Trophic structure of fish assemblages in the lower Miranda River, Pantanal, Mato Grosso do Sul State, Brazil

Of a total of 101 fish species caught in the Lower Miranda River floodplain, 29 were omnivorous, 16 ichthyophagous, 12 herbivorous, 18 detritivorous, 8 zooplanktophagous, 7 insectivorous, 2 lepidophagous, 4 ichthyophagous/insectivorous and 4 zooplanktophagous/insectivorous. Almost half of the species belong to omnivorous and detritivorous trophic guilds. The same is not true when biomass is considered. The number of fish species by trophic guild didn't change along the year whereas the biomass changed significantly. The frequency of abundant fish species was not the same for the sampled environments.     

Spatial patterns of epilithic algal and detrital resources on a windward coral reef

Algae and detritus co-occur on reef substrata, but their relative importance to consumers, in terms of biomass and nutrient content, is poorly understood. Epilithic algae, sediment and detritus were sampled among four windward zones at Lizard Island, Australia, using a vacuum sampler. Total N, P and biomass (total organic C) were quantified for algae and detritus. Algal and detrital biomass varied among zones and both were positively correlated with sediment load. Algal biomass was approximately six times higher than detritus on the reef crest. In other zones, the two components were more similar in abundance. Particulates on the reef crest had the highest organic:inorganic ratios, a feature likely to be favoured by herbivorous and detritivorous fishes. C:N ratios of algae and detritus, while locally variable, were broadly comparable among zones. C:P ratios of both components decreased in leeward zones. Although locally variable, detritus had a higher content of both N and P. Overall, detritus is relatively abundant on windward reef substrata and of equal or greater nutritional quality than algae. It represents a potentially important resource for both detritivorous and herbivorous fishes.     

Do fish regulate phytoplankton in shallow eutrophic Northeast Brazilian reservoirs?

SUMMARY 1. In a comparative study, we examined the potential for fish to structure planktonic food webs in shallow mesotrophic to hypereutrophic Northeast Brazilian reservoirs. The food webs were dominated by three guilds of fish (facultative piscivores, generalist planktivores and omnivores), small herbivorous zooplankton and bloom‐forming cyanobacteria, with few littoral macrophytes. 2. A principal component's analysis on data from 13 reservoirs (27 sampling dates in 1995–99) revealed that euphotic depth, the relative density of phytoplankton (i.e. the percentage of overall phytoplankton density) represented by cyanobacteria, and the relative biomass of fish (i.e. percentage of overall biomass) represented by omnivores and facultative piscivores, explained most of the variance in the data. Physico‐chemical conditions, lake morphometry and rainfall were secondary factors. 3. Phytoplankton was related to fish guild structure. Chlorophyll concentration increased with total phosphorus and the relative biomass of omnivorous fish, decreased with the relative biomass of facultative piscivores, but was unrelated to the biomass and mean body size of herbivorous zooplankton. Chlorophyll concentration and the densities of filamentous and colonial cyanobacteria decreased with the ratio of the biomass of facultative piscivores to that of omnivores (FP : OM). 4. We propose two complementary mechanisms for the observed relationships between fish and phytoplankton. At a low biomass of facultative piscivores, juvenile zooplanktivorous fishes may induce a trophic cascade on zooplankton in the littoral zone. Regardless of piscivore biomass, piscivores and omnivores may regulate phytoplankton via multichannel omnivory because of the predominance of omnivorous or detritivorous foraging behaviour. 5. Manipulative experiments are needed to explore further whether, depending on priorities in the use of the reservoir, fisheries management could alter the FP : OM ratio either to enhance fish yields or to reduce phytoplankton densities and cyanobacterial blooms.     

Multiscale habitat associations of detrivorous blennies (Blenniidae: Salariini)

The distribution and habitat associations of detrivorous blennies on a tropical coral reef were investigated at several spatial scales and compared with other fish that feed on the epilithic algal matrix to assess density and biomass contributions of small detrivorous fishes to these assemblages. At broad spatial scales total blenny abundance and biomass were highest on the tops of reefs exposed to prevailing winds. On the finer scale of microhabitat use, all species showed a preference for non-living corals, although the type of coral utilised differed between species. The high abundance of blennies on reef tops and non-living corals may be partially related to the quality and availability of detritus in these habitats. Comparisons of total blenny abundance and biomass with other territorial detrivores found that blennies accounted for approximately 60% of this functional group's density and 21% of their biomass on exposed reef tops. Overall, territorial detrivores were found to constitute approximately 37% of the density and 26% of the biomass of the detrivorous/herbivorous fish assemblage on exposed reef tops. Small detrivorous fish therefore represent a substantial proportion of fish assemblages that feed on epilithic algae and associated detritus on coral reefs.     

An ecological model of the artificial ecosystem (northern Hangzhou Bay,China): analysis of ecosystem structure and fishing impacts

The artificial ecosystem is a large-scale enclosure in northern Hangzhou Bay, China. Using the Ecopath with Ecosim software, a trophic structure model is constructed for 2006–2007 to characterize the food web structure, functioning, and describing the ecosystem impacts of fishing. Input information for the model were gathered from published and unpublished reports and from our own estimates during the period 2006–2007. Pedigree work and simple sensitivity analysis were carried out to evaluate the quality and the uncertainty of the model. Results show that the food web in the enclosed sea area was dominated by a detritus pathway. The trophic levels of the groups varied from 1.00 for primary producers and detritus to 3.90 for piscivorous fish in the artificial system. Using network analysis, the system network was mapped into a linear food chain, and five discrete trophic levels were found with a mean transfer efficiency of 9.8% from detritus, 9.4% from primary producer within the ecosystem. The geometric mean of the trophic transfer efficiencies was 9.5%. Detritus contributed 57% of the total energy flux, and the other 43% came from primary producers. The ecosystem maturity indices-TPP/TR (total primary production/total respiration), FCI (Finn cycling index), A (ascendancy) and TB/TDET were 2.672, 25%, 31.5%, and 0.013, respectively, showing that the artificial system is at developmental stage according to Odum’s theory of ecosystem development. The ‘Keystoneness’ result indicates that herbivorous zooplankton was identified as keystone species in this system. Furthermore, a simple dynamical simulation was preformed for varying fishing mortality over 10 years. The biomass of most fish groups has a small increase when the fishing mortality at current level. Increasing fishing mortality by twofold resulted in a marked decrease in biomass of piscivorous fish accompanied by an increase in that of other fish groups, notable zooplanktivorous fish. Generally, this study represents the first attempt to evaluate the food web structure and the potential effects of fisheries in the artificial coastal ecosystem. It is concluded that this model is a potential tool for use in the management of the artificial ecosystem in northern Hangzhou Bay.     

杭州湾北岸大型围隔海域人工生态系统的能量流动和网络分析

根据2006年在杭州湾北岸大型围隔海域进行的生态调查数据,利用EwE软件构建围隔海域人工生态系统的能量流动模型.模型由13个功能组构成,分别是肉食性鱼类、底栖捕食鱼类、浮游动物性鱼类、草食性鱼类、蟹类、虾类、软体动物、底栖动物、肉食性浮游动物、植食性浮游动物、大型藻类、浮游植物和有机碎屑,每一组都代表在生态系统中具有相似地位的有机体,基本覆盖了该人工生态系统能量流动的主要过程.能量流动分析表明,围隔海域人工生态系统中能量流动主要以碎屑食物链途径为主,其中植食性浮游动物在能量从低级向高层次转换中起关键作用.人工生态系统的营养级范围为1.00～3.90级,系统的能量流动主要有6级,来自初级生产者的能流效率为9.4%,来自碎屑的转换效率为9.8%,平均能量转换效率为9.6%.经生态网络分析,直接来源于碎屑的比例占总流量的57%,而直接来源于初级生产者的比例为43%,生态系统特征参数:总初级生产计算量/总呼吸量(TPP/TR)、系统物质和能量循环率(FCI)和系统聚合度(A)值分别为2.672、0.25、0.315,表明围隔海域人工生态系统目前正处于发育时期.该研究为首次利用Ecopath模型分析大型围隔海域人工生态系统的结构和能量流动,旨在为富营养化近岸海域的生态修复提供理论依据.     

Effects of stream predator richness on the prey community and ecosystem attributes

It is important to understand the role that different predators can have to be able to predict how changes in the predator assemblage may affect the prey community and ecosystem attributes. We tested the effects of different stream predators on macroinvertebrates and ecosystem attributes, in terms of benthic algal biomass and accumulation of detritus, in artificial stream channels. Predator richness was manipulated from zero to three predators, using two fish and one crayfish species, while density was kept equal (n = 6) in all treatments with predators. Predators differed in their foraging strategies (benthic vs. drift feeding fish and omnivorous crayfish) but had overlapping food preferences. We found effects of both predator species richness and identity, but the direction of effects differed depending on the response variable. While there was no effect on macroinvertebrate biomass, diversity of predatory macroinvertebrates decreased with increasing predator species richness, which suggests complementarity between predators for this functional feeding group. Moreover, the accumulation of detritus was affected by both predator species richness and predator identity. Increasing predator species richness decreased detritus accumulation and presence of the benthic fish resulted in the lowest amounts of detritus. Predator identity (the benthic fish), but not predator species richness had a positive effect on benthic algal biomass. Furthermore, the results indicate indirect negative effects between the two ecosystem attributes, with a negative correlation between the amount of detritus and algal biomass. Hence, interactions between different predators directly affected stream community structure, while predator identity had the strongest impact on ecosystem attributes.     

Seasonality in Dietary Shifts in Size-Structured Freshwater Fish Assemblages in Three Reservoirs of Sri Lanka

We studied seasonal changes in feeding habits of size-structured fish assemblages in three freshwater reservoirs in Sri Lanka. We obtained fish samples for diet analysis from three reservoirs during the months of rising water level (RIWL) and receding water level (REWL). During RIWL, peripheral areas with terrestrial/semi-terrestrial macrophytes get inundated, which resulted in increased food availability for macrophyte feeding fish. During REWL, detrital food sources increase due to decaying terrestrial plant material, which has inundated. Based on the dietary habits of individual species in the three reservoirs during RIWL and REWL, it is evident that detritivorous and phytoplanktivorous fish species, which belong to low trophic levels do not show significant variation in dietary habits between the two seasons (e.g. Oreochromis mossambicus, Oreochromis niloticus and Amblypharyngodon melettinus). Stenophagous species such as benthic invertebrate predators (Puntius chola and Puntius dorsalis), macrophytophagous species (Etroplus suratensis and Tilapia rendalli) and zooplanktivorous Hemirhamphus limbatus do not exhibit significant variation in dietary habits between seasons. Also their feeding habits do not vary with body size. Euryphagous species such as Puntius filamentosus on the other hand, exhibit variations in dietary habits between seasons as well as with body size. Stenophagous species, which feed on detritus and phytoplankton and euryphagous species, which exhibit temporal dietary plasticity, are therefore abundant in fish assemblages of these reservoirs.     

Trophic interactions and community structure in the upwelling system off Central Chile (33-39°S)

Trophic interactions and community structure in the upwelling system off Central Chile (USCCh) (33-39°S) are analyzed using biological and ecological data concerning the main trophic groups and the Ecopath with Ecosim software version 5.0 (EwE). The model encompasses the fisheries, cetaceans, sea lion, marine birds, cephalopods, large-sized pelagic fish (sword fish), medium-sized pelagic fish (horse mackerel, hoki), small-sized pelagic fish (anchovy, common sardine), demersal fish (e.g. Chilean hake, black conger-eel), benthic invertebrates (red squat lobster, yellow squat lobster) and other groups such as zooplankton, phytoplankton and detritus. Input data was gathered from published and unpublished reports and our own estimates. Trophic interactions, system indicators and food web attributes are calculated using network analysis routines included in EwE. Results indicate that trophic groups are aligned around four trophic levels (TL) with phytoplankton and detritus at the TL=1, while large-sized pelagic fish and cetaceans are top predators (TL>4.0). The fishery is located at an intermediate to low trophic level (TL=2.97), removing about 15% of the calculated system primary production. The pelagic realm dominates the system, with medium-sized pelagic fish as the main fish component in biomass, while small-sized pelagic fish dominate total landings. Chilean hake is by far the main demersal fish component in both, biomass and yield. Predators consume the greater part of the production of the most important fishery resources, particularly juvenile stages of Chilean hake. Consequently, mortality by predation is an important component of total mortality. However, fishery also removes a large fraction of common sardine, anchovy, horse mackerel, and Chilean hake. The analysis of direct and indirect trophic impacts reveals that Chilean hake is a highly cannibalistic species. Chilean hake is also an important predator on anchovy, common sardine, benthic invertebrates, and demersal fish. The fisheries heavily impact on Chilean hake, common sardine, anchovy, and horse mackerel. Total system biomass (B=476 t km⁻² year⁻¹) and throughput (T=89454 t km⁻² year⁻¹) estimated in the USCCh model are in accordance with models of comparable systems. Considering system attributes derived from network analysis, the USCCh can be characterized as an immature system, with short trophic chains and low trophic transfer efficiency. Finally, we suggest that trophic interactions should be considered in stock assessment and management programs in USCCh. In addition, future research programs should be carried out in order to understand the ecosystem effects of fishing and trophic control in this highly productive food web.     

Biomass flow and structure of a tropical upwelling ecosystem in La Guajira, Colombian Caribbean

La Guajira is an exploited tropical upwelling ecosystem in the Colombian Caribbean coast. A trophic model of 27 functional groups was constructed using the ECOPATH 5.0 Beta software to integrate the available information on the ecosystem. The model allowed a comparison with other trophic flow models of upwelling ecosystems. Total system biomass (68 t/km2/year), net system production (1,248.5 t/km2/year), and total system throughput (3,275 t/km2/year) make La Guajira moderate when compared with other systems. The largest amount of energy throughput is achieved from trophic level I to II (68.93 %), although an important proportion of the total flow originates from detritus (32 %). The production/respiration ratio exceeds 1, suggesting that La Guajira is an immature ecosystem and is in development, as determined by its low ascendency (33.7 %) and high development capacity (66.3 %), similar to other upwellings that have values of ascendency between 20 % and 35 %. Although the basic input data were good and covered 1995 to 2000, appropriate information is still not available on some trophic groups such as biomass (for phytoplankton, invertebrates, catfishes and pelagic predator fishes), secondary production data (invertebrates, pelagic predator fishes, and small pelagic fishes), and seabird and mammal populations, which are top trophic levels and an essential part of upwelling ecosystems.     

Fisheries impact on the East China Sea Shelf ecosystem for 1969–2000

An ecosystem model representing the continental shelf of the East China Sea was fitted to a time series of data available from 1969 to 2000 using Ecopath with Ecosim. We used a process-oriented model to explore the extent to which changes in marine resources and the ecosystem were driven by trophic interactions and fishing activities. Fishing effort was used to drive the model, and observed catches were compared with the predicted catches in modeling. A reduction in the sum of the squared deviations of the observed and predicted catches was used as a metric for calibrating and assessing the goodness-of-fit of the model. Trophodynamic indicators were used to explore the ecosystem’s structural and functional changes from 1969 to 2000. The model’s predictions were consistent with observed catches for most functional groups. Trophodynamic indicators suggest a degradation pattern over time: both the mean trophic level of community and a modified version of Kempton’s index of biodiversity decreased over the time, while the total flow to detritus and the loss of production due to fishing increased from 1969 to 2000. Additionally, the ratio of demersal/pelagic abundances decreased as a result of an overall decrease in the abundance of demersal species and increase in pelagic fish in the ecosystem.     

Fish community response to the longitudinal environmental gradient in Czech deep-valley reservoirs: Implications for ecological monitoring and management

Ecological quality assessment of non-natural water bodies is, in contrast to natural systems, less developed and requires determining biological indicators that reliably reflect environmental conditions and anthropogenic pressures. This study was motivated to propose fish indicators appropriate for assessment of reservoir ecosystems in central Europe. We analysed changes in water quality, total biomass and the taxonomic, trophic and size composition of fish communities along the longitudinal axes of four elongated, deep-valley reservoirs. Due to high nutrient inputs from their catchments, the reservoirs exhibited pronounced within-system gradients in primary productivity and water transparency. Although fish communities were similar among the reservoirs and dominated by few native species, the community structure and biomass systematically changed along the longitudinal axes of the reservoirs. The biomass and proportion of planktivores/benthivores in the fish community were highest at eutrophic sites near the river inflow and declined substantially towards deep, more oligotrophic sites close to the dam. The biomass and proportion of piscivores significantly increased downstream within the reservoirs alongside improving water quality. At species level, perch Perca fluviatilis and bream Abramis brama responded most sensitively, although in opposite directions, to the longitudinal environmental gradient. The major longitudinal changes in fish community characteristics were found to be consistent between pelagic and benthic habitats. The results of this study suggest that fish communities are appropriate indicators of eutrophication and can be used for ecological quality assessment of non-natural lentic water bodies, such as reservoirs. Moreover, our results underline the necessity to consider within-system gradients in water quality and the fish community when planning sampling programmes for deep-valley reservoirs.     

Exploring the dynamics of ecological indicators using food web models fitted to time series of abundance and catch data

Previously, standardized snap-shot models of the Southern Benguela (1980–1989), Southern Humboldt (1992) and Southern Catalan Sea (1994) ecosystems were examined and found to facilitate assessment of ecosystem characteristics related to the gradient in exploitation status of the ecosystems; highest level of exploitation in the South Catalan Sea (North-western Mediterranean), high in the Southern Humboldt and lower in the Southern Benguela. Subsequently, these models were calibrated and fitted using available catch, fishing effort/mortality and abundance data series and incorporated environmental and internal drivers. This study furthers the previous comparative analyses by comparing changes in ecosystem structure using a selection of ecosystem indicators from the calibrated models and assessing how these indicators change over time in these three contrasting ecosystems. Indicators examined include community turnover rates (production/biomass), trophic level of landings and the community, biodiversity indicators, ratios of predatory/forage fish and pelagic/demersal fish biomass, catch ratios, and network analysis indicators. Using the set of model-derived indicators, the three ecosystems were ranked in terms of exploitation level. This ranking was performed using the values of these indicators in recent years (ecosystem state) as well as their trends over time (ecosystem trend). The non-parametric Kruskal–Wallis and Median tests were used to test for significance of the difference between indicators from the three ecosystems in the last 5 years of the simulation to compare present ecosystem states. We compared the slope of the lineal trend and its significance between ecosystems using the generalized least-squares regression taking auto-correlation into consideration to analyse ecosystem trends. The indicators that capture better the high impacts of fishing prevalent in the Mediterranean and Humboldt ecosystems, and the more conservative exploitation of the Southern Benguela, are the fish/invertebrates biomass and catch ratio, the demersal/pelagic fish biomass and catch ratio (depending on the ecosystem and the fishery being developed), flows to detritus, and the mean trophic level of the community (when large, poorly quantified groups such as zooplankton and detritus are excluded). This study suggests that the best option for classifying ecosystems according to the impact of fishing is to consider a broad range of indicators to understand how and why an ecosystem is responding to particular environmental or fishing drivers (or more likely a combination of these). Our results highlight the importance of including indicators capturing trends over time as well as recent ecosystem states. We also identified 23 pairs of indicators that correlated similarly in the three ecosystems (they showed a significant correlation with same sign). Further comparisons may contribute towards generalization of this list, progressing towards a better understanding of the behaviour of ecological indicators.     

永兴岛附近海域珊瑚礁鱼类群落结构特征

为更好地保护和管理西沙永兴岛附近海域珊瑚礁鱼类,于2020—2021年对永兴岛上岸渔获物进行了调查研究,分析了鱼类群落结构组成及其变化和演替特征。结果表明:调查共发现永兴岛附近海域珊瑚礁鱼类101种,隶属于5目21科,以鲈形目鱼类最多,占总种类的84.16%,生物量超总渔获物的90%;科级水平鹦嘴鱼科鱼类最多,达21种,生物量超总渔获物的45%。28种珊瑚礁鱼类是永兴岛附近海域主要捕捞对象,占总渔获物的80%以上。永兴岛附近海域珊瑚礁鱼类呈现过度捕捞,一是主要渔获物中的中大型鱼类均重偏小;二是本海域个体体型最大的鱼类出现较多消亡;三是肉食性鱼类大量消亡;四是植食性鱼类生物量占比超过了肉食性鱼类。永兴岛附近海域珊瑚礁鱼类已经演替到以植食性鱼类为主导的生态系统;大量海胆的出现,表明了这一珊瑚礁生态系统在进一步衰退,向以海胆为主导的生态系统演变。保护西沙永兴岛附近海域珊瑚礁鱼类已经刻不容缓,需要严格地控制本海域的捕捞强度。     

An assessment of the biomass production theory in the Baltic Sea using fish landings data

Fish landings in the Baltic Sea from 1970 to 2000 were used as a proxy for fish biomass to explore variability of total fish biomass. Total demersal (total D) and total pelagic (total P) landings proved relatively invariant over time compared with most of their component species. This was explained in terms of the energy limitation imposed on the ecosystem by its carrying capacity, forcing species interactions (predation, competition, etc.) with compensations that allowed the total biomasses to remain relatively stable. Extensive interactions were demonstrated among the Baltic fish species by linear correlation with appropriate negative signs, indicating compensatory interactions consistent with the energy limitation theory. The variances of the landings of cod, herring, sprat and total landings reflected the magnitudes of variation of their biomasses as estimated from the Virtual Population Analysis (VPA), thus justifying the use of landings data in this analysis as a proxy for biomass. Significant demersal–pelagic coupling was indicated from the landings data, which could be explained by trophic interactions. Species interactions generally explained between 17 and 66% of the variations in landings. Thus, substantial portions of the variations in the landings must be attributed to other factors: biological, fishery and environmental.     

Primary production in a tropical reservoir in Sri Lanka*

Primary production was measured every 2 weeks during 16 months (N = 33) in Tissawewa, a tropical shallow reservoir in the lowlands of south-east Sri Lanka. Results are interpreted in relation to selected environmental conditions such as oxygen concentrations, water temperature, Secchi-disc depth, wind force, conductivity, and morphoedaphic index and water level fluctuations. Because of regularly reoccurring high wind speeds the water column is well mixed. Daily gross primary production per unit area was plotted as a function of the algal biomass per unit area over the euphotic zone. Chlorophyll-a concentration in the euphotic zone was taken as measure for the algal biomass. The literature comparisons showed that the primary productivity in Tissawewa was in the same range as in 29 tropical lakes and reservoirs, of which 27 were from Africa. The productivity of these 30 tropical lakes and reservoirs was compared with: (a) 27 lakes of which 25 were temperate lakes, and (b) 49 North American temperate lakes. Firstly, comparisons were made on an annual basis for the tropical water bodies, but restricted to May–September, the growing season, for temperate water bodies. The gross primary productivity of tropical water bodies was ca. three times higher than that of temperate water bodies. These differences were even more dramatic if the two geographical regions are compared on an annual basis, i.e. the tropical systems are ca. six times more productive than their temperate counterpart.     

Leaf breakdown in an Atlantic Rain Forest stream

The hypothesis of this study was that colonizers in decaying leaf litter prefer native species (Erythrina verna) to exotic ones (Eucalyptus camaldulensis and Protium heptaphyllum). Therefore, native species are expected to show higher breakdown rates, increased biomass, richness and density of invertebrate species, and increased biomass of decomposer fungi. Breakdown of leaf litter from these three species was assessed in an Atlantic Rain Forest stream. Four samples were collected during a period of 90 days and washed on a sieve to separate the invertebrates. Then, a series of leaf disks were cut to determine ash‐free dry mass and fungal biomass, and the remaining material was oven‐dried to determine the dry weight. Eucalyptus camaldulensis and E. verna showed higher breakdown rates than P. heptaphyllum, due to differences in leaf physical and chemical characteristics. The harder detritus (P. heptaphyllum) broke down more slowly than detritus with high concentrations of labile compounds (E. camaldulensis). The density of the invertebrates associated with detritus increased with time. There were no differences in density, taxonomic richness or biomass of invertebrates among the leaf types, which indicated that the invertebrates did not distinguish between exotic and native detritus. Fungal colonization varied among samples; E. camaldulensis showed the lowest ergosterol concentrations, mainly due to a high concentration of total phenolics. The detritus with the highest hardness value was colonized most slowly by fungi. These results showed that leaf breakdown in Atlantic Rain Forest streams could be affected either by changes in riparian vegetation, or by becoming more savanna‐like process due to climate change.     

本地和外来草本物种对水分条件时间异质性的可塑响应

极端气候导致的干旱和水淹事件频发，影响了外来植物和本地植物的生长。为了解外来种和本地种植物对干旱和水淹事件发生顺序的响应，探讨草本植物适应水分时间异质性的策略，该文以美国蒙大拿州西部4种本地植物和4种外来植物为研究对象，将所有植物分别进行持续湿润(对照，CK)、水淹-干旱(I-D)和干旱-水淹(D-I)处理，并观测一系列形态和生物量特征的变化。结果表明：(1)与CK相比，D-I和I-D处理均显著降低了外来种的总生物量(P<0.05)。(2)D-I显著降低了本地种早期总生物量、后期地下生物量和根冠比，但显著提高了其后期的相对生长(P<0.05)。(3)D-I处理显著降低了所有植物的地下-地上生物量关系的异速指数，外来种异速指数显著高于本地种(P<0.05)。综上认为，极端事件(水淹和干旱)的发生顺序能改变外来植物和本地植物的生物量分配，早期干旱比后期干旱更容易减少植物生物量的积累，但能促进本地种后期的生长；本地种在环境胁迫下不被降低的总生物量表现说明维持表型稳定的能力较强；D-I处理下本地种和外来种地上和地下生物量关系的分配方式不同。     

Fish population density in Rybinsk Reservoir pelagic area

The density of individual species and the total density of pelagic fishes at stations in the Rybinsk Reservoir was evaluated in 1991, 1994, 2006, and 2007. A reliable difference was found to exist between the total fish density in pelagic areas in the 1990s and the 2000s. The density of many species (smelt, zander, perch, and zope) showed considerable variations in both abundance and biomass.     

Biomass and distribution of herbivorous blennies in the southern Great Barrier Reef

At the small scale (<1 m²), a correlation between microhabitat availability and abundance of comb–toothed blennies was apparent at Heron Island. Investigation of medium scale (>20 m2) differences, showed that community structure and biomass of herbivorous blennies differed among the 14 geomorphological zones identified. Large scale differences (>10 km²), detected using comparisons between Heron, Lady Elliot and North West reefs, revealed that species composition and biomass, but not density, differed significantly. At Heron Reef, density and biomass of comb–toothed blennies exceeded published estimates for most groups of conspicuous herbivorous fish in equivalent zones. The influence of scale on interpretation of patterns of fish distribution and the role of inconspicuous grazers such as comb–toothed blennies, deserves closer attention.