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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]

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]

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]

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.

The author reflects on the study of ecological relationships of freshwater copepods based on the article written by A.G. Lowndes on Entomostraca. He explains the interrelationship of Eurytemora ladnulata and Diaptomus gracilis; and the seasonal occurrence of Cyclops strenuus, Calanoid fuscus and Calanoid albidus. The author argues that it is doubtful to state that the absence of Diaptomus gracilis is caused by slow rate of spread.

The author reflects on the study on eurytemora lacinulata and diaptomus gracilis and the inter-relationship between the occurence of these two copepod calanoids. The author argues that there is a false statement in saying that only one calanoid occurs in the abselce of the other. He explains that in the rock ponds located in Parks at Oxford, Diaptomus occurs as well as the Eurytemora.

We investigated the effects of a common mysid predator, Neomysis americana on the mating success of an estuarine copepod, Eurytemora herdmani. The presence of a mysid predator, or only a predator cue, reduced copulation frequency and spermatophore transfer success of E. herdmani, and led to a substantial decrease in E. herdmani nauplius production. Thus, mysid predators can influence copepod population growth through nonconsumptive processes by reducing the frequency and success of mating events. This highlights the need to look beyond population-level demographic factors (i.e., sex ratio and population density) and consider community-level ecological factors (such as predation risk) when modeling population growth rates of prey species critical to marine food webs. [ABSTRACT FROM AUTHOR]

Eurytemora affinis (Copepoda) were fed 15N-labeled Rhodomonas salina (Cryptophyta) or 15N-labeled Nodularia spumigena (Cyanobacteria) in excess under controlled laboratory conditions. Zooplankton collected from the Baltic Sea were fed natural phytoplankton amended with 15N-labeled N. spumigena. We quantified the direct incorporation of 15N tracer from N2-fixing N. spumigena (diazotroph nitrogen) and ammonium-utilizing R. salina into the amino acid nitrogen (AA-N) of zooplankton using complementary gas chromatography-combustion-isotope ratio mass spectrometry, gas chromatography-mass spectrometry, and elemental analysis-isotope ratio mass spectrometry approaches. Specific and mass-specific TN and AA-N incorporation rates of the 15N tracers were calculated for zooplankton. Highest incorporation of 15N was found in field zooplankton relying on N. spumigena and in E. affinis relying on R. salina. Lowest incorporation was found in E. affinis relying on N. spumigena. Decreasing specific and mass-specific rates during field experiments possibly were due to food shortage, whereas decreasing rates in E. affinis grazing on R. salina were more likely due to satiation. Specific and mass-specific rates were consistently low in E. affinis when exposed to N. spumigena, suggesting that these animals were reluctant to feed on N. spumigena. Essential isoleucine received most of the diazotroph nitrogen in field zooplankton, while nonessential amino acids received most 15N tracer in E. affinis. N. spumigena was clearly an important amino acid nitrogen source for Baltic Sea zooplankton. [ABSTRACT FROM AUTHOR]