Planktonic Microcrustaceans Research Articles

Spatial and Temporal Changes of Planktonic Microcrustaceans (Cladocera, Copepoda) and their Relationship with Physicochemical Parameters in Kırklareli Reservoir (Kırklareli-Türkiye)

The present study focused on monthly densities and abundances of planktonic microcrustaceans (Cladocera and Copepeda) in Kırklareli reservoir, as well as their relationship with some physicochemical parameters at three stations for the period from May 2018 to April 2019. In the present study, a total of 26 planktonic microcrustaceans species, 14 from Cladocera and 12 from Copepoda were identified. The mean annual microcrustacean abundance recorded during the study was 24076 ind/m3, 67% of which was Cladocera (16054 ± 12414 ind/m3) and 33% was Copepoda (8022 ± 5564 ind/m3). The maximum abundance of planktonic microcrustaceans were found in September (51521 ind/m3) and the minimum was found in January (2919 ind/m3). The most common species in the reservoir were Bosmina longirostris, Daphnia pulex, Daphnia cucullata, Daphnia galeata, Daphnia longispina and Diaphanosoma brachyurum from Cladocera and Cyclops abyssorum, Cyclops vicinus, Eudiaptomus vulgaris and Arctodiaptomus wierzejskii from Copepoda. The environmental parameter values measured in the reservoir were acceptable to support aquatic life, especially the zooplankton community. The total density and abundance of zooplanktonic microcrustaceans showed positive correlation with the water temperature and Chlorophyll-a. According to these results, we concluded that Kırklareli reservoir has a mesotrophic character in terms of the microcrustacean fauna and the physicochemical parameters.

Sediment as a Refuge Spot for Planktonic Crustaceans

The littoral zone of shallow water bodies (SWB) is often considered in relation to predator–prey interactions. In this study we assumed that the littoral sediment serves as a refuge for planktonic microcrustaceans, mediated by size-dependent fish predation. In order to recognise the impact of fish on their prey, we determined: (i) the assemblage and size structure of crustaceans and fish; and (ii) the biotic interactions along the gradient of the heterogeneity of the littoral zone. The results showed that in the sediment of macrophyte-dominated SWB, large-sized cladocerans predominated and were preyed upon by smaller-sized fish. In the sediment of macrophyte-absent SWB, large-sized copepods dominated, due to the predation risk of larger-sized fish. Cladoceran females with egg broods mostly selected sediment as shelter. Cladocera/Copepoda ratios were lower in the littoral of vegetated SWB, and higher in unvegetated SWB. The ratios in the adjacent sediment revealed an opposite pattern. It is important to point out the findings of planktonic crustacean species in the sediment of SWB are not recorded in the littoral water. The result of this study will contribute to the knowledge of defence strategy mechanisms developed by zooplankters against predators.

Alpha and beta diversity of planktonic microcrustaceans are associated with environmental heterogeneity in the Frades River Basin, Brazil

ABSTRACT Plankton in rivers are good indicators of water quality and their study along the longitudinal axis allows for understanding the interactions between natural and anthropogenic variations and diversity at different spatial scales. We compared the taxonomic biodiversity of planktonic microcrustaceans in two sections of the Frades River Basin, Brazil. Water and microcrustaceans were sampled in August 2018, April 2019, July 2019, and October 2019 in the basin. We recorded 43 taxa as the regional diversity of microcrustaceans. Alpha diversity was statistically higher in the upper section of the basin. The analysis of indicator species showed that nine species were characteristic of the studied sections. The upper section was represented by Nicsmirnovius paggii, Acroperus tupinamba, Alonella dadayi, Alona guttata, and Microcyclops finitimus and characterized by higher dissolved oxygen, higher values of pH of water and lower nitrate and total coliforms concentrations. Diaphanosoma birgei, Alona sp., Grimaldina brazzai, and Ilyocryptus spinifer were characteristic of the lower sections of the basin, with the highest concentrations of nitrate and total coliforms. The microcrustaceans in the lower sections were limited by the gradient of environmental conditions, making local communities simpler (low species richness) and with few species probably adjusted to narrow ranges of environmental conditions.

Phylogenetic analysis of eight species of Anomopoda based on transcriptomic and mitochondrial DNA sequences.

Anomopoda is the widespread planktonic microcrustacean, which plays a crucial role in aquatic ecosystem. There are few studies about the evolutionary relationships among various Anomopoda basing on molecular data. In the present study, phylogenetic analysis of eight Anomopoda was carried out. Firstly, the culture system was developed to breed cladocerans. By using this system, eight species (Daphnia magna, D. pulex, D. sinensis, Ceriodaphnia reticulata, Moina micrura, Scapholeberis kingi, Simocephalus vetulus and Eurycercus lamellatus) were purified and cultured stably in the laboratory. Then, transcriptomic sequences and partial mitochondrial DNA sequences were both used to reconstruct the phylogenetic tree among 8 species. Transcriptomic sequences were sequenced on Illumina Hiseq 2500 platform. After assembly and annotation, transcriptomic sequences were spliced together and aligned for phylogenetic analysis. Basing on the orthologous genes derived from transcriptomic sequences, the phylogenetic analysis showed that 4 genera of Daphniidae were clustered into one group, and among the 4 genera, Ceriodaphnia was closer to Daphnia than Simocephalus, while Scapholeberis was farthest from other species. In addition, Eurycercidae was closer to Daphniidae than Moinidae. The phylogenetic trees based on both 12S rRNA and 16S rRNA sequences were similar with that based on transcriptomic sequences. Meanwhile, the phylogenetic tree based on 16S rRNA sequences was more suitable than that based on 12S rRNA sequences. These results suggested that the phylogenetic analysis basing on the transcriptomic sequences was available in cladocerans, which will help us to effectively understand the phylogenetic relationships among various cladocerans.

Kayalıköy Barajı’nın (Kırklareli/Türkiye) planktonik mikrokrustase (Copepoda, Cladocera) tür çeşitliliği, bolluğu ve mevsimsel dağılımı

This study was carried out to determine the diversity, abundance and seasonal distribution of planktonic microcrustaceans (Cladocera, Copepoda) in Kayalıköy Reservoir. Cladocera and Copepoda samples were collected from May 2018 to April 2019 at three stations in the reservoir and some environmental parameters were measured. The qualitative evaluation of the samples revealed presence of 40 species, 24 from Cladocera and 16 from Copepoda, in the reservoir. The quantitative evaluation of the samples showed that 52690 ind./m³ zooplankton on average was found in the reservoir. The most common species in the reservoir were Daphnia cucullata, D. longispina, D. pulex, Bosmina longirostris and Chydorus sphaericus from Cladocera, and Arctodiaptomus wierzejskii, Acanthocyclops robustus and Thermocyclops crassus from Copepoda. According to the water quality standards, the measured values of water temperature, dissolved oxygen, sulfate, salinity and chloride indicated the first quality of water, while the light permeability, nitrite-nitrogen, nitrate-nitrogen, ortho-phosphate and chlorophyll-a values indicated the second and third quality of water levels. According to these results, we conclude that Kayalıköy Reservoir has a mesotrophic character in terms of the microcrustacean fauna and the physicochemical parameters.

Interactions between a planktivorous fish and planktonic microcrustaceans mediated by the biomass of aquatic macrophytes

AbstractHabitat complexity is recognized to mediate predator–prey relationships by offering refuge or not. We investigated the availability of planktonic microcrustaceans and the diet of a planktivorous fish (Hyphessobrycon eques) at different levels (low, intermediate and high) of aquatic macrophyte biomass. Sampling was carried out in a river with low flow speed, located in a Neotropical floodplain. We collected fish and microcrustaceans in macrophyte stands with variations in biomass. There were no differences in microcrustacean density in the water among the levels of macrophyte biomass, but microcrustacean richness and diet composition of H. eques differed. Microcrustacean richness and trophic niche breadth of the planktivorous fish were higher in high biomass stands. There was high consumption of a small cladoceran species in low macrophyte biomass, which was replaced by larger species, such as copepods, in intermediate and high biomass. Thus, the selection of some species was different among the biomass levels. These results suggest that plant biomass plays an important role in the interaction between fish and microcrustaceans, and prey characteristics such as size, escape ability and energy value make them more or less subject to predation by fish according to habitat structuring.

Non-predatory mortality of planktonic microcrustaceans (Cladocera and Copepoda) in neotropical semiarid reservoirs.

The accuracy of traditional methods to sample planktonic microcrustaceans depends on two assumptions: that organisms are alive during sampling and that all carcasses can be identified despite their degradation state, but fresh carcasses are not easy to distinguish by traditional methods. Previous studies about mortality have shown that neglecting dead organisms can provide biased ecological information. Thus, our objective was to determine the mortality rate and the proportion of dead microcrustacean in three tropical reservoirs. Sampling was carried out in 12 stations during two periods. The proportion of dead organisms was verified using aniline blue and it varied between 0.6% and 90.6%. The carcass decomposition period varied between 3 to 16 days and microcrustaceans mortality rate varied between 0.005 and 0.314 d-1. Traditional preservation techniques with formalin do not significantly overestimate species abundance. However, these values should not be disregarded, because corrected (disregarding organisms that were dead) and formalin-preserved abundances were correlated with distinct limnological descriptors. Therefore, the traditional formalin preservation technique could provide misleading ecological interpretations. Other studies over larger temporal scales in addition to experiments to evaluate the effects of viruses, parasitism and the toxic effects of cyanobacteria on zooplankton would enlighten mortality rate patterns in freshwater ecosystems.

Planktonic Microcrustacean Community Structure Varies with Trophic Status and Environmental Variables in Tropical Shallow Lakes in Malaysia

A study was conducted to evaluate planktonic microcrustacean species composition, abundance, and diversity in lakes with different trophic status and to determine the relationship between microcrustacean community structure and lake environmental conditions. This study hypothesized that there are correlations between eutrophication levels and microcrustacean community structures in a lake. Three shallow lakes of different trophic status (Sembrong, Putrajaya and Subang lakes) were selected for this study. Two-Way Analysis of similarities (ANOSIM) revealed differences in microcrustacean diversity and density amongst lakes, where the hypereutrophic condition in Sembrong lake resulted in the lowest diversity but the highest density of microcrustaceans. Similarity percentage (SIMPER) analysis identified the discriminator species among lakes where the domination of small-sized microcrustaceans was observed in lakes with high levels of eutrophication; the hypereutrophic Sembrong lake (Ceriodaphnia cornuta, 74.0%); the meso-eutrophic Putrajaya lake (Bosmina longirostris, 46.9%; C. cornuta, 19.4%). Chlorophyll a, total phosphorus and water transparency showed significant roles in the distribution of microcrustaceans. The canonical correspondence analysis (CCA) scores indicated that small-sized C. cornuta and B. longirostris were related to the eutrophic conditions of lakes. This study elucidated that the lake trophic status could be one of the main factors contributing to the community restructuring of microcrustaceans in tropical lakes.

Oligotrophication affects the size structure and potential ecological interactions of planktonic microcrustaceans

The oligotrophication of freshwater is the reduction of the nutrient concentration in the water column, which causes the depletion of organic matter and diminishes the biological production of the ecosystem. To elucidate the zooplankton response to nutrient depletion (oligotrophication), an experiment was performed in mesocosms simulating real scenarios. Phytoplankton and zooplankton inocula were collected in the Upper Parana River Floodplain and subjected to combinated nutrient and transparency treatment. We evaluated whether resource limitation and increased transparency (both associated with oligotrophication) affect the size structure of planktonic crustaceans. The effects of predation were corroborated in the treatments with low nutrient concentrations. Thus, the oligotrophic scenario (high transparency and low nutrient concentration) indicated a decreased size structure of zooplankton, probably because of the predation pressure, supporting the predictions of the size-efficiency hypothesis (SEH). When resources were abundant (in treatments with high nutrient concentrations), the decrease in the size structure indicated that the enrichment of nutrients favoured small individuals. Our results showed that nutrient and transparency manipulation affected species richness, the abundance of individuals, and the zooplankton community size structure. Therefore, we suggest that oligotrophication affects predation and competition dynamics in zooplankton.

Distribution of planktonic microcrustaceans (Cladocera and Copepoda) in lentic and lotic environments from the semiarid region in northeastern Brazil

Abstract The present study aimed to inventory the biodiversity of planktonic microcrustaceans (Cladocera and Copepoda) in 44 environments from the semiarid region of Brazil, increasing the knowledge about zooplankton community, including phytophilous species. Between 2011 and 2017, organisms were collected in a non - systematic way in the states of Rio Grande do Norte, Pernambuco, Ceará and Paraíba. A total of 60 species of planktonic microcrustaceans were identified, of which 52 were cladocerans and eight were copepods. The basin that presented the highest richness was Pajeú River with 41 species. Nevertheless, the extrapolated number of species shows an increasing tendency for this basin. The genus composition was different between the basins, with Moxotó basin (Pernambuco) being isolated from the others, probably since lagoons were the only type of environment sampled in this basin. Richness and abundance patterns were higher for the basins where sampling was mainly performed in lentic environments, such as Pajeú and Moxotó. Microcrustacean inventories and long-term studies need to be conducted more frequently to better understand the biodiversity of continental aquatic ecosystems in the semiarid region of Brazil.

Nanoecotoxicity assessment of graphene oxide and its relationship with humic acid.

The risk assessment of nanomaterials is essential for regulatory purposes and for sustainable nanotechnological development. Although the application of graphene oxide has been widely exploited, its environmental risk is not well understood because several environmental conditions can affect its behavior and toxicity. In the present study, the graphene oxide effect from aquatic ecosystems was assessed considering the interaction with humic acid on 9 organisms: Raphidocelis subcapitata (green algae), Lemna minor (aquatic plant), Lactuca sativa (lettuce), Daphnia magna (planktonic microcrustacean), Artemia salina (brine shrimp), Chironomus sancticaroli (Chironomidae), Hydra attenuata (freshwater polyp), and Caenorhabditis elegans and Panagrolaimus sp. (nematodes). The no-observed-effect concentration (NOEC) was calculated for each organism. The different criteria used to calculate NOEC values were transformed and plotted as a log-logistic function. The hypothetical 5 to 50% hazardous concentration values were, respectively, 0.023 (0.005-0.056) and 0.10 (0.031-0.31) mg L-1 for graphene oxide with and without humic acid, respectively. The safest scenario associated with the predicted no-effect concentration values for graphene oxide in the aquatic compartment were estimated as 20 to 100 μg L-1 (in the absence of humic acid) and 5 to 23 μg L-1 (in the presence of humic acid). Finally, the present approach contributed to the risk assessment of graphene oxide-based nanomaterials and the establishment of nano-regulations. Environ Toxicol Chem 2018;37:1998-2012. © 2018 SETAC.

Can nearby eutrophic reservoirs sustain a differentiated biodiversity of planktonic microcrustaceans in a tropical semiarid basin?

This paper aims to compare alpha and beta diversities of planktonic microcrustaceans from three reservoirs located nearby in a tropical semiarid basin. Our hypothesis was that alpha and beta diversities of the community are different, although the ecosystems are located close to each other. We carried out two sampling campaigns: dry and rainy seasons. The sampling of microcrustaceans and environmental variables (dissolved oxygen, chlorophyll a and nutrient) was performed at twelve stations and were distributed throughout the three zones (river, transition, and lacustrine), using a plankton net (45 µm). The reservoirs showed different uses and types of nitrogen predominance: Cachoeira (supply/nitrate), Borborema (sewage/ammonia) and Saco (aquaculture/ammonia). Seventeen species were recorded whose richness was assessed as particularly specific to each one of the studied reservoirs. Seasonally, both reservoirs with high anthropogenic alteration showed greater richness in the dry season. The three reservoirs located in a same basin showed different richness and composition, but the diversity did not differ between the zones of the reservoirs. Although communities are close to each other, their composition and richness were found to be distinct for each reservoir. This may be in response to the peculiar particularities, such as nitrogen sources and the different uses.

Are the littoral zone conditions suitable for tropical planktonic microcrustaceans?

The occupation of the littoral and limnetic zones by planktonic species has led to questions about whether littoral macrophytes would be a suitable habitat or refuge. These questions guided our field and laboratory studies on the spatial occupation and the food suitability for microcrustaceans of a shallow tropical lake. Replicated zooplankton samples were collected over 18 days, at intervals of 3 days, at three zones (the middle and edge of the stands of the emergent macrophyte, Ludwigia sp., and the limnetic zone). Some species, such as the cladocerans Diaphanosoma birgei and Daphnia ambigua , showed preference for the littoral zone and the limnetic zone, respectively. Copepodites, and adult copepods Thermocyclops decipiens and Tropocyclops prasinus meridionalis are mainly limnetic dwellers. The size of the cladocerans Ceriodaphnia richardi and Daphnia gessneri did not differ between the zones, nor did the clutch size of the former species; smaller individuals of D. ambigua were found within macrophyte stands. In laboratory experiments, the seston of the three zones did not negatively affect the development of the cladocerans C . richardi and D. birgei . On the contrary, the seston of the middle of the macrophyte stands promoted better growth rates of both cladocerans and some of the life table parameters of D. birgei than the seston of the other two zones. Food quantity and quality are not negative factors to microcrustaceans in the littoral and limnetic zones. The preference or indifference of microcrustaceans to habitats may be part of their adaptive strategies regarding other factors, including predation.

ABUNDANCE AND ISOTOPIC COMPOSITION OF PLANKTONIC MICROCRUSTACEANS IN A CENTRAL AMAZON FLOODPLAIN LAKE: IMPLICATIONS FOR THE TROPHIC DYNAMICS OF THE PLANKTON COMMUNITY

<p>During the hydrological year from December 2007 to November 2008, monthly samplings in the pelagic, littoral and macrophytes zones were conducted in the Lago Catalão, a floodplain lake receiving a mixture of water from Negro and Solimões Rivers, in front of Manaus city. Taxonomic composition and their relative abundance of the planktonic microcrustaceans community was studied. Natural abundances of carbon (C) and nitrogen (N) stable isotopes were measured to indicate energy sources. Cladocerans were the most abundant, with a relative abundance of 60%, followed by the calanoid and cyclopoid copepods with relative abundances of 29% and 11%, respectively. Diaphanosoma spp. was the dominant cladoceran group during all the sampling periods. Cladocerans were also represented by Moina spp., Ceriodaphnia spp. and Daphnia gessneri. Three genera of calanoid copepods were found: Notodiaptomus spp, Rhacodiaptomus spp., and Argyrodiaptomus spp. The genus Mesocyclops spp. was identified among the cyclopoid copepods. Zooplankton δ13C values indicated that the aquatic macrophyte zone was distinct, with a mean of -27.31‰, which was more enriched than zooplankton in the pelagic and littoral zones, where they had mean δ13C values of -33.11 and -34.66‰, respectively. Overall, analysis of stable isotopes showed that regardless of the pathways, the initial source of carbon for the zooplankton was phytoplankton, with a minimal participation of heterotrophic bacteria.</p>

Identification of common cladocerans and calanoids in two south Australian reservoirs using DNA barcoding and morphological analysis: an integrative approach

Valid identification of species of freshwater zooplankton is the first step to understand population structures, abundance, and diversity in the pelagic environment. While some Australian taxa can be easily identified morphologically, e.g.,Calamoecia ampulla(Searle, 1911), most other species of freshwater micrometazoans are difficult to identify without specialised training, resulting in limited and even incorrect identification of the various taxa. The use of DNA barcodes, for species identification and discrimination, has added a new dimension to the traditional phenotypic approach and allows researchers to understand the patterns of genetic variability and to overcome taxonomic difficulties in the identification of the species from different life history stages. We used mitochondrial gene cytochrome coxidase I (COI) to examine the species status of common planktonic microcrustaceans in two South Australian reservoirs. COI analyses indicated that the zooplankton specimens examined from the order Diplostraca and the class Maxillopoda, which were assigned binomial names a priori from the generaBosmina,Boeckella,Chydorus,CalamoeciaandDaphnia, possessed distinct COI sequences and nested cohesively within the genealogy, except for individuals ofCeriodaphniacf.cornutaand aCeriodaphniaspecies complex that formed 4 clusters. These clusters were not explicitly identified morphologically. The present study does improve and contribute to the understanding of the status of taxonomy and biogeography of micro-crustaceans in South Australia. This information is crucial for the application of these species in studies of local and regional environmental change over varying time scales. We recommend the integration of traditional morphology with DNA barcoding-based examination, to facilitate species identification, especially for applied research.

The effect of epibiont ciliates on the behavior and mating success of the copepod Eurytemora affinis

Epibiotic relationships in aquatic ecosystems usually involve planktonic micro-crustaceans (e.g. copepods) as hosts, and a variety of other microorganisms (e.g. bacteria, algae, ciliates) as epibionts. Several studies have reported the presence of epibionts on various species of calanoid copepods. However, the consequences of copepod behavior have not been extensively studied. Epibionts can impede reproduction and mating and increase predation pressure on copepods by limiting their swimming and escape capabilities.In late winter of 2009, we collected the copepod Eurytemora affinis from the Seine estuary and maintained them in the laboratory. We cultured copepods infested by the ciliate epibiont Zoothamnium sp. separately from uninfested copepods for one month under laboratory conditions. We then recorded the behavior of both the heavily infested and the clean copepods using 2D infrared video techniques, and analyzed the trajectories obtained using appropriate statistical methods. The trajectories revealed that the presence of large numbers of epibionts could negatively affect the behavior of the host, in terms of swimming activity (break, cruise, sink, and jump). Females were less affected than males. The high proportion of infestation also dramatically affected mating success. Mating was rare and practically nonexistent after one week in culture.This study indicates some of the difficulties that E. affinis could face during critical periods of its life span. In late winter, the population is mainly composed of old copepods, in low temperature water. Limited food resources and the presence of epibionts on their bodies eventually weaken the copepods, thus impairing their mating success and decreasing their survival rates.

Copepods (Crustacea, Maxillopoda) from shallow reservoirs

AIM: Among the planktonic microcrustaceans, copepods Cyclopoida and Calanoida are the most representative groups, being the largest biomass of the plankton community. The aim of this work is to catalogue and analyze the distribution of copepod species (Crustacea, Maxillopoda) in pelagic and littoral zones from small reservoirs in the northwest of the São Paulo State, in dry and rainy seasons (2007 and 2009). METHODS: Zooplankton samplings were carried out in littoral and pelagic zones of 13 small shallow reservoirs (mean depth: 2.6 m) using vertical hauls and plankton net (45 µm). Water physical and chemical parameters were also monitored with a multiparameter Horiba® U10. RESULTS: Eighteen species of copepods were identified, 13 Cyclopoida and 5 Calanoida. There was no statistical difference between the distributions of species from the littoral and pelagic zones and neither between dry and rainy seasons. Three species occurred exclusively in the littoral zone - Eucyclops elegans, Paracyclops chiltoni and Mesocyclops ogunnus. Tropocyclops prasinus and Thermocyclops decipiens were the most frequent species in the studied environments. CONCLUSION: Our data suggest that in shallow reservoirs copepods present a homogeneous distribution between the littoral and pelagic zones and Cyclopoida are more diverse than Calanoida. Shallow depths and eutrophic state may be regarded as limiting conditions for the development of Calanoida in these reservoirs.

Predation on microcrustaceans in evidence: the role of chaoborid larvae and fish in two shallow and small Neotropical reservoirs

This study was focused on the predation upon microcrustaceans by an invertebrate predator (chaoborid larvae), and vertebrate predators (fish), in two small reservoirs in southeastern Brazil, with and without macrophytes, in two climatic periods (dry and rainy seasons). Chaoborus larvae were sampled in the limnetic zone, as they are scarce in the littoral, and fish in both limnetic and littoral zones. Their diets were evaluated by the analysis of the crop (chaoborid) or stomach contents (fish). Chaoborid larvae consumed the dinoflagellate Peridinium sp. or other algae, rotifers, and planktonic microcrustaceans. The fish species that included microcrustaceans in their diets were juveniles caught in the littoral. Aquatic insects, plant fragments, and detritus were their major dietary items, microcrustaceans representing a minor item. Planktonic copepods contributed more to the diet of chaoborid larvae than planktonic cladocerans. Fish preyed on planktonic microcrustaceans, as well as on benthic and macrophyte-associated species. Microcrustaceans were not heavily preyed on by chaoborid larvae and fish in both reservoirs.

Vulnerability of microcrustaceans to predation by the invasive filter-feeding mussel Limnoperna fortunei (Dunker)

Limnoperna fortunei is an Asian mussel introduced to South America around 1990. One of the most important impacts of this invader is probably its grazing on the plankton. In this study we evaluate the vulnerability of several planktonic microcrustaceans from the Paraná River floodplain to predation by adult L. fortunei. We conducted 2-h laboratory feeding experiments where the bivalves were offered microcrustaceans differing in overall body shape, size, and locomotive abilities. Ingestion and clearance rates for each taxon were estimated. Results suggest that, in addition to detritus and phytoplankton, microcrustaceans may be a very important food item for this invasive mollusc. Limnoperna fortunei can prey on larger organisms (up to 1100 µm) than Dreissena polymorpha, the European and North American invasive mussel.

Prevalence of Colacium vesiculosum (Colaciales: Euglenophyceae) on planktonic crustaceans in a subtropical shallow lake of Argentina

Colacium vesiculosum (Euglenophyceae) is an epibiont common on planktonic microcrustaceans of continental waters. The interaction between epibionts and substrate organisms is not very well known, particularly in subtropical environments of South America. In the present work, we analyzed the prevalence, density, biomass and attachment sites of C. vesiculosum on planktonic microcrustaceans from Paiva Lake, a subtropical lake of Argentina. With the aim to evaluate whether epibionts affect the filtering rates of Notodiaptomus spiniger, the dominant planktonic crustacean, we carried out bioassays using phytoplankton < 53 microm. Crustaceans were sampled using a PVC tube (1.2m long and 10cm in diameter), filtering 50L of water through a 53 microm-mesh. Microcrustaceans were counted in Bogorov chambers under a stereoscopic microscope. The infested organisms were separated and observed with a photonic microscope to determine density and biovolume of epibionts, by analyzing their distribution on the exoskeleton. The prevalence of C. vesiculosum was higher in adult crustaceans than in their larvae and juveniles. The most infested group was that of calanoid copepods, related to their high density. The attachment sites on the exoskeleton were found to be the portions of the body which have a higher probability of encounter with epibionts during locomotion and feeding, i.e., antennae and thoracic legs in copepods, and thoracic legs and postabdomen in cladocerans. The similar values found in the filtering rate of infested and uninfested individuals of N. spiniger and the constant prevalence (< 40%) of epibiont algae, suggest that C. vesiculosum does not condition the life of planktonic crustaceans of Paiva Lake.