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Among invasive species there is a special group so named cryptic species for which morphological identification is very difficult. This review is devoted to analysis of the dispersal routes of two copepod cryptic species complexes into aquatic ecosystems. Eurytemora carolleeae introduction was revealed in 2007 with bar-code. The species was described as a new taxon; its distribution was also studied using morphology. Biological invasions of two other Copepod species Acanthocyclops americanus and Eurytemora caspica were mainly studied using morphological methods since the species have already been described. At the same time, to confirm their distinctions from local forms molecular genetic tools were also used. Two scenarios resulting from cryptic species' invasions and their competitions with native species were the partly (E. carrolleeae) or full displacement (A. americanus). When assessing the possible negative impact of invasive species on competitors, the most attention should be paid to predator species. Identification of cryptic species significantly complicates the situation with the assessment of bioinvasion and needs the use of molecular methods. [ABSTRACT FROM AUTHOR]

Food availability is a key determinant of the nursery value of a given habitat for larval and juvenile fishes. Growth, survival, and recruitment success are often inter-correlated and influenced by prey availability and associated feeding success. This is likely true for the threatened population of Longfin Smelt (Spirinchus thaleichthys) in the San Francisco Estuary (SFE) which has collapsed in recent decades along with its preferred prey. In years with high precipitation and freshwater outflow, larval Longfin Smelt are found in shallow wetland habitats throughout the SFE, but variation in the availability of food and feeding success in these habitats remains unexplored. To examine spatial variation in the trophic value of different rearing habitats, we quantified variation in prey availability, feeding success, and prey selection for larval and juvenile Longfin Smelt captured in restored tidal marshes, sloughs, and open-water habitats in the northern and southern SFE. Prey abundance varied spatially, with densities approximately tenfold greater in southern sloughs and restored tidal ponds relative to northern and open-water habitats. Feeding success of larval Longfin Smelt was positively correlated with both fish length and prey density. Larval Longfin Smelt fed selectively on the copepod Eurytemora affinis, with larger individuals (> 25 mm total length) exhibiting an ontogenetic diet shift to larger mysid shrimps. Our results suggest that wetland habitats across the SFE vary greatly in their trophic value, with previously unexplored habitats exhibiting the highest densities of prey and the highest foraging success for larval Longfin Smelt. [ABSTRACT FROM AUTHOR]

Thermal pollution leads to short-term heat shock in aquatic invertebrates; however, the modulation of tolerance and life history of these invertebrates by thermal stress varies among regions, phenology, species, and their acclimation. To assess the effect of thermal shock, we conducted experiments on Daphnia magna and Eurytemora carolleeae at 25 °C, 30 °C, 35 °C, and 40 °C (in relation to 20 °C) in a different exposure time of the stressor (10, 30, and 60 min). The results showed that short-term heat shock leads to increased mortality and reduced fertility of the studied planktonic crustaceans. D. magna was more resistant to thermal shock than E. carolleeae according to all variants of exposure based on the calculated LT50 values for 24, 48, and 72 h. Thermal shock decreased the potential of the Daphnia population in terms of the total number of births, however, with regard to individual reproductive abilities, the non-lethal heat shock did not reduce the birth rate. Although Eurytemora is more sensitive to thermal shock than Daphnia, the type of parental care in Eurytemora might be more favorable for offspring survival following thermal shock than in Daphnia. In Eurytemora, despite maternal deaths, a relatively high number of newborns who survived high temperatures were observed. The obtained results can help to understand the ecological processes occurring due to anthropogenic thermal pollution. [ABSTRACT FROM AUTHOR]

Epibionts often colonize the exoskeleton of crustaceans, which sometimes results in the development of a long-term relationship between them. Our present work confirmed that a specific epibiont is closely associated with the pelagic calanoid copepod Eurytemora lacustris, regardless of the region, which suggests a preserved interaction between these species. Molecular analyses revealed that the epibiont belongs to the genus Tokophrya. We also found that the level of basibiont colonization is related to its size and identified that the most intensely inhabited body parts are those located near the center of the copepod body. We hypothesize that the relationship between Eurytemora (basibiont) and Tokophrya (epibiont) was established during the Quaternary period, following which these two populations were fragmented into lakes where they survived in close interaction. In addition, we suppose that the close relationship between the two species indicates the coevolution of stenotherms. Further studies on the interactions between Eurytemora lacustris and Tokophrya are required in order to gain insight into the long-term relationship between the copepods and the epibionts. [ABSTRACT FROM AUTHOR]

The noncanonical 5′ intron donor splice sites GA and GG are exceedingly rare in described eukaryotic genomes; however, they are present in ∼12% of introns in the genome of the copepod Eurytemora affinis. Failure to recognize the high frequency of these donor sites compromised the modeling of genes in this newly sequenced genome, including 10 conserved ionotropic glutamate receptor (GluR) family genes curated herein. These introns appear to have been acquired recently, along with many additional idiosyncratic introns. Their high frequency implies the evolution of modified intron donor splice site recognition in this copepod.

Abstract The present study shows the results of laboratory experiments addressing the effects of different water qualities on E. americana 's fecundity and survival. The study was carried out with cultured females, incubated under different water qualities and controlled conditions during ten days (7 ± 2 °C, 14 h light, salinity of 32 ± 2, Tetraselmis sp. and Nannochloropsis sp. as food). Four treatments were established: P = subsurface water from sewage plume of Bahía Blanca city, D = the dissolved phase of P, I = bottom water in the sewage discharge point of Bahía Blanca city, and C = water from the low-impacted area of Monte Hermoso, used as a control treatment. Egg production, number of nauplii, number of faecal pellets, survival and fertility-state of females were evaluated. The differences and relationships among copepod factors, environmental variables and pollutants levels (cadmium, lead, copper, zinc, chrome and ammonium-phosphate dissolved), were analysed among treatment using non-parametric multivariate analysis. The copepod factors showed a negative association with pollutants levels and the turbidity. No mortality was observed in C, P and D treatments, whereas 100% mortality was observed in treatment I. Females from C, showed the highest egg production (22.6 ± 6.5 egg/female.clutch), as well as gonads regeneration and a second egg laying. Egg production, number of nauplli and faecal pellets were similar for P and D treatments, but significantly lower than those registered in C. In P treatment, only 40% of females showed regeneration of their gonads for a second egg laying (12.4 ± 2.9 egg/female.clutch) and in D treatment, no female regenerated their gonads for a second egg laying (12.5 ± 3 egg/female.clutch). The results indicate that bioavailable contaminants from dissolved phase of sewage effluent reduce the fertility in Eurytemora americana , while the bottom water at the sewage discharge site is undoubtedly lethal for this species. [ABSTRACT FROM AUTHOR]

Two calanoid species, Arctodiaptomus laticeps (Sars, 1863) and Eurytemora velox (Lilljeborg, 1853), are reported from the Danube River basin in Croatia. Our findings present the first record of A. laticeps and E. velox at the territory of Croatia. Both species were found in the lowland floodplain area during the spring-summer inundation throughout the years. Their occurrence in the waterbodies studied has not overlapped, and different environmental parameters characterized the periods of occurrence of the individual species. The existence of E. velox in this region seems to be permanent, whereas the appearance of A. laticeps is rather confounding. [ABSTRACT FROM AUTHOR]

The species composition, density, biomass, and distribution of zooplankton of the northeastern Sakhalin shelf, Sea of Okhotsk (Chaivo, Pil’tunskii, and Morskoi regions) were studied in October 2014. Zooplankton was represented by 15 taxonomic groups, which were dominated by Copepoda (13 species). The average density and biomass was highest in the Chaivo region (14112 ± 4322 ind./m3, 395 ± 107 mg/m3) and in the Pil’tunskii region (16692 ± 10707 ind./m3, 346 ± 233 mg/m3); the abundance of detected taxonomic groups was minimal (8-12). The average density and biomass of zooplankton was up to 4304 ± 2441 ind./m3, 133 ± 77 mg/m3 in the Morskoi region and increased with depth; the abundance of taxa was maximum (15). Four species of copepods made up the majority of the density and biomass of zooplankton: Acartia hudsonica, Eurytemora herdmani, Pseudocalanus newmani, and Oithona similis. In the Chaivo region, species of the genera Acartia, Eurytemora, and Oithona dominated and subdominated; in Pil’tunskii region, species of the genera Acartia and Oithona dominated and subdominated; and in the Morskoi region, species of the genera Oithona, Pseudocalanus, and Acartia dominated and subdominated. [ABSTRACT FROM AUTHOR]

The estuarine planktonic calanoid copepod Eurytemora americana is described for the first time from Japan based on specimens from Dokai Bay, a small inlet of northern Kyushu in 1975, when the species was exclusively dominant in the innermost bay. This is the southernmost record of the species in the Northern Hemisphere. Morphological descriptions are provided, especially on characters different from or overlooked in previous descriptions. Compared with the recent description of the species from Korea, a distinct morphology is found in the spinule number on the male fifth leg, suggesting inter-population variation and therefore no gene flow between the Japanese and Korean populations. Eurytemora americana in Dokai Bay is regarded as an invasive alien species introduced via ship ballast water. Despite the dominance in 1975, the copepod was not collected from brackish waters in the innermost part of the bay in 2008. Global warming in spring and/or winter periods after the 1970s is a possible reason for the disappearance of this cold water species. [ABSTRACT FROM AUTHOR]

Background: The brackish calanoid, Eurytemora americana Williams, 1906, is reported in the northern part of Korea. It is found to be an important copepod in the mesozooplankton community structure from the estuarine and shallow waters. The range extension and of E. americana is reported additionally to previously known distributional range from brackish waters of the South Atlantic Ocean, United Kingdom, Canada, English Channel, Iceland, the North Atlantic Ocean, the North Pacific Ocean (Japan, Korea, and Russia), and the North Sea. In this study, both sexes of E. americana are redescribed and illustrated including their undescribed mouthparts. Results: The most important characters that have been overlooked in the previous descriptions are: shape of the last pedigerous somite in female, structure of the genital double-somite, and ornamentation of the fifth leg in both sexes. Conclusion: The distributional range of E. americana is now given with its northern and southern hemisphere limit as 70 to 37°N in the North Pacific and 38°S in the Southwest Atlantic. [ABSTRACT FROM AUTHOR]

The copepod Eurytemora carolleeae dominates vernal zooplankton biomass in the Chesapeake Bay estuarine turbidity maximum (ETM) region, where it is an important prey item for larval anadromous fish. Although there have been several zooplankton studies in the Chesapeake Bay ETM focused on spring, the importance of winter zooplankton populations for establishing these vernal conditions has not been investigated. We examined the abundance, distribution, and individual sizes of E. carolleeae in winter of 2007 and 2008 and we investigated the potential impact of varying winter conditions and rising winter temperatures on Eurytemora female carbon content, egg production rate, and generation time. We found higher abundances and larger individuals in the colder 2007 than in 2008 under similar freshwater flow conditions. Empirical estimates showed that overall zooplankton productivity was higher in 2007 than in 2008. Published recruitment indices for anadromous fish including white perch and striped bass were higher in 2007 than in 2008 in the study region. Based on these findings, we hypothesize that colder conditions resulted in larger individuals and therefore increased prey biomass available to larval fish. We further hypothesize that rising winter water temperatures will negatively impact trophic transfer of primary production to copepods and ultimately to fish. [ABSTRACT FROM AUTHOR]

Our understanding of the systematics of the Eurytemora affinis complex developed at a fast pace over the last decades. Formerly considered as a complex of cryptic species, it is now believed to include three valid species: E. affinis , Eurytemora carolleeae , and Eurytemora caspica . American and European representatives have been studied in detail with respect to fine-scale geographic distribution, levels of genetic subdivision, evolutionary and demographic histories. Morphological components have been less explored. In this study, an analysis of the phylogeny and morphology of E. affinis was done, with a special focus on European populations. A total of 447 individuals of E. affinis from Europe were analyzed with genetic tools and 170 individuals according to morphological criteria. Common and new morphological and genetic features were analyzed. For this, we used ML and Bayesian methods to analyze the bar coding mt-DNA gene cytochrome c oxidase I subunit. Both genetic and morphological analyses showed high heterogeneities among the E. affinis populations from Europe. As a result, three local populations of E. affinis in Western Europe, including the European part of Russia, were established. Their genetic and morphological heterogeneity corresponded to the subspecies level. [ABSTRACT FROM AUTHOR]

The noncanonical 59 intron donor splice sites GA and GG are exceedingly rare in described eukaryotic genomes; however, they are present in ~12% of introns in the genome of the copepod Eurytemora affinis. Failure to recognize the high frequency of these donor sites compromised the modeling of genes in this newly sequenced genome, including 10 conserved ionotropic glutamate receptor (GluR) family genes curated herein. These introns appear to have been acquired recently, along with many additional idiosyncratic introns. Their high frequency implies the evolution of modified intron donor splice site recognition in this copepod. [ABSTRACT FROM AUTHOR]

We examined whether copepod naupliar survival rate can be impacted by winter estuarine dinoflagellate blooms and compared winter nauplii grazing rates with other reported rates. Grazing and survival experiments were conducted in the laboratory at 4°C and showed that increased prey concentration resulted in increased naupliar survival over 2 weeks. High survival rate of winter nauplii could result in higher spring copepodite abundances, which would have a positive impact on fish larvae recruitment. [ABSTRACT FROM AUTHOR]

Lagoon Notoro-ko, located on the northeastern coast of Hokkaido, Japan, and connected to the Okhotsk Sea by a human-made channel, is strongly influenced by local hydrography, as water masses in the lagoon are seasonally influenced by the Soya Warm Current and the East Sakhalin Current. We here report on the succession of copepod communities during the warm season in relation to water mass exchange. Copepods were categorized into four seasonal communities (spring/early-summer, mid-summer, late-summer/fall, and early-winter) via a cluster analysis based on Bray–Curtis similarities. Spring/early-summer and early-winter communities were characterized by the temperate–boreal calanoid Pseudocalanus newmani , comprising 34.9%–77.6% of the total abundance of copepods during times of low temperature/salinity, as influenced by the prevailing East Sakhalin Current. Late-summer/fall communities were characterized by the neritic warm-water calanoid Paracalanus parvus s.l., comprising 63.9%–96.3% of the total abundance, as influenced by the Soya Warm Current. Mid-summer communities comprised approximately equal abundances of P. parvus , Eurytemora herdmani , Scolecithricella minor , and Centropages abdominalis (12.8%–28.2%); this community is transitional between those of the spring/early-summer and late-summer/fall. Copepod community succession in Lagoon Notoro-ko can be largely explained by seasonal changes in water masses. [ABSTRACT FROM AUTHOR]

Abstract: The red pigment astaxanthin is a powerful antioxidant, which occurs in eggs and body tissues of crustaceans and fish. It is produced by crustaceans from algal carotenoids. In a two-year field study we assessed natural concentrations and dynamics of astaxanthin in mesozooplankton communities in the brackish Baltic Sea area. Astaxanthin levels varied between 0.37 and 36ngL−1. They increased with salinity along the Baltic Sea gradient and were linked to zooplankton biomass and phytoplankton community composition. Astaxanthin concentrations showed typical seasonal patterns and varied from 0.2 to 5.1ngind−1, 0.2 to 3.4ng (μgC)−1 and 6 to 100ngmm−3. These concentrations were inversely related to water temperature and strongly linked to zooplankton community composition. Communities dominated by the calanoid copepods Temora longicornis, Pseudocalanus acuspes and Eurytemora spp. generally held the highest concentrations. With increasing cladocerans:copepods biomass ratios community astaxanthin concentrations decreased and with higher relative biomass of Acartia spp. the proportion of astaxanthin diesters decreased. Diesters prevailed in the cold season and they are thought to improve the antioxidant protection of storage lipids during winter. Climate change causes higher temperature and lower salinity in the Baltic Sea proper. This modifies zooplankton community composition, but not necessarily into a community with lower concentrations of astaxanthin since T. longicornis (high concentrations) has been reported to increase with higher temperature. However, decreased astaxanthin production in the ecosystem is expected if a basin-wide increase in the cladocerans:copepods biomass ratios would occur with further climate change. [Copyright &y& Elsevier]

The seasonal abundance and hatching success of calanoid benthic eggs were examined during the coexistence of Acartia tonsa and Eurytemora americana in the Bahía Blanca Estuary (BBE). The dormancy behaviour of eggs extracted from surface sediment layers was tested by simulating seasonal conditions during incubation. There was a greater abundance of benthic eggs of E. americana (≤8.68×106 eggs m−2) than of A. tonsa, the latter consistently showing low egg abundance (≤0.8×106 eggs m−2). The emergence of most E. americana nauplii occurred at 17°C after the experimental warming phase (refractory phase of 280 days), confirming the diapause character of these eggs. The emergence of the first A. tonsa nauplii from initial cold season samples occurred at 9–12°C after 60–70 days of incubation. However, a 180-day delay in hatching at temperatures ≥15°C was also observed in A. tonsa eggs from the last sampling days of the cold season, thus suggesting an intermediate behaviour between diapause and quiescence. The benthic egg bank in the inner zone of the BBE provides a temporary reservoir for both key copepods, thus contributing in their survival. [ABSTRACT FROM AUTHOR]

The Baltic Sea is one of the world's most intensive centres for maritime traffic. This sea has become an important recipient of alien species transported with ballast water from all over the world. Sibling species are a special group of invasive animals that are hardly distinguishable from relative but often ecologically different local species. In this study, a molecular genetic diagnosis was performed, based on the analysis of DNA nucleotide sequences (barcoding) in the populations of a dominant circumpolar speciesEurytemora affinis(Poppe, 1880) from the Gulf of Finland and the Atlantic coast of European estuaries and ofEurytemora carolleeaeAlekseev and Souissi, 2011, a new North American suspected invasive form. The results of the diagnosis were completed by morphological analyses. Considering the key role ofE. affinisin the Baltic Sea zooplankton community, the invasion ofE. carolleeaemight have consequences for biodiversity, biogeography, conservation and ecosystem management in this area. [ABSTRACT FROM AUTHOR]

Information on physiological rates and tolerances helps one gain a cause-and-effect understanding of the role that some environmental (bottom-up) factors play in regulating the seasonality and productivity of key species. We combined the results of laboratory experiments on reproductive success and field time series data on adult abundance to explore factors controlling the seasonality of Acartia spp., Eurytemora affinis and Temora longicornis, key copepods of brackish, coastal and temperate environments. Patterns in laboratory and field data were discussed using a metabolic framework that included the effects of 'controlling', 'masking' and 'directive' environmental factors. Over a 5-year period, changes in adult abundance within two south-west Baltic field sites (Kiel Fjord Pier, 54°19′89N, 10°09′06E, 12-21 psu, and North/Baltic Sea Canal NOK, 54°20′45N, 9°57′02E, 4-10 psu) were evaluated with respect to changes in temperature, salinity, day length and chlorophyll a concentration. Acartia spp. dominated the copepod assemblage at both sites (up to 16,764 and 21,771 females m at NOK and Pier) and was 4 to 10 times more abundant than E. affinis (to 2,939 m at NOK) and T. longicornis (to 1,959 m at Pier), respectively. Species-specific salinity tolerance explains differences in adult abundance between sampling sites whereas phenological differences among species are best explained by the influence of species-specific thermal windows and prey requirements supporting survival and egg production. Multiple intrinsic and extrinsic (environmental) factors influence the production of different egg types (normal and resting), regulate life-history strategies and influence match-mismatch dynamics. [ABSTRACT FROM AUTHOR]

A comparative analysis of the habitat characteristics, the gut content, and the elemental composition of the cutting edge of the mandibles is provided for two species of crustaceans (Copepoda, Calanoida), Eurytemora velox (Lilljeborg, 1853) and Eurytemora lacustris (Poppe, 1887). These representatives of the brackish and marine fauna inhabit the Belarusian freshwaters. The paper presents the generalized data on the recent state and changes in the ranges of species. The differences in the silicification of mandibles of species may reflect the different nutrition strategies and habitat selection. [ABSTRACT FROM AUTHOR]

Menéndez, M. C., Dutto, M. S., Piccolo, M. C., and Hoffmeyer, M. S. 2012. The role of the seasonal and semi-diurnal tidal cycle on mesozooplankton variability in a shallow mixed estuary (Bahía Blanca, Argentina). – ICES Journal of Marine Science, 69: 389–398.The role of the seasonal and semi-diurnal tidal cycle on mesozooplankton dynamics was investigated in the inner zone of the Bahía Blanca Estuary (BBE), Argentina. Hydrological data and mesozooplankton samples were obtained bimonthly from December 2004 to April 2006, during 14 h tidal cycles. The mesozooplankton community was represented by 33 taxa. Taxa richness was greater near the bottom, where the contribution of benthic forms was notable. Abundances were greatest during summer (>5500 ind. m−3) and lowest during winter (<70 ind. m−3). The mesozooplankton community was dominated by Acartia tonsa and Eurytemora americana. Multivariate analyses revealed significant seasonal differences in community structure, especially in terms of density. Seasonal differences in community structure are well explained by the natural change of abiotic and biotic conditions, but temperature played a key role in structuring the mesozooplankton community. The zooplankton was significantly more abundant during the ebb, suggesting that local hydrological conditions are responsible for the spatial variations. The results demonstrate how variable the mesozooplankton community structure can be over different time-scales and provide a better understanding of zooplankton variability in the BBE and other temperate, turbid, mixed systems. [ABSTRACT FROM PUBLISHER]

Berasategui, A. A., Hoffmeyer, M. S., Dutto, M. S., and Biancalana, F. 2012. Seasonal variation in the egg morphology of the copepod Eurytemora americana and its relationship with reproductive strategy in a temperate estuary in Argentina. – ICES Journal of Marine Science, 69: 380–388.Seasonal variation in the morphology of Eurytemora americana eggs and its relationship with reproductive strategy were studied in the Bahía Blanca Estuary. Eggs from field females were analysed morphologically by optical (OM) and electron microscopy [scanning electron microscopy (SEM)–transmission electron microscopy (TEM)] during the population pulse. Additionally, egg-carrying females were incubated simulating in situ environmental conditions to evaluate the resting egg character. Subitaneous and resting eggs were indistinguishable by OM, but showed different chorion appearance under SEM and TEM. Sinuous patterned chorion eggs, mainly produced during the period of population growth, were classed as subitaneous eggs based on their high level of hatching success. Eggs with a sponge-like appearance, produced after the population peaked, were classed as diapause eggs based on their inability to hatch even under favourable conditions. There were significant differences in egg size through the population pulse and diapause eggs were significantly bigger than subitaneous eggs. The observation of both morphotypes in egg-carrying females after peak population abundance confirms the existence of a transitional reproductive stage before the exclusive production of diapause eggs at the end of the pulse. Diapause egg production enables E. americana to resist adverse conditions, ensuring its survival in temperate estuaries. [ABSTRACT FROM PUBLISHER]

Abstract: Benthic, viable resting eggs of calanoid copepods were found for the first time in the Seine estuary (France) during July 2008. Vertical distribution of the resting eggs in the sediment was determined up to 10 cm depth. Hatching success of the eggs extracted from different 1-cm thick sediment layers was experimentally tested immediately after extraction and after a long refractory phase (i.e. 11 months) of storage at low temperature (4–5 °C). The hatching success of resting eggs obtained immediately after sediment incubation was lower (0.72%) than the value observed after 11 months (4.50%) with an overall hatching success of 2.37%. The marine, calanoid copepod Temora longicornis was the primary species to hatch from the eggs; however, the estuarine calanoid copepod Eurytemora affinis also hatched from resting eggs. The mean abundance of eggs found in sediment (1.42 × 106 eggs m−2) was comparable to that reported for other marine and estuarine calanoid copepods. The Seine estuary sediment had a high variability of egg abundance (between 0.14 and 8.10 × 107 eggs m−3) suggesting that the hydrodynamics of this macrotidal estuary are likely responsible for this variability. Significant sediment resuspension occurs in the Seine estuary during flood periods and spring tides leading to resting eggs to contribute along the year to the nauplii recruitment of calanoid copepods. On average, around 400,000 nauplii m−3 month−1 of the main calanoid copepods can emerge from the surface layer sediment in the Seine estuary, suggesting that resting eggs could play an important role in the population dynamics of key calanoid copepods in the Seine estuary. [Copyright &y& Elsevier]

The copepod genus Eurytemora occupies a wide range of habitat types throughout the Northern Hemisphere, with among the broadest salinity ranges of any known copepod. The epicenter of diversity for this genus lies along coastal Alaska, where several species are endemic. Systematic analysis has been difficult, however, because of a tendency toward morphological stasis in this genus, despite large genetic divergences among populations and species. The goals of this study were to (1) analyze patterns of morphological variation and divergence within this genus, focusing on Eurytemora species that occur in North America, and (2) determine patterns of geographic and salinity distribution of Eurytemora species within the ancestral range in Alaska. We applied a comparative multivariate morphological analysis using 16–26 characters from 125 specimens from 20 newly collected sites in Alaska and 15 existing samples predominantly from North America. Results from principal component and hierarchical cluster analyses identified seven distinct morphological species of Eurytemora in North America ( E. affinis, E. americana, E. canadensis, E. composita, E. herdmani, E. pacifica, and E. raboti), and identified diagnostic characters that distinguish the species (forming the basis for a new identification key). Several previously named species were regarded as synonyms. The sites we sampled in Alaska were remarkable in the high levels of sympatry of Eurytemora species, to a degree not seen outside of Alaska. Future studies of Eurytemora should shed light on patterns of habitat invasions and physiological evolution within the genus, and yield insights into mechanisms leading to its remarkably broad geographic and habitat range. [ABSTRACT FROM AUTHOR]

The response of phytoplankton to the presence of two mesozooplanktonic grazers was studied in a 44-h laboratory experiment from the phytoplankton perspective. The <45-μm-filtered plankton community, as well as females of the copepod Eurytemora affinis and nauplii of the barnacle Balanus improvisus originated from the northern Baltic Sea. The phytoplankton community was dominated by the dinoflagellate Heterocapsa triquetra, which was preferred as food by the mesozooplanktonic grazers, especially E. affinis. Cryptophytes were eaten by the B. improvisus nauplii, while heterotrophic nanoflagellates increased in the presence of B. improvisus nauplii, and colonial cyanobacteria increased in the presence of E. affinis. Because of the strong selective feeding on the dominant, large-sized phytoplankton species, the negative effect of the mesozooplanktonic grazers on total chlorophyll a was stronger than any cascade effect releasing phytoplankton from protozoan grazing. [ABSTRACT FROM AUTHOR]

Abstract: Eurytemora americana has been only reported as invader in Bahía Blanca Estuary, Argentina within the South Hemisphere. There are a few experimental researches under laboratory conditions done with this species and its reproductive behaviour around the world is very scarce. Consequently, it is still not possible to completely understand its population dynamics. In the present study, E. americana reproductive temporal behaviour and relationships among abundance, female size, egg production and hatching success were examined in the Bahía Blanca Estuary, during 2007 pulse. In order to determine the potential relationships between these variables and the environmental variables, experimental incubations were conducted in the laboratory simulating natural conditions. Spearman’s rank correlation was used to analyze the relationships among all variables. Temporal change of biotic and environmental variables was corroborated by a Mann–Whitney/Kruskal–Wallis non-parametric tests, with significant differences (p ≪0.01) in all variables throughout the study. Abundance population results showed very high values in relation to those recorded in recent years in Bahía Blanca Estuary. This response could be due to the unusual combination of environmental factors (polar wave with temperatures ≤6°C and a drought period with high salinities, 32.7–36.6) recorded during the studied winter period. Significant positive correlations between abundance and salinity (p <0.01, n =226), and hatching success (p <0.01, n =25) as well as a significant negative correlation between abundance and chlorophyll a (p <0.01, n =226) were found. Although E. americana shows a k-strategy within its annual pulse, it presented two markedly distinct behaviours depending on temporal environmental variability. From July to early september, when the estuary evidenced high salinity, low temperature and high food availability, E. Americana showed large females, large clutch size and high hatching success. When environmental conditions became unfavorable from September to October, small females, small clutch size and very low hatching success were observed. The latter is associated with diapause egg laying which ensures population recruitment. According to our findings the particular combination of low temperatures, high salinities and high available food (i.e. variables which each year modulate its pulse) during 2007 winter–spring, favored the great development of E. americana. This invading species in its opportunistic role has managed to exploit a vacant niche in the estuary, developing two different behaviours within the k-strategy depending on change in environmental conditions. [Copyright &y& Elsevier]

The Mattaponi River is part of the York River estuary in Chesapeake Bay. Our objective was to identify the organic matter (OM) sources fueling the lower food web in the tidal freshwater and oligohaline portions of the Mattaponi using the stable isotopes of carbon (C) and nitrogen (N). Over 3 years (2002-2004), we measured zooplankton densities and C and N stable isotope ratios during the spring zooplankton bloom. The river was characterized by a May-June zooplankton bloom numerically dominated by the calanoid copepod Eurytemora affinis and cladocera Bosmina freyi. Cluster analysis of the stable isotope data identified four distinct signatures within the lower food web: freshwater riverine, brackish water, benthic, and terrestrial. The stable isotope signatures of pelagic zooplankton, including E. affinis and B. freyi, were consistent with reliance on a mix of autochthonous and allochthonous OM, including OM derived from vascular plants and humic-rich sediments, whereas macro-invertebrates consistently utilized allochthonous OM. Based on a dual-isotope mixing model, reliance on autochthonous OM by pelagic zooplankton ranged from 20% to 95% of production, declining exponentially with increasing river discharge. The results imply that discharge plays an important role in regulating the energy sources utilized by pelagic zooplankton in the upper estuary. We hypothesize that this is so because during high discharge, particulate organic C loading to the upper estuary increased and phytoplankton biomass decreased, thereby decreasing phytoplankton availability to the food web. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms are a common phenomenon in the Baltic Sea, and the hepatotoxin nodularin has been frequently detected in certain Baltic Sea fishes and mussels. However, there is no knowledge about the naturally occurring concentrations of nodularin in Baltic Sea zooplankton. The aim of this study was to survey the concentrations of nodularin in natural zooplankton assemblages, and to study the depuration of nodularin in one common copepod species, Eurytemora affinis, experimentally. The nodularin concentrations in common zooplankton species were determined from field-collected samples from the northern Baltic Proper in 2001 and 2002, during cyanobacterial blooms, and the samples were analysed by ELISA immunoassay. Nodularin could be detected from the field-collected zooplankton, suggesting that during a natural bloom event toxins accumulate in their tissues. The concentrations were relatively low (0.07±0.01 μg g−1 ww), ranging from below detection limit to 0.62 μg g−1 ww. Some variation occurred in the concentrations between species and years; generally concentrations were higher in 2001 than in 2002. In the depuration experiment E. affinis copepods were fed with toxic Nodularia spumigena for 24 h, and their toxin contents were monitored for 24 h after transferring them to filtered seawater. A rapid decrease in nodularin concentrations occurred during the first 0.5–3 h after the exposure. However, after a 24-h depuration period in filtered seawater, nodularin could be still detected in E. affinis tissues, indicating that part of the accumulated nodularin, or its derivatives, could be transferred to planktivores. [ABSTRACT FROM AUTHOR]

Feeding ecology of white perchMorone americanalarvae, a major component of the ichthyoplankton community in the estuarine turbidity maximum(ETM) region of upper Chesapeake Bay, was evaluated in years of contrasting physical conditions. In 1998, high river flow led to an ETM with high turbidity and pronounced salinity stratification. In 1999, under low river flow conditions, turbidities in the ETM region were lower and the salt front was located 15 km up-stream of its location in 1998. Copepodites and adults ofEurytemora affiniswere the predominant prey in guts of all length classes of larvae(3·2–9·8 mm standard length,LS) that were examined. Repeated-measures, multiple regression analyses were conducted to evaluate the influence of several factors on feeding success by determining if physical conditions(temperature, current velocity, salinity, turbidity and light) and prey concentrations explained variability in mean gut fullness(gut contents mass per body mass) of small(<5 mmLS) and large(>5 mmLS) white perch larvae.Eurytemora affinisconcentrations were significant in the statistical models for both small and large larvae. High concentrations ofE. affinis, which enhanced encounter rates of white perch larvae with prey, may have been the most important factor determining feeding success in the ETM region. Larval feeding incidence(percentage of guts with food) was higher in 1998, suggesting that annual variability in river flow influenced larval feeding success by controlling physical and biological conditions in the ETM region. [ABSTRACT FROM AUTHOR]

Abstract: Given recent reports suggesting that certain contaminants may be present in sewage effluents at levels, which may exert a deleterious impact on fish, it seems pertinent to extend ecological hazard evaluation for such substances to aquatic invertebrates. For this reason, we sought to determine whether 17β-estradiol (E2), benzo(a)pyrene (BaP), 4-nonylphenol (NP), di(ethyl-hexyl)-phthalate (DEHP), and atrazine (A), individually or in binary mixture, can inhibit the survival, development, or reproductive output of the estuarine copepod Eurytemora affinis. In the first experiment nauplii were exposed to graded concentrations of individual contaminants to determine the 96-h LC50, 10-day no observed effect concentration (NOEC) and 10-day lowest observed effect concentration of each compound. In the second experiment newly released (<24-h-old) nauplii were exposed either to an individual contaminant at the NOEC or to binary mixtures, where each compound was used at half NOEC. The effects were monitored daily for development and sex ratio. After 10 days of exposure, adult males and females were paired and exposures continued to investigate effects on reproductive output (maximum 28 day total exposure). Based on these life cycle parameters the lowest 10-day NOECs were 6±4μgL-1 for E2, 7±3μgL-1 for NP, 12±3μgL-1 for BaP, 25±3μgL-1 for A, and 109±29μgL-1 for DEHP. BaP, NP, and DEHP inhibited naupliar development, but in binary mixture with E2 these compounds did not inhibit larval development. The results suggest that endocrine disruption could occur in copepods following exposure to estrogenic compounds, especially if they are exposed starting from embryonic development. [Copyright &y& Elsevier]

Calanoid copepod abundance and distribution were measured by monthly plankton tows from May through November in 1998 and March through August in 1999 in three subestuaries of the Waquoit Bay estuarine system. There was a dramatic seasonal change in the composition of calanoids in Waquoit Bay with a spring community consisting of Acartia hudsonica, Centropages hamatus, and Eurytemora affinis, replaced by Acartia tonsa in the summer. The abundance of A. hudsonica, A. tonsa, and C. hamatus was higher in the saltier reaches of the subestuaries, but the abundance of E. affinis and copepod nauplii was not affected by salinity. Even though different land-derived nitrogen loads created different concentrations of chlorophyll in the water of Waquoit Bay subestuaries, there was no apparent response in the abundance of most calanoid copepods to differences in nitrogen load to the subestuaries. The uncoupling of phytoplankton food from mesozooplankton consumers suggests that other factors such as water residence time, phytoplankton quality and composition, or variations in microzooplankton food play a role in the abundance dynamics of Waquoit Bay calanoid populations. [Copyright &y& Elsevier]

Variation in nuclear DNA content within some eukaryotic species is well documented, but causes and consequences of such variation remain unclear. Here we report genome size of an estuarine and salt-marsh calanoid copepod, Eurytemora affinis, which has recently invaded inland freshwater habitats independently and repeatedly in North America, Europe, and Asia. Adults and embryos of E. affinis from the St. Lawrence River drainage were examined for somatic cell DNA content and the presence or absence of embryonic chromatin diminution, using Feulgen–DNA cytophotometry to determine a diploid or 2C genome size of 0.6–0.7 pg DNA/cell. The majority of somatic cell nuclei, however, have twice this DNA content (1.3 pg/nucleus) in all of the adults examined and possibly represent a population of cells arrested at the G2 stage of the cell cycle or associated with some degree of endopolyploidy. Both suggestions contradict assumptions that DNA replication does not occur in adult tissues during the determinate growth characteristic of copepods. Absence of germ cell nuclei with markedly elevated DNA values, commonly found for species of cyclopoid copepods that show chromatin diminution, indicates that E. affinis lacks this trait. The small genome size and presumed absence of chromatin diminution increase the potential utility of E. affinis as a model for genomic studies on mechanisms of adaptation during freshwater invasions. [ABSTRACT FROM AUTHOR]

As a prevalent species complex in temperate estuaries and salt marshes of the Northern Hemisphere, populations of Eurytemora affinis that inhabit these environments must be adapted to salinity fluctuations. Some populations have invaded freshwater environments. In this work, we focus on the combined effects of temperature and salinity fluctuations on mortality rates and development time of the first naupliar stages under starvation. Two temperatures (10 and 15 °C) and eight salinities, ranging from 0 to 35 psu are investigated. We show (i) that among all experimental conditions the optimal temperature and salinity for naupliar survival and development are 15 psu and 15 °C, and (ii) that only the most extreme salinities (i.e. 0 and 35 psu) have a negative effect on naupliar survival. Nauplii develop faster and reach a higher developmental stage at 15 than at 10 °C, independent of salinity. The relevance of this metabolic adaptive pattern is discussed in the general framework of in situ behavior, tidal forcing and biogeographic variability, as well as the potential sources of the observed individual variability. [Copyright &y& Elsevier]

Seasonal zooplankton succession (mainly of the mesozooplankton) in the inner zone of Bahía Blanca estuary during the period 1990–1991 was compared to that from the period 1979–1980 in order to detect changes having taken place in 10 years. Taxonomic composition, zooplankton abundance, species occurrence and temperature–salinity conditions were studied within the two annual cycles. This estuarine ecosystem has been deeply affected by a population increase and by the rapid growth of industrial activity and maritime traffic over the last two decades. Several changes in the zooplankton assemblage composition and structure were detected, probably due to temperature–salinity gradient patterns, which showed discernible differences. Dominance, during winter–spring, of two new invading species, namely, the cirriped Balanus glandula and the copepod Eurytemora americana, causing a decrease in the autochthonous key copepod Acartia tonsa, was one of the principal features of the period 1990–1991. Seasonal changes in diversity and species richness, as well as differences in the multivariate general pattern of the zooplankton community structure with a consequent decrease in the community stability during the second period, were also observed. [ABSTRACT FROM AUTHOR]

Laboratory experiments were carried out to investigate the effect of two strains of Microcystis aeruginosa and a strain of Nodularia spumigena on the survival of Eurytemora affinis (Copepoda) and on the embryonic and larval development of the Baltic spring-spawning herring Clupea harengus membras. The trials were made in water taken from Pärnu Bay, at a salinity of 3.7–5.1 psu, a constant temperature (15°C ± 1°C in trials with Eurytemora and herring embryos; 18°C ± 2°C with herring larvae), and an oxygen concentration of 8.8–10.4 ppm. The strains tested had a negative impact on the survival of Eurytemora, as well as on the embryonic development and hatching regime of the Baltic herring. In Eurytemora the response depended on the sex of the animals: the survival was clearly higher in females. In the embryonic stages of herring, the influence resulted in an increase in deviations from the normal pattern of development and a higher mortality. The impact of the strains on the larval development of herring was rather moderate. © 2003 Wiley Periodicals, Inc. Environ Toxicol 18: 236–242, 2003. [ABSTRACT FROM AUTHOR]

Invasive species are commonly thought to have broad toler-ances that enable them to colonize new habitats, but this as-sumption has rarely been tested. In particular, the relative im-portance of acclimation (plasticity) and adaptation for invasion success are poorly understood. This study examined effects of short-term and developmental acclimation on adult salinity tolerance in the copepod Eurytemora affinis. This microcrus-tacean occurs in estuarine and salt marsh habitats but has in-vaded freshwater habitats within the past century. Effects of short-term acclimation were determined by comparing adult survival in response to acute versus gradual salinity change to low salinity (fresh water). Effects of developmental acclimation on adult tolerance were determined using a split-brood factorial experimental design for one brackish-water pop- 4 #2 ulation from Edgartown Great Pond, Massachusetts. Twenty full-sib clutches were split and reared at four salinities (fresh, 5, 10, and 27 practical salinity units [PSU]). On reaching adult-hood, clutches from three of the salinity treatments (no sur-vivors at fresh) were split into low- (fresh) and high- (40 PSU) salinity stress treatments, at which survival was measured for 24 h. Short-term acclimation of adults did not appear to have a long-term affect on low-salinity tolerance, given that gradual transfers to fresh water enhanced survival relative to acute transfers in the short term (after 7 h) but not over a longer period of 8 d. Developmental acclimation had contrasting ef-fects on low- versus high-salinity tolerance. Namely, rearing salinity had a significant effect on tolerance of high-salinity (40 PSU) stress but no significant effect on tolerance of low-salinity (freshwater) stress. In addition, there was a significant effect of... [ABSTRACT FROM AUTHOR]

The copepod Eurytemora affinis generally lives under estuarine conditions, where the suspended particulate matter (SPM) is strongly dominated by non-living particles. This article investigates as to how far E. affinis is capable of feeding selectively on phytoplankton under these extreme circumstances. Selectivity for phytoplankton by E. affinis was studied from samples taken from the Westerschelde (Belgium/The Netherlands). Copepod clearance rates exerted on natural phytoplankton quantified from the gut pigment content were significantly higher than those exerted on total particulate matter, calculated from microscopic image analysis of total gut content and total particulate matter concentration in the water. In addition, gut pigment content data on adult E. affinis measured during spring in three European estuaries (the Gironde (France), the Westerschelde and the Elbe (Germany)) were used to study the quantitative response of gut pigment content to varying ratios of phytoplankton to total SPM. A model, expressing maximum gut fluorescence as a function of body weight and gut fluorescence as a product of maximum gut fluorescence with the proportion of phytoplankton to total SPM in the feeding medium, satisfactory fitted the gut fluorescence observations made in the three estuaries. Over the range of phytoplankton-carbon/particulate organic carbon ratios observed in the three estuaries, gut fluorescence decreased with SPM concentration, but maximum gut fluorescence was reached when phytoplankton-carbon was >5% of particulate organic carbon. Limitation of selective feeding apparently only occurred under extremely high SPM loads, such as observed in the Gironde. Maximum gut fluorescence values corresponded exactly to those obtained previously for planktonic copepods in general, affirming the relationship with copepod size. [Copyright &y& Elsevier]

The mass occurrence of toxic cyanobacteria is a recurrent phenomenon in the Baltic Sea. Grazers may obtain toxins either through ingestion or by direct exposure to dissolved toxins. Despite this, there is little knowledge about the accumulation of cyanobacterial toxins in planktonic organisms present during these blooms. Toxin analyses of tissue samples are complicated to carry out and, because of the small size of microscopic planktonic organisms, often difficult to execute. Therefore, we wanted to use a precise and sensitive method to study toxin uptake and accumulation in zooplankton. We used chemically tritiated nodularin, [sup3]H-dihydronodularin, to study the uptake of dissolved nodularin, a cyanobacterial hepatotoxin produced by Nodularia spumigena. Cultures of the calanoid copepods Acartia tonsa and Eurytemora affinis, and an oligotrich ciliate Strombidium sulcatum were exposed to [sup3]H-dihydronodularin in filtered seawater, using naturally occurring concentrations of dissolved nodularin (5 wg L[supm1]). All three species took up measurable amounts of radiolabeled nodularin. After 48 h we detected 0.37 - 0.22 wg toxin g C[supm1] (mean - sd) in A. tonsa and 0.60 - 0.15 wg toxin g C[supm1] in E. affinis, whereas 1.55 - 0.50 wg toxin g C[supm1] was detected in S. sulcatum after 24 h. The minimum bioconcentration factor (BCF) of [sup3]H-dihydronodularin was 12 for A. tonsa and 18 for E. affinis. For S. sulcatum our results indicate a maximum BCF of 22. However, because the uptake studies for this species were done in the presence of bacteria, possible particulate transfer cannot be excluded. Nevertheless, our results indicate that dissolved nodularin can be taken up by planktonic organisms. Therefore, the vectorial transport of dissolved toxins to higher trophic levels seems possible, even if some planktonic grazers would avoid feeding on toxic cyanobacteria filaments. [ABSTRACT FROM AUTHOR]

Cyanobacteria blooms are common in the Baltic Sea and are considered to be a poor food source and sometimes toxic to zooplankton. Most experiments demonstrating harmful effects have been short-term incubations with monocultures or simple mixtures of food. In this study, a mesocosm approach was used to examine zooplankton responses over generation timescales. A toxic strain of the cyanobacterium Nodularia spumigena was added to bag enclosures of ambient water. The initial mesozooplankton concentration was either reduced by prescreening the water or enriched with locally caught zooplankton. Experiments ran for 15 days, long enough to monitor reproductive success and development of the next mesozooplankton generations. There was no major harmful effect on the zooplankton assemblage, even though the concentration of the toxin nodularin was in the upper range of field observations. The copepod Eurytemora affinis, rotifers Synchaeta spp. and the cladoceran Bosmina longispina maritima were able to develop and reproduce successfully in the presence of N. spumigena. The only species showing impaired recruitment was the copepod Acartia bifilosa. The general lack of population level effects from N. spumigena in this study can be reconciled with previous observations of adverse effects. Cyanobacteria alone may be poor food and toxic to zooplankton, but in the mesocosms a rich assemblage of microbiota developed, similar to that associated with blooms in the field. We suggest that, in the context of otherwise food-depleted summer situations in the open Baltic Sea, zooplankton can derive benefit from cyanobacteria bloom assemblages. [ABSTRACT FROM PUBLISHER]

Morphological stasis has long been regarded as one of the most challenging problems in evolutionary biology. This study focused on the copepod species complex, Eurytemora affinis, as a model system to determine pattern and degree of morphological stasis. This study revealed discordant rates of morphological differentiation, molecular evolution, and reproductive isolation, where speciation was accompanied by lack of morphological differentiation in secondary sex characters. Thus, in all but the European populations, evolution of the secondary sex characters was marked by morphological stasis, even between reproductively-isolated populations.

Individual variability in development rates of the calanoid copepod Eurytemora affinis was studied using previously published data that are here normalised for the effects of food and temperature. The late-developing individuals died before reaching the adult stage. The development of individuals was studied using two different stage aggregations. In the one case, the stages were aggregated into four groups: early nauplii (N1–N3), later nauplii (N4–N6), early copepodites (C1–C3) and later copepodites (C4–C5). In another case, only total nauplii (N1–N6) and total copepodites (C1–C5) were used. The distributions of development time in the first groups obtained from the normalised data show distinct asymmetry. The gamma density function is asymmetrical to fit the distributions of development in the different groups under different experimental conditions. For one experimental condition (103 cells ml–1, 15°C) the development of E. affinis was simulated using an age-within-stage model together with the fitted distributions of moulting probabilities. We showed that the asymmetrical gamma distribution was an adequate parameterization of the transfer process. It was also useful to simplify the life cycle representation by lumping developmental stages. However, the comparison of the simulated abundance with two life cycle representations showed another source of error due to the heterogeneity of stage-specific mortality rates. The error of the estimation increases in proportion to the difference of mortality rates between two successive stages. [ABSTRACT FROM PUBLISHER]

Investigates the effect of different densities of the burrowing, deposit-feeding amphipod Monoporeia (M.) affinis on the recruitment of copepod nauplii from benthic resting eggs in the Baltic Sea. Taxonomy and number of hatched zooplankton specimens; Effects of M. affinis on Eurytemora and Bosmina longispina maritima; Mechanisms for reduced survival or hatching of Eurytemora.

Presents abstracts of several studies which appeared in Vol. 62, 1992 issue of 'Crustaceana.' 'Studies on the Status of Eurytemora Affinis (Poppe, 1880) (Copepoda, Calanoida),' by Andreas Busch and Ulrich Brenning; 'Biogeographical Variation in Size-Specific Fecundity of the Amphipoda Hyalella Azteca,' by R.L. France; 'Bogidiella (Amphipoda) in Japanese Inland Waters,' by Jan H. Stock.

Arsenic uptake from water and from phytoplankton was followed in the copepod Eurytemora affinis and the barnacle Balanus improvisus collected from the Patuxent River estuary, Chesapeake Bay, eastern coast of the USA in 1987, and in the oyster Crassostrea virginica obtained from a hatchery on the shore of Chesapeake Bay in 1987. Dissolved arsenic was readily taken up by phytoplankton and by shell material of B. improvisus and C. virginica; however, no dissolved arsenic was incorporated into the invertebrate tissues. When E. affinis, B. improvisus and C. virginica were fed phytoplankton containing elevated arsenic contents, significant arsenic incorporation occurred. Juvenile B. improvisus incorporated relatively more arsenic than adults of all three species. Compared to the 100 to 200% increase in arsenic content by phytoplankton exposed to dissolved arsenic, the 25 to 50% increase in these invertebrate species via trophic transfer is relatively small. Even though the trophic pathway for arsenic transfer is the major one for higher trophic levels within an ecosystem, the potential for direct arsenic impact to trophic levels other than phytoplankton appears to be minimal. [ABSTRACT FROM AUTHOR]

The calanoid copepod Eurytemora velox was collected from rock pools at Castletown, Isle of Man, UK. Its optimum environmental requirements, particularly temperature and salinity, were determined, with a view to its possible future use as living food in intensive fish and shellfish farming. The species was cultured in 21 different temperature and salinity combinations. Investigations covered a period of two years from December 1983 to December 1985. Complete development from hatching to adult stage was followed in 21 temperature and salinity combinations. Nauplii suffered relatively high mortalities, indicating the sensitivity of this development stage to variations in temperature and salinity. Highest nauplii survival was observed in the combinations 15°C with 25 and 20‰ S and 20°C with 20‰ S, the highest copepodite survival at 10°C and 20‰ S. Lower salinities were tolerated better at higher temperatures and higher salinities at lower temperatures. Development time varied with the temperature and salinity combinations. Lower salinities at the lower temperatures of 10° and 15°C and both lower and higher salinities at 20°C prolonged development, particularly of the naupliar stage. Highest Q values (i.e., rate of change of development with a 5 C° increase in temperature) were recorded for the naupliar stage. Statistical analysis indicated that salinity influences the survival of both nauplii and copepodites; however, this effect is not linear. [ABSTRACT FROM AUTHOR]

The reproduction of Eurytemora velox, a brackish copepod from temporary lakes of the south of France, was studied in winter and spring 1978, under various temperature and salinity conditions, using Chlorella sp. and Amphidinium sp. as food. Maximum numbers of successive eggs sacs (9), eggs per sac (39.3) and total egg production per female (311) were recorded for the witner generation, only 4.8, 34.8 and 109, respectively, for the spring generation. In contrast, the number of eggs per female per day was highest (11.3) in the spring generation, which displayed a more rapid reproductive cycle. Despite strong individual variations in the rhythm of egg sac production and in abundance of eggs per sac, egg production was generally higher during the first third of adult life, attaining a maximum after production of the second or the third egg sac. The continuous presence of the males was necessary to assure complete fertilization of eggs throughout the whole life of adult females. Hatching rate displayed high individual variability, in particular for the spring generation, which had lower average hatching rates (between 0 and 26%, depending on salinity or temperature) than the winter generation (14 to 64%). These differences may be related to the ability of E. velox to produce resting eggs during spring, allowing the species to maintain itself in a temporary water milieu. Temperature significantly affected longevity and daily egg production of females; presence or absence of males did not affect these parameters. An increase in salinity from 20 to 30%. reduced longevity, number of egg sacs, and daily egg production in the winter generation, but not in the spring generation. The specific daily production of females during their adult life was calculated from the egg production:biomass ratio of females, in carbon units. In the winter generation, this ratio increased between 10° and 15°C compared to ratios between 15° and 20°C; the opposite was observed for the spring generation. The seasonal differences in the effects of temperature and salinity on reproduction could indicate an adaptation mechanism to the strongly thermal and haline seasonal fluctuations which characterize the habitat of Ex. velox (brackish waters, drying-up in summer). Larval mortality was high, except at 20%. S for the spring generation. The sex-ratio of the offspring was unaffected by variations in breeding conditions. Hatching time and development time of larvae could be described by two Bělehrádek equations displaying close b and (α) coefficients. We calculated the energy balance of adult females from data obtained in a previous study on feeding and respiration in E. velox, and this is discussed in context with the egg production results. Net growth efficiency varied with algal concentration according to an asymptotic curve, reaching a maximum of 0.43 with Tetraselmis maculata as food or 0.53 with Amphidinium sp. Actual egg production rate obtained in the present study was in good agreement with that calculated by the difference between assimilated food and respiration expenses. [ABSTRACT FROM AUTHOR]

The respiration and excretion (ammonia and phosphate) of Eurytemora velox, a brackish copepod from temporary lakes of the south of France, were studied in 1978-1979 in relation to food ingestion, temperature and salinity. Suspensions of Tetraselmis maculata were used as food. Respiration was closely dependent on the quantity of the ingested food, displaying a linear relationship with a strong positive-slope coefficient. In most cases, the temperature effect on respiration and excretion was well described by a power-type equation ( M=a b, where M=metabolism and T=temperature) over a rather large temperature range. In some experiments, metabolism curves displayed a maximum at 20°C. The metabolismtem-temperature curves differed between successive experiments, depending on season and/or sampling area, perhaps as a result of different acclimatization processes developing in individuals from different generations and/or among geographically isolated populations. Salinity variations significantly affected respiration, but not excretion. Respiration increased in individuals placed in hypo- or hyper-salinity conditions for a period of 24 h. This inability for complete metabolic regulation is unexpected in a species from a habitat subjected to variable salinity, and may have resulted from a too short acclimatization time in the experiments. [ABSTRACT FROM AUTHOR]

The genetic expression of temperature tolerance in Eurytemora affinis Poppe in different environments was investigated by testing temperature tolerances of broods in pairs of salinity and temperature environments. Three methods were used to identify interaction between genotype and environment: (1) the correlation between mean tolerances of halves of broods grown in the two environments, (2) brood by environment interaction and (3) heritabilities in the two environments. All correlations between means of half broods were positive, only one of six brood by environment interactions was significant and the heritability estimates were not markedly different. Thus, the variability in temperature tolerance in different salinities and in different temperatures seems to be due to the same genes; and selection pressure on temperature tolerance is in the same direction with seasonal changes in temperature and salinity. [ABSTRACT FROM AUTHOR]

The article discusses various observations made by Charles S. Elton, author of the book "Animal Ecology," regarding the population of fresh-water Calanoids, Diaptomus gracilis and Eurytemora, in the filter-tanks of the Oxford Corporation Waterworks. It offers information on a series of breeding experiments carried out in the waterworks during the period of September to November 1929 to present various facts with regard to the Elton's statements such as that Diaptomus gracilis does not live in the filter-tanks because its eggs cannot withstand being dried up and the Eurytemora population was derived from resting eggs that had survived the drying process. It is inferred that contrary to the Elton's statement, the resting eggs of Eurytemora play no part in the population of the filter beds.