Food quality for Eudiaptomus gracilis: the importance of particular highly unsaturated fatty acids

1. Development times and survival of nauplii and copepodites of the freshwater calanoid Eudiaptomus gracilis were measured on comparably sized Cryptomonas sp. and two strains of Chlamydomonas reinhardii under food saturated conditions (1 mg C L−1) to investigate the nutritional quality of these algae.
2.  Cryptomonas sp. supported complete ontogenesis of nauplii to adults, whereas both strains of C. reinhardii were inadequate for the development of nauplii and copepodites and resulted in high mortality. The nutritional deficiency of both strains of C. reinhardii was compensated for by Cryptomonas sp. when the latter constituted ≥50% of dietary carbon. Pulses of Cryptomonas sp. had a similar compensatory effect.
3. In comparison to Cryptomonas sp., both strains of C. reinhardii were deficient in the three highly unsaturated fatty acids (HUFAs) stearidonic, eicosapentaenoic and docosahexaenoic acid. We manipulated the fatty acid content of C. reinhardii by externally adding these three HUFAs to the alga so that the fatty acid profile resembled that of Cryptomonas sp. This supplementation did not improve food quality, however, indicating that the nutritional deficiency of both strains of C. reinhardii for the ontogenesis of E. gracilis is not due to a lack of these three HUFAs.     

In situ grazing pressure and diel vertical migration of female Calanus euxinus in the Black Sea

Gut pigment and abundance of the female Calanus euxinus (Hulsemann) weremeasured from several water layers (defined by density values), with3–5 h intervals during 30 h and 21 h at a station in the southwesternBlack Sea in April and in September 1995, respectively. The female C.euxinus was observed to begin migration to the upper phytoplankton-richlayer approximately 3 or 4 hours before the sunset. Only a fraction of thefemale Calanus population (0.2% in April and 3.6% inSeptember) did not migrate but remained at the depth of the oxygen minimumzone during the nighttime. The migrating population was determined to havespent 7.5 h in the euphotic zone in April and 10.5 h in September. Thegrazing rate of female Calanus euxinus was measured from the gut contentdata collected from the layers which contain the euphotic zone. Thepercentage of primary production grazed by the female C. euxinus wascalculated as 14.5% in April and 9.5% in September. This revised version was published online in July 2006 with corrections to the Cover Date.     

Morphometric differentiation of Pseudocalanus minutus populations in the Barents Sea

Dvoretsky VG. and Dvoretsky AG. 2011. Morphometric differentiation of Pseudocalanus minutus populations in the Barents Sea. —Acta Zoologica (Stockholm) 00 : 1–12. We investigated spatial variations in the morphometric characteristics (total length of body, lengths of cephalothorax, abdomen and antennules, and their relative proportions) of Pseudocalanus minutus, an abundant copepod species across the Barents Sea in August–September 2007. Females were found to have higher values for the measured parameters than males. The average absolute morphometric characters of both sexes increased from the south to the north. In most cases, parameters were similar in the southern, central, and eastern regions delineated by cluster analyses of oceanographic variables. The morphometric characteristics were strongly correlated with environmental variables in both males and females. Multiple regression analysis showed that temperature together with salinity explained 72–85% (in females) and 38–91% (in males) of the total variations in the log₁₀‐transformed morphometric parameters. According to principal component analysis and discriminant function analysis, two distinct groups could be separated in the Barents Sea. The first group included the copepods from the northern region; the other included populations from the southern, central, and eastern regions. The observed morphological variation can be interpreted as geographical variation connected with hydrological variability.     

The Saphirella problem

The problem — one of an assemblage of small planktonic copepods with mixed larval and adult characteristics — is reviewed. It is suggested that some forms are poecilostomatoid first copepodids which have failed to find the definitive milieu and so are unable to moult further. This indicates a need for experimental work. The known species are summarised.     

Impact of Microzooplankton and Copepods on the Growth of Phytoplankton in the Yellow Sea and East China Sea

Dilution and copepod addition incubations were conducted in the Yellow Sea (June) and the East China Sea (September) in 2003. Microzooplankton grazing rates were in the range of 0.37–0.83 d⁻¹ in most of the experiments (except at Station A3). Correspondingly, 31–50% of the chlorophyll a (Chl a) stock and 81–179% of the Chl a production was grazed by microzooplankton. At the end of 24 h copepod addition incubations, Chl a concentrations were higher in the copepod-added bottles than in the control bottles. The Chl a growth rate in the bottles showed good linear relationship with added copepod abundance. The presence of copepods could enhance the Chl a growth at a rate (Z) of 0.03–0.25 (on average 0.0691) d⁻¹ ind⁻¹ l. This study, therefore parallels many others, which show that microzooplankton are the main grazers of primary production in the sea, whereas copepods appear to have little direct role in controlling phytoplankton.     

THE GENOMIC TRAJECTORY OF HYBRID SWARMS: OUTCOMES OF REPEATED CROSSES BETWEEN POPULATIONS OF TIGRIOPUS CALIFORNICUS

Introgressive hybridization between genetically divergent populations is an important evolutionary process. The degree to which repeated hybridization events between the same parental taxa lead to similar genomic outcomes is unknown. This study addressed this question by following genomic trajectories of replicate hybrid swarms of the copepod Tigriopus californicus over many generations of free mating. Swarm composition was determined both by differential reproductive success of founder individuals and subsequent selection on hybrid genotypes. For one cross, between two populations showing differential fitness in the laboratory and no hybrid breakdown, the genetic trajectory was highly repeatable: replicates rapidly became dominated by alleles from the fitter parent. In a second cross, between two populations showing similar fitness and significant F2 hybrid breakdown, alleles from alternative populations dominated different replicates. Swarms exhibited a general temporal trend of decreasing cytonuclear mismatch. Some patterns of differential introgression across the genome were strikingly congruent amongst swarm replicates, both within and between cross types, and reflected patterns of segregation distortion previously observed within controlled crosses between the same parental populations. Differences in heterozygosity between the sexes, and evidence for a previously suspected sex‐distortion locus, suggest that complex interactions between sex and genotype influence hybrid swarm outcome.     

Projected marine climate change: effects on copepod oxidative status and reproduction

Zooplankton are an important link between primary producers and fish. Therefore, it is crucial to address their responses when predicting effects of climate change on pelagic ecosystems. For realistic community‐level predictions, several biotic and abiotic climate‐related variables should be examined in combination. We studied the combined effects of ocean acidification and global warming predicted for year 2100 with toxic cyanobacteria on the calanoid copepod, Acartia bifilosa. Acidification together with higher temperature reduced copepod antioxidant capacity. Higher temperature also decreased egg viability, nauplii development, and oxidative status. Exposure to cyanobacteria and its toxin had a negative effect on egg production but, a positive effect on oxidative status and egg viability, giving no net effects on viable egg production. Additionally, nauplii development was enhanced by the presence of cyanobacteria, which partially alleviated the otherwise negative effects of increased temperature and decreased pH on the copepod recruitment. The interactive effects of temperature, acidification, and cyanobacteria on copepods highlight the importance of testing combined effects of climate‐related factors when predicting biological responses.     

Trophic coupling of the microbial and the classical food web in Lake Baikal,Siberia

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