Impact of hydrology on aquatic communities of floodplain lakes along the Daugava River (Latvia)

During July 2004, various limnological characteristics of 24 floodplain lakes and reservoirs have been explored along the Middle Daugava for the first time in order to reveal possible impact of the long-term mean annual flooding frequency on their phytoplankton, zooplankton, macrozoobenthos and macrophyta communities. Obtained data series were analysed by Spearman’s rank correlation method, Principal Component Analysis (PCA) method and Renkonen’s similarity test. UPMGA method was used for single linkage clustering of the lakes based on the abundance of phyto- and zooplankton taxa. Low similarity between the obtained cluster trees and hydrological grouping was stated indicating minor impact of the flooding hydrology on summer plankton communities of these lakes. Significant correlation between the flooding frequency and several physicochemical and biological parameters was found. Six main factors, which explain observed variations, were extracted by PCA. Significant negative impact of hydrological connectivity on zooplankton species diversity as well as positive impact on Oligochaeta density was stated, whereas other biotic parameters were affected by local factors, such as lake morphology, internal loading of nutrients from sediments, throphic interactions as well as local source of dissolved organic matter.     

Pleuston communities are buffered from regional flood pulses: the example of ostracods in the Paraná River floodplain, Brazil

1. It is widely acknowledged that sudden, large‐scale flood pulses are drivers of benthic and planktonic biodiversity change in floodplains. The impact of such pulses on pleuston (biotic communities associated with root systems of floating plants) remains to be demonstrated. Here, we investigate the effects of local and regional drivers on seasonal changes in abundance and diversity of ostracod communities in pleuston. 2. Temporal and spatial distribution patterns of species richness, abundance, diversity and evenness of ostracods associated with the floating water hyacinth, Eichhornia crassipes, in a lentic environment from the upper Paraná River floodplain, were investigated in relation to local, as well as regional, environmental factors. Ostracods were sampled monthly over an annual cycle (March 2004–February 2005). Twenty‐seven species were found, representing the families Cyprididae, Candonidae, Limnocytheridae and Darwinulidae. Both diversity and abundance of ostracod communities showed seasonal changes, although species turn‐over during the year was limited. 3. We tested two hypotheses concerning the causality of these fluctuations: seasonal recruitment and influx of allochthonous ostracods during the flood pulse. Our results indicate that seasonal recruitment is more likely to be the driver of fluctuations in relation to the flood pulse. We postulate that pleuston communities are buffered against possible detrimental effects of flood pulses.     

The influence of flood regime on fish catch and fish communities of the Cross River floodplain ecosystem,Nigeria

Synopsis The morphology, climate and flood regime of the Cross River floodplain are summarized and related to the catch, species distribution and abundance of the economically important fishes of the floodplain ecosystem. Two flood indices, FI-1 and FI-2, are used to assess, statistically. the relationship between fish catch and flood regime. There are good positive correlations between the catch (C_T) of year T and the flood index 1 of 1 year T-1 and between (C_T) and the sum of the flood indices 1 and 2 of year T-1 (r = 0.6516 and 0.6894, respectively, both at P = 0.05). Cross River is a relatively highly productive system (in terms of fish catch) and this productivity is attributable mainly to the yearly flooding of the plain when fish find allochthonous food materials in the expanded habitat. Changes in hydrometeorological conditions, such as the drought that affected the northern part of the Cross River basin in 1983–1984. if they persist can effectively reduce fish catch from the system.     

Typology of shallow lakes of the Salado River basin (Argentina), based on phytoplankton communities

The phytoplankton communities of eleven shallow lakes from Buenos Aires Province, Argentina, were studied seasonally from 1987 to 1989. Several physical and chemical properties were measured in each lake (pH, temperature, dissolved oxygen, transparency, nutrients), in order to interpret the structural and dynamic traits of the phytoplankton community.Important differences between the lakes studied were put in evidence by means of multivariate techniques (Cluster Analysis and PCA). The shallow lakes densely populated by macrophytes hosted lowest phytoplanktonic densities, with average values ranging from 690 to 16500 algae ml^–1. High species diversities were observed in these lakes (4.0–4.8). Lakes less colonized by macrophytes had higher phytoplankton densities. In some of them important blooms of Cyanophyceae were recorded, with between 60 000 and 179 000 algae ml^–1, and concomitant low diversities.The results of this investigation support the hypothesis that the phytoplankton community is strongly influenced by the macrophytes, by direct competition and/or by competition from periphytic algae associated with higher plants.     

Rotifer communities of floodplain lakes of the Brahmaputra basin of lower Assam (N.E. India): biodiversity, distribution and ecology

The rotifer communities of 15 acidic – alkaline and soft – marginally hard water floodplain lakes of the lower Assam valley of the Brahmaputra river basin, characterized by low ionic concentrations, reveal 164 species (178 taxa) belonging to 39 genera and 20 families and represent the richest biodiversity known to date in these ecotones of the Indian subcontinent. Nine species are new to the Indian Rotifera. Cosmopolitan (59.7%) > pantropical (15.2%) > cosmotropical (12.2%) species dominate the taxocoenosis. Biogeographically interesting elements constitute a notable component (13.4%); important members of this category include six Oriental, two Australasian and seven Palaeotropical species. The examined fauna depicts a tropical character with predominance of Lecanespp. (28.0%). Littoral or periphytic rotifers (76.2%) dominate the planktonic species. Rotifers comprise a dominant qualitative (67–103, 79.1±11.0 species) and an important quantitative (mean: 41.1–65.9%) component of zooplankton in all floodplain lakes, register a moderate diversity (mean: 2.036–2.642), low dominance (mean: 0.019–0.216) and high evenness (mean: 0.840–0.893). The examined material indicates several interesting acidophilous elements. Richness depicts significant inverse correlation with pH. Water temperature, conductivity, dissolved oxygen and alkalinity record significant direct relationships with the rotifer abundance. Diversity is influenced by abundance and is also directly correlated with water temperature and conductivity. Canonical analysis shows a notable cumulative impact of six abiotic factors on richness, density and diversity.     

The impact of bait-pumping on populations of the ghost shrimp Trypaea australiensis Dana (Decapoda: Callianassidae) and the sediment environment

This study investigated the relative effects of bait-pumping and the associated disturbance of mudflats on populations of the ghost shrimp Trypaea australiensis and various sediment properties at Coronet Bay, Western Port, southern Australia. The experiment followed a BACI design, with 3 months of sampling before and after the simulated impact. Control plots were left undisturbed while two disturbance treatments (impact and procedural control) were bait-pumped. Ghost shrimp were removed from the impact plots, whereas ghost shrimp were allowed to re-burrow in the procedural control plots. The purpose of the procedural control was to test for the effect of the disturbance associated with bait-pumping. Initial destruction of burrows and compaction of sediment due to bait-pumping and trampling of the mudflat, reduced sediment porosity and created more reducing conditions to depths of 20 cm. The proportion of small particles (<250 μm) and abundance of benthic microalgae increased in surface sediments, whereas organic carbon content decreased. Ghost shrimp density decreased considerably and was slow to recover over the experimental period. Both disturbance treatments responded similarly indicating that the mudflat disturbance associated with bait-pumping was the major cause of the effects observed.     

Seasonal changes on planktonic diatom communities along an inshore-offshore gradient in the Gulf of Gabes (Tunisia)

We investigated the composition, biomass and cell size dynamics of the marine planktonic diatom species along a coastal-open sea gradient in relation to the hydrological characteristics, during four oceanographic cruises in July 2005, May–June 2006, September 2006 and March 2007 in the Gulf of Gabes. The study of the marine planktonic diatoms throughout the sampling period showed the presence of 40 different species belonging to 22 pennate and 18 centric diatom species. Centric diatoms were more abundant than the pennate ones; 56% and 44% of total diatom abundance, respectively. Diatoms were very abundant, representing about 60% of the total phytoplankton abundance, with an exception in July 2005 (19%) during which Dictyochophyceae were the most dominant group (41% of the total phytoplankton abundance). Diatoms, which were dominant in the coastal samples, mainly proliferate in the semi-mixing conditions (May–June 2006), whereas they declined in the offshore area, most likely due to silicate shortage. In this period, in spite of the high abundance of diatom planktonic cells, only diatom biomass was correlated with silica amount, proving that biomass was a better ecological bio-indicator than abundance. The results suggest that the marine planktonic diatoms taxa were generally adapted to specific hydrological structure. In fact, the dominance index of diatoms showed that the biodiversity of diatoms increased gradually along the coastal-open sea gradient except in May–June 2006 during which a slight decrease along the inshore towards offshore areas was observed. This index increase depended on a coastal-open sea distance during thermal stratification (July 2005 and September 2006) and mixing periods (March 2007).     

Multivariate analysis of microbial communities in the River Elbe (Germany) on different phylogenetic and spatial levels of resolution

The microbial communities of three different habitat types and from two sediment depths in the River Elbe were investigated by fluorescence in situ hybridization at various levels of complexity. Differences in the microbial community composition of free-flowing river water, water within the hyporheic interstitial and sediment-associated bacteria were quantitatively analyzed using domain- and group-specific oligonucleotide probes. Qualitative data on the presence/absence of specific bacterial taxa were gathered using genus- and species-specific probes. The complete data set was statistically processed by univariate statistical approaches, and two-dimensional ordinations of nonmetric multidimensional scaling. The analysis showed: (1) that the resolution of microbial community structures at microenvironments, habitats and locations can be regulated by targeted application of oligonucleotides on phylogenetic levels ranging from domains to species, and (2) that an extensive qualitative presence/absence analysis of multiparallel hybridization assays enables a fine-scale apportionment of spatial differences in microbial community structures that is robust against apparent limitations of fluorescence in situ hybridization such as false positive hybridization signals or inaccessibility of in situ oligonucleotide probes. A general model for the correlation of the phylogenetic depth of focus and the relative spatial resolution of microbial communities by fluorescence in situ hybridization is presented.     

Effect of main-stem dams on zooplankton communities of the Missouri River (USA)

The persistence of plankton in flowing water presents an enigma, i.e., how can populations be sustained while constantly losing individuals downriver? We examined the distribution and abundance of zooplankton from 146 sites on the Missouri River (USA) and found large shifts in the dominance of major taxa between management zones of this regulated river. Crustacean zooplankton were dominant in the inter-reservoir zone of the river, and their taxonomic composition was similar to regional lakes and reservoirs. The exponential decline of cladocerans and copepods with distance from main-stem dams suggests that conditions within the river are adverse to population growth and that reservoirs are the main source of these crustaceans in the river. Rotifers dominated in the channelized zone of the river. High algal biomass and rapid population growth rates likely allow persistence of rotifers in segments of the river that do not receive direct reservoir inputs. Rotifers were less abundant in the inter-reservoir zone, suggesting that their numbers are limited by internal processes, such as food or predators. Since zooplankton are known to be an important food for larval fishes in rivers, this shift of major taxa in regulated rivers has implications for river food webs.     

Epibiont protozoan communities on Caridina lanceolata (Crustacea, Decapoda) from the Malili lakes of Sulawesi (Indonesia)

The epibiont protozoan communities living on the freshwater shrimp Caridina lanceolata Woltereck, 1937a from the three major lakes (Towuti, Matano and Mahalona) of the Malili lake system (Sulawesi, Indonesia) were studied. The number of epibionts varied between 2 and 971 per shrimp. Seven protozoan ciliate species were found: Acineta sulawesiensis n. sp., Cothurnia sp., Zoothamnium sp. (in all three lakes), Vorticella sp. (Lake Mahalona and Lake Matano), Opercularia sp. (Lake Mahalona), Epistylis sp. (Lake Mahalona and Lake Matano), and Podophrya sp. (Lake Mahalona). Although these ciliates had been found previously on other crustaceans, they have not been observed as epibionts on Caridina H. Milne Edwards, 1837. The distribution of the different epibiont species on the anatomical units of the shrimp was analyzed in each lake. There is a statistical significant difference between the three lakes in respect to the number of epibionts on each anatomical unit of all analyzed shrimps. The total and mean densities of each epibiont species on the different analyzed shrimps showed a significant difference between the three lakes; i.e., the presence of each epibiont species on the population of C. lanceolata varied from one lake to another. In Lake Towuti the highest density of epibionts was found on the anterior part of the shrimp body (rostrum, antennae, antennulae and eyes) (32.41%), while in the other two lakes, the highest colonization corresponded to the maxillipeds (31.56% Lake Matano, 40.89% Lake Mahalona). In Lake Towuti the rest of epibionts colonized mainly maxillipeds and pleopods (both 45.76% of epibionts). In Lake Matano, other epibionts were distributed principally on the anterior part of the body and pleopods (in total 57.18% of epibionts). In Lake Mahalona, other epibionts were divided among the anterior part of the body, pereiopods and pleopods (in total 57.39% of the epibionts). Uropods and telson were the units less colonized in Lake Matano (3.64%) and Lake Mahalona (1.72%), while in Lake Towuti, they presented a moderate density (13.18% of the epibionts). Taking into account the distribution of epibionts along the antero-posterior axis of the shrimp, considering the different anatomical units, there was a significant correlation between the three lakes. This fact indicates that, in the three lakes, the colonization on C. lanceolata followed a similar distribution pattern, independently of the epibiont species present. The comparison between the distributions of the same epibiont species along the longitudinal axis of the shrimp on the diverse lakes showed that they correlated respect to their density values on the anatomical units of the shrimp. Diverse aspects of the colonization patterns are discussed. Morphological features, taxonomic identification, and particular distribution of the epibiont species in each lake are also included.     

Biodiversity of testate amoebae (Arcellinida and Euglyphida) in different habitats of a lake in the Upper Paraná River floodplain

This study aimed to investigate the testate amoebae (Arcellinida and Eugliphida) species diversity in plankton, macrophytes and aquatic sediment samples from a shallow lake of the Upper Paraná River floodplain. Samples were carried out from April 2007 to March 2008. We recorded 89 taxa, belonging to 10 families. Eighty-two taxa were found in the aquatic sediment, 71 in the macrophytes and 53 in the plankton. Highest values of alpha diversity were observed in the aquatic sediment. Although the plankton had the highest number of accidental species, accessory and constant species were also observed in this habitat. Most of the species classified as constant for the plankton belonged to the genus Arcella. Most of the constant species in the macrophytes and aquatic sediment belonged to the genus Difflugia. This study supports the idea that the presence of these protists in the plankton should not be attributed only to stochastic processes because (i) the species diversity recorded in this habitat was remarkably high in relation to the total biodiversity of the lake, and (ii) we also recorded frequent and constant species in the plankton.     

Evaluation of the fatty acid profiles of two fairy shrimp species,Branchipus pasai Cottarelli, 1969 and Chirocephalus kerkyrensis Pesta, 1936 (Crustacea,Anostraca) fed different diets

Laboratory cultured fairy shrimps Branchipus pasai and Chirocephalus kerkyrensis, fed on an alga (Selenastrum capricornutum), a yeast (Saccharomyces cerevisiae) and an HUFA enriched yeast (Lansy PZ, produced by Artemia Systems, Gent, Belgium) were evaluated for their fatty acid (FA) profiles and total lipid content in order to obtain information on species differences in food conversion. The results indicate significant qualitative and quantitative differences (P < 0.001) in FA profiles both of feed and of fairy shrimp species. Among the three different diets, an appreciable lipid amount was recorded in the alga, as compared with baker‘s yeast which showed the poorest lipid content. The algal fatty acid profile showed adequate amounts of the EFA 18:2n6, 18:3n3 and20:5n3 (the most meaningful for aquacultural purposes). The enriched yeast was characterised by a considerable total lipid amount and by the presence of all the EFA. The overall amounts of fatty acids in the fairy shrimps correlated well with their levels in the feed(r > 0.9, P <0.001). An exception was noted in then-3 HUFA (highly unsaturated fatty acids) and n-6acids, among the individuals fed on yeast. Highly significant differences (P < 0.001) were also noted between the two fairy shrimp species fed on the same food type. When fed enriched yeast, both B. pasai and C. kerkyrensis profiles roughly reflected diet composition. However, when fed on algae or baker‘s yeast, the two species, though to different extents, exhibited higher EFA levels than those recorded in the food. This seems to support the existence of a partial FA bioconversion capacity in fairy shrimps previously noted in the case of the brine shrimp Artemia. This revised version was published online in August 2006 with corrections to the Cover Date.     

Impact of an exceptional winter flood on the population dynamics of bearded tits (Panurus biarmicus)

Mark–recapture data are used to investigate the impact of an exceptional winter flood on the population dynamics of an isolated bearded tit Panurus biarmicus population in north-west England. Adult numbers increased threefold (from 60 to 180 individuals) between 1992 and 2000, but declined by 94% during 2000/2001. This large reduction in numbers was caused by severe over-winter mortality associated with a prolonged flood of the Phragmites litter layer, the main winter foraging habitat of bearded tits, followed immediately by cold weather. At the end of the flood, bearded tits were 20% lighter than during previous winters. Population changes in other years were accurately predicted by annual variation in recruitment, and there was evidence that recruitment was higher following the introduction of artificial nest boxes and was density dependent. This study highlights the potential threat to bearded tits in Europe of predicted increases in the frequency and extent of winter flooding, and the potential utility of measures like artificial nest boxes that aim to promote recruitment. Recent extensions of methodology now permit a detailed exploration of animal population dynamics from mark–recapture data alone.     

Impact of grazing on the species richness of plant communities in Mediterranean temporary pools (western Morocco)

The impact of grazing on the vegetation of Moroccan temporary pools has been studied at 2 scales: regional (inter-pools) and local (intra-pools). Half of the 16 forest pools studied is located in a reserve and ungrazed. The other half, located within public forest, is grazed. Vegetation relevés coupled to water-depths measurements were carried out in each pool. The results showed a significant effect of grazing on both scales of analysis. This effect was found in the species composition of the vegetation, which differed between the 2 types of pools, and in the lower species richness and abundance of plant species in the grazed pools. These differences are interpreted as resulting from the selection by herbivores and the differential tolerance of species to disturbance. These impacts are likely to expose certain species to local extinction by reducing their populations.     

Impact of human activities on stonefly (Insecta,Plecoptera) ecological metrics in the Hron River (Slovakia)

A total of 57 stonefly species have been recorded in the Hron River. The natural gradient (slope and stream width) and pollution gradient of the river were defined using CCA based on physical, chemical and stonefly data. Stonefly metrics (abundance, richness/diversity, sensitivy/tolerance and functional metrics) were used to estimate the quality of the Hron River and the degree of proximity to its natural state. Similar results were obtained using two different methods. The first method was based on the homogeneity of variance and the interquartile range of different groups of stretches of the Hron River and the second was based on deviations from the expected values of biological metrics in a given stretch of the river. These values continuously decreased with increasing distance from the spring area, with the exception of the saprobic index, which increased in a downstream direction, and the stonefly average score, which did not change significantly along the whole river flow. The Stonefly Average Score (SAS) metric is universal for a variety of habitats such as the Hron River upstream and downstream, and is a reliable indicator of water quality and the natural course of a stream.     

Impact of porcine circovirus type 2 (PCV2) vaccination on boar semen quality and quantity using two different vaccines

Porcine circovirus type-2 (PCV2) is widespread in domestic pig populations. It can be shed with boar semen, but the role boars have in epidemiology is still unclear. Vaccinating boars against PCV2 can reduce disease and virus load in semen, but may have unwanted side effects, that is, impairment of spermatogenesis. Therefore, the aim of this study was to investigate the effect and impact of two different PCV2 vaccines on boar semen quality and quantity. Healthy normospermic Large White boars in three groups of 12 each were vaccinated with either Circovac, Ingelvac CircoFLEX, or received NaCl. Eight ejaculates were collected starting 1 week after vaccination and assessed for quantitative traits. In general, sperm quantity and quality parameters did not change due to the vaccination (P > 0.05). Only DNA integrity between the Circovac and control group was P < 0.05 but remained at a low level (<2%). One boar showed clinical signs with body temperature up to 39.9 °C and went off feed. For this animal, a clear relation between vaccination, fever period, and impaired sperm quality could be observed. The results indicate that both vaccines did not have a major impact on sperm quality or quantity. Therefore, vaccination of boars against PCV2 seems to be feasible. However, one boar treated with the oil-based vaccine showed a temporarily impaired semen quality after elevated body temperature after vaccination. Thus, possible systemic reactions and the subsequent impact on sperm quality should be taken into account when choosing a PCV2 vaccine for boars.     

The feeding rates ofPleurobrachia (ctenophora) andSagitta (chaetognatha), with notes on the potential seasonal role of planktonic predators in the dynamics of north sea zooplankton communities

The zooplankton off the north-east coast of England has been the subject of a number of studies focusing on its productivity. It has also been shown to be representative of the zooplankton of much of the western North Sea. The community contains a number of predatory species, three of which are widely described as ‘voracious’, the ctenophorePleurobrachia pileus, the chaetognathSagitta elegans and the hyperiid amphipodThemisto compressa (≡ Parathemisto gaudichaudi). This study investigates the role of these planktonic predators in this community, with special reference to the seasonal changes in predation pressure. The functional response ofPleurobrachia pileus feeding onAcartia was determined from laboratory experiments. It was found to be linear at prey densities typical of UK coastal waters, although the linear relationship appeared to break down at low and high prey densities. Feeding rate data forSagitta elegans were obtained from gut content analysis and published laboratory derived estimates of digestion time. Of the 1,789 individuals examined 198 (11.1%) had food remains in the gut. A linear relationship betweenSagitta length and prey size was established and the daily feeding rate ofSagitta elegans was estimated to be 0.4 prey items d⁻¹ ind⁻¹. For comparative purposes, the proportion of the copepod standing stock removed bySagitta elegans, Pleurobrachia pileus andThemisto gaudichaudi was estimated for each month of the year. From this model it was shown thatThemisto applied the most predation pressure, andSagitta elegans applied the least predation pressure of the three planktonic predators considered. The impact ofPleurobrachia will be to a large extent offset due to its peak of seasonal abundance coinciding with the zooplankton peak in the summer.     

The comparative reproductive styles of two closely related African minnows (Pseadobarbus afer andP. asper) inhabiting two different sections of the Gamtoos River system

Synopsis Two species of a monophyletic lineage of flexible-rayed redfin minnows,Pseudobarbus afer andP. asper, were studied to establish if there were any significant differences in their reproductive styles. They are sister species with few morphological or meristic differences.P. afer andP. asper are open substrate benthic spawners on coarse bottoms (rocks) and non-guarders of non-adhesive eggs. Their young are photophobic as free embryos. Riverine spawning sites indicated a conservative tendency and represented a phylogenetic constraint as compared to the more variable attributes, such as egg size, which were under environmental control within the limits expressed by the genotype. The combination of life-history attributes, gonadosomatic index, fecundity, egg size, investment per clutch, number of clutches per season and reproductive lifespan was found to be different forP. afer andP. asper. P. asper is derived and atypical of otherPseudobarbus species studied to date. Differences betweenP. afer andP. asper are directly related to the two distinct environments inhabited by these species-coastal Cape Fold Belt mountain streams and the inland Karoo streams of the Gamtoos River system.P. asper may have reverted, by juvenilization, to a more altricial form to survive the turbid, intermittent Karoo stream.