 10% formalin for later processing. The life cycles of the two dominant chironomids were analysed by the monthly size-class frequency distribution, the cohort and annual production were estimated by size frequency method. The results showed that the Pencaneura sp. and Polypedilum sp. appeared to develop 3 generations for one year, Microtendipes sp. and Pagastia sp. had two generations one year, while Chaetocladius sp. just developed one generation per year, The standing stocks of Pentaneurn sp. and Pagastia sp. had two peaks, that of Polypedilum. sp. had three, while that of Microtendipes sp. and Chaetocladius sp. only had one. The estimated annual production of Pentaneura sp. by size-frequency method was 19. 9233g/(m²·a)(FW), and the P/B ratios was 8.7. The annual production of Polypediluna sp. was 7. 2177 g/(m²·a), and the P/B ratios was 8.1. Annual productiont of Microtendipes sp.was 0.8996g/(m²·a), and P/ B was 6.0;production of Chaecodadius sp. was 3. 2533g/(m²·a), and P/B was 3.4; and that of Pagastia sp. was 8. 5132 g/(m²·a) and 8.4, respectively. By analyzing their fore-gut contents, it was found that all species except Pentaneura sp. consumed a large portion of amorphous detritus, constituting more than 90% of their diets, and contributing 77%-90% to their secondary production.

Patterns of macroinvertebrate abundance in inland saline wetlands: a trophic analysis

We used stable isotopes and gut-content analysis to compare trophic relations of macroinvertebrates between two types of saline wetlands in the Laramie Basin, Wyoming, USA. Amphipods (Hyallela azteca), chironomid larvae, and predatory insects (mainly Zygopteran larvae) occurred in both wetland types. However, in oligosaline wetlands (0.5–5‰ total dissolved solids) amphipods were dominant, whereas in mesosaline wetlands (5–18‰) amphipods were scarce and chironomid larvae and predatory insects were much more abundant. Salinity alone seemed inadequate to explain these differences, so we examined trophic interactions to address three main questions: (1) why are predatory insects more abundant in mesosaline wetlands, (2) why are chironomid larvae less abundant in oligosaline wetlands, and (3) why are amphipods uncommon in mesosaline wetlands? Zygopteran larvae ate mainly chironomid larvae and zooplankton, and did not eat amphipods; chironomid larvae were an average 93 dry mass of zygopteran intake. Guts of amphipods contained no animal parts and little vascular plant tissue, but rather mainly amorphous detritus. Chironomid larvae ate amorphous detritus as well as diatoms. There is potential for competition between amphipods and chironomids, but the nature of amorphous detritus in these wetlands needs further study. Because amphipods appear unavailable as prey for predatory insects, top-down impacts on chironomid larvae may be greater in oligosaline than in mesosaline wetlands. Our results suggest that (1) predatory zygopteran larvae and hemipterans are more abundant in mesosaline wetlands due to more abundant chironomid prey, (2) chironomids are less common in oligosaline wetlands because of both competition with amphipods and greater per capita consumption by predatory insects, and (3) amphipods are scarce in mesosaline wetlands because, lacking a resting stage and mode of direct dispersal, they do not cope well with extremes created by hydrologic instability in mesosaline wetlands. These mechanisms may apply to wetlands in other regions where similar patterns of invertebrate community structure have been reported.