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Zooplankton community assembly after flooding in temporary ponds depends mostly on abundance and diversity of the dormant propagule bank. However, our understanding of the hatching patterns of zooplankton is imperfect. We performed an ex situ experiment to study the species composition and temporal sequence of zooplankton emergence from sediments in three ponds that were restored at different times: 1998, 2003 and 2007. The patterns of species hatching observed in our microcosms were compared with the emergent zooplankton community of their equivalent, synchronically inundated ponds. An escalation in species richness and a delay in hatching time were detected with increasing restoration age. In addition, some discrepancies between the egg bank and active populations were observed, especially in the oldest pond. This study illustrates the use of hatching experiments in comparing ponds with different characteristics. Nevertheless, egg bank hatching and water column sampling should complement each other in order to afford a full reflection of past diversity and contribute to a better understanding of the efficiency of restoration practices.

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.

Zooplankton abundance and composition is sensitive to eutrophication, and its top-down effect in the planktonic food web can alter the classification of the trophic state of waterbodies based on th...

Based on our results, we propose the use of zooplankton abundance (density or biomass) as an indicator to complement the information currently being used concerning the quality of water in reservoirs. Until now, the Water Framework Directive (EU) for lakes and reservoirs has not included zooplankton because the classification of the water trophic state is based on a bottom-up model: an increase in nutrients implies an increase in primary producers and, therefore, poorer water quality. The use of zooplankton has recently been claimed due to their sensitivity to environmental changes and their control over primary producers. From our work, carried out from 2006 to 2009 (summer and winter seasons) in 20 reservoirs found in various Mediterranean river basins, we prove the relationship of the abundance of zooplankton with the trophic state. Zooplankton abundance, with or without interaction with other agents, explained much of the distribution of total phosphorus in the reservoirs, thus relating the trophic status with the aquatic food chain. In addition, we have found, illustrated by the zooplankton: phytoplankton ratio, how the top-down control masked high production situations in the system. Zooplankton's ability to cover up these cases of poor water quality highlight that the indicators presently being used are frequently insufficient.

Biomass and size-based estimations provide relevant information regarding ecosystem functioning and biotic interactions. Our aims were to study the effect of fish and macrophytes on the size structure of invertebrate assemblages (from rotifers to insects) in a set of coastal water bodies, estimating the biomass (total and main invertebrate groups), the biomass-size spectra (model of Pareto) and size diversity. In fishless ponds, cladoceran and ostracod biomass were higher, and they presented greater size diversity. In fish ponds, rotifer biomass presented greater proportion; while in fishless ponds, cladocerans were usually the most abundant taxa and the largest organisms. The biomass size spectra showed more irregularities in fishless ponds, due to the low densities of small taxa (rotifers and copepod juveniles) and big taxa (malacostraceans or insects). Differences is size structure and diversity were also observed between spring and summer, suggesting a higher recruitment of juveniles in spring, and thus, a higher predation pressure upon zooplankton at that moment. Macrophyte cover did not apparently influence those parameters, except for the biomass of ostracods, copepods, and insects. Therefore, predation by fish strongly affected invertebrate biomass, reflecting their selective feeding, and allowing high densities of small taxa. Predation pressure decreased size diversity, by limiting the abundance of vulnerable taxa of specific size. Seasonal changes were likely related to the spring recruitment of fish juveniles. The presence of small fish and invertebrate predator taxa among the macrophytes, restrict their role as refuges for prey invertebrates.

Nutrients and carbon were studied in the temporary and permanent dune ponds of one of the few restored Mediterranean dune systems. The results indicate that small, low nutrient dune ponds can have a relevant role for carbon storage and processing, especially in the limestone areas. Despite the low percentage of organic matter in the sediment and water nutrient concentrations, most of the ponds had supersaturated carbon dioxide partial pressure levels with concentrations in half of them greater than the mean global value for lakes. Concentrations gradually decreased from old to newly restored ponds and with the presence of submerged plants. Carbon content was greater in temporary ponds. DOC was half of the mean global value for lakes. Particulate forms of nutrients and dissolved inorganic carbon predominated. Organic matter was a key variable for storage of nutrients and carbon in the sediment. Flooding of the ponds significantly reduced total organic carbon in the sediment by about 60%, but did not change significantly the concentrations of nitrogen and phosphorus. However, about 25% of organic matter and 37% of nitrogen accumulated in the sediment during consecutive summer droughts. Benthic algae incorporated part of the sediment nutrient pool after flooding.

The red swamp crayfish (Procambarus clarkii), originally from North America, is one of the world's worst aquatic invaders. It is a favoured prey item for waterbirds, but the influence of this novel predator–prey relationship on dispersal of other organisms has not previously been considered. We investigated the potential for dispersal of plants and invertebrates by migratory waterbirds feeding on alien P. clarkii in European ricefields at harvest time. In November–December of 2014–2015, we collected propagules from the outside of 13 crayfish captured as they moved out of ricefields during harvest in Doñana, south‐west Spain. We also collected excreta (N = 76 faeces, 14 pellets) of lesser‐black backed gull (Larus fuscus). We recorded diaspores from at least 11 plant species (161 seeds from 10 angiosperm taxa, and 14 charophyte oogonia) on the outside of crayfish, together with 54 eggs from eight aquatic invertebrate taxa. Adults and juveniles of at least nine microcrustaceans, including the alien ostracods Hemicypris reticulata and Ankylocythere sinuosa, were also recovered from crayfish. No intact propagules were present in the digestive system of the crayfish. Contents of regurgitated pellets confirmed P. clarkii as the main food item for gulls. Diaspores from at least 12 plant species (154 seeds from 11 angiosperm taxa, and 17 charophyte oogonia) were recovered from gull excreta, together with 129 eggs of 12 aquatic invertebrate taxa. A statoblast of the alien bryozoan Plumatella vaihiriae was found in gull faeces. Seven of the plant species are important agricultural weeds, and two are alien to Spain. Diaspores from six plant taxa were germinated, confirming viability. These propagules were from a similar set of plants and invertebrates to those found on the outside of crayfish, suggesting that propagules in gull excreta were ingested inadvertently with their crayfish prey. Ricefields constitute a major artificial aquatic habitat covering an increasing proportion of the world's land surface and typically support native or alien crayfish. Crayfish invasion can lead to novel secondary dispersal pathways for plants and invertebrates through interactions with their predators, promoting the expansion of alien and native species (including weeds) through long‐distance dispersal via migratory waterbirds and increasing connectivity of organisms between artificial and natural ecosystems. This represents a previously overlooked impact of crayfish invasion on ecosystem services. Supporting Information

Invertebrate aquatic assemblages in ponds from Mediterranean wetlands are composed of organisms belonging to different taxonomic groups, which present a wide range of sizes (from small rotifers to large crustaceans or insects). Although they are often sampled and analyzed separately, the ecological links among these organisms should be considered, especially in very shallow waters. In our study, invertebrate assemblages (including micro-, macrozooplankton and macroinvertebrates) were characterized in eight shal- low lakes from Mediterranean wetlands in Southeastern Spain. A great spatial and temporal variability in the assemblages and in some environmental features was observed. The community was dominated in abundance and species richness by rotifers in most of the water bodies. Fish greatly contributed to the differences in community composition, as fishless ponds presented abundant and diverse cladoceran populations. Nutrient and chlorophyll-a concentration, conductivity and macrophyte cover had also a great influence on these as- semblages, especially in micro- and macrozooplankton. The temporal changes observed in some of these vari- ables affect the proportion of invertebrate biomass of the different groups along the study period. All this environmental heterogeneity produces similar responses in the invertebrate groups, in general well adapted to salinity changes or high trophic conditions. Although the heterogeneity and human disturbances can increase regional diversity, they can cause the disappearance of valuable habitats, and finally, the homogeneity in invertebrate assemblages.

Restoration projects in wetlands are becoming increasingly frequent to recover or to create new aquatic ecosystems, after the significant impact and high degradation they have undergone. In the present study, we focused on the changes in the zooplankton community in a permanent peridunal pond where a restoration was carried out in order to increase its surface as a main objective. For this purpose, the community was compared before and after the restoration (15 years before, the year after and between 3 and 6 years later). Significant changes in environmental variables were observed after pond restoration: chlorophyll a concentration decreased and dissolved oxygen increased. Substantial modifications in the aquatic community were also observed, since species richness and diversity increased after restoration: a large number of new species appeared (84%, mainly cladocerans), from external or internal sources. In addition, zooplankton community structure and composition changed from a low specific richness community copepod-dominated in density (mostly nauplii) before restoration, to another one with higher richness and different composition co-dominated in density by rotifers and nauplii, but with greater abundance of cladoceran species. All this suggests an important change in the ecological functioning of the pond, mainly produced by improvement in habitat heterogeneity and water quality after restoration.

In temporary ponds, reestablishment of zooplankton communities depends on recruitment from the egg bank, the arrival of dispersers from within the region, and on successful establishment of newly arrived species following interaction with local abiotic and biotic factors. When the ponds dry up, zooplankton species may survive as dormant eggs, and since not all eggs hatch in the next season, eggs will accumulate in the sediment over time, representing an archive of the pond's historical biodiversity. To study the effect of “restoration age” (the time since a water body was restored), we studied groups of ponds that were restored in different years (1998, 2003 and 2007). The restoration process involved extensive dredging of sediments which were used to bury the ponds in the 1960s. Our expectation was that the oldest ponds would have the richest zooplankton community, as they have been accumulating biodiversity over a longer time period. We took weekly quantitative samples of zooplankton during four consecutive weeks after flooding to compare taxon richness and zooplankton community composition between ponds of different restoration age during an early stage of zooplankton community re-establishment. Taxon richness was high and similar to regional levels in all the ponds under investigation, suggesting restoration success and unlimited dispersal. Although cumulative richness at the end of the period was not significantly different between ponds, we observed temporal changes within the study period and certain age-related trends in relation to differences in zooplankton composition. These results suggest a difference in the succession of zooplankton communities depending on restoration age (which could be due to historical or local factors) and that this effect becomes evident from the beginning of the pond hydroperiod.

Some of the predicted effects of climate warming in Mediterranean climate are the increase of temperature, change of precipitation patterns and the rise in sea levels. This will have major consequences, mainly in coastal aquatic ecosystems, by the increase of salinity and the reduction of the flooding period, affecting the whole aquatic community. To assess on the possible consequences of the global change in the zooplankton community of Mediterranean coastal lakes, we analized the zooplankton diversity in a set of lakes with different salinity and water permanence time. The ponds were classified in four groups: permanent and temporary freshwater ponds, and permanent and temporary brackish ponds. Whereas we did not detect a great effect of hydroperiod on zooplankton community, the increase in salinity produced (through direct and indirect interaction) a rise in rotifer density and a reduction in cladoceran cumulative richness, richness per visit and diversity. All these differences were remarkable in Permanent Brackish lakes, the group which showed the higher dissimilarity with the other groups of lakes. The disappearance of cladocerans in these systems can lead to an increase in the eutrophication and a reduction of diversity.

Diel vertical migration (DVM) of zooplankton is commonly considered an adaptation for feeding in food-rich and warm surface waters at night and avoiding visual predators during the day. However, the critical assessment of migration patterns frequently suggests that: (i) zooplankton may leave deeper waters with rich, deepchlorophyll layers and move into the epilimnion where food resources are lower and/or (ii) the night-time increase in epilimnetic plankton abundance is not matched by a density decrease in deeper strata. To study these discrepancies, we measured DVM of zooplankton in a 1.3-ha Spanish karst lake (Laguna del Tejo) where the phytoplankton in the deep chlorophyll layer had been labelled with the isotopic tracer 15 N. There were only limited changes in the vertical distribution patterns of rotifers and copepods over the diel cycle, but night-time biomass (mg L 21 ) of the cladoceran, Diaphanosoma brachyurum in the water column of the oxic zone increased 168% in the central area of the lake but there was not a parallel reduction in their density in the metalimnion or hypolimnion. Additionally, the isotopic signatures of the zooplankton in the epilimnion stayed constant from day to night, suggesting that there was little vertical migration. The results suggest that horizontal movements rather than vertical migration explain the increasing abundance of zooplankton in the central epilimnion of Laguna del Tejo during the night and that low food resources in this layer provide no incentive for DVM.

New habitats are an interesting tool to monitor colonization processes in the light of changes in genetic structure and evolutionary potential of populations. Cladocerans are cyclical parthenogens that offer the possibility to track genetic changes during the colonization process due to the alternation of sexual and asexual phases. The locally called “malladas” are shallow and temporary peridunal ponds in Eastern Spain that were silted in the 1960s and have been recently dug to their original basin. We here describe the colonization process in two of these newly restored ponds by the cladoceran Daphnia magna during their first 3 years. This colonization process followed three critical steps: population founding by the initial colonists, arrival of secondary immigrants and consolidation of the population structure. We found a low number of genotype colonists followed by the establishment of secondary immigrants and a slight decrease in gene flow with time. We discuss the importance of dispersal, founder effects, natural selection, inbreeding depression and genetic drift during the colonization process in the light of the most recent literature.

We compared two freshwater mountain ponds during an annual cycle by focusing on Rotifera and Crustacea. These ponds, Laguna de Bezas and Laguna de Rubiales, are located only 4.5 kilometers apart and share a similar altitude (ca. 1200 m.a.s.1) on the Iberian Mountain range, in Teruel (Spain). Bezas is near-permanent and dries out only in severe droughts; Rubiales is temporary, drying out periodically. They also show important differences in other limnological traits. Bezas has transparent water, harbors a fish population, and has a dense macrophyte cover, whereas Rubiales has elevated turbidity and neither fish nor macrophytes during most of the hydroperiod. These differences are probably why they have significantly different aquatic fauna. We found that rotifers were density-dominant in the zooplankton of Bezas, while Rubiales was dominated by microcustaceans. Ostracods were practically absent at Bezas, whereas the ostracod community at Rubiales was rich and variable.

The hatching of diapausing eggs from sediment samples of ponds and lakes is a fast, easy, and economical technique proven useful for the assessment of diversity and abundance of zooplankton in permanent habitats. Here, we extend and optimize this approach for temporary brackish ponds which may experience great within-year variation in salinity conditions. We studied the species and numbers of rotifers emerging from the sediments of several brackish ponds and saline lakes from Eastern Spain incubated at the full range of salinity conditions observed at the study sites. On average, 82 % of the total observed species in weekly sampling for one year were detected in a single sample of both the sediments and water column. No statistical difference was found between both methods. However, some rotifer species were only observed in the water column samples, but not in sediment hatchlings, and vice versa. We concluded that both methods are not exhaustive by themselves but are complementary. Salinity affected the estimation of both rotifer richness and the density of individuals of each rotifer species that emerged from the incubated sediments. Differences in the density of emerging animals were also found among sites and among combinations of sites and salinities. The latter result indicates that in order to obtain an estimate of the emergence rate for each rotifer species present at a site, it is necessary to incubate sediments at salinity conditions close to their local values.

Zooplankton assemblages in neighboring ponds can show important spatial and temporal heterogeneity. Disentangling the influence of regional versus local factors, and of deterministic versus stochastic processes has been recently highlighted in the context of the metacommunity theory. In this study, we determined patterns of temporal and spatial variation in zooplankton diversity along one hydrological year in restored ponds of different hydroperiod and age. The following hypotheses regarding the assembling of species over time were tested: i) dispersal is not limited in our study system due to its small area and high exposure to dispersal vectors; ii) community dissimilarity among ponds increases with restoration age due to an increase in environmental heterogeneity and stronger niche-based assemblages;and iii) similarity increases with decreasing hydroperiod because hydroperiod is a strong selective force filtering out organisms with long life cycles. Our results confirmed dispersal as a homogenizing force and local factors as gaining importance with time of restoration. However, short hydroperiod ponds were highly dissimilar, maybe due to the environmental differences among these ponds, or to high stochasticity followed by priority effects under a weak selection pressure. By adding a temporal dimension to the study of zooplankton structuring, we could identify the first months after flooding as being crucial for species richness, especially in short hydroperiod ponds; and we detected differences in seasonal species richness related to hydroperiod and pond age.

An in vitro nutrient addition bioassay was performed to test the relative inorganic nitrogen (N) and phosphorus (P) limitation of phytoplankton in a Spanish karst lake (El Tejo) during the last part of the stratification period, when nutrient limitation is most pronounced. Nutrient deficiency was tested in samples from three different layers of the lake: the epilimnion, metalimnion and oxic hypolimnion. Nitrogen additions, either without or combined with P, increased phytoplankton growth in all three strata, compared with controls or P treatments. This showed that N was the nutrient limiting phytoplankton growth in late summer-early fall. Since both hypolimnetic diffusion and groundwater fluxes of N-rich waters into the lake are much reduced during summer, N becomes the limiting nutrient as stratification advances. We suggest that in this Mediterranean area with low atmospheric deposition of anthropogenic N and in lakes relatively free of surface run-off, nutrient supply by atmospheric deposition might be a key factor in controlling nutrient deficiency for phytoplankton growth.

The seasonal features of the water chemistry in the saline shallow lakes Laguna de Manjavacas and Laguna del Pueblo (Castilla – La Mancha, Central Spain) were studied during 1990–1991 and in 1997. These lakes were both affected by sewage inputs driving them to a high trophic status. However, whereas sewage inputs entered Laguna del Pueblo directly, wastewater reached Laguna de Manjavacas after running for 8 km through a small riverbed, where natural processes caused partial mineralisation of organic matter. Moreover, water quality was further improved before entering the main water body of Laguna de Manjavacas, since water crossed through a wetland and high amounts of organic matter and inorganic nutrients were retained there. Anyway, in both lakes spatial heterogeneity was mainly associated with the distance to sewage inputs, and this was also reflected by the sediment chemistry. The patterns of water evaporation and precipitation-dissolution of salts strongly determined the salinity of their waters. During the warmest period (which coincided with the main drought period) water losses by evaporation increased water salinity, whereas a higher dilution was found during the cold rainy period. However, the relatively higher amount of low-salinity sewage inputs in Laguna del Pueblo allowed this lake to maintain its hyposaline characteristics. In contrast, Laguna de Manjavacas shifts from hyposaline to hypersaline following the seasonal cycle with different rain and temperature regimes, as the relative importance of the permanent wastewater inputs was lower here than in Laguna del Pueblo. Inorganic nutrient dynamics was determined in both lakes both by the sewage supply and by consumption by phytoplankton, with soluble P depletion following algal blooms.

A large spatial heterogeneity was detected in La Safor, a coastal area with different kinds of small and shallow water bodies. The area exhibits a sharp gradient in eutrophication (0.004–20 mgP l−1; 0.6–457 μg Chl a l−1) and varied water body features (morphology: size, depth; hydrology; vegetation, etc.). These factors result in a high diversity of aquatic habitats within the area. One hundred and twenty eight species of microalgae were identified in the 32 sampling stations studied (in the wet and dry periods). The phytoplankton richness varied between 1 and 21 species, the Shannon-Wiener index range was 0–3 bits, the index of floral originality (IFO) range was 0.1 – 0.6. A total number of 126 species of zooplankton were identified. The zooplankton specific richness ranged from 4 to 26 species, the diversity index and IFO were 0.9–3.7 and 0.1–0.6, respectively. A PCA allowed the ordination of different water body types as a function of total phosphorus, flux of water, water transparency, presence of macrophytes and oxygen. Plankton richness, diversity index, equitability and IFO showed weak relationships to the trophic gradient. The global planktonic biodiversity was higher than expected for such an anthropogenically affected ecosystem. The different, above mentioned conditions contributed to the limitation of biodiversity loss often observed in eutrophic conditions.

Cladoceran assemblages were studied in littoral samples from 44 water bodies in Central Spain, showing great differences in salinity and permanence of water. Principal component analyses (PCA) were performed with data on cladoceran relative abundances to identify the main groups of species. Five main groups of species were found, defining the following types of environments: (I) Small but deep hard water lakes (II) permanent but shallow hard water lakes fed by surface springs, rich in macrophytes (III) ephemeral and shallow soft waters lakes (IV) subsaline and hyposaline lakes in their lower range, specially the permanent ones and (V) saline lakes (salinities>6 mg l−1) subject to short or long periods of dryness. The main species constituting these groups were: Group (I): Acroperus neglectus, Alona guttata, Pleuroxus truncatus, Daphnia longispina; group II: Phrixura leei, Latonura rectirostris, Eurycercus lamellatus; Alonella excisa, Daphnia pulicaria; group III: Ephemeroporus phintonicus, Macrothrix rosea, Moina micrura; group IV: Alona rectangula, Ceriodaphnia reticulata, Tetrocephala ambigua, Diaphanosoma mongolianum; group V: Alona salina, Pleuroxus letourneuxi, Dunhevedia crassa, Moina brachiata, Daphnia magna and Daphnia mediterranea. Sample scores from PCA extracted from the correlation matrix of cladoceran proportions were correlated with limnological measurements. Significant correlations with salinity, alkalinity anions and cations indicate that salinity is an important factor in the distribution of the species. However, species assemblages also reflect other factors, such as temporality and littoral development.

Grazing rates of zooplankton were analysed in the summer of 1999 in Yellow Belly Lake, an oligotrophic system in the Sawtooth Mountains of Idaho (U.S.A.). The colonial rotifer Conochilus unicornis was a dominant species in the epilimnion, with densities reaching 20 colonies 1−1 (ca. 400 ind. 1−1). Clearance rates were measured with an in situ Haney Grazing chamber and synthetic microspheres 5, 9 and 23/μm in diameter. At epilimnetic temperatures of around 14 °C, mean clearance rates for 5µm particles ranged from 30 to 65 µ1 ind.−1 h −1. Clearance rates were 2–9 times higher on the 5µm spheres than on the 9 µm spheres, and C. unicornis almost never fed on the 23 µm spheres. Grazing rates did not change over the diel cycle. Clearance rates declined more than 10-fold as temperatures declined from 14 °C in the epilimnion to 7 °C in the metalimnion. In the epilimnion, grazing by C. unicornis was more important than grazing by crustaceans in the community, at least on particles ≤9µm. The results show the importance of grazing by rotifers in lakes, and the significance of spatial variations that influence grazing rates.

The study of diel vertical movements of zooplankton in a small meromictic karstic lake (lake La Cruz), presenting highly stratified waters, was performed using two different methodologies: (i) samples were taken along the vertical profile and were compared at different hours in a diel cycle; (ii) some plankton traps were located at different depths, covering different periods of time, to catch organisms going upwards and downwards. The main subject of this study has been the vertical movements affecting rotifers since they were dominant in the zooplankton of this lake, but we have also included the results obtained for other zooplankton groups. The results indicate an almost general movement in epilimnetic waters corresponding to the 'normal' pattern of migration (ascent at dusk and descent at dawn); in metalimnetic and hypolimnetic waters, vertical movements were greatly reduced and were more independent of the diel cycle. The results also confirm that the dense populations at these levels of the oxic-anoxic boundary are made up of active animals. Among the causes accounting for our results, the cycles of activity (mainly feeding) connected with the diel cycle could be important in explaining vertical movements of filter-feeder rotifers. In larger zooplankters, visual predation might be the main reason for such behavior.

The zooplankton communities from several lakes and pools in three zones of a karstic area in central Spain were studied in spring and early autumn, in relation to morphometric, physical and chemical characteristics of the lakes. Zooplankton diversity was higher in autumn than in spring and it was positively correlated with lake size (area and depth) in spring, but not in early autumn. This effect is partially explained by the sharp zooplankton stratification in deep lakes, in early autumn. Some morphometric characteristics of lake basins were also correlated with the structure of zooplank- ton communities. Principal component analyses (PCA) and Two-Way Indicator Species Analysis (TWINSPAN) performed on zooplankton data and a posterior correlation analysis with the extracted factors and main limnological parameters showed that trophic state in the first place, and mineral- ization in the second place, were the main sources of variance to explain our data. However, the results of these analyses also show that important sources explaining the variance of zooplankton data include some factors not quantified in the standard limnological analysis, but evidently related to lake typology, such as shallowness and type of water feeding and flux.

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.