Lecane tenuiseta rotifers improves activated sludge settleability in laboratory scale SBR system at 13°C and 20°C

Two experiments at different temperatures were conducted in five laboratory‐scale bioreactors with enhanced nutrient removal simulating the work of sequencing batch reactors (SBRs). The process was operated in three 8‐hour cycles. The oxygen concentration, pH and temperature were controlled and maintained at 1 mg of O₂/L, 7 and 13°C, respectively, throughout the first two weeks and at 20°C for the next 10 days. The introduction of Lecane tenuiseta improved the settling properties of the activated sludge dominated by Microthrix parvicella at both temperatures tested. L. tenuiseta rotifers led to a reduction in filamentous bacteria abundance and did not negatively affect the chemical parameters of the effluent. For each temperature, there were no differences in COD, N_tot, N‐NH₄ or P‐PO₄ values between the treatment and control bioreactors. The results have shown that the application of L. tenuiseta is a promising biological tool for bulking prevention especially in a cold season.     

A comparison of benthic meiofaunal communities in the oldest European lake

The comparison of isolated stable habitats, that share major ecological parameters and organism groups, generates valuable knowledge about ecology and evolution. In this study we want to identify the most suitable habitat and organisms for comparisons. For this, we needed to study the effects of seasonality, habitat variability and diversity. Therefore, we studied the benthic meiofaunal communities in the sediment and hard substrates of Lake Ohrid’s littoral and profundal sediments as well as littoral rotifers collected monthly and seasonally between 2000 and 2010. Our results showed that, among the over two million meiobenthic organisms per square meter, nematodes dominated the profundal (mean proportion: 91%) and littoral (mean proportion: 87%) sediments; whereas, rotifers were the most abundant group in littoral periphyton (mean proportion: 64%). The community composition was very typical of each habitat-type, homogeneous in the profundal and more heterogenous in the littoral. Rotifer communities were only significantly less diverse and abundant in winter. Thus, a comparison of ancient lake nematodes living in the deep profundal is potentially quite valuable. However, littoral communities are less stable in terms of seasonality and heterogeneity.     

The Effects of Zebra Mussels on the Lower Planktonic Foodweb in Lake Champlain

Selective grazing by zebra mussels has altered phytoplankton communities in many North American lakes, but the specific changes are not the same in each ecosystem. Because of this variation in response, we investigated the impacts of zebra mussels on the plankton community of Lake Champlain with two objectives: first to determine whether zebra mussels increased the dominance of potentially toxic cyanobacteria in the phytoplankton, and second to explore the impact of zebra mussels on protozoans, rotifers, copepod nauplii, and other microzooplankton in the lower food web. Experiments were conducted in 200-L mesocosms filled with Lake Champlain water filtered through a 150-μm sieve to remove macrozooplankton. Zebra mussels were added to half of the mesocosms while the others were maintained as controls. Over a 96-hour experimental period, we tracked nitrogen and phosphorus concentration, chlorophyll a, microcystin concentration, and both phytoplankton and microzooplankton composition and abundance. We found an increase in SRP and total nitrogen concentration and a decrease in the ratio of TN:TP in the zebra mussel treatments over time. Microcystin was undetectable throughout the experiment using the ELISA assay. Phytoplankton biovolume, including cyanobacteria biovolume, declined significantly in the zebra mussel treatments, as did rotifer, protozoan and nauplii abundance. By both direct (consumption) and indirect (altered nutrient availabilities and increased competition) means, zebra mussels clearly seem capable of strongly influencing the lower planktonic foodweb in the many shallow water habitats of Lake Champlain.     

A review of regulation mechanisms of metazoan plankton in riverine ecosystems: aquatic habitat versus biota

This review summarizes the key factors of a series of articles about animal plankton in rivers, a topic that remains poorly investigated. Running water, in which sampling processes are variable and often difficult, acts as a constraint as well as a resource for plankton. Assessment of the potamoplankton reveals that good swimmers of the true plankton are mixed with numerous poor swimmers among littoral and epibenthic forms. Small taxa dominate communities in most of rivers all over the world and, in comparison with crustaceans; the successful development of rotifers rests on their shorter development times. According to hydraulic and geomorphological features, the diversity of the habitats and the ability of individuals to avoid washout was examined, decrease in flow creating standing zones favourable to zooplankton development. Many species can find suitable conditions for the development of dense populations in stream habitats and examples of taxa‐specific response, regardless of the habitat structure, are observed. While the challenge for riverine plankton remains ‘eat to be fruitful and multiply’, their activities have been poorly investigated in turbulent conditions, those able to continue growing in a current of 20 cm s^?1, such as brachionid species, being usually dominant in rivers. Examination of the distribution of plankton populations, in the Middle Loire and in other rivers, showed that the flow regime, which plays a central role in organizing river habitats, explains the presence/absence of these fast‐growing organisms. While reservoirs are major sources of crustaceans, lateral exchanges as well as downstream transport are important in determining the plankton. These ecosystems are primarily governed by abiotic factors, biological control taking place after physical control has happened. Because animals arrive by chance in any habitat during dispersion, zooplankton in rivers remains primarily governed by unpredictable physical processes and depends on the age of the water and the availability of habitats. In this way, the hydro‐dynamics of river habitats need to be more documented with regard to their key role in the planktonic life. Preservation of the lentic areas remaining at the heart of the matter, the contrasting ecology of the rotifers should be a reliable tool with which to estimate the changes in habitats diversity of main channels, particularly during droughts, while crustacean's diversity would be more representative of flood plain annexes, particularly during flood events. Copyright © 2006 John Wiley & Sons, Ltd.     

The influence of seasonality and duration of flooding on zooplankton in experimental billabongs

The regulation of Australian lowland rivers such as the River Murray has resulted in changes to the flooding characteristics of many associated wetlands. It has been suggested that these changes in flooding have changed the pattern of response of many wetland biota. The substantial variability in the size and shape of these wetlands makes limited field observations difficult to interpret. To overcome this variability 16 experimental billabongs were constructed in which factors that may cause changes to populations within billabongs could be manipulated. In this paper we report on experiments that test the hypothesis that changing the pattern of flooding alters the density and diversity of rotifers and microcrustaceans in billabongs. The experimental billabongs were sampled fortnightly for two years. During this time four flood events were imposed. Flooding of the experimental billabongs resulted in increased microcrustacean abundance. Rotifer abundance rarely increased following flooding. Changing the time of flooding did not modify this response. Observed changes in community structure following flooding result from changes in the relative densities of taxa already present rather than changes in the community composition. Copyright © 2002 John Wiley & Sons, Ltd.     

Zooplankton partitioning in a tropical alkaline–saline endorheic Lake Nakuru,Kenya: Spatial and temporal trends in relation to the environment

Spatial and temporal zooplankton variations were studied for 1 year in tropical alkaline–saline Lake Nakuru to determine how they partition in the habitat, relative to environmental variables. Monthly samples were collected at 10 sampling sites, with subsurface tows, using 33.5‐μm mesh plankton nets. Physicochemical parameters displayed clear seasonal variations associated with precipitation patterns. Nine species, belonging to two main zooplankton taxonomic groups (ciliates; rotifers), were identified in the samples. Brachionus dimidiatus dominated the samples, accounting for 80% of the total zooplankton abundance. Kruskall–Wallis tests indicated significant (P < 0.05) temporal and spatial variations among all taxonomic groups. Different zooplankton species displayed a clear succession throughout the year. The total abundance of the rotifers and ciliates peaked at sampling sites near inlets during the long rainy seasons, while those in the inshore sites displayed variable succession patterns. Spatiotemporal structure of the zooplankton assemblages, and its correlation with environmental variables, indicated each species displayed distinct niche‐based partitioning. The ciliates niche was associated with increasing soluble reactive phosphorus, total phosphorus and nitrite–nitrogen (NO₂–N) concentrations. Niche partitioning in rotifers was associated with nitrate–nitrogen (NO₃–N), conductivity and pH. These results indicate physical niche separation, even in a small, relatively homogenous lake among species of rotifers and ciliates, providing information from which future changes in their abundance and spatial distributions can be predicted, given continuous water quality changes.     

Microinvertebrate dynamics in riverine slackwater and mid‐channel habitats in relation to physico‐chemical parameters and food availability

Microinvertebrates play a critical role in riverine food webs, and recent studies have hypothesized that slackwaters, non‐flowing regions associated with the main channel, are important for their reproduction and recruitment. However, little is known regarding the population and community dynamics of microinvertebrate communities in slackwater regions, or how they compare with those in mid‐channel regions. This study examined microinvertebrate communities in the epibenthic and pelagic zones of slackwater and mid‐channel regions (i.e. four habitats) of an Australian floodplain river in relation to physico‐chemical parameters and food availability (as estimated by chlorophyll‐a concentration) between September 2005 and November 2006. Results from this study indicate that microinvertebrate abundance and diversity were greater in slackwater habitats than mid‐channel habitats overall, corresponding with the slower current velocities associated with the former. Nevertheless, communities in all four habitats were most abundant and diverse in late spring (coinciding with an increase in water temperature), and followed similar seasonal trajectories in terms of density, taxon richness and community structure. These findings support the view that slackwaters are important for in‐channel microinvertebrate production, and suggest that animals frequently disperse (either actively or passively) among slackwater and other main channel regions year round. Given the critical importance of microinvertebrates in riverine food webs, rivers should be managed with a view to maintaining a natural variety of accessible slackwater regions in order to support the production and survival of microinvertebrate communities. Copyright © 2009 John Wiley & Sons, Ltd.     

Reduction of suspended biomass in municipal wastewater using bdelloid rotifers

Clarification of municipal wastewater was shown to be improved significantly by the addition of cultured bdelloid rotifers. The rate and degree of suspended particle removal were correlated with rotifer number. The size range of unsettled particles suspended in wastewater was determined and found to overlap with the size range of particles consumed by rotifers. Rotifers were shown to have two distinct effects on suspended particles: consumption of biomass due to feeding activity; and improved settling, probably due to enhanced aggregation. These experiments demonstrate the potential for the use of bdelloid rotifers in an enhanced wastewater treatment process, with reduced biomass production and improved effluent clarity.     

Comparison of the components of the planktonic food web in three large rivers (Rhine,Moselle and Saar)

The dynamics of phyto‐, bacterio‐, proto‐ and metazooplankton were investigated for a period of 22 months fortnightly from March 1999 until December 2000 in the rivers Moselle, Saar and Rhine. Plankton abundances reached the lowest values in the Rhine and the highest in the Saar. Protozoa and not the much more studied metazoa clearly dominate the zooplankton not only by number but also by biomass by about 90%. We show that the plankton biomass in each of the rivers is the result of the interplay of the grazing by benthic predators and of the human induced factors such as river morphology, water residence time and nutrient load. Furthermore, we compare our study with the planktonic food web of three other large European rivers. The comparison between all studies revealed a general rise of the absolute mean biomass of all heterotrophic planktonic food web components (bacteria, protozoa, metazoa) parallel to an increase of the algal biomass of the river. For the rivers Rhine, Moselle and Saar, the average biomass of all investigated plankton groups was very low compared to the values obtained in the rivers Meuse, Loire and Elbe. The relative importance of organisms of the microbial food web increased with a decrease of the algal biomass or organic carbon content, respectively, in each of the rivers. We postulate that with a sinking nutrient level in the Rhine, the microbial food web components will become even more important within the plankton than they already are. Copyright © 2008 John Wiley & Sons, Ltd.     

Chemical suppression of feeding in larval weakfish (Cynoscion regalis) by trochophores of the serpulid polychaeteHydroides dianthus

We studied the effect of exudates from trochophore larvae of the polychaeteHydroides dianthus on feeding in larval weakfish (Cynoscion regalis). Laboratory prey consisted ofH. dianthus trochophores and/or comparably sized rotifers (Brachionus plicatilis). When experiments were conducted in filtered seawater, ingestion of rotifers was always greater than ingestion of trochophores. However, consumption of rotifers was depressed when water fromH. dianthus cultures (=trochophore water) was the experimental medium. The same effect was noted whether we added trochophore water from polychaete cultures that were two or five days postfertilization. However, no effect was noted when we used water from rotifer cultures. We concluded thatH. dianthus trochophores release a water-soluble compound that inhibits feeding in weakfish larvae.