Zoobenthic Community Research Articles

Assemblages of Trichoptera larvae on water moss in the middle reaches of the Yenisei River (Siberia, Russia).

This study provides first data on species composition of trichopterans inhabiting water moss, Fontinalis antipyretica Hedw., in the middle reaches of the Yenisei River. Analysis of Trichoptera larvae collected from samples of water moss in tail waters of the Krasnoyarsk Hydroelectric Plant in 2008-2021 revealed nine species of the order, which belonged to four families. Among them, six species belonging to the Limnephilidae family have not been mentioned in previous studies of the Yenisei invertebrates. Images of species are provided. One species, Apatania crymophyla McLachlan, was the most dense in all samples of water moss. The densities of A. crymophyla in samples of water moss in 2021 ranged within 1.2-7.0 thousand individuals / kg f.w. Other representatives of the order occurred in samples of water moss sporadically or consistently but in very low densities, which did not allow reliable quantification of their abundances. Consequently, numerous large clumps of water moss in the fast-flowing waters of the Yenisei favor an abundance of Trichoptera larvae, providing these insects refuge, food, and material for their cases. However, the reasons for the predominance of one species, A. crymophyla, are to be elucidated in further studies. The present study suggests that the contributions of Trichoptera and the total invertebrate community inhabiting water moss to biomass and energy budgets in the Yenisei have been usually underestimated before now. Hence, seasonal trends of species composition and abundance of invertebrates associated with water moss in the Yenisei River, including comparison with the entire zoobenthic community, are to be studied in the future.

Use of biomonitoring tools to detect water quality-dependent ecosystem (macroinvertebrate) responses in lentic systems: the examples of Lakes İznik and Manyas, Türkiye

Lakes İznik and Manyas located in Türkiye are important biodiversity resources in the Palearctic region. No studies to date have explored the ecological statuses of these lakes together with their water quality based on biotic indices utilizing benthic macroinvertebrates. In this study, some parameters listed in the SWQMR of Türkiye were measured to determine the ecological quality of the lakes. Biotic indices included in the WFD and bacteriological parameters in terms of human health were also evaluated for these lakes. Sampling was performed at 6 stations in 2018-2019. Results for the zoobenthic community structure indicate that Lake İznik has started to become organically polluted and Lake Manyas is more polluted. Also, the biological index results for Lake İznik also show that the lake water quality has started to decrease and that pollution conditions have occurred, pointing to class III water quality. It is clear that there is pollution pressure in Lake İznik. However, according to the results, the macrozoobenthic community structure, diversity, and water quality of Lake İznik seem to be better than those of Lake Manyas. According to the results of the water qualities in the lakes, precautions should be taken to eliminate the negative pressures seen in both lakes.

Zoobentik komünite yapısına bazı çevresel değişkenlerin etkilerinin araştırılması: Porsuk Çayı (Sakarya Nehri, Türkiye) örneği

In order to examine the effects of some physicochemical parameters on the zoobenthic community structure in Porsuk Stream, seasonal zoobenthic samples were collected from 6 stations between 2020-2021, and some physicochemical parameters were also measured. Within the scope of the study, a total of 30 families, 4 from the Gastropoda, 1 from the Bivalvia, 3 from the Clitellata, and 22 from the Insecta, were identified. Families Tubificidae, Erpobdellidae, and Chironomidae were identified at each station. Dominant groups in Porsuk Stream zoobenthos; Tubificidae (41.90 %), Chironomidae (16.68 %), Gammaridae (7.84), Valvatidae (6.16 %), Naididae (5.30 %), Asellidae (3.73 %), Physidae (% 3.48 %), Dreissenidae (3.16 %), Baetidae (3.07 %), Simuliidae (1.70 %), Erpobdellidae (1.69%) and Lymnaeidae (1.32 %), respectively. The highest dissolved oxygen value was measured in the Sobran Stream with an average of 11.3 mg/L. Detection of Caenidae from Ephemeroptera and Hydropsychidae from Trichoptera with low tolerance to pollution and results of the Canonical Correspondence Analysis in this station shows that dissolved oxygen concentration is effective on the distribution of taxa determined in the basin. At the same time, this station has the highest BMWP (64) and Shannon (2.22) values.

Succession of macrozoobenthic communities and implications for ecological restoration in an urban Lake Wuli, Jiangsu Province

底栖动物作为湖泊生态修复中常用的淡水生物类群，对维持和稳定湖泊生态系统结构与功能具有重要作用，探明底栖动物群落演变特征对湖泊生态修复实践具有重要的指导意义.本研究于2007-2017年对太湖五里湖底栖动物群落结构开展了11年的长期调查，结合底栖动物历史数据以及水体、沉积物和浮游植物等相关资料的分析，探讨了五里湖底栖动物群落结构演变特征及潜在的影响因素.在综合分析底栖动物及环境因子变化特征的基础上，结合五里湖开发与修复工程的特点和发生时间，发现五里湖底栖动物群落演变过程总体可划分为自然演变、快速退化、生境修复和缓慢恢复4个阶段.在自然演变阶段，生境特征为底栖动物群落演变的直接影响因素，如水深、溶解氧和底质类型等；在快速退化阶段，人类活动干扰（如围湖造田）剧烈成为此阶段底栖动物群落演变的主要影响因素；在生境修复阶段，五里湖内开展的综合整治（包括生态清淤、污水截流、退渔还湖、动力换水、生态修复、湖岸整治和环湖林带建设等工程）等各项生态修复工程成为群落演变的主要影响因素，但在此阶段底栖动物优势种仍为耐污种；自2014年以来进入缓慢恢复期，软体动物投放成为底栖动物群落演变的一个重要影响因素，铜锈环棱螺等软体动物成为优势种.综合以上分析结果及底栖动物在生态修复中的应用实践，今后应加强对底栖动物生态修复投放过程及之后的维护管理等方面的研究.;Zoobenthos play crucial roles in maintaining and stabilizing the structure and function of lake ecosystem. Moreover, various zoobenthic species are valuable in freshwater eco-restoration. Uncovering the succession of zoobenthic community evolution could provide important information for the application of zoobenthic species in freshwater eco-restoration. In the present study, succession of macrozoobenthic communities was examined by combing field investigation from 2007 to 2017 and various documents. It was found that the succession of zoobenthos community in Lake Wuli can be divided into four stages, including natural succession stage, rapid degradation stage, habitat restoration stage and slow recovery stage. Besides, taking the water quality, sediment characteristics, phytoplankton community, and the reported eco-restoration activities in Lake Wuli into consideration, we discussed the major impact factors in different succession stages of zoobenthos community. Summarily, based on the above results and practical application of zoobenthos in freshwater eco-restoration, the present study pointed out the research directions which should be enhanced at last.

Impact of deposit-feeding chironomid larvae (Chironomus riparius) on meiofauna and protozoans

AbstractChironomid larvae are common members of benthic systems in freshwaters. Their diet consists mainly of detritus, which often leads to the passive ingestion of attached organisms. We hypothesized that larvae would have a strong trophic effect on protozoans and meiofauna. We investigated experimentally the direct effect of 2 densities (1 and 4 larvae/16 cm2) of Chironomus riparius, a nonselective macrofaunal deposit feeder, on a natural zoobenthic community. Larvae significantly reduced the abundance of total meiofauna (nematodes, rotifers, oligochaetes, and copepods) to 56 (1 larva) and 52% (4 larvae) of their initial abundance after 1 d. Protozoans were slightly reduced by 1 larva but their densities increased when 4 larvae were present. A strong decrease in copepod abundance led to a decrease in total meiofaunal biomass to 40 (1 larva) and 43% (4 larvae) of their initial biomass after 8 d. Organisms with body lengths between 0.125 and 1 mm were ingested preferentially. These results indicate that ...

Macrobenthic fauna associated with the invasive alien species Brachidontes pharaonis (Mollusca: Bivalvia) in the Levantine Sea (Turkey)

The invasive alien mytilid species, Brachidontes pharaonis, forms a biogenic habitat in the mediolittoral and upper-infralittoral zones of the Levantine Sea, hosting a number of alien and native species. Examinations of samples taken from dense, continuous mussel beds at seven stations along the coast of northern Levantine Sea yielded 187 macro-benthic invertebrate species belonging to 11 taxonomic groups. Polychaeta accounted for 46% and 37% of the total number of species and individuals, respectively. The top three dominant species in the mussel beds were Stenothoe gallensis, Spirobranchus kraussi and Mytilaster minimus. The species with the highest frequency values on the mussel beds were Pseudonereis anomala, Phascolosoma stephensoni and Elasmopus pocillimanus. The highest density and biomass of the associated fauna were estimated as 42,550 ind m−2 and 1503 wwt g m−2, respectively. The species number in samples varied between 14 and 47 species. The environmental variables best explaining variations in zoobenthic community structures were salinity, dissolved oxygen and total inorganic nitrogen in the water column. The biotic indices, TUBI and ALEX, classified the ecological status of one or two stations as moderate or poor, based on the relative abundances of ecological and zoogeographic groups, respectively. A total of 21 alien species were found to be associated with the mussel bed, of which Syllis ergeni is being newly considered as a new established alien species for the Mediterranean Sea. The maximum density of associated alien species was calculated as 30,300 ind m−2. The alien species assemblages were greatly affected by salinity and total inorganic nitrogen.

Benthic conditions around a historic shipwreck: Vrouw Maria (1771) in the northern Baltic proper

Since her shipwreck in 1771, the wooden vessel Vrouw Maria has been lying on the seabed at 41m depth on the border between the Archipelago Sea and the northern Baltic proper, off the southern coast of Finland. The wreck lies in an upward position in a right angle to the dominating bottom current, which is potentially affecting seabed topography, sediment characteristics and zoobenthic communities both upstream (NE) and downstream (SW) of the wreck. This multidisciplinary study attempts to clarify abiotic and biotic patterns and processes in the vicinity of the wreck by combining field investigations with physical simulation studies in the field and in the laboratory. Multibeam echo-sounder techniques were utilised to generate a map of the wreck area and sediment grab samples were taken to characterize the sediment type and its zoobenthic community. A medium-sized field experiment generated data on the accumulation of sediment organic matter in the presence and absence of a current and/or a barrier on the seafloor and a small-scaled laboratory study was conducted to simulate scour forming processes.The results showed that a deeper basin, scour area, with the dimensions 150×300m, was present downstream of the wreck and there was also a smaller scour area upstream of the wreck. Similar traces on the bottom were simulated in the laboratory. The organic content (recent mud) and the proportion of finer sediment were more pronounced in areas closer to both sides of the wreck. These results were in turn imitated in a field experiment, where the accumulation of organic matter in the sediment increased significantly downstream, when a current was interrupted by a barrier. Regarding zoobenthos in the wreck area, 11 taxa and a mean total abundance of 773 individuals per m2 were registered. The dominant species were Macoma balthica and Marenzelleria sp., which together made up >80% of the total number of individuals. Multivariate data analyses showed significant differences in community structure between upstream and downstream sides of the wreck and these differences were basically expressed as more individuals upstream of the wreck of the seven most common species. Univariate data analyses also showed significantly more species and higher total abundance in the scour area upstream of the wreck compared to the downstream scour area. The weakened communities downstream of the wreck were possibly due to accumulation of organic matter and more frequent occurrence of hypoxia. The results are useful for describing bottom areas around long-term physical barriers/artificial reefs, as background measurements ahead of possibly increased archaeological diving activities, sediment excavations or measures taken to raise the wreck to the surface, as well as for any attempts to preserve the wreck in situ.

Responses of benthic invertebrates to repeated hydropeaking in semi‐natural flume simulations

AbstractWe assessed the effects of repeated hydropeaking over five consecutive days on the zoobenthic community by manipulating discharge in five experimental flumes directly fed by an Alpine stream. Treatment consisted of two different hydropeaking intensities which increased discharge two‐ and threefold from baseflow and lasted for 5 h each day. The resulting sudden changes in flow directly affected benthic invertebrates through the induction of catastrophic drift as a direct response to high (hydropeaking) flow conditions, and of behavioural drift in the low, baseflow conditions (at the conclusion of each hydropeaking event) for some taxa. We observed: an initial strong peak in catastrophic drift within the first 3 min of increased discharge, followed by a decreased drift rate throughout the following hours of the experiment; a strong response in the first day of the simulation, with successive days having substantially decreased drift; taxa‐specific responses over the short and long‐time scales: least‐resistant taxa (i.e. Baetis spp.) were removed via the initial catastrophic drift, while more resistant taxa began to behaviourally drift later in each hydropeak (i.e. Simuliidae). Peaks in drift rates corresponded to the initial removal of CPOM which, during low flows, provided habitat and food resource for a high number of individuals and taxa. Quantification of drift responses over time scales larger than the single hydropeaking event underlines the relevance of the typical intermittency and repetition frequency as a stress factor for benthic communities, and that the response to hydropeaking is closely related to the time elapsed since the last perturbation. Copyright © 2015 John Wiley & Sons, Ltd.

Does richness of Oligochaeta (Annelida) follows a linear distribution with habitat structural heterogeneity in aquatic sediments?

Sediment of aquatic environments supports several local communities, among them aquatic invertebrates. Habitat structural heterogeneity in sediments of aquatic ecosystems is related to a number of factors, including variability in the particle size of the substrate and availability of different food resources, the two structures that comprise the aquatic sediment. These structures are necessary for the stability of zoobenthic community, including the Oligochaeta assemblage, favoring richness as habitat heterogeneity increases. To analyze the habitat structural heterogeneity, we use these following structures: granulometric composition and organic matter composition, and we tested these structures together (habitat heterogeneity) and separately (granulometric and organic matter heterogeneity). This study investigated the relationship between habitat structural heterogeneity and richness of the Oligochaeta assemblage. We hypothesized that there is a positive linear relationship between habitat structural heterogeneity and richness of Oligochaeta, and predicted that the granulometric composition is more important than organic matter composition for increasing richness. There was no linear relationship between Oligochaeta richness and habitat heterogeneity; but the analysis showed an asymmetric triangular dispersion pattern, being granulometric heterogeneity more important than organic matter heterogeneity for richness of Oligochaeta. These results indicated that habitat structural heterogeneity was beneficial for richness of Oligochaeta until certain threshold and after this, the relationship between structural heterogeneity of habitats and richness of Oligochaeta is negative with decrease of diversity due to the filling of interstitial spaces which gradually reduces the ability to colonize these habitats.

Changes in Lake Erie benthos over the last 50 years: Historical perspectives, current status, and main drivers

During the last 50years the ecosystem of Lake Erie has experienced major environmental changes, from anthropogenic eutrophication in 1930–1960s, to nutrient and pollution abatement in the 1970s, and then the introduction of exotic dreissenids in the 1980s. We used multivariate statistical techniques to examine long-term changes in the zoobenthic community, comparing contemporary collections (2009, 2011–2012) and historical data (1963–1965, 1978–1979, 1993, and 1998). The Lake Erie benthic community underwent significant changes during each decade examined, showing signs of recovery following ecosystem restoration in the 1970s, but then experiencing major structural and functional changes after dreissenid (Dreissena polymorpha and D. r. bugensis) introductions. There was a significant temporal trend in community composition changes from 1963 to 2012, and the largest difference was found between pre- and post-dreissenid invasion communities. Currently the lake-wide benthic community is dominated by dreissenids both in density (41%) and total wet biomass (97%), followed by oligochaetes and chironomids. The largest benthic density was found in the central basin, and the greatest biomass in the eastern basin. The number of exotic species found in benthic surveys increased every decade, from 1 in 1963 to 10 in 2009–2012, and the majority of the invaders were molluscs. Whereas the role of benthic invaders in community diversity is still low, their impact has had enormous consequences for the whole ecosystem.

Coastal Habitats as Surrogates for Taxonomic, Functional and Trophic Structures of Benthic Faunal Communities

Due to human impact, there is extensive degradation and loss of marine habitats, which calls for measures that incorporate taxonomic as well as functional and trophic aspects of biodiversity. Since such data is less easily quantifiable in nature, the use of habitats as surrogates or proxies for biodiversity is on the rise in marine conservation and management. However, there is a critical gap in knowledge of whether pre-defined habitat units adequately represent the functional and trophic structure of communities. We also lack comparisons of different measures of community structure in terms of both between- (β) and within-habitat (α) variability when accounting for species densities. Thus, we evaluated a priori defined coastal habitats as surrogates for traditional taxonomic, functional and trophic zoobenthic community structure. We focused on four habitats (bare sand, canopy-forming algae, seagrass above- and belowground), all easily delineated in nature and defined through classification systems. We analyzed uni- and multivariate data on species and trait diversity as well as stable isotope ratios of benthic macrofauna. A good fit between habitat types and taxonomic and functional structure was found, although habitats were more similar functionally. This was attributed to within-habitat heterogeneity so when habitat divisions matched the taxonomic structure, only bare sand was functionally distinct. The pre-defined habitats did not meet the variability of trophic structure, which also proved to differentiate on a smaller spatial scale. The quantification of trophic structure using species density only identified an epi- and an infaunal unit. To summarize the results we present a conceptual model illustrating the match between pre-defined habitat types and the taxonomic, functional and trophic community structure. Our results show the importance of including functional and trophic aspects more comprehensively in marine management and spatial planning.

Long-term changes in coastal zoobenthos in the northern Baltic Sea: the role of abiotic environmental factors

AbstractRousi, H., Laine, A. O., Peltonen, H., Kangas, P., Andersin, A-B., Rissanen, J., Sandberg-Kilpi, E., and Bonsdorff, E. 2013. Long-term changes in coastal zoobenthos in the northern Baltic Sea: the role of abiotic environmental factors – ICES Journal of Marine Science, 70: 440–451. We investigated site-specific changes in a coastal zoobenthic community during 1964–2007 in the northern Baltic Sea. Multivariate analysis indicated that the community structure had changed. The amphipods Monoporeia affinis and Pontoporeia femorata decreased drastically in the late 1970s–early 1980s, and by the early 1990s P. femorata vanished and M. affinis abundance was low. The decline of M. affinis and P. femorata was followed by an increase of the bivalve Macoma balthica and the arrival of the polychaete genus Marenzelleria in the 1990s. Trend analyses showed a rising trend for near-bottom temperature from the late 1960s. There was a significant decline in salinity during the early 1980s, which stabilized during the early 1990s. A negative trend was observed for oxygen concentration during the entire study period. There were interannual variations in the phosphorus and nitrogen concentrations, and a step-like increase in phosphorus concentration at the beginning of the 21st century. The correlations of temperature, salinity, oxygen, total phosphorus and nitrogen with zoobenthic communities were examined using Constrained Correspondence Analysis. Temperature was the most highly correlated explanatory variable for the benthic species. The study highlights the importance of long-term data sets in assessing the state and ecological processes of zoobenthic systems.

Change in a lake benthic community over a century: evidence for alternative community states

Aquatic communities are one of the most studied systems where alternative states or regime shifts have been detected. We used data spanning a century of time to test whether the zoobenthic community of Lake Mendota, Wisconsin, USA, was relatively stable through time, variable, or whether there was any evidence of alternative community states. We used multivariate statistical analyses to test for community structure similarity and whether detected differences corresponded to major changes in the local environment. Surprisingly, the benthic community in Lake Mendota was not statistically different from the mid 1960s to the present. Similarly, the benthic community was not significantly different from 1914 to the 1950s. However, between the 1950s and mid 1960s there was a dramatic change in the zoobenthic community, including the loss of key taxa and a decrease in the diversity of several major taxa. This dramatic change cannot be attributed to any single environmental factor, and is correlated with multiple factors acting simultaneously, including increased urban development, human population density, intensive agriculture, and the introduction of a major invasive species, Eurasian watermilfoil. The long-term similarity in the benthic community before and after the shift suggests two alternative states that switched with the confluence of multiple stressors.

Secondary production of a zoobenthic community under metal stress

Little is known about the influence of toxicants on the function of freshwater sediments. To better understand these effects, a long-term microcosm experiment was carried out with cadmium (Cd) as the model pollutant (50 and 400 mg Cd kg−1 dw). In a seven-month study the effect of Cd was examined on secondary production of the zoobenthos (higher taxonomic level) and specifically of the nematode community (species level). Production of almost all taxa decreased under low Cd stress, with rotifers as the only taxon that was able to thrive under this condition. High Cd stress resulted in a decrease in secondary production of all groups with strong differences between taxa. Nematode production likewise decreased, with strongest effects in the higher Cd concentration. Interestingly, at the end of the study, several bacteria-feeding species had benefited from the low Cd stress, probably due to their rapid development in relation to other species and/or the high bacterial density under this condition. Taken together, the results of this study provide insight into secondary production of sediment communities and the important effects of a toxicant thereon.

Spatio-temporal distributions of zoobenthos in soft substratum of Izmir Bay (Aegean Sea, eastern Mediterranean), with special emphasis on alien species and ecological quality status

The soft-bottom zoobenthic community structure of Izmir Bay was examined seasonally at eight stations (depth-range: 19–67 m) in 2009. A total of 427 species were found. Polychaeta had the highest number of species (50% of total species) and individuals (75%), whereas Echinodermata possessed the highest biomass (47%). The number of species varied from 3 to 79 (0.1 m−2), the density from 60 to 5360 ind.m−2, and the biomass from 1 to 530 g.m−2. The most numerically dominant species were the polychaetesAricidea claudiae, Streblospio gynobranchiata, Levinsenia demiriandSternaspis scutata. The distribution of zoobenthos was strongly related to spatial differences in total organic carbon, sediment texture and depth among different regions of the bay rather than temporal differences among seasons. However, significant seasonal variability in community structure (mainly differences in the relative abundance of species) was present. The inner region of the bay can be classified as ‘poor’ or ‘bad’ based on the results of biotic indices (H′, AMBI, m-AMBI and BENTIX). Among biotic indices, only H′ and m-AMBI appeared to be capable of explaining the bay's benthic quality status. Thirteen alien species were also found.Streblospio gynobranchiata, Prionospio pulchra, Pseudopolydora paucibranchiataandPolydora cornutaformed dense populations in the inner most polluted part of the bay and are considered to be new pollution indicator species in the eastern Mediterranean Sea.

Seagrass colonization: Knock-on effects on zoobenthic community, populations and individual health

This study provided evidence that Zostera noltii presence affects macrofauna community structure independently from median sediment grain-size and that the notion of ecosystem health is rather subjective: in the present case, we recorded “good health” in terms of seagrass development, “no impact” in terms of macrobenthic biotic indices and “negative effect” for a given key-population. The occurrence and development of a Z. noltii seagrass bed was surveyed at Banc d’Arguin, Arcachon Bay (France), to estimate the modification of the macrozoobenthic community and of the dynamics of a key-population for the local ecosystem, – the cockle Cerastoderma edule. Even though median grain-size of the sediment decreased only at the very end of the survey, i.e. when seagrass totally invaded the area, most of the macrofauna community characteristics (such as abundance and biomass) increased as soon as Z. noltii patches appeared. The structure of the macrofauna community also immediately diverged between sand and seagrass habitats, without however modifying the tested biotic indices (BENTIX, BOPA, AMBI). The health of the cockle population (growth, abundance, recruitment) was impacted by seagrass development. Related parasite communities slowly diverged between habitats, with more parasites in the cockles from seagrass areas. However, the number of parasites per cockle was always insufficient to alter cockle fitness.

Flow refugia for the zoobenthos of a sand-bed river: the role of physical-habitat complexity

AbstractGreat Plains rivers are characterized by unpredictable, thunderstorm-generated flow events that can abruptly restructure their physical complexity. These morphodynamic disturbances force river organisms to overcome hydrologic challenges. Some organisms surmount these challenges by using refugia, which play a key role in the ecological processes that govern lotic systems. The physical complexity of rivers can determine the availability and diversity of refugia both within and among rivers. However, physical complexity often changes with the hydrologic cycle and position along the river. We determined how the benthic community was affected by changes in the structure and abundance of in-channel refugia created by hydrologic fluctuations. We worked on and around sandbars in the Kansas River (Kaw), a multithread, sand-bed river. The composition of the zoobenthic community was directly related to the complexity of river morphology and flow rates. The community of 1 side channel consistently shifted ove...

Biological characteristics of the improved extensive shrimp system in the Mekong delta of Vietnam

Low and unstable shrimp yields of the improved extensive shrimp system has been a tremendous obstacle for economic development in the coastal areas of Southern Vietnam. To investigate the biological characteristics of this system, ponds in the coastal Cai Nuoc district, Mekong delta of Vietnam, were monitored. Results showed that the system was not optimal for shrimp. While chlorophyll a (chl a) (1.51–37.2 μg L−1), phytoplankton density (6333–974 444 cells L−1) and zooplankton density (7.1–517.2 ind L−1) were abundant and comparable to shrimp farms elsewhere, zoobenthic community was very poor (7–1971 ind m−2). Toxin-producing cyanobacteria (Oscillatoria limosa, Oscillatoria formosa, Anabaena sp. and Phormidium tenue) were found. Total bacteria and Vibrios were present in large numbers (respectively 1.04 × 105 and 6.64 × 102 CFU mL−1 in pond water, 6.33 × 105 and 9.47 × 103 CFU g−1 in sediment). Presence of toxin-producing organisms, poor zoobenthic community and abundance of Vibrios all can enhance shrimp susceptibility to diseases. The following measures are recommended to improve the situation: (1) complete testing of seeds for pathogens, (2) not to incorporate fish into shrimp ponds and (3) applying no-culture breaks and pathogen-killing chemicals.

Crayfish as trophic agents: Effect ofAustropotamobius torrentiumon zoobenthos structure and function in small forest streams

Crayfish are among the largest and most threatened invertebrates in freshwater habitats. Due to their size, behaviour and feeding activity they may affect structure and function of aquatic ecosystems and their organisms. Despite their importance in many freshwaters and available information on their ecology for several species little is known about the European crayfish Austropotamobius torrentium . In order to evaluate the potential effects of indigenous crayfish presence on the structural and functional composition of the zoobenthic community, we measured population size and densities of three A. torrentium populations and compared macroinvertebrate assemblages and physicochemical parameters in three streams with and three without crayfish. The experimental setup considered crayfish effects at a large scale in defined reaches of pristine headwaters in association with the whole benthic fauna under natural conditions. Presence of A. torrentium significantly affected zoobenthic abundance, diversity and the relative proportions of functional feeding groups. In crayfish streams, especially Trichoptera and collector gatherers were more abundant and diverse, while sites without crayfish had significantly higher abundances and diversities of shredders and wood feeders. Our study provided strong evidence that the presence of the indigenous crayfish A. torrentium had important effects on the trophic cascades of headwater stream communities.

Physical and biological changes to a lengthening stream gradient following a decade of rapid glacial recession

AbstractIn mountains, environmental gradients are steep in both terrestrial and aquatic systems, and climate change is causing upward shifts of physical and biological features of these gradients. Glacial streams are an interesting system to evaluate such shifts both because streams have a linear nature (for simplicity of analysis), and because the stream habitat will at least temporarily lengthen as it follows receding glaciers upward. The Tschierva Glacier, Swiss Alps, receded 482 m upstream from 1997 to 2008. We tested the null hypothesis that the physical and biological stream gradient below this glacier maintained the same structure between these time periods, but simply shifted upward following the glacial source. We compared longitudinal patterns of water temperature and zoobenthic community structure in 1997 and 2007–2008 during three seasons (spring, summer, fall) along the uppermost ca. 5 stream km. Upward shifts were evident, including colonization of the newly exposed stream reaches by cold‐adapted taxa, and the appearance in 2007/2008 of four lower‐altitude species that were previously absent. Overall, however, results rejected the null hypothesis, instead revealing significant changes in gradient structures. These included a more steeply increasing temperature profile downstream of the glacier and increased amplitude of seasonal community turnover in 2007/2008 vs. 1997. Long‐term (1955–2007) flow records revealed increasing short‐term and seasonal hydrologic variability, which might have influenced the increased intra‐annual community variability. The steepening of the temperature gradient was likely caused by a warming lake‐outlet tributary upon which glacial influence was diminished between 1997 and 2007/2008. These results suggest that upward‐shifting gradients in glacial streams can involve complex interactions with other landscape elements and that local‐scale climate response can progress even more rapidly than the rate of glacial recession.