Search

Some species of freshwater microcrustaceans have been widely used for biological control of mosquito larval populations. These zooplankton communities play an important role against some species of mosquitoes by exerting competitive pressure or predation. However, zooplankters are scarcely studied in many Caribbean islands such as Hispaniola. The goal of this study was to improve the knowledge of these microcrustaceans in order to better understand the biodiversity and ecology of this Antillean Island. Samples of zooplankton were taken from 28 ponds in the northern Dominican Republic during 2020. The total richness of microcrustaceans was 25 species, comprising 17 copepods and 8 cladocerans. Most of the collected species were previously described for the island, and some of them are registered as potential biological controllers of mosquito larvae populations. Five genera (including 6 species) of microcrustaceans that inhabit the ponds are recorded for the first time for Hispaniola: Simocephalus Schoedler, 1858; Pleuroxus Baird, 1853; Ilyocryptus G.O. Sars, 1861; Apocyclops Lindberg, 1942; and Diacyclops Kiefer, 1927. Here, we discuss these new findings in relation to the competitive and/or predatory potential of these species against mosquito larvae. The present study improves the knowledge of biodiversity in ponds in the Dominican Republic.

Entre 2017 y 2018 se realizó un estudio limnológico de 30 lagunas temporales de Costa Rica. Entre otros organismos, se estudiaron las esponjas de agua dulce (Porifera: Spongillidae), en cuya distribución se centra el presente estudio. De las muestras se aislaron 15 552 gémulas de esponjas repartidas en 21 localidades de la provincia de Guanacaste. Este material se obtuvo a lo largo de seis campañas de muestreo efectuadas entre mayo de 2017 y diciembre de 2018. Las especies de esponjas identificadas fueron Radiospongilla crateriformis (Potts, 1882), Corvoheteromeyenia heterosclera (Ezcurra de Drago, 1974), Tubella variabilis Bonetto & Ezcurra de Drago, 1973 y Ephydatia fluviatilis (Linnaeus, 1759) con nuevas localidades. Se recolectaron las cuatro especies juntas en una laguna denominada “El Sitio” y se citan dos nuevas localidades de T. variabilis en “Sainalosa” y “El Sitio” junto con Ephydatia fluviatilis y Corvoheteromeyenia heterosclera en la primera, ambas lagunas localizadas en la provincia de Guanacaste. Además, destaca la recolección de gémulas de T. variabilis aglutinadas en el tubo de alojamiento del oligoqueto Aulophorus vagus Leidy, 1880 (Annelida: Oligochaeta: Naididae). Todas las gémulas se recolectaron únicamente en la vertiente Pacífica de Costa Rica, mientras que no se encontró ninguna en las lagunas muestreadas en la vertiente Atlántica, correspondiéndose con una mayor disponibilidad de fitoplancton en la primera, y mayor transparencia y menor concentración de sales del agua en la segunda.

The metacommunity concept provides a theoretical framework that aims at explaining organism distributions by a combination of environmental filtering, dispersal and drift. With the development of statistical tools to quantify and partially isolate the role of each of these processes, empirical metacommunity studies have multiplied worldwide. However, few works attempt a multi-taxon approach and even fewer compare two distant biogeographical regions using the same methodology. Under this framework, we tested the expectation that temperate (mediterranean-climate) pond metacommunities would be more influenced by environmental and spatial processes than tropical ones, because of stronger environmental gradients and greater isolation of waterbodies.We surveyed 30 tropical and 32 mediterranean temporary ponds from Costa Rica and Spain, respectively, and obtained data on 49 environmental variables (including limnological, hydrogeomorphological, biotic, climatic, and landscape variables). We characterized the biological communities of Bacteria and Archaea (from both the water column and the sediments), phytoplankton, zooplankton, benthic invertebrates, amphibians and birds, and estimated the relative role of space and environment on metacommunity organization for each group and region, by means of variation partitioning using Generalized Additive Models (GAMs).Environmental selection was important in both tropical and mediterranean ponds, but markedly stronger in the latter, probably due to their larger limnological heterogeneity. Spatialized environment and pure spatial effects were greater in the tropics, related to higher climatic heterogeneity and dispersal processes (e.g. restriction, surplus) acting at different scales. The variability between taxonomic groups in spatial and environmental contributions was very wide. Effects on passive and active dispersers were similar within regions but different across regions, with higher environmental effects in mediterranean active dispersers. The residual (unexplained) variation was larger in tropical pond metacommunities, suggesting a higher role for stochastic processes and/or effects of biotic interactions in the tropics. Overall, these results provide support, for a wide variety of organisms related to aquatic habitats, for the classical view of stronger abiotic niche constraints in temperate areas compared to the tropics.

The analysis of macroinvertebrate communities is essential in aquatic ecology studies. Nonetheless, sample collection, processing and species determination of macroinvertebrates are extremely time-consuming and require huge efforts. Moreover, despite the crucial need for refined sampling protocols, investigations on viable benchmark sampling efforts are still scarce. This study provides a preliminary analysis on the optimisation of the sampling effort required to study macroinvertebrate communities from rice fields. Twenty core sediment samples were collected from a non-vegetated Mediterranean lagoon (rice field) in Valencia (Spain), and their macroinvertebrate community assemblages were obtained. Characterisations of the minimum number of samples needed for both faunistic inventories and environmental quality assessments were carried out using diversity indexes (number of taxa, Shannon, Simpson, and Margalef indexes), ecological indicators (Nutritional Mode Index, IMN) and several species richness estimators (Chao 1, Chao 2, Jacknife 1, Jacknife 2, ACE, ICE, Bootstrap and EstimateS 9.1.0). Our results indicate that in surveys in which the taxa richness of the communities is the objective, 20 samples or even more could be needed. However, when the objective of the study is to assess the environmental quality by means of ecological indexes such as the IMN, three samples could be an acceptable benchmark. Our findings, despite being limited by our experiment conditions, can provide methodological guidelines for ecological assessments in Mediterranean rice fields and shallow non-vegetated lagoons. Further research involving multiple study areas and seasonal patterns will help meliorate the accuracy of this protocol and refine sampling efforts in wetlands.

The processes behind the heterogeneous distribution of species involve a combination of environmental and spatial effects. In the spatial context, stream networks constitute appropriate systems to compare the relative importance of two dispersal modes in aquatic organisms: overland and watercourse dispersal. In the present study, we analyzed the distribution of ostracod species in a river network in the eastern Iberian Peninsula, with variation partitioning between environmental and spatial factors, using Moran and Asymmetric Eigenvector Maps (MEMs, AEMs) as spatial variables. Our aims were to determine the relative importance of environmental and spatial control and to compare the importance of overland and watercourse dispersal for species distribution of passively-dispersing aquatic organisms. Our results suggest that watercourse was the most important dispersal mode, favoring mass-effects. The role of species sorting was significant and related to temperature, stream width and water quality, measured as a biotic index (IBMWP). These results stress the major importance of connectivity, besides niche-related factors, in structuring riverine communities of passively-dispersing aquatic organisms.

The Mediterranean coast holds a wide and rich variety of wetlands, some of which are protected by international laws, but at the same time have been historically subjected to threatening activities such as agriculture, pollution and aquifer overexploitation. As part of a conservation and restoration project at the Marjal dels Moros coastal wetland (Eastern Iberian Peninsula) we initiated investigations to begin to characterise aquatic environments, and evaluate changes in the system experienced in recent times. To this aim, we collected four seasonal samples at seven points of the Marjal dels Moros wetland, varying in salinity, permanence and other environmental conditions, and studied the recent past (early modern to contemporary remains) and present (living) communities of Ostracoda. We found relatively poor species richness overall, possibly related to the brackish and seasonal character of large parts of the wetland. Of the seven species encountered the most common ostracods were tolerant to these stressing conditions: Heterocypris salina, Sarscypridopsis aculeata, Ilyocypris gibba and Cypridopsis vidua. A comparison of dead and living assemblages showed no significant differences, suggesting that the overall ostracod metacommunity was resilient to the perturbations experienced in the area, despite some particular locations recording notable shifts in their communities during the sampling period.

Symbiont spillover involves the emergence of new interactions that can influence both the symbiont and the host invasion processes. Here we aimed at experimentally testing the transmission of an exotic ectosymbiont, Ankylocythere sinuosa (Ostracoda, Entocytheridae), from a crayfish invader (Procambarus clarkii) to a native European crayfish (Austropotamobius italicus). Crayfish transmitter and receiver were placed in the same container during 4 days. Three experimental treatments were designed: (i) crayfish transmitter alone (i.e. control group); (ii) cleaned P. clarkii as crayfish receiver; (iii) A. italicus as crayfish receiver. The proportions of colonised crayfish were 92% for P. clarkii and 100% for A. italicus. Mean symbiont emission rate of the control group was 2.75%, with 2.5 times odds increase under the presence of crayfish receiver. Mean transmission rate in treatments with P. clarkii receivers was 38.48%, with higher odds to bigger crayfish receivers (5% increase per gram) and to A. italicus (2.1 times). All entocytherid growth stages were transmitted. We demonstrated that entocytherids harbour transmission features that allow them to achieve successful spillover in nature. However, the symbiont was not found on native crayfish in nature hitherto, probably due to host competitive exclusion and crayfish plague acting on native hosts.

Invasive alien species present a global threat to biodiversity, particularly where pathogens and symbionts are involved. Branchiobdellidans are clitellate annelids with an obligate ectosymbiotic association primarily on astacoidean crayfish. There are several examples of branchiobdellidan species adopting a geographically exotic host where endemic and exotic crayfishes cohabit the same water body. The first records of a western North American branchiobdellidan, Xironogiton victoriensis , adopting the eastern North American crayfish, Procambarus clarkii , in 2 river basins in Spain provide further evidence of the ectosymbionts’ tolerance to adopt an exotic host. Given worldwide translocations of these and other commercial crayfish species, limnologists and agency managers need to be alert for further introductions of X . victoriensis and other branchiobdellidans. Impacts of these exotic ectosymbionts on habitat and biota at a new location are unknown, as are their consequences on native biodiversity.

18 páginas, 6 figuras, 1 tabla., The deficiency in the distributional data of invertebrate taxa is one of the major impediments acting on the bias towards the low awareness of its conservation status. The present study sets a basic framework to understand the large branchiopods distribution in the Iberian Peninsula and Balearic Islands. Since the extensive surveys performed in the late 1980s, no more studies existed updating the information for the whole studied area. The present study fills the gap, gathering together all available information on large branchiopods distribution since 1995, and analysing the effect of human population density and several landscape characteristics on their distribution, taking into consideration different spatial scales (100 m, 1 km and 10 km). In overall, 28 large branchiopod taxa (17 anostracans, 7 notostracans and 4 spinicaudatans) are known to occur in the area. Approximately 30% of the sites hosted multiple species, with a maximum of 6 species. Significant positive co-occurring species pairs were found clustered together, forming 4 different associations of large branchiopod species. In general, species clustered in the same group showed similar responses to analysed landscape characteristics, usually showing a better fit at higher spatial scales., MF is supported by a grant from the Brazilian Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo´gico—CNPq (401045/ 2014-5), program Cieˆncia sem Fronteiras. DC-M held a grant from the Spanish Ministry of Education, Culture and Sport (FPU014/06783).

In invasion processes, both abiotic and biotic factors are considered essential, but the latter are usually disregarded when modeling the potential spread of exotic species. In the framework of set theory, interactions between biotic (B), abiotic (A), and movement-related (M) factors in the geographical space can be hypothesized with BAM diagrams and tested using ecological niche models (ENMs) to estimate A and B areas. The main aim of our survey was to evaluate the interactions between abiotic (climatic) and biotic (host availability) factors in geographical space for exotic symbionts (i.e., non-free-living species), using ENM techniques combined with a BAM framework and using exotic Entocytheridae (Ostracoda) found in Europe as model organisms. We carried out an extensive survey to evaluate the distribution of entocytherids hosted by crayfish in Europe by checking 94 European localities and 12 crayfish species. Both exotic entocytherid species found, Ankylocythere sinuosa and Uncinocythere occidentalis, were widely distributed in W Europe living on the exotic crayfish species Procambarus clarkii and Pacifastacus leniusculus, respectively. No entocytherids were observed in the remaining crayfish species. The suitable area for A. sinuosa was mainly restricted by its own limitations to minimum temperatures in W and N Europe and precipitation seasonality in circum-Mediterranean areas. Uncinocythere occidentalis was mostly restricted by host availability in circum-Mediterranean regions due to limitations of P. leniusculus to higher precipitation seasonality and maximum temperatures. The combination of ENMs with set theory allows studying the invasive biology of symbionts and provides clues about biogeographic barriers due to abiotic or biotic factors limiting the expansion of the symbiont in different regions of the invasive range. The relative importance of abiotic and biotic factors on geographical space can then be assessed and applied in conservation plans. This approach can also be implemented in other systems where the target species is closely interacting with other taxa.

Niche segregation may prevent competitive exclusion and promote local coexistence. This typically results in the occupation of different habitats. In the freshwater ostracod Eucypris virens (Jurine, 1820), the distribution of sexual and parthenogenetic populations in the temporary Lake Caracuel, central Spain, was not homogeneous. Parthenogens were found everywhere including the littoral, whereas sexuals were restricted to the centre. We investigated the hypothesis that spatial distribution responded to ecological differences. We studied the ecological significance of this segregation by linking environmental data to male presence, sexual fraction, ploidy, and genetic structure of our model organism in 12 ponds in the lake basin. Hydro-chemical and biological data indicated that the observed segregation is not only spatial but also ecological, with sexual E. virens occurring in ponds with shorter and probably more unpredictable hydroperiod. The correlations between environmental gradients and E. virens population structure suggest that sexual and parthenogenetic lineages are ecologically segregated. Sexual populations appeared restricted to sufficiently unpredictable environments, while parthenogens dominated environments with longer hydroperiods. Local coexistence seems mediated by spatial heterogeneity in habitat stability.

Coastal pond systems can account for a rich aquatic faunal diversity and complex functioning due to interplay between freshwater wetlands and marine influences. Within the large Albufera wetland Natural Park, Raco de l'Olla is constituted by a set of permanent and temporary ponds with strict protection level for migrating bird conservation. Its terrestrial faunal diversity and dynamics has been partially characterized in previous studies, but nothing was known about its ostracod communities. Benthic samples collected monthly for 1 year in 11 points through the pond system, together with limnological information, allowed establishing a sound knowledge on its ostracod community and population ecology. The most common species found were the euryhaline Cyprideis torosa and Heterocypris salina . In addition, it was remarkable the finding of a well-established population of Candonocypris novaezelandiae , a new finding for Europe and considered a potential alien invader. We used multivariate ordination and classification (PCA, RDA and TWINSPAN) to characterize the ostracod biocoenoses and taphocoenoses and their relation to the environmental variables. Our results suggest that hydroperiod and salinity are the main factors structuring ostracod communities in this system. Finally, we discuss the distribution and morphological aspects of C. novaezelandiae and its relation with passive dispersal in such a wetland with a dense population of migrating birds.

The American red swamp crayfish Procambarus clarkii (Girard, 1852) was introduced in 1973 into the Iberian Peninsula for commercial purposes. As a result of both the expansion from the Iberian Peninsula and, probably, further introductions in other European countries, now it is widely distributed throughout much of Europe. The ecological impacts of this invading crayfish have received increasing attention, but nothing is known about its symbiotic entocytherid ostracods outside the American continent. The present survey has examined more than 200 crayfishes from 12 localities distributed over a wide area of Eastern Spain. Entocytherid ostracods were extracted from individual crayfishes and they were identified, counted, assigned to developmental instars and sexed. In all the study locations but one, we found at least one crayfish individual infected by entocytherid ostracods and the species determined was the same in all cases: Ankylocythere sinuosa (Rioja, 1942). The number of ostracods on individual P. clarkii varied notably in relation to crayfish size and also differed significantly among sampling sites. The crayfish size effects on ostracod densities might be related to the amount of resources and to the crayfish age and moulting frequency affecting ostracod distribution and population structure. In addition, the spatial variation in ostracod densities could also be related to site-specific habitat traits and the variability of crayfish population dynamics. Our study represents the first citation of an alien entocytherid species in Europe and demonstrates its wide distribution in the Iberian Peninsula. Further research is needed to know the potential effects of this ostracod species on the ecology of P. clarkii and of native species, with implications on the management of this aquatic invader.

1. The coastal area of Valencia (Spain) in the Western Mediterranean is rich in freshwater and brackish wetlands. These areas are mostly protected for bird conservation but are also highly affected by human impacts. Six shallow lakes located in Ramsar wetland sites of this area were studied in order to assess past and present ostracod biodiversity and relate it to the status of the lakes, taking into consideration the indicator value of these easily fossilizable crustaceans. 2. In all the wetlands studied, ostracod taphocoenoses showed much higher species richness than the corresponding biocoenoses. This is expected from the time accumulative character of the taphocoenosis, but the trend is clearly evident in the most disturbed sites which indicated loss of ostracod diversity owing to human impacts. 3. By considering the ecology of most frequent species, multivariate ordination of both tapho- and biocoenoses showed trends within and between lakes in their limnological status, which were related mainly to water chemistry, and also to temporality and eutrophication to a certain extent. Some lakes have apparently lost most of their past ostracod community owing to an increasing trophic status in some cases and to modifications of the hydrological regime in others. Copyright © 2007 John Wiley & Sons, Ltd.

Sediment and plant-associated macroinvertebrates were sampled in six shallow water bodies along the central part of the coast of Mediterranean Spain. The size of ponds, salinity and hydroperiod were highly variable. Seventy-one taxa were recorded, some of them were endemic or uncommon species, evidencing the important contribution of these ponds to biodiversity. Crustaceans and gastropods of biogeographical interest were found in the most primeval site. Correspondence analysis showed that macroinvertebrate assemblages responded to environmental variables such as salinity, temporality and eutrophication. The brackish water fauna was dominated by crustaceans, while oligochaeta and insect larvae were abundant in freshwater conditions. Oligochaetes were abundant at localities with high trophic level, whereas localities with semi-permanent waters were dominated by chironomids. The density of macroinvertebrates was clearly related with trophic state but we did not find significant relationships between density and salinity or water permanence. For plant associated samples our results showed negative relationships between species richness and temporality or salinity, contrary to sediment samples, where the Oligochaeta/Chironomidae ratio in sediments and the percentage of sensitive taxa (Ephemeroptera, Odonata, Trichoptera) were useful indices, and were dependent on pond typology. This study emphasizes the broad ecological variety of ponds found in these wetlands and their importance for biodiversity. Some ponds act as permanent biodiversity reservoirs in fluctuant marshes with seasonal dryness, calling for more attention on their ecological relevance for management strategies.

Summary 1. Nutrient and fish manipulations in mesocosms were carried out on food-web interactions in a Mediterranean shallow lake in south-east Spain. Nutrients controlled biomass of phytoplankton and periphyton, while zooplankton, regulated by planktivorous fish, influenced the relative percentages of the dominant phytoplankton species. 2. Phytoplankton species diversity decreased with increasing nutrient concentration and planktivorous fish density. Cyanobacteria grew well in both turbid and clear-water states. 3. Planktivorous fish increased concentrations of soluble reactive phosphorus (SRP). Larger zooplankters (mostly Ceriodaphnia and copepods) were significantly reduced when fish were present, whereas rotifers increased, after fish removal of cyclopoid predators and other filter feeders (cladocerans, nauplii). The greatest biomass and diversity of zooplankton was found at intermediate nutrient levels, in mesocosms without fish and in the presence of macrophytes. 4. Water level decrease improved underwater light conditions and favoured macrophyte persistence. Submerged macrophytes (Chara spp.) outcompeted algae up to an experimental nutrient loading equivalent to added concentrations of 0.06 mg L−1 PO4-P and 0.6 mg L−1 NO3-N, above which an exponential increase in periphyton biomass and algal turbidity caused characean biomass to decline. 5. Declining water levels during summer favoured plant-associated rotifer species and chroococcal cyanobacteria. High densities of chroococcal cyanobacteria were related to intermediate nutrient enrichment and the presence of small zooplankton taxa, while filamentous cyanobacteria were relatively more abundant in fishless mesocosms, in which Crustacea were more abundant, and favoured by dim underwater light. 6. Benthic macroinvertebrates increased significantly at intermediate nutrient levels but there was no relationship with planktivorous fish density. 7. The thresholds of nutrient loading and in-lake P required to avoid a turbid state and maintain submerged macrophytes were lower than those reported from temperate shallow lakes. Mediterranean shallow lakes may remain turbid with little control of zooplankton on algal biomass, as observed in tropical and subtropical lakes. Nutrient loading control and macrophyte conservation appear to be especially important in these systems to maintain high water quality.

1. The impacts of nutrients (phosphorus and nitrogen) and planktivorous fish on phytoplankton composition and biomass were studied in six shallow, macrophyte-dominated lakes across Europe using mesocosm experiments. 2. Phytoplankton biomass was more influenced by nutrients than by densities of planktivorous fish. Nutrient addition resulted in increased algal biomass at all locations. In some experiments, a decrease was noted at the highest nutrient loadings, corresponding to added concentrations of 1 mg L1 P and 10 mg L1 N. 3. Chlorophyll a was a more precise parameter to quantify phytoplankton biomass than algal biovolume, with lower within-treatment variability. 4. Higher densities of planktivorous fish shifted phytoplankton composition toward smaller algae (GALD

Background: Previous studies have identified rice fields in the Mediterranean region as ‘hot spots’ for the introduction of alien freshwater organisms. Consequently, special attention should be paid when rice fields are located inside or near protected areas for the conservation of native, endangered species. To analyse the relationship between rice field environmental traits and the ecology of aquatic invaders, a study of zoobenthic communities was carried out in JulySeptember 2008 and May-August 2009 in ten rice fields located in the Albufera Natural Park (E Spain), with focus on Ostracoda. Results: A total of nine ostracod species were found including four considered exotic: Candonocypris novaezelandiae, Stenocypris macedonica, Cypris subglobosa and Hemicypris barbadensis. The presence of H. barbadensis is remarkable, which is recorded for the first time in Europe and S. macedonica in the Iberian Peninsula. A checklist of Ostracoda from Albufera Natural Park is presented, including 11 exotic species, mostly unknown from Holocene sedimentary records. The analysis of ostracod assemblages showed a significant relationship between oxygen content and ostracod species associations, suggesting that their abundance are partially controlled by habitat variables in the rice fields. The exotic species C. novaezelandiae was more abundantly collected in samples with reduced oxygen concentrations, in contrast to other native species whose abundances were lower in such conditions. Conclusions: Rice fields in Mediterranean areas present a summer inundation period which is unlikely in natural temporary water bodies in the area and which may facilitate invasion by (sub-)tropical species. Lower proportion of exotic to native ostracods is observed in less disturbed areas compared to rice fields with intense human activities. We emphasize the role of anthropogenic effects in the dispersal and colonization processes of exotic ostracods and their particular strong influence in the protected areas closest to rice fields.

Reservoirs are the most common deep lakes in Spain, as a consequence of water needs and dry climate. Although these aquatic systems can play an important ecological role in such an area with few large natural lakes, they can also provide new habitats for exotic species, which can colonize ecosystems that native species have not explored yet. Here we present our results for a biannual survey of the ostracod fauna from 24 reservoirs in Xuquer River basin. We check which variables affect ostracod presence, test for differences between winter and summer assemblages, and compare our data with previous available ostracod records from the same river drainage network. Our results reveal that ostracod presence is positively related to high diversity of the invertebrate community and reservoir volume, and negatively with phosphorus concentration. Among the 22 species found, it is noteworthy the first Iberian record of Ilyocypris getica and the second European record of Candonocypris novaezelandiae . Ostracod assemblages significantly vary between summer and winter, and strong differences are found between ostracod communities of reservoirs and those from their connected rivers. Remarkably higher frequency of exotic species in the reservoirs confirms previous findings about the facilitation that artificial ecosystems confer to aquatic invasions.

The present survey examines possible trends in the ecology of ostracod assemblages in a small Mediterranean river affected heavily by sewage and industrial effluents. Between January and July 1995, ten sampling stations situated along a 50 km stretch of the main channel of the River Magre (Valencia, eastern Iberian Peninsula) were sampled monthly (physico-chemical variables being measured simultaneously). Although the entire site fauna was used to calculate diversity and biotic indexes, only Ostracoda were studied in depth, as little is known of the ecological preferences of this group. Ostracod assemblages encompassed 10 species, the most abundant genera being Herpetocypris and Heterocypris . Most species peaked in abundance towards the end of the study period (May–June) when water temperatures were rising. Ostracods were completely absent from the most disturbed sites, i.e. those with the lowest water quality index values. Different ostracod assemblages occurred along a gradient from high pollution towards the final `recovery' zone. Combined classification (TWINSPAN, MDA) and ordination (DCA) techniques using species and site variable data showed that different groups of samples, related to the abundance of a particular ostracod assemblage, were linked to particular habitat features. Eucypris virens appeared in samples near to the source in winter, and in the early months of spring. During this period these sites were characterised by cool waters and relatively high alkalinity/Cl − ratios. Furthermore two major groups of samples were related to the relative abundance of either Heterocypris incongruens and Herpetocypris intermedia , or Herpetocypris brevicaudata . Moderately polluted, clean waters are linked to these two groups, respectively. Additional division of both groups of samples was based on the total abundance of individual animals, and may be related to water temperature and season. These results may be used to assess possible changes in the trophic status of a palaeoenvironment when the species taken into account are recorded from a given sedimentary sequence.

Aim Geographical parthenogenesis – in which parthenogenetic populations are more widely distributed than sexually reproducing populations – is observed in many plant and animal species. Many hypotheses have been proposed to account for this biogeographical pattern, and these often invoke historical processes such as the influence of glaciation. However, there are relatively few empirical studies of the contemporary factors associated with geographical parthenogenesis. The aim of this study was to understand its causes by linking contemporary environmental gradients with reproductive modes in the freshwater ostracod Eucypris virens. Location Europe and North Africa. Methods We sampled populations of E. virens from 147 sites in 20 countries from Estonia to Morocco and from Portugal to Turkey. At each site we measured aspects of pond geography (latitude, longitude, elevation, pond area and depth), water chemistry (temperature, pH, conductivity, oxygen and ion concentrations) and macroinvertebrate assemblages. We used principal components and logistic regression analyses to test for the associations between environmental variables and the presence of males, indicating sexual reproduction, in a population. Results Sexual populations were restricted to the Mediterranean, whereas parthenogenetic populations extended into the Baltic and Ponto-Caspian areas. Significant environmental features were not only latitude, but also elevation, aridity and principal components summarizing water chemistry and invertebrate communities: sexual populations were more common at high elevations, in arid regions, and in turbid ponds. Ponds harbouring exclusively parthenogenetic populations were also characterized by having longer-hydroperiod biological communities. Main conclusions The link between current environmental conditions and the reproductive modes of E. virens suggests a contemporary adaptation besides historical factors such as climatic cycles or the differential colonization success of sexual and asexual lineages. We propose that the pattern of geographical parthenogenesis in E. virens reflects the ability of asexual populations to colonize rapidly, and the higher adaptability of sexual populations to unpredictable hydroperiods.

Hydrobiologia, 636 (1), ISSN:0018-8158, ISSN:1573-5117

1. Responses of zooplankton to nutrient enrichment and fish predation were studied in 1998 and 1999 by carrying out parallel mesocosm experiments in six lakes across Europe. 2. Zooplankton community structure, biomass and responses to nutrient and fish manipulation showed geographical and year-to-year differences. Fish had a greater influence than nutrients in regulating zooplankton biomass and especially the relative abundances of different functional groups of zooplankton. When fish reduced the biomass of large crustaceans, there was a complementary increase in the biomasses of smaller crustacean species and rotifers. 3. High abundance of submerged macrophytes provided refuge for zooplankton against fish predation but this refuge effect differed notably in magnitude among sites. 4. Large crustacean grazers (Daphnia, Diaphanosoma, Sida and Simocephalus) were crucial in controlling algal biomass, while smaller crustacean grazers and rotifers were of minor importance. Large grazers were able to control phytoplankton biomass even under hypereutrophic conditions (up to 1600 g TP L1) when grazer biomass was high (>8090 g dry mass L1) or accounted for >30% of the grazer community. 5. The littoral zooplankton community was less resistant to change following nutrient enrichment in southern Spain, at high temperatures (close to 30 °C), than at lower temperatures (1723 °C) characterising the other sites. This lower resistance was because of a greater importance of nutrients than zooplankton in controlling algal biomass. 6. Apart from the reduced role of large crustacean grazers at the lowest latitude, no consistent geographical patterns were observed in the responses of zooplankton communities to nutrient and fish manipulation. [KEYWORDS: eutrophication ; fish predation ; littoral zooplankton ; mesocosm experiments ; nutrient enrichment]

In a survey for conservation of non-marine aquatic systems, the ostracod compositions of 43 water bodies sampled in central Spain were analysed by multivariate ordination (DCA) and classification (TWINSPAN) methods, showing a clear division in lake typology. The wide variety of life modes and habitat requirements of non-marine ostracod species yields assemblages of species of value as ecological indicators. Endorheic shallow lakes, highly temporary, are characterized by an assemblage of circum-Mediterranean and endemic species. Karstic and more stable lakes are inhabited by northern Holarctic or Palaearctic species, depending on the history and environmental conditions of the water body. Between these two extremes, the study of ostracod assemblages permits the distinction, on a finer scale, of a gradient of lake types with different disturbance conditions, resulting from a combination of hydrological, climatic, chemical and anthropogenic factors. At the extreme of that gradient, highly tolerant cosmopolitan species play an important role in the ostracod community of sites severely affected by human activities.