Calanoid Copepod Pseudocalanus Research Articles

Species-specific patterns of distribution and abundance of the cryptic copepods Pseudocalanus moultoni and P. newmani on Georges Bank (NW Atlantic Ocean) during spring 1995–2012

Time-series analysis of zooplankton species diversity, distribution, and abundance are essential for ecosystem assessment and fisheries management on continental shelves. This study analyzed two morphologically cryptic species of the calanoid copepod Pseudocalanus, P. moultoni and P. newmani, in zooplankton samples collected during May–June 1995–2012 over Georges Bank, NW Atlantic Ocean. Samples were collected 1995–1999 by US Global Ocean Ecosystem Dynamics (US GLOBEC) and 2002–2012 by NOAA Northeast Fisheries Science Center Ecosystem Monitoring (EcoMon). The species were discriminated by real-time quantitative PCR (qPCR) based on DNA sequence variation of the mitochondrial cytochrome oxidase I (COI). Multivariate statistical analysis revealed significant positive correlation between the geometric mean abundance of P. moultoni and depth-averaged temperature at the collection locations; P. newmani abundances showed no relationship to temperature, suggesting different temperature niches and potential responses to environmental conditions. Interannual patterns of variation of the species-specific abundances of P. moultoni and P. newmani differed significantly from pooled Pseudocalanus spp. Nonmetric multidimensional (NMDS) and regression analyses confirmed significant interannual differences between P. moultoni and P. newmani geometric mean abundances during 1995–2012. This study demonstrates the need for discrimination of closely-related and cryptic zooplankton species to understand and predict impacts of environmental variation and climate change on marine ecosystems.

Ocean acidification causes no detectable effect on swimming activity and body size in a common copepod

Ocean acidification can impair an animal’s physiological performance and energetically demanding activities such as swimming. Behavioural abnormalities and changed activity in response to ocean acidification are reported in fish and crustacean species. We studied swimming activity in the calanoid copepod Pseudocalanus acuspes in response to near-future ocean acidification. Water and copepods were sampled from ten mesocosms deployed on the Swedish west coast. The experiments were conducted on animals reared in the mesocosms for 2 months during spring. Copepods were filmed after long-term (chronic) high-CO2, and after 20 h acute exposure to CO2. There was no significant effect of CO2 on copepods in chronic high-CO2, nor significant effect after the 20 h acute exposure. In addition, we measured prosome length from a large number of adult copepods, but no effect of acidification on body size was found. In this study, P. acuspes did not show sensitivity to near-future pCO2 levels. Even if a number of papers suggest that copepods seem robust to future ocean acidification, interaction between multiple stress factors, such as elevated temperature, hypoxia and salinity changes may impair a copepod’s ability to resist lowered pH.

Community barcoding reveals little effect of ocean acidification on the composition of coastal plankton communities: Evidence from a long-term mesocosm study in the Gullmar Fjord, Skagerrak.

The acidification of the oceans could potentially alter marine plankton communities with consequences for ecosystem functioning. While several studies have investigated effects of ocean acidification on communities using traditional methods, few have used genetic analyses. Here, we use community barcoding to assess the impact of ocean acidification on the composition of a coastal plankton community in a large scale, in situ, long-term mesocosm experiment. High-throughput sequencing resulted in the identification of a wide range of planktonic taxa (Alveolata, Cryptophyta, Haptophyceae, Fungi, Metazoa, Hydrozoa, Rhizaria, Straminipila, Chlorophyta). Analyses based on predicted operational taxonomical units as well as taxonomical compositions revealed no differences between communities in high CO2 mesocosms (~ 760 μatm) and those exposed to present-day CO2 conditions. Observed shifts in the planktonic community composition were mainly related to seasonal changes in temperature and nutrients. Furthermore, based on our investigations, the elevated CO2 did not affect the intraspecific diversity of the most common mesozooplankter, the calanoid copepod Pseudocalanus acuspes. Nevertheless, accompanying studies found temporary effects attributed to a raise in CO2. Differences in taxa composition between the CO2 treatments could, however, only be observed in a specific period of the experiment. Based on our genetic investigations, no compositional long-term shifts of the plankton communities exposed to elevated CO2 conditions were observed. Thus, we conclude that the compositions of planktonic communities, especially those in coastal areas, remain rather unaffected by increased CO2.

Transgenerational effects alleviate severe fecundity loss during ocean acidification in a ubiquitous planktonic copepod.

Ocean acidification (OA) caused by anthropogenic CO2 emission is projected for thousands of years to come, and significant effects are predicted for many marine organisms. While significant evolutionary responses are expected during such persistent environmental change, most studies consider only short-term effects. Little is known about the transgenerational effects of parental environments or natural selection on the capacity of populations to counter detrimental OA effects. In this study, six laboratory populations of the calanoid copepod Pseudocalanus acuspes were established at three different CO2 partial pressures (pCO2 of 400, 900 and 1550μatm) and grown for two generations at these conditions. Our results show evidence of alleviation of OA effects as a result of transgenerational effects in P.acuspes. Second generation adults showed a 29% decrease in fecundity at 900μatm CO2 compared to 400μatm CO2 . This was accompanied by a 10% increase in metabolic rate indicative of metabolic stress. Reciprocal transplant tests demonstrated that this effect was reversible and the expression of phenotypic plasticity. Furthermore, these tests showed that at a pCO2 exceeding the natural range experienced by P.acuspes (1550μatm), fecundity would have decreased by as much as 67% compared to at 400μatm CO2 as a result of this plasticity. However, transgenerational effects partly reduced OA effects so that the loss of fecundity remained at a level comparable to that at 900μatm CO2 . This also relieved the copepods from metabolic stress, and respiration rates were lower than at 900μatm CO2 . These results highlight the importance of tests for transgenerational effects to avoid overestimation of the effects of OA.

Population dynamics of Pseudocalanus minutus elongatus in the Gulf of Gdansk (southern Baltic Sea) – experimental and numerical results

The seasonal and spatial distribution of the pelagic calanoid copepod Pseudocalanus minutus elongatus was studied in the Gulf of Gdansk (southern Baltic Sea) between January 2006 and December 2007 based on experimental data (from six stations) and numerical simulations. Numerical calculations were performed using a structured zooplankton population model that was adapted to this species and coupled to the ecosystem model. Spatiotemporal distribution of this species depends on salinity as a masking factor. Highest abundances at station J23, an open sea site, were observed in July 2006 and March 2007 (10,050 and 11,000 ind. m−3, respectively) and resulted from the large numbers of earlier copepodites C1–C3 in 2006 and nauplii in 2007. In shallow stations abundances declined. Our results show that only one complete generation of this copepod species developed during the year in this region. Differences in development between the experimental and numerical data are analysed.

Change in prey selectivity during the larval life of Atlantic cod in the southern Gulf of St Lawrence

Atlantic cod larvae showed strong selectivity for the medium-size calanoid copepod Pseudocalanus spp. Naupliar stages comprised 62.4% of total prey number in the gut of first-feeding larvae. Selectivity shifted to Pseudocalanus spp. females at the mid-larval stage, representing 43% of all prey ingested by > 12 mm larvae.

Species-specific PCR discrimination of species of the calanoid copepod Pseudocalanus, P. acuspes and P. elongatus, in the Baltic and North Seas

Two species of the calanoid copepod Pseudocalanus, P. acuspes and P. elongatus, have been reported from the Baltic and North Seas. Morphometric analysis based on Frost (Can J Zool 67:525–551, 1989) did not identify the species in samples collected during the German GLOBEC program; the majority of measurements fell outside reported ranges for Baltic and North Sea specimens. A multiplexed species-specific PCR (SS-PCR) protocol was designed from a ~700 bp sequence of mitochondrial cytochrome oxidase I (mtCOI), with primers designed to amplify regions of different sizes for the two species to allow detection by gel electrophoresis. The accuracy and reliability of the multiplexed SS-PCR reaction was confirmed by sequencing the mtCOI region. Preliminary SS-PCR analysis of geographic distributions of the two species indicated that P. acuspes occurred exclusively at sampling sites in the Baltic Sea, whereas P. elongatus was found in the southern North Sea and at one site in the Baltic. The SS-PCR protocol can be used for routine identification of the two species for studies of population, community and ecosystem dynamics.

Effects of intra- and inter-annual variability in prey field on the feeding selectivity of larval Atlantic mackerel (Scomber scombrus)

We identified to the lowest taxonomical level possible the preferred prey of Atlantic mackerel larvae from the southern Gulf of St Lawrence and assessed the extent to which prey selectivity varied within and among years. Mackerel laroae and their zooplankton prey were sampled in the summer of four consecutive years (1997-2000). The nauplii of the calanoid copepod Pseudocalanus sp. strongly dominated the diet of larvae 7 mm mainly fed on fish larvae (including conspecifics) and cladocerans. Chesson's alpha index revealed strong selectivity in all years for Pseudocalanus sp. nauplii in first-feeding larvae. Selectivity shifted to cladocerans and fish larvae around a body length of 7 mm. Intra- and inter-annual prey selectivity changes were mainly observed for alternative prey, during the period surrounding the shift in diet from small to large prey. Our results underscore the importance of considering the availability of the main prey Pseudocalanus sp. nauplii (early larval stage) as well as cladocerans and fish larvae (late larval stage), rather than the entire prey field in the future assessment of the role played by prey availability on larval mackerel vital rates.

Effects of intra- and inter-annual variability in prey field on the feeding selectivity of larval Atlantic mackerel (Scomber scombrus)

We identified to the lowest taxonomical level possible the preferred prey of Atlantic mackerel larvae from the southern Gulf of St Lawrence and assessed the extent to which prey selectivity varied within and among years. Mackerel larvae and their zooplankton prey were sampled in the summer of four consecutive years (1997–2000). The nauplii of the calanoid copepod Pseudocalanus sp. strongly dominated the diet of larvae <7 mm both in terms of numbers and carbon content, whereas larvae ≥7 mm mainly fed on fish larvae (including conspecifics) and cladocerans. Chesson’s alpha index revealed strong selectivity in all years for Pseudocalanus sp. nauplii in first-feeding larvae. Selectivity shifted to cladocerans and fish larvae around a body length of 7 mm. Intra- and inter-annual prey selectivity changes were mainly observed for alternative prey, during the period surrounding the shift in diet from small to large prey. Our results underscore the importance of considering the availability of the main prey Pseudocalanus sp. nauplii (early larval stage) as well as cladocerans and fish larvae (late larval stage), rather than the entire prey field in the future assessment of the role played by prey availability on larval mackerel vital rates.

Living conditions, abundance and biomass of under-ice fauna in the Storfjord area (western Barents Sea, Arctic) in late winter (March 2003)

The under-ice habitat and fauna were studied during a typical winter situation at three stations in the western Barents Sea. Dense pack ice (7–10/10) prevailed and ice thickness ranged over <0.1–1.6 m covered by <0.1–0.6 m of snow. Air temperatures ranged between −1.8 and −27.5°C. The ice undersides were level, white and smooth. Temperature and salinity profiles in the under-ice water (0–5 m depth) were not stratified (T=−1.9 to −2.0°C and S=34.2–34.7). Concentrations of inorganic nutrients were high and concentrations of algal pigments were very low (0.02 μg chlorophyll a l−1), indicating the state of biological winter. Contents of particulate organic carbon and nitrogen ranged over 84.2–241.3 and 5.3–16.4 μg l−1, respectively, the C/N ratio over 11.2–15.5 pointing to the dominance of detritus in the under-ice water. Abundances of amphipods at the ice underside were lower than in other seasons: 0–1.8 ind. m−2 for Apherusa glacialis, 0–0.7 ind. m−2 for Onisimus spp., and 0–0.8 ind. m−2 for Gammarus wilkitzkii. A total of 22 metazoan taxa were found in the under-ice water, with copepods as the most diverse and numerous group. Total abundances ranged over 181–2,487 ind. m−3 (biomass: 70–2,439 μg C m−3), showing lower values than in spring, summer and autumn. The dominant species was the calanoid copepod Pseudocalanus minutus (34–1,485 ind. m−3), contributing 19–65% to total abundances, followed by copepod nauplii (85–548 ind. m−3) and the cyclopoid copepod Oithona similis (44–262 ind. m−3). Sympagic (ice-associated) organisms occurred only rarely in the under-ice water layer.

Dependency of larval fish survival on retention/dispersion in food limited environments: the Baltic Sea as a case study

AbstractA three‐dimensional hydrodynamic model has been used to analyse temporally and spatially resolved circulation patterns in the Baltic Sea with special emphasis on drifting particles representing larval fish. The main purpose of this study was (i) to investigate potential drift patterns of larval fish, (ii) to identify its intra‐ and inter‐annual variability for time periods based on the timing of spawning and (iii) to analyse its seasonal and spatial variability in dependence of the atmospheric forcing conditions. For the time period 1979–1998 temporally and spatially resolved simulated flow fields were used to describe the potential drift from the centre of main reproductive effort of Baltic cod (Gadus morhua). The results of the model runs demonstrate a general change in circulation pattern from retention during a first decade (1979–1988) to dispersion in the following decade (1989–1998). This increase in dispersion was related to an increase in the variability of the local wind forcing conditions over the Baltic. The more frequent occurrence of dispersion in spring of the recent decade was accompanied by a strong decay in biomass of one of the main larval fish feeding component in the central basin, the calanoid copepod Pseudocalanus elongatus. Larger dispersion of this prey organism may have affected the spatial overlap and thus the contact rates between predator and prey. Hence, this may have resulted in a food limitation for early life stages of Baltic cod and potentially contributed to the pronounced shift in cod peak spawning time from spring to late summer. Early life stages of cod originating from late spawning fish, benefited from a stronger dispersion in late summer and autumn, into shallow coastal areas with higher calanoid abundance.

Effect of temperature on development, growth and reproduction in the marine copepod Pseudocalanus newmani at satiating food condition

Post-embryonic development time, somatic growth, egg production rate, survival and sex ratio for the marine calanoid copepod Pseudocalanus newmani from the Pacific coast off southwestern Hokkaido were determined at five temperatures (3, 6, 10, 15 and 20°C) when a mixed algal diet was provided at satiating food condition (0.36 μg C ml -1 ) in the laboratory. At temperatures between 3 and 15°C, the development time from hatching to adult female increased exponentially with decreasing temperature, being 23.3, 33.1, 46.7 and 74.6 days at 15, 10, 6 and 3°C, respectively. Males developed into adults 2-5 days earlier than did the females. At the highest temperature of 20°C, both embryonic and post-embryonic development and egg production of P newmani were suppressed. This inhibitory effect of high temperature is consistent with the vertical distribution range and seasonal abundance cycle of this copepod in the field; it tends to avoid the warm surface layer (>15°C) and scarcely appears in the water column during summer and autumn. Body size of P newmani was not affected by temperature until C1, but increased with decreasing temperature after C2. The weight-specific growth rate (SGR) increased linearly with temperature (T) until 15°C, which is expressed as SGR = 0. 0095T + 0.0462 (r = 0.996). This growth pattern may also indicate high-temperature stress to this copepod, the general pattern of copepod growth being exponential. The weight-specific egg production rate (SER) also increased with temperature (SER = 0. 02T + 0.014, r = 0.99), below 15°C. The proportion of male offspring of P newmani that grew to adulthood was nearly 50% at 3 and 6°C, but decreased with increasing temperature at 10-15°C. This unequal sex ratio may be due to sex change during juvenile development under temperature control. These results suggest that temperature plays an important role in life history traits of P newmani through not only temperature- dependent growth and reproduction, but also through high-temperature inhibition and temperature- controlled sex ratio under sufficient food supply.

Biophysical modeling of larval Baltic cod (Gadus morhua) growth and survival

A coupled hydrodynamic–trophodynamic individual-based model of drift and feeding was utilized to analyze the intra- and inter-annual variability in growth and survival of cod (Gadus morhua) larvae in the central Baltic Sea. Highly temporally and spatially resolved simulated flow fields were used to investigate the potential drift of larval cod from the centre of spawning effort in the Bornholm Basin towards their nursery areas through temporally resolved three-dimensional idealized prey fields. Stomach content analyses of larval cod from the Bornholm Basin revealed calanoid copepod nauplii and early copepodite stages to be the preferred prey organisms. The results of the model runs indicate that larval cod changed from a nonlimited to a food-limited stage because of the strong decrease in abundance of the calanoid copepod Pseudocalanus elongatus during the last two decades. The modeling study revealed retention and dispersal from the main spawning ground to be a key process influencing larval survival. When P. elongatus was available in the prey fields, high cod larval survival rates occurred in spring and early summer. In contrast, when P. elongatus was not available, hatched larvae had only high survival probabilities later in the year or if they were transported into shallower coastal regions.

The Demographic Benefits of Diel Vertical Migration by Zooplankton

Three types of diel vertical migration behavior were expressed within a fjord population of the calanoid copepod Pseudocalanus newmani: (1) reverse migration (nocturnal descent), (2) normal migration (nocturnal ascent), and (3) no detectable migration. Reverse migration by P. newmani occurred in all three study years, but only at a deep (185 m) station at times of year when normally migrating predatory zooplankton (the copepod Euchaeta elongata, the chaetognath Sagitta elegans, and the omnivorous euphausiid Euphausia pacifica) were abundant. A predator—exclusion "natural experiment" tested the hypothesis that the reverse migration is a predator avoidance mechanism: at a shallow (55 m) station within the same fjord, large predatory zooplankton were absent or reduced markedly in abundance. In conditions of reduced nocturnal predation by predatory zooplankton, no reverse migration by P. newmani was detected on any of 11 cruises, consistent with the hypothesis. Instead, at the shallow station, where diurnal predation by planktivorous fish was of increased importance, normal diel vertical migration by P. newmani was observed on several occasions. No migration was detectable at either the deep station or the shallow station at times of year of low feeding activity of predators in surface waters. The predominant migration behavior (reverse, normal, or no migration) varied depending whether the primary source of mortality was predation by nocturnally feeding zooplankton or visually hunting planktivorous fish, and appeared unrelated to resource distributions or temperature gradients. The relative advantage of the three migration behaviors is explored with theoretical life table analyses. Re—examination of the demographic advantage hypothesis proposed by McLaren (1974) illustrates that vertical migration across a thermocline carries a fitness cost, not a benefit. The realized rate of increase of a migrant population of Pseudocalanus is found to be lower than a nonmigrant population for all combinations of surface temperatures, positive thermal stratification, and ratios of mortality for early and late developmental stages. However, avoidance of predators by vertical migrants reverses the outcome of this analysis. Predator avoidance by Pseudocalanus, accompanied by reduced mortality rates, confers a fitness advantage upon a population that migrates across a thermocline. Remarkably small reductions in mortality rates (as little as 12%) confer this advantage, whether migrants avoid nonvisually hunting predatory zooplankton by night or visually hunting planktivorous fish by day. The behavioral variation documented here confirms that diel vertical migration is dynamic rather than a fixed, invariant behavioral trait within a population. In environments where predation pressure and other factors vary through time, studies of limited scope and short duration are unlikely to illuminate the ultimate causes for diel vertical migration. The heritability of the vertical migration trait is unclear. The different phenotypic responses reflected within this single populations of P. newmani may reflect altered behavior of individuals. Alternatively, this behavioral variation may represent a balanced polymorphism maintained by differential mortality of genotypes experiencing selection pressures that vary through time.

The ecology of the calanoid copepod Pseudocalanus minutus Krøyer in Tessiarsuk, a coastal meromictic lake of northern Labrador : Carter John C. H., 1965. Limnol. Oceanogr., 10 (3): 345–353.

The ecology of the calanoid copepod Pseudocalanus minutus Krøyer in Tessiarsuk, a coastal meromictic lake of northern Labrador : Carter John C. H., 1965. Limnol. Oceanogr., 10 (3): 345–353.

THE ECOLOGY OF THE CALANOID COPEPOD PSEUDOCALANUS MINUTUS KRØYER IN TESSIARSUK, A COASTAL MEROMICTIC LAKE OF NORTHERN LABRADOR

A study of the ecology of the calanoid copepod Pseudocalanus minutus Krøyer in Tessiarsuk, a deep coastal meromictic lake of northern Labrador, was made in the summer of 1961 and spring of 1962. The lake, containing two basins, is separated from Anaktalik Bay by a shallow threshold and receives periodic volumes of tidal water. Maximum salinity at depth was 21.5‰, while surface salinity was less and increased through the season. Temperatures were stable in the monimolimnion but variable in the chemocline and mixolimnion. Gradual deoxygenation occurred with depth; the profundal waters contained only traces of oxygen. In both lake basins P. minutus produced two generations each year with a possibility that some animals might have been annual. Females in the spring spawned two broods in succession. An inverse relationship existed between water temperature and copepodite length. All stages were concentrated in the upper waters; the copepodites underwent a gradual seasonal descent. The salinity gradient produced a distinct spatial separation of Pseudocalanus from the other autochthonous calanoids, Acartia clausi and Eurytemora hirundoides.