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Molecular identification of Calanus helgolandicus has revealed a more northern distribution for this boreal species than previously reported. We investigated an Arctic fjord to determine if local reproduction is taking place. Combining time series data from depth stratified sampling with molecular tools for species identification, we found C. helgolandicus from all stages throughout the year including males and females as well as a nauplius. These findings constitute strong evidence that C. helgolandicus is reproducing north of the Arctic Circle and their role in the ecosystem should be investigated further. [ABSTRACT FROM AUTHOR]

Diatoms are the dominant component of the marine phytoplankton. Several diatoms produce secondary metabolites, namely oxylipins, with teratogenic effects on their main predators, crustacean copepods. Our study reports the de novo assembled transcriptome of the calanoid copepod Calanus helgolandicus feeding on the oxylipin-producing diatom Skeletonema marinoi. Differential expression analysis was also performed between copepod females exposed to the diatom and the control flagellate Prorocentrum minimum, which does not produce oxylipins. Our results showed that transcripts involved in carbohydrate, amino acid, folate and methionine metabolism, embryogenesis, and response to stimulus were differentially expressed in the two conditions. Expression of 27 selected genes belonging to these functional categories was also analyzed by RT-qPCR in C. helgolandicus females exposed to a mixed solution of the oxylipins heptadienal and octadienal at the concentration of 10 µM, 15 µM, and 20 µM. The results confirmed differential expression analysis, with up-regulation of genes involved in stress response and down-regulation of genes associated with folate and methionine metabolism, embryogenesis, and signaling. Overall, we offer new insights on the mechanism of action of oxylipins on maternally-induced embryo abnormality. Our results may also help identify biomarker genes associated with diatom-related reproductive failure in the natural copepod population at sea.

Abstract A two-dimensional biomarker approach including fatty acids and stable isotopes of seston and copepods was applied to examine how the variability at the base of the food web affects trophic interactions between primary producers and copepod consumers over a sampling period of two years. We investigated how the composition of the seston affected feeding behaviour by analysing the fatty acid and stable isotope signals of the copepods Calanus helgolandicus , Acartia spp., Centropages spp. and Temora longicornis at Helgoland Roads, North Sea. Our results indicate that the relative contributions of autotrophic and heterotrophic fractions in the seston determined the stable isotope signal of the seston and hence the δ15N of copepods. Our findings show that the combination of stable isotope and fatty acid analyses provides an ideal tool to address the complexity of trophic relations in planktonic food-webs and to define relative trophic position and feeding preferences of e.g. copepods. Defining accurate baselines from bulk seston samples containing a mixture of auto- and heterotroph protist communities still remains a challenge when defining lower food-web dynamics in natural plankton communities. Highlights • A combined tracer approach provided insights on how the variability at the base of planktonic food webs affects trophic interactions. • The relative contributions of autotrophic and heterotrophic fractions in the seston determined the δ15N of copepods. • The complexity of trophic relations in planktonic food-webs and relative trophic position was assessed. • Accurate baseline signals are still considered as a major challenge in food-web studies [ABSTRACT FROM AUTHOR]

Abstract: While losses from mortality are as important as gains from reproduction in zooplankton population dynamics, the former are more challenging to quantify. We used two approaches to provide complementary insights into the mortality of a biomass‐dominant copepod, Calanus helgolandicus, at Station L4 in the English Channel. Using a neutral‐red staining method, we found that dead carcasses represented a mean of 9% of the C. helgolandicus copepodites sampled. The resulting nonconsumptive mortality rates are the first that have been derived for C. helgolandicus; and estimates suggest a contribution of 0–54% (median of 4.4%) to the total mortality rate. Consumptive mortality (i.e., that due to removal by predation), dominated for most of the year and contributed a mean of 89% to total mortality. Nonconsumptive mortality increased during summer and winter, and was positively related to maximum wind speed during the preceding 72 h, indicating that extreme weather events may lead to increased mortality. Using the Vertical Life Table approach, mortality rates across the CV‐adult male stage pair were on average ∼ 2.5 times greater than those of CV‐adult females. Adult male consumptive mortality rates were ∼ 6 times greater than those for females; adult male nonconsumptive rates were twice those of females, suggesting that predation is of greater significance to male loss rates. Summer CV‐adult mortality rates were positively correlated to temperature, and to the abundance of predatory chaetognaths and siphonophores, suggesting that the gelatinous predator assemblage is the dominant agent for population control of late stage copepodites of C. helgolandicus at L4. [ABSTRACT FROM AUTHOR]

The pelagic copepods Oithona similis and Calanus helgolandicus have overlapping geographic ranges, yet contrast in feeding mode, reproductive strategy and body size. We investigate how these contrasting traits influence the seasonality of copepod abundance and reproductive output under environmental variation, using time series data collected over 25 years at the Western Channel Observatory station, L4. The proportional change in egg production rate (EPR, eggs female-1 d-1) over the annual cycle was ~10-fold and similar for both species, although EPR of O. similis was only ~ 11% that of C. helgolandicus. The timing of EPR maxima for O. similis coincided with increased sea surface temperature (SST) in summer, likely due to a temperature-dependent brooding period. Conversely, EPR of broadcast spawning C. helgolandicus was more strongly related to net heat flux and diatom biomass, both parameters associated with the spring phytoplankton bloom. In both species, female body mass correlated negatively with SST, with a 7.5% reduction in body mass per °C in C. helgolandicus compared to just 2.3% in O. similis. Finally, seasonality of EPR and adult and copepodite abundance was strongly decoupled in both species, suggesting that optimum conditions for reproduction and abundance occurred at different times of the year. [ABSTRACT FROM AUTHOR]

Copepods can respond to predators by powerful escape jumps that in some surface-dwelling forms may propel the copepod out of the water. We studied the kinematics and energetics of submerged and out-of-water jumps of two neustonic pontellid copepods, Anomalocera patersoni and Pontella mediterranea, and one pelagic calanoid copepod, Calanus helgolandicus (euxinus). We show that jumping out of the water does not happen just by inertia gained during the copepod's acceleration underwater, but also requires the force generated by the thoracic limbs when breaking through the water's surface to overcome surface tension, drag and gravity. The timing of this appears to be necessary for success. At the moment of breaking the water interface, the instantaneous velocity of the two pontellids reached 125 cm s-1, while their maximum underwater speed (115 cm s-1) was close to that of similarly sized C. helgolandicus (106 cm s-1). The average specific power produced by the two pontellids during out-of-water jumps (1700-3300 W kg-1 muscle mass) was close to that during submerged jumps (900-1600 W kg-1 muscle mass) and, in turn, similar to that produced during submerged jumps of C. helgolandicus (1300 W kg-1 muscle mass). The pontellids may shake off water adhering to their body by repeated strokes of the limbs during flight, which leads to a slight acceleration in the air. Our observations suggest that out-of-water jumps of pontellids are not dependent on any exceptional ability to perform this behavior but have the same energetic cost and are based on the same kinematic patterns and contractive capabilities of muscles as those of copepods swimming submerged. [ABSTRACT FROM AUTHOR]

Chemical interactions play a fundamental role in the ecology of marine foodwebs. Dimethyl sulfide (DMS) is a ubiquitous marine trace gas that acts as a bioactive compound by eliciting foraging behavior in a range of marine taxa including the copepod Temora longicornis. Production of DMS can rapidly increase following microzooplankton grazing on phytoplankton. Here, we investigated whether grazing-induced DMS elicits an increase in foraging behavior in the copepod Calanus helgolandicus. We developed a semi-automated method to quantify the effect of grazing-mediated DMS on the proportion of the time budget tethered females allocate towards slow swimming, typically associated with feeding. The pooled data showed no differences in the proportion of the 25 min time budget allocated towards slow swimming between high (23.6 ± 9.74%) and low (29.1 ± 18.33%) DMS treatments. However, there was a high degree of variability between behavioral responses of individual copepods. We discuss the need for more detailed species-specific studies of individual level responses of copepods to chemical signals at different spatial scales to improve our understanding of chemical interactions between copepods and their prey.

The vertical distribution of copepods, and the factors determining it, has been studied extensively. Some copepods appear to maintain their vertical position in the water column with high precision, even against downwelling and upwelling currents. The adaptive benefits of this behavior are unknown. We hypothesized that changes in hydrostatic pressure alter the buoyancy of copepods and, in turn, affect their grazing rate. We tested this hypothesis in laboratory grazing experiments with three calanoid species, Calanus helgolandicus, Pleuromamma indica and Rhincalanus nasutus, grazing on cultured phytoplankton. The study was based on a comparison of gut pigment content between individuals that fed in chambers at two different pressure levels: 1 bar and 4 bars. A significant effect of pressure was found for C. helgolandicus (lower gut content at 4 bars) but not for P. indica and R. nasutus. If the effect observed in C. helgolandicus is common, it would add a new dimension to our understanding of copepod ecology in the oceanic realm, where plankton is often exposed to vertical currents and internal waves. [ABSTRACT FROM AUTHOR]

Calanus helgolandicus is a key copepod of the NE Atlantic and fringing shelves, with a distribution that is expanding northwards with oceanic warming. The Plymouth L4 site has warmed over the past 25-years, and experiences large variations in the timing and availability of food for C. helgolandicus . Here we examine the degree to which these changes translate into variation in reproductive output and subsequently C. helgolandicus population size. Egg production rates (eggs female −1 day −1 ) were maximal in the spring to early-summer period of diatom blooms and high ciliate abundance, rather than during the equally large autumn blooms of autotrophic dinoflagellates. Egg hatch success was lower in spring however, with a greater proportion of naupliar deformities then also. Both the timing and the mean summer abundance of C. helgolandicus (CI–CVI) reflected those of spring total reproductive output. However this relationship was driven by inter-annual variability in female abundance and not that of egg production per female, which ranged only two-fold. Winter abundance of C. helgolandicus at L4 was much more variable than abundance in other seasons, and reflected conditions from the previous growing season. However, these low winter abundances had no clear carry-over signal to the following season’s population size. Overall, the C. helgolandicus population appears to be surprisingly resilient at this dynamic, inshore site, showing no long-term phenology shift and only a four-fold variation in mean abundance between years. This dampening effect may reflect a series of mortality sources, associated with the timing of stratification in the early part of the season, likely affecting egg sinking and loss, plus intense, density-dependent mortality of early stages in mid-summer likely through predation. [ABSTRACT FROM AUTHOR]

Most diatom species produce at least two classes of oxylipins, polyunsaturated aldehydes (PUAs) and non-volatile oxylipins (NVOs). These compounds can act as grazer deterrents by reducing the reproductive success of copepod grazers. The aim of the present study was to better understand the impact of late-winter diatom blooms and of diatom-derived PUAs and NVOs on the reproduction of two dominant copepod species in the northern Adriatic Sea, in two consecutive years. Higher diatom abundance in 2005 compared to 2004 coincided with higher egg-production rates in both Acartia clausi and Calanus helgolandicus . The increased contribution of diatoms to the phytoplankton assemblage in 2005 also led to a higher phytoplankton production of NVOs, whereas PUA levels were low in both years. These three-times-higher oxylipin levels correlated with a decrease in average hatching success in both A. clausi and C. helgolandicus from ∼80% in 2004 to ∼60% in 2005, indicating that the observed negative effects on copepod recruitment in the latter year were related to the greater production of diatom NVOs. Our findings reveal the importance of these metabolites and offer an explanation as to why diatom blooms may be more toxic for copepods in some years compared to others. [ABSTRACT FROM AUTHOR]

Highlights: [•] A SSH was done on Calanus helgolandicus feeding for 48h on Skeletonema marinoi. [•] 475/947 ESTs and 200/376 Unigenes of C. helgolandicus were annotated. [•] GO terms of signal transduction and protein folding were enriched in the copepod. [•] Genes belonging to these GO terms were 1.6–3.4 fold over-expressed in RT-qPCR. [•] 48h feeding on S. marinoi elicited a Cellular Stress Response (CSR) in the copepod. [Copyright &y& Elsevier]

The diet of the Pacific Sand Lance (Ammodytes hexapterus) was quantified from the stomach contents of 115 Pacific Sand Lance caught in the Strait of Georgia and Saanich Inlet (Vancouver Island) in the Salish Sea, British Columbia, in the spring and summer of 1966, in the Strait of Georgia in the spring and summer of 1967, and in the Strait of Georgia and Saanich Inlet in the spring and summer of 1968. There were 12 major taxa of prey in diets, 8 of which were Crustacea. Based on an index of relative importance, copepods were the dominant prey in 1966 and 1968, but not in 1967, when cladocerans, larvaceans, and teleosts also were common. The copepods Pseudocalanus spp. and Calanus marshallae were the only taxa to appear in diets in all three years. Pseudocalanus dominated the copepod component of diets in 1966, when sampling occurred in July; unspecified copepod nauplii (an early larval stage) were dominant in 1967 and 1968, when sampling occurred earlier (April to June). With the profound changes that have occurred in the Salish Sea over recent decades, these data can serve as a baseline for comparison. [ABSTRACT FROM AUTHOR]

Copepods can be associated with different kinds and different numbers of bacteria. This was already shown in the past with culture-dependent microbial methods or microscopy and more recently by using molecular tools. In our present study, we investigated the bacterial community of four frequently occurring copepod species, Acartia sp., Temora longicornis, Centropages sp. and Calanus helgolandicus from Helgoland Roads (North Sea) over a period of 2 years using DGGE (denaturing g radient g el electrophoresis) and subsequent sequencing of 16S-rDNA fragments. To complement the PCR-DGGE analyses, clone libraries of copepod samples from June 2007 to 208 were generated. Based on the DGGE banding patterns of the two years survey, we found no significant differences between the communities of distinct copepod species, nor did we find any seasonality. Overall, we identified 67 phylotypes (>97 % similarity) falling into the bacterial phyla of Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria. The most abundant phylotypes were affiliated to the Alphaproteobacteria. In comparison with PCR-DGGE and clone libraries, phylotypes of the Gammaproteobacteria dominated the clone libraries, whereas Alphaproteobacteria were most abundant in the PCR-DGGE analyses. [ABSTRACT FROM AUTHOR]

Vertical distribution of the mesozooplankton community down to 1000 m was investigated in the oligotrophic Aegean Sea during March and September 1997. Total biomass and abundance decreased with depth with a sharp decline <100 m. However, in the northern part, higher biomass values in the 500–1000 m layer than in the 300–500 m layer were observed, due to the abundance of Calanus helgolandicus in deep waters. Species depth preferences and ranges resulted in statistically distinct communities in different zones, as well as in a differentiation along the north–south gradient of oligotrophy in the epipelagic and deep zones. The communities in these zones showed seasonal differences, while in the mesopelagic zone seasonal and horizontal differences were less significant. The discrimination between the north and the south deep communities was mainly due to the dominance of Calanus helgolandicus and Subeucalanus monachus respectively, which had similar seasonal and vertical distribution patterns and were found oversummering in the deep layers. The north–south distinction was related to the gradient of oligotrophy and the hydrological heterogeneity of the Aegean Sea. Spatial community structure and variability between seasons might facilitate an efficient carbon flow in the Aegean Sea under very oligotrophic conditions. [ABSTRACT FROM PUBLISHER]

Chemical interactions play a fundamental role in the ecology of marine foodwebs. Dimethyl sulfide (DMS) is a ubiquitous marine trace gas that acts as a bioactive compound by eliciting foraging behavior in a range of marine taxa including the copepod Temora longicornis. Production of DMS can rapidly increase following microzooplankton grazing on phytoplankton. Here, we investigated whether grazing-induced DMS elicits an increase in foraging behavior in the copepod Calanus helgolandicus. We developed a semi-automated method to quantify the effect of grazing-mediated DMS on the proportion of the time budget tethered females allocate towards slow swimming, typically associated with feeding. The pooled data showed no differences in the proportion of the 25 min time budget allocated towards slow swimming between high (23.6 ± 9.74%) and low (29.1 ± 18.33%) DMS treatments. However, there was a high degree of variability between behavioral responses of individual copepods. We discuss the need for more detailed species-specific studies of individual level responses of copepods to chemical signals at different spatial scales to improve our understanding of chemical interactions between copepods and their prey. [ABSTRACT FROM AUTHOR]

Abstract: The copepods Calanus finmarchicus and Calanus helgolandicus co-exist in the North Sea, but their spatial distribution and phenology are very different. Long-term changes in their distributions seem to occur due to climate change resulting in a northward extension of C. helgolandicus and a decline of C. finmarchicus in this region. The aim of this study is to use life-stage structured models of the two Calanus species embedded in a 3D coupled hydrodynamic–biogeochemical model to investigate how the biogeography of C. finmarchicus and C. helgolandicus is modified by changes in ±2°C sea water temperatures, overwintering and oceanic inflow in the North Sea. Life-stage structured models are validated against CPR data and vertical distributions north of the Dogger Bank in the North Sea for the reference year 2005. The model shows that (1) ±2°C changes from the current level mainly influence the seasonal patterns and not the relative occurrence of the two species, (2) changes due to oceanic inflow mainly appeared in the northern and southern part of the North Sea connected to the NE Atlantic and not in the central part and (3) the abundance of Calanus species were very sensitive to the degree of overwintering within the North Sea because it allows them to utilise the spring bloom more efficiently and independently of the timing and amount of oceanic inflow. The combination of lower temperatures, higher overwintering and oceanic inflow simulating the situation in the 1960s largely favoured C. finmarchicus and their relative contribution to Calanus spp. increased from 40% in the reference year to 72%. The +2°C scenario suggest that in a warmer future, C. finmarchicus is likely to decline and C. helgolandicus abundance will probably continue to increase in some areas. [Copyright &y& Elsevier]

Abstract: We tested the amenability of the calanoid copepod Calanus helgolandicus to be mass cultivated in a large volume system. The copepod was reared on two different occasions (during 2009 and 2010), for at least four generations and six months with a mixed flagellate diet of Isochrysis galbana, Rhodomonas baltica and Prorocentrum minimum, or a mixed diet of I. galbana, R. baltica and the diatom Thalassiosira weissflogii. The generation time of C. helgolandicus from nauplius to adult was 21days, with relative duration of naupliar and copepodid phases of 7 and 14days, respectively. Population growth rates when the second generation of adults developed and reproduced in the tank, were ~2-times higher (0.067d−1 vs. 0.038d−1) and abundances increased 6-times more (40-fold vs. 6.7-fold) during 2010 than 2009. This higher production was related to the addition of T. weissflogii to the mixed R. baltica + I. galbana diet at low concentrations (0.17mgCl−1) and for short periods (<2months), which induced higher egg production rate and percentage of spawning females and lower copepodid mortality in the population. However, supplementation of T. weissflogii at higher concentrations (0.40mgCl−1) or longer feeding times (>3months), reduced copepod egg hatching success, and hence population growth of C. helgolandicus. In conclusion, our study shows that by using an appropriate mixed diatom assemblage for short periods, it is possible to obtain healthy individuals of all larval stages of C. helgolandicus for biological, toxicological and gene expression studies year-round. [Copyright &y& Elsevier]

Abstract: In this study we develop gene expression tools in Calanus helgolandicus to study the effects of toxic diatom diets on copepod fitness and survival. We demonstrate that when adult females are fed on the control dinoflagellate Prorocentrum minimum and the flagellate Rhodomonas baltica, which are not known to produce toxic oxylipins, there are no significant changes in alpha- and beta-tubulin (microtubule subunits) gene expression levels. By contrast, the oxylipin-producing diatom Skeletonema marinoi influences tubulin expression levels which were markedly down-regulated. We scored a panel of putative reference genes (ACT, EFA, GAPDH, 18S, S7, S20, ATPs, UBI and IST) and found that two (S20 and S7) were highly stable in the tested conditions and can be used for further experiments. To normalize reverse transcription-quantitative real time polymerase chain reaction (RT-qPCR) data we also used the third best reference gene, GAPDH, considering the possibility that the two ribosomal proteins could be co-regulated. This pilot study will pave the way for further investigations on which genes are affected by diatom diets and clarify when and if a stress response or a detoxification mechanism becomes visible in C. helgolandicus. Moreover, the RT-qPCR analysis presented here may also be useful to study the effects of other diets and/or environmental factors such as salinity, temperature, pollution and other toxic compounds, on gene expression levels in this copepod species. [Copyright &y& Elsevier]

The article examines spatial population structuring of Celanus helgolandicus and Calanus euxinus in European waters of the Atlantic Ocean and Mediterranean Sea based on morphometric and genetic characters. Barriers to dispersal were related to hydrographic characteristics, from which historical patterns of distribution and demography were inferred. Strong spatial population structuring between and within basins were indicated through estimates of genetic differentiation between samples and hierarchical analyses of molecular variance. Seven phylogeographic groups were also identified which explained almost 40 percent of the total genetic variation.

Comparison of abundance, vertical distribution and reproduction of the cousin species, the boreal Calanus finmarchicus and temperate Calanus helgolandicus was carried out on four cruises in July and August north of the Dogger Bank, North Sea. During this period, the water column was highly stratified with a tidally generated deep chlorophyll maximum at 30 m depth. When co-occurring, a separation of the species was evident, where C. finmarchicus preferred colder (9°C) deeper waters, while C. helgolandicus stayed in the warmer (16°C) surface waters. Egg production rates (EPRs) were not statistically different between the species, and the population egg production depended primarily on female abundance and was generally higher for C. finmarchicus. EPRs of the Calanus spp. were best explained by the abundance of autotrophic and heterotrophic dinoflagellates, flagellates and ciliates. Hatching success remained over 90% at all times but the estimated naupliar survival (N1–N6) was only 9%. The chlorophyll maximum supported highest faecal pellet production and egg production at the stations close to the bank. This study shows that C. finmarchicus can remain reproductively active in the North Sea ecosystem longer than previously thought, and with warmer surface temperatures retreat to cooler, deeper waters utilizing the deep chlorophyll maximum. This implies that C. finmarchicus cannot be reliably sampled with the Continuous Plankton Recorder during summer. [ABSTRACT FROM AUTHOR]

Seasonal variation in community composition, abundance and biomass of protozooplankton (PZP) was investigated at L4 in the English Channel from 2002 to 2004 and the importance of feeding of Acartia clausi and Calanus helgolandicus on natural populations of phytoplankton and PZP was investigated between May and August, 2002. Calanus helgolandicus ingested between 1 and 12 µg phytoplankton carbon ind.-1 day-1 (2-13% total body carbon); A. clausi ingested between 1 and 6 mg C ind.-1 day-1 (20-166% total body carbon). Clearance rates on PZP prey increased linearly with increase in food concentration and ranged from 120 and 304 mL ind.-1 day-1 and between 26 and 150 mL ind.-1 day-1 for C. helgolandicus and A. clausi, respectively. Calanus helgolandicus obtained 2-27% of its daily ration as a percentage of body carbon from phytoplankton and 2-17% of its daily ration from PZP. Acartia clausi obtained 22-161% of its daily ration from phytoplankton and 3-44% daily ration from PZP. Calanus helgolandicus and A. clausi populations together grazed up to 21% of the total PZP standing stock daily. Both C. helgolandicus and A. clausi demonstrated selective feeding on large choreotrich ciliates and heterotrophc dinoflagellates. Our results support the hypothesis that PZP comprise a significant proportion of the copepod diet after the spring bloom when the phytoplankton community is dominated by small cells. [ABSTRACT FROM AUTHOR]

We used a long-term monitoring data set at station L4 (1988–2004), Western English Channel, to assess the predation pressure by the chaetognath Sagitta setosa on the copepod Calanus helgolandicus. Maximum abundances of Calanus helgolandicus are correlated with years when Sagitta setosa and the Siphonophore, Muggiae atlantica, abundances are low, between February and June. As a significant correlation does not necessarily imply a prey–predator interaction, we analysed the gut content of S. setosa to investigate the presence or absence of Calanus helgolandicus in the chaetognath diet. Molecular analysis of the gut content of three Sagitta each month during a year shows that C. helgolandicus is present in the diet of S. setosa throughout the year. Estimates of S. setosa minimal predation pressure suggest that up to 19% of the C. helgolandicus population can be removed. Peaks of S. setosa follow peaks of Calanus helgolandicus total egg production. We suggest that S. setosa is an important predator of C. helgolandicus at station L4 and might be an important influence on its population dynamics. [ABSTRACT FROM PUBLISHER]

Abstract: There are now compelling observations of the ecological impacts of global change on marine ecosystems. A predicted 10% increase in UVB doses at the Earth''s surface has been shown to impair indirectly the reproductive output of marine copepods. Wild females of Calanus helgolandicus fed with UVB-irradiated diatoms produced fewer eggs and unhealthy offspring exhibiting a large proportion of high lethal naupliar deformities. By reproducing the same irradiative stress on the pelagic diatom Skeletonema costatum, we looked for potential modifications of the algal properties (cell size, biovolume, chlorophyll content) and biochemical characteristics (fatty acid and amino acid contents). Our results confirmed that the metabolism of S. costatum is adversely affected by enhanced UVB exposure: cell growth was reduced and the biochemical characteristics, and thus the algal nutritional quality, were significantly altered. UVB irradiation reduced cell division, leading to cell elongation and thus increasing the biovolume. Meanwhile, the amino acid and fatty acid contents did not increase concomitantly to the cell enlargement and were thus diluted in the cell. Because of this dilution, the irradiated S. costatum represents a poorer diet for its potential consumers. Moreover, UVB dramatically affects the relative contribution of certain essential fatty acids such as eicosapentanoic acid (EPA), which are essential for the development of marine invertebrates. [Copyright &y& Elsevier]

Abstract: A one year long monthly sampling series at a fixed station was combined with a high-spatial resolution survey (May 2003) to investigate factors controlling zooplankton distribution in the south-eastern corner of the Bay of Biscay. Species abundance and gonad maturity for Calanoides carinatus and Calanus helgolandicus were estimated to clarify whether the observed spatial patterns were attributable to increased population growth or to mechanical accumulation. The two studies included distinct oceanographic regimes. The eastern corner of the grid was characterized by Adour river plume waters and the Cap Breton canyon, and the rest of the area by an alternating pattern of physical convergences and divergences. In the river plume, the zooplankton community diversity and abundances were highest in response to the nutrient enriched river plume waters and the submarine canyon. In the rest of the area, distribution and abundance patterns were the result of a combination of behaviour and physical transport. [Copyright &y& Elsevier]

Abstract: Feeding rates and selectivity of the calanoid copepods Calanus helgolandicus and Para-Pseudocalanus spp. on natural assemblages of microplankton were evaluated in the English Channel and western Celtic Sea during non-bloom and bloom conditions in April 2002. Ingestion rates of total chlorophyll-a were low at non-bloom stations where the phytoplankton community was dominated by cells <5 μm in length and higher during the bloom when the >5 μm size fraction was dominant. Protozooplankton contributed to the copepod diet in all experiments, C. helgolandicus clearance and ingestion rates were highest for the ciliate Myrionecta rubra (626–1347 ml cop−1 d−1; 0.3–27 μg C cop−1 d−1). C. helgolandicus ingested between 1 and 18 μg C cop−1 d−1 (1–12% body C) from phytoplankton+protozooplankton food sources. The total carbon ingested by Para-Pseudocalanus spp. was lower (0.5–6 μg cop−1 d−1) but this was equivalent to between 6 and 78% of body carbon being ingested daily. Our data suggest that C. helgolandicus selected prey according to size; this was not the case for Para-Pseudocalanus spp. which became more selective as chlorophyll-a concentration increased. Grazing impact of the entire copepod community on protozooplankton was assessed. We found that at non-bloom stations between 12 and 17% of the protozooplankton community was being removed daily by the copepod community, whereas during the peak of the bloom the proportion being removed daily was only 2%. We conclude that during the spring bloom period copepods gained the majority of their carbon from phytoplankton ingestion but during non-bloom periods, protozooplankton and the ciliate M. rubra made a significant contribution to copepod diet. [Copyright &y& Elsevier]

The food selectivity of tethered females of the copepod Calanus helgolandicus was examined by using the colorimetric approach. First, feeding behavior of the copepod did not show any differences between the red-color stained with neutral red and non-stained diets using the diatom Coscinodiscus curvatulus. Then, the copepods were fed a mixtures of two diets, the diatom C. curvatulus, stained with neutral red, and the dinoflagellate Gymnodinium sanguineum for 14~60 minutes of feeding duration. The foregut colors of females were examined using a stereo-microscope and a video monitor. The foreguts of animals fed with a high density of diatoms in mixed diets showed a dark red color, whereas those fed with a high density of dinoflagellate in mixed diets were a dark yellow. The results suggest that this species of copepod may not selectively feed either one of the diets used for this study. Their feeding activity may be more likely related to the density of available prey in their environment. Therefore, this quick and easy colorimetric approach could provide very useful information, like the pre-screening procedure before designing and conducting the time-consuming and complex feeding experiments to understand the feeding ecology of copepods. [ABSTRACT FROM AUTHOR]

Abstract: Recent predictions anticipate a solar ultraviolet-B increase of 5–10% over temperate latitudes within the next 15 years. As Mediterranean waters are clear, enabling deep UVB penetration, we used controlled experiments to test the effects of equivalent levels of UVB on trophic plankton interactions. We grew the diatom Skeletonema costatum in the laboratory under daily 4 h UVB exposure in doses of 10% higher than today in contrast to control cultures (no UVB). UVB-exposed algae showed modification in cell structure, volume increase and delay in cell division, eventually leading to lysis and cell death after five days of daily 4 h exposure. Both control and UVB-stressed S. costatum cultures were used as food for wild Calanus helgolandicus females collected in the NW Mediterranean. Those fed on control diatoms produced three times more eggs, healthier offspring with fewer lethal naupliar deformities than females fed on UVB-exposed diatoms. Our results provide the first experimental evidence of indirect UVB effects on reproductive output through trophic response in marine plankton. The sensitivity of the S. costatum strain is discussed as well as the reduced reproductive output of the female copepods. We suggest that the low egg numbers and high naupliar deformity ratios are possibly a consequence of UVB-induced deficiency of essential components in the UVB-stressed maternal diet. [Copyright &y& Elsevier]

Abstract: Calanus helgolandicus is a widespread epipelagic copepod species whose geographical range extends from the temperate Atlantic Ocean to the northern Mediterranean Sea. Calanus euxinus, recently designated as a distinct species though closely related to C. helgolandicus, occurs in the Black Sea. Very subtle morphological differences distinguish the two species. Pseudocalanus elongatus has a similar geographic range including North Atlantic Ocean, Mediterranean Sea and the Black Sea. In this study, population genetic variation of C. helgolandicus, C. euxinus and P. elongatus was investigated using DNA sequence variation of 540 base pair (Calanus spp.) and 575 base pair (P. elongatus) regions of mitochondrial cytochrome oxidase I (mtCOI) gene. C. helgolandicus was collected from the English Channel, the Adriatic Sea, and C. euxinus was collected from various regions of the Black Sea. P. elongatus was collected from the English Channel and the Black Sea. Intraspecific differentiation in mtCOI was <1% for all species; mtCOI sequence variation between C. helgolandicus and C. euxinus was <0.5%. The absence of substantial genetic differentiation between C. helgolandicus and C. euxinus is particularly striking in comparison to other close species pairs in these genera. Statistically significant haplotype frequency differences were determined for different locations of the Black Sea, English Channel, and Adriatic Sea Calanus populations (, ). The haplotype diversity was high for all species: C. euxinus (), C. helgolandicus (), P. elongatus (). No haplotype sharing was reported for different locations of P. elongatus, whereas the presence of haplotype sharing between C. helgolandicus and C. euxinus was remarkable. The size distribution in terms of prosome length measurements was found to be region-specific. The lack of phylogenetic differentiation between the Calanus species pair may suggest ancestral polymorphisms. The morphological and genetic similarities between C. euxinus and C. helgolandicus raise new questions about the status of C. euxinus as a different species. [Copyright &y& Elsevier]

The effect of the parasite Ellobiopsis sp., on the fecundity of Calanus helgolandicus and Calanoides carinatus in the Bay of Biscay, was investigated in May 2003. An average of 6.8% of C. helgolandicus females were infected with Ellobiopsis sp., whereas none of the C. carinatus were found to be infected. An objective method of estimating gonad development was applied to quantitatively measure the effect of the parasitism on the reproduction of the copepod. Parasitism by Ellobiopsis sp. has the potential to reduce the fecundity of C. helgolandicus females. [ABSTRACT FROM AUTHOR]

Analysis of the demographic structure of Calanus species in the North Atlantic presents particular difficulties due to the overlapping spatial distributions of four main congeneric species (Calanus finmarchicus, Calanus helgolandicus, Calanus glacialis and Calanus hyperboreus). These species have similar morphologies, making microscopic discrimination only possible between some of the species at late copepodite or adult stages. However, molecular techniques now offer the possibility of screening significant numbers of specimens and unambiguously identifying them to species, regardless of developmental stage. Unfortunately, the processing rate of specimens by molecular methods is still too low to offer a realistic alternative to microscopy for analysis of samples from large field surveys. Here, we outline and test an approach involving the use of molecular methodology in conjunction with conventional microscopy to assess the species assignment of developmental stage abundances of Calanus congeners. Our study has highlighted many important methodological issues. First, it cannot be assumed that the species composition is homogeneous across the development stages; applying proportional species composition of adults to morphologically undistinguishable earlier development stages can result in error. The second important conclusion is that prosome length may be a highly unreliable discriminator of C. finmarchicus and C. glacialis. [ABSTRACT FROM AUTHOR]

Abstract: We review current knowledge and understanding of the biology and ecology of the calanoid copepod Calanus helgolandicus in European waters, as well as provide a collaborative synthesis of data from 18 laboratories and 26 sampling stations in areas distributed from the northern North Sea to the Aegean and Levantine Seas. This network of zooplankton time-series stations has enabled us to collect and synthesise seasonal and multi-annual data on abundance, body size, fecundity, hatching success and vertical distribution of C. helgolandicus. An aim was to enable comparison with its congener Calanus finmarchicus, which has been studied intensively as a key component of European and north east Atlantic marine ecosystems. C. finmarchicus is known to over-winter at depth, whereas the life-cycle of C. helgolandicus is less well understood. Overwintering populations of C. helgolandicus have been observed off the Atlantic coast between 400 and 800m, while in the Mediterranean there is evidence of significant deep-water populations at depths as great as 4200m. The biogeographical distribution of C. helgolandicus in European coastal waters covers a wide range of habitats, from open ocean to coastal environments, and its contribution to mesozooplankton biomass ranges from 6% to 93%. Highest abundances were recorded in the Adriatic and off the west coast of Spain. C. helgolandicus is generally found in 9–20°C water, with maximum abundances from 13–17°C. In contrast, C. finmarchicus is found in cooler water between 0 and 15°C, with peak abundances from 0 to 9°C. As water has warmed in the North Atlantic over recent decades, the range of C. helgolandicus and its abundance on the fringes of its expanding range have increased. This review will facilitate development of population models of C. helgolandicus. This will not only help answer remaining questions but will improve our ability to forecast future changes, in response to a warming climate, in the abundance and distribution of this important species. [Copyright &y& Elsevier]

At small spatial scales basking sharks (Cetorhinus maximus) forage selectively on zooplankton along thermal fronts, but the factors influencing broader scale patterns in their abundance and distribution remain largely unknown. Using long-term sightings data collected off southwest Britain between 1988 and 2001, we show that the number of basking sharks recorded was highly correlated with abiotic factors, principally sea surface temperature (SST) and the lagged effect of SST in the previous month, but only very weakly to zooplankton density. This suggests that the changes in number of basking sharks recorded over large spatio-temporal scales are more closely related to the availability of climate-driven thermal resources than prey availability, whereas the converse is supported by previous studies at local scales. Taken together, these results imply scale-dependent behavioural responses in basking sharks, with small-scale foraging movements linked by broad scale responses to temperature variation. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to investigate the production of Calanus helgolandicus off Plymouth, Western English Channel, from April to August 1998 comparing a range of different methods. The abundance of all developmental stages from NI to adult was determined. Body carbon and nitrogen and length were measured on individual NVI to adults. Female egg production was also monitored. All developmental stages were generally represented but four main periods of recruitment were determined. Two periods of low egg production were observed on the 13th and on the 27th of July: (i) the first was due to the arrival of newly moulted or not yet fertilised females in the population and (ii) the second low period was possibly due to the senescence of the females. Finally, the total production of C. helgolandicus was estimated using four different methods: the weight increment, the egg production, Huntley and Lopez and Hirst and Lampitt methods. Depending on the methods used, the production accumulated over the period from May 14 to August 10 ranged between 12 and 45 mg C m−3. [Copyright &y& Elsevier]

Abstract: We studied in situ weight increment of Calanus helgolandicus developing under field conditions. Weight increment between successive stages was rather similar for early nauplii (NII–NV ∼2.00 μgC μgC−1) and for early copepodites (NVI–CIII mean: ∼2.40 μgC μgC−1) but lower for late copepodites (CIV ∼0.80 and CV ∼0.20 μgC μgC−1). Weight increment of CIV and particularly CV was found to be closely linked to the method used to estimate the weight: either (i) directly measured weights, or (ii) weights estimated from a length–weight regression. The weight of CV, which has a relatively long stage duration, shows wide variations within the stage while length variations within stage are very low. For example, on the 17th of August, some CV had a carbon weight three times higher than other ones. The main cause of variation is the age of the individuals within the stage. We recommend direct weight measurement rather than the use of length–weight regression to estimate weight increment. However, and especially for stages with large variations in weight, whether the individuals are at the mid-point of their stage should be checked. [Copyright &y& Elsevier]

The vertical distribution of zooplankton in the upper 700 m of the water column was investigated across the Almeria–Oran front (Alboran Sea) during winter 1997/98 (Almofront 2 cruise). Eight sites corresponding to three hydrodynamic structures (the Atlantic jet, an anticyclonic gyre and the surrounding Mediterranean waters) were explored, by day and at night, using multiple-net sampling. Results are presented for the major species of copepods (>500 μm), macroplankton and microplankton. Species inhabiting the surface layer or occupying it at night extended deeper in the gyre. On the other hand, mesopelagic species (e.g. Pleuromamma borealis, Pleuromamma abdominalis, Euphausia krohni and Cyclothone braueri) were found to live deeper, at least by day for the migrants, in the Mediterranean waters compared with the two other structures. These changes in preferential depths across the front are discussed in relation to environmental features, such as light level, abundance of food and mixed layer depth. This study also documented the vertical distribution of some overwintering copepod species (Calanus helgolandicus, Eucalanus hyalinus and Eucalanus monachus). [ABSTRACT FROM AUTHOR]

The seasonal and interannual variability in abundance of Calanus finmarchicus and Calanus helgolandicus in the Irish Sea was examined on the west side of the Isle of Man (central Irish Sea) between 1995 and 2001. There was considerable interannual variability in abundance of both species that was greater than that seen in adjacent seas. In general, maximum abundance occurred between May and July each year with C. finmarchicus tending to occur earlier in the year than C. helgolandicus. There was a significant difference in interannual maximum abundances in the area (14–18 stations treated as replicates) with most years having a low abundance and one year a relatively high abundance. The maximum abundance of C. finmarchicus (1996) coincided with a low (negative) index value of the North Atlantic Oscillation (NAO), and with a high abundance of young gadoids (cod, haddock and whiting) in the water column and a large settlement of plaice. A high abundance of C. helgolandicus coincided with a relatively high (positive) index value of the NAO in 2000. The magnitude of interannual and seasonal variability in abundance was in close agreement with data from an inshore area (Port Erin Bay, Isle of Man) between 1907 and 1920. As with many Calanus populations, the adults in both species were predominantly female. As shown previously, Calanus is not one of the numerically dominant copepod species in the Irish Sea. However, the presence of young stages of Calanus within the central Irish Sea suggests that it must support a breeding population. [ABSTRACT FROM AUTHOR]

Abstract This study investigates long-term monthly changes in both the hydroclimatic (sea surface temperature and wind) and biological (calanoid copepod diversity, abundance of Calanus finmarchicus and Calanus helgolandicus ) environment of the north-east Atlantic. On the basis of the long-term variability of the hydroclimatic environment, three regions are defined: the west European basin, the subarctic gyre and the North Sea. A numerical procedure, used in climatology and terrestrial ecology to detect stepwise changes, is presented and applied to both hydroclimatic and biological data. This method reveals that a regime shift in the North Sea occurred after a stepwise change in both regional hydroclimatic parameters (wind and temperature) and large-scale hydroclimatic parameters (e.g. Northern Hemisphere Temperature anomalies). However, it is also suggested that ecological changes (e.g. calanoid copepod diversity, abundance of C. finmarchicus, C. helgolandicus ) observed in the North Sea after the mid-1980s also resulted from a major structural reorganization in calanoid copepod diversity in the north-east Atlantic, which has been related to an increasing trend in sea surface temperature in the west European basin. Although from the present study it is difficult to quantify the respective influence of advective processes versus the impact of changes in the regional hydroclimatic environment on Calanus species, it seems likely that both processes can play a substantial role. [ABSTRACT FROM AUTHOR]

During 12 months from April 1997, Calanus spp. copepodites were sampled in the 380-m deep Saltfjord by means of a 200-μm WP-2 net at four depth intervals. Nauplii were sampled with a 100-μm bongo net. Chlorophyll a and phytoplankton were sampled with a hose in the 0–40 m depth range. Environmental variables were recorded by CTD and an in situ fluorimeter. C. helgolandicus occurred in low numbers as adults and CV during most of the year. During the spring bloom in April, it avoided the upper cold 0–50 m depth range, where C. finmarchicus reproduced. In August–September, adults of the two species were equally numerous in the 0–50 m depth range. The adult C. finmarchicus had probably developed from the local spring generation, whereas C. helgolandicus had probably been imported from shelf waters. Nauplii present in August may be attributed to both species, but they did not grow into CI locally. Therefore, C. finmarchicus CV that accumulated in September–October were more likely imported from the shelf, probably by surface advection. Predators possibly reduced numbers up to January 1998, when both species again increased, probably because of deep inflow of shelf water. [ABSTRACT FROM PUBLISHER]

The effect of five non-phytoplankton and one phytoplankton diets on reproduction is described for the copepod Calanus helgolandicus and compared to field fecundity estimates. A fecundity increase followed ingestion of larvae of the sea urchin Sphaerechinus granularis (LSU) and the oyster Crassostrea gigas (OYS) by copepod females, whereas a decrease followed ingestion of eggs of the copepods Acartia and Temora spp. (COP), as a function of protein concentration in diets. With larvae of the sea urchin Paracentrotus lividus (SSU) and the dinoflagellate Prorocentrum minimum (PM; standard phytoplankton diet), fecundity was identical. Although protein concentrations differed greatly from one food treatment to the other, mean fecundity values were rather low. For unknown reasons, and despite their very high protein concentrations in comparison to in situ, none of these diets could improve female fecundity or reach maximum egg production rates reported in C.helgolandicus. Hatching rates were >80%, stable and similar with both PM and COP diets. With SSU, LSU and OYS diets, egg viability was lower than in situ and with PM, showing a strong and mild decrease with time with LSU and SSU, respectively. Ingestion of zygotes of the brown alga Fucus spiralis (ZYG) led to the death of females. These results suggest that dense blooms of zygotes of macroalgae and invertebrate embryos and larvae, occurring in the continental shelf as part of copepod diets, could have different effects on the demographic response of C.helgolandicus. [ABSTRACT FROM PUBLISHER]

Some investigators have proposed aspartate transcarbamylase (ATCase) activity as an overall index of mesozooplankton productivity. However, seasonal changes in mesozooplankton species composition have never been investigated as a possible source of variation in ATCase activity. In this study, we investigate mesozooplankton composition in terms of (i) developmental stages, (ii) species and developmental stages body mass and (iii) species composition, and their relationship to ATCase activity. In controlled laboratory conditions, ATCase activity variability was closely related to changes in somatic growth rate of the copepod Calanus helgolandicus, but was not related to changes in nucleic acid concentrations. It can be argued, however, that the activity of this enzyme is partially involved in copepod somatic productivity, and should be a good index of embryogenesis. In addition, changes in ATCase activity were not significantly influenced by variability in mesozooplankton biomass, when investigated at a fixed station off Plymouth (English Channel), ATCase activity was not correlated with the abundance of any mesozooplankton species apart from copepodites and adult C.helgolandicus. Furthermore, ATCase activity measured both on mesozooplankton and female C.helgolandicus was significantly correlated (R2=0.72, n=33, P<0.001) throughout the year, apart from April. At that particular time of the year, ATCase activity was in phase with the peak of abundance of copepod eggs and nauplii. It is suggested that mesozooplankton peaks of ATCase activity reflect two periods in the life history of the copepod: embryogenesis and terminal moult. We propose further experiments to test this hypothesis and to promote the development of molecular biomarkers in order to characterize specific zooplankton metabolic processes. [ABSTRACT FROM PUBLISHER]

Long-term variations in zooplankton abundance in the north-east Atlantic, the North Sea, and in freshwater UK lakes are investigated by means of the Continuous Plankton Recorder survey and the Windermere and Esthwaite lakes data. Inter-annual variability of plankton abundance in these data sets shows strong correlation with two modes of climatic variability in the North Atlantic: the latitudinal shifts of the north wall of the Gulf Stream and the North Atlantic Oscillation. Detailed analyses reveal that the connection between environmental forcing and plankton response depends on various mechanisms, i.e., timing and intensity of the spring phytoplankton bloom resulting from changes in stratification levels, changes in temperature, and, in the case of the copepod Calanus finmarchicus, advection of the population into the North Sea at the end of the winter season. Future attempts to predict changes in marine ecosystems on the basis of climate scenarios will require focusing major effort on biological–physical modelling and large-scale plankton population ecology. The maintenance of long-term monitoring programmes is also essential to determine whether the climate–plankton connections observed during several decades will persist in the future or will be overruled by other mechanisms and principally human-induced perturbations. [ABSTRACT FROM PUBLISHER]

Zooplankton production is greatly dependent on the governing stability regimes of the ecosystems determining the flow of biomass transfer. Mutual predation causes bifurcations or phase transitions between two or more stable equilibria in pelagic communities. Minute changes in the phytoplankton reproduction rates caused by, for example, pollution may induce system changes from one stability regime to another. This pivotal behaviour of a simplified ecosystem was simulated, applying novel definitions of population interactions in age-structured population models. The simulation model was then used for the localization of the most sensitive parts of the ecosystem, which were taken as guidelines for the experimental investigation of ecosystems synthesized according to the model requirements. It was possible to determine the congruencies as well as a non-compliance between the simulation model and the experimental results. By changing it accordingly, the simulation model was improved and developed further into a conceptual model of the catastrophic behaviour of plankton communities under the impact of mutual predation, a very general phenomenon in planktonic ecosystems. [ABSTRACT FROM PUBLISHER]

The lengths, wet and dry weights, nitrogen and carbon contents of fresh, frozen and formaldehyde-fixed specimens of Calanus helgolandicus (Claus) were determined. Samples were collected during May 1980 in the Celtic Sea. Individual Copepodite Stages 3, 4, 5, and Adult Male and Female Stage 6 were measured and analysed, and 36 linear regression equations derived for these variables together with mean values, standard deviations and 95% confidence limits. The range of nitrogen values in the fresh material, expressed as a percentage of dry weight, ranged from 8.08%±0.80 (Copepodite Stage 3) to 10.89%±0.27 (adult female); carbon values changed from 41.6%±3.05 (mean ±95% confidence limits) for Copepodite Stage 3 to 50.97%±2.63 in Copepodite Stage 5. The adult females had a high nitrogen and relatively low carbon content, while the converse was true for Stage 5 copepodites. There was a loss of dry weight from the frozen samples (57%) and the fixed samples (38%) compared with the mean of the fresh dry weight of all stages. The material lost from the copepods was rich in nitrogen, thus, artificially high percentage carbon values were determined from the frozen and fixed samples (52.0 to 60.3% and 44.7 to 58.5%, respectively). [ABSTRACT FROM AUTHOR]

A controlled-temperature plankton wheel is described that is suitable for use on board a ship. The 'IMER plankton wheel' system allows the use of various sizes of experimental bottles, up to 2.2 litres, the simulation of ambient light regimes and variable speed control for the rotation of the experimental bottles. The flexibility of the system was demonstrated by investigating the relationship between temperature and ingestion rate of an herbivorous copepod. Using four of the IMER plankton wheels simultaneously at four different temperatures (5°, 10°, 15° and 20° C), the ingestion rate of Calanus helgolandicus, feeding on Thalassiosira weissflogii, was shown to increase with increasing temperature; from a transformation of log (ingestion rate), this relationship was calculated as a Q (10° to 20°C) for Copepodite Stage V (Q 4.5) and adult female (Q 2.7) C. helgolandicus. The possibility of damaging cells, by rotation at 2 rpm, was investigated using the spinose form of the diatom T. weissflogii. Such rotation did not cause any damage to the spines of T. weissflogii, but mixing this diatom with a magnetic stirrer bar did damage the spines to varying degrees, depending on the volume being mixed. [ABSTRACT FROM AUTHOR]