Pseudocalanus Spp Research Articles

Investigations into the relationship between domoic acid and copepods in Scottish waters

Abstract This study investigated impacts of the algal toxin domoic acid (DA) on copepods in Scottish waters. Inspection of seasonal patterns revealed that several common copepods (Acartia spp. Dana, 1846, Calanus spp. Leach, 1816, Centropages spp. Krøyer, 1849, Pseudocalanus spp. Boeck, 1872, and Temora longicornis (Müller O.F., 1785)) regularly coexist with potentially toxic species from the diatom genus Pseudo-nitzschia H. Peragallo in H. Peragallo and M Peragallo, 1900. A short field study investigating the DA content of Calanus spp. at the Scottish Coastal Observatory site at Stonehaven recorded DA during every sampling event. The highest DA levels were associated with a July bloom (∼135000 cells L−1) of Pseudo-nitzschia cf. plurisecta Orive & Pérez-Aicua 2013. Several studies have previously investigated effects of ingested DA on copepods but information on effects of dissolved DA is lacking, therefore, simple exposure experiments were carried out to measure mortality of copepod species at ecologically relevant concentrations of dissolved DA. The highest concentrations tested (≥ 50 ng DA mL−1) decreased survival in Temora longicornis only; survival of other copepod species was unaffected. However, T. longicornis feeding on non-toxic algae in the presence of dissolved DA did not accumulate DA in their tissue. This study provides evidence of the potential for Calanus spp. to act as vectors for DA to higher trophic levels in Scottish waters.

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.

Zooplankton abundance trends and patterns in Shelikof Strait, western Gulf of Alaska, USA, 1990–2017

Abstract A multivariate approach was used to analyze spring zooplankton abundance in Shelikof Strait, western Gulf of Alaska. abundance of individual zooplankton taxa was related to environmental variables using generalized additive models. The most important variables that correlated with zooplankton abundance were water temperature, salinity and ordinal day (day of year when sample was collected). A long-term increase in abundance was found for the calanoid copepod Calanus pacificus, copepodite stage 5 (C5). A dynamic factor analysis (DFA) indicated one underlying trend in the multivariate environmental data that related to phases of the Pacific Decadal Oscillation. DFA of zooplankton time series also indicated one underlying trend where the positive phase was characterized by increases in the abundance of C. marshallae C5, C. pacificus C5, Eucalanus bungii C4, Pseudocalanus spp. C5 and Limacina helicina and declines in the abundance of Neocalanus cristatus C4 and Neocalanus spp. C4. The environmental and zooplankton DFA trends were not correlated over the length of the entire time period; however, the two time series were correlated post-2004. The strong relationship between environmental conditions, zooplankton abundance and time of sampling suggests that continued warming in the region may lead to changes in zooplankton community composition and timing of life history events during spring.

The importance of Calanus glacialis for the feeding success of young polar cod: a circumpolar synthesis

Understanding the feeding ecology of polar cod (Boreogadus saida) during its first year of life is crucial to forecasting its response to the ongoing borealization of Arctic seas. We investigated the relationships between diet composition and feeding success in 1797 polar cod larvae and juveniles 4.5–55.6 mm standard length (SL) collected in five Arctic seas from 1993 to 2009. Prey were identified to species and developmental stages when possible, measured, and their carbon content was estimated using taxon-specific allometric equations. Feeding success was defined as the ratio of ingested carbon to fish weight. Carbon uptake in polar cod larvae < 15 mm was sourced primarily from calanoid copepods eggs and nauplii which were positively selected from the plankton. With increasing length, carbon sources shifted from eggs and nauplii to the copepodites of Calanus glacialis, Calanus hyperboreus and Pseudocalanus spp. Calanus glacialis copepodites were the main carbon source in polar cod > 25 mm and the only copepodite positively selected for. Pseudocalanus spp. copepodites became important replacement prey when C. glacialis left the epipelagic layer at the end of summer. Calanus glacialis was the preferred prey of polar cod, contributing from 23 to 84% of carbon uptake at any stage in the early development. Feeding success was determined by the number of prey captured in larvae < 15 mm and by the size of prey in juveniles > 30 mm. As Arctic seas warm, the progressive displacement of C. glacialis by the smaller Calanus finmarchicus could accelerate the replacement of polar cod, the dominant Arctic forage fish, by boreal species.

The cross-shore distribution of plankton and particles southwest of Iceland observed with a Video Plankton Recorder

The high resolution distribution of plankton and particles along a transect extending from the coast and across the shelf southwest of Iceland was studied in relation to hydrographic features and chlorophyll a fluorescence in late May 2010–2013 with a Video Plankton Recorder. The different groups of plankton and particles showed distinctive distributional pattern. Decaying organic matter (marine snow) was a very significant component of the system. Calanus finmarchicus stayed generally shallower than egg carrying Pseudocalanus spp. Diel variability in depth distribution of C. finmarchicus was not evident. Ctenophores, jellies and fish larvae were most abundant above ~50m depth. Ctenophores were relatively abundant across the whole transect, while jellies and fish larvae were mainly seen on the landward half of the transect. The data on distribution of copepods (mainly C. finmarchicus) were combined with the results of a numerical circulation model (CODE), thus obtaining an estimate of fluxes of copepods in the area. The results show that C. finmarchicus may be transported by currents both eastwards and westwards along the south coast, while retention on the bank is also possible. Based on the results of the synthesis of the distributional data and the CODE model, it is hypothesized that the populations off the south coast are at least partly self-sustained in the region.

Decadal Distribution and Abundance Trends for the Late Stage Copepodites of Pseudocalanus spp. (Copepoda: Calanoida) in the US Northeast Continental Shelf Ecosystem.

The average annual cycle of abundance and the bimonthly distributions of the copepod Pseudocalanus spp. are described for U.S. Northeast continental shelf waters from samples collected on broad-scale plankton surveys 1977–2012. Population levels begin to increase during January–February, surge in March–April, and peak throughout the region during May–June. The copepod’s population density declines sharply after June and becomes minimal from September–December. Spatially, seasonal high levels persist throughout the year in coastal waters surrounding and adjacent to the Cape Cod peninsula. During late spring, dense concentrations are found in Gulf of Maine coastal waters and in a high abundance band that extends southwestward from Georges Bank into the northern half of Middle Atlantic Bight waters. Pseudocalanus spp. interannual abundance variability was substantial; displaying several extended low and high periods through the time series. In general, numbers were high from the late 1970s through the early 1980s, low in the mid-1980s, elevated in the 1990s, and low again in the 2000s. This pattern was correlated negatively with temperature and positively with phytoplankton abundance trends. It is proposed that the copepods low abundance in the 2000s may have been caused by warmer temperatures that indirectly depressed the abundance of phytoplankton that this copepod uses for food. Survey data also indicate that predation pressure from salps and perhaps some additional species may contribute to the precipitous summer decline of Pseudocalanus spp. The copepod’s abundance was found to be independent from the climatic variation associated with either the North Atlantic or Arctic Oscillation.

Spatial variability in zooplankton and feeding of larval Atlantic mackerel (Scomber scombrus) in the southern Gulf of St. Lawrence

The availability of adequate zooplankton prey during the larval stage is a keyfactor for the emergence of a strong year class. There are inconsistencies in the lit-erature on the importance of various zooplankton prey taxa for determiningAtlantic mackerel recruitment in the southern Gulf of St Lawrence. Previousstudies identified the copepod Calanus finmarchicus as the most important prey or-ganism influencing Atlantic mackerel recruitment, while a recent study pointed tothe importance of the copepod Pseudocalanus spp. The aim of this research was toexamine the influence of various assemblages of copepod prey on the feeding oflarval Atlantic mackerel. Fish larvae and their zooplankton prey were sampledover a grid of 65 stations covering the entire southern Gulf of St Lawrence in June2008 and 2010. We pooled stations into four groups based on zooplankton speciesassemblages. One assemblage was dominated by the copepods Oithona spp. andTemora longicornis and the three others were dominated by different proportions ofOithona spp. and Pseudocalanus spp. Feeding selectivity of mackerel larvae was mea-sured by comparing zooplankton prey in their gut contents to zooplankton foundin their environment. The diets of the 3.5–5.4 mm and the .5.4 mm size classeswere dominated by Oithona spp. nauplii and T. longicornis nauplii and copepodites.These prey were generally positively selected by the larvae, unlike Pseudocalanusspp. This is the first study to demonstrate strong predation by mackerel larvae onOithona spp. nauplii in the Gulf of St Lawrence. We suggest that an exceptionalmackerel year class will be produced by a very high availability of large copepodprey throughout the southern Gulf of St Lawrence rather than a high availabilityof small copepod prey. These results on the preferred prey of Atlantic mackerellarvae will be useful in adjusting predictive models of recruitment based oncopepod production for this commercial fish.KEYWORDS: recruitment; larval feeding; Atlantic mackerel; Gulf of St Lawrence

Late-summer zooplankton community structure, abundance, and distribution in the Hudson Bay system (Canada) and their relationships with environmental conditions, 2003–2006

Zooplankton communities were examined for the first time in three different hydrographic regions of the Hudson Bay system (HBS) in early August to early September from 2003 to 2006. Sampling was conducted at 50 stations distributed along different transects located in Hudson Bay (HB), Hudson Strait (HS), and Foxe Basin (FB). Variations in zooplankton biomass, abundance, taxonomic composition, and diversity in relation to environmental variables were studied using multivariate techniques. During all sampling years, the total zooplankton biomass was on average four times lower in HB than in HS and FB. Clustering samples by their relative species compositions revealed no interannual variation in zooplankton community but showed a marked interregional variability between the three regions. Water column stratification explained the greatest proportion (25%) of this spatial variability. According to redundancy analysis (RDA), the zooplankton taxa that contribute most to the separation of the three regions are Microcalanus spp., Oithona similis, Oncaea borealis, Aeginopsis laurentii, Sagitta elegans, Fritillaria sp., and larvae of cnidaria, chaetognatha, and pteropoda in HB; hyperiid amphipods in FB; and Pseudocalanus spp. CI–CV, Calanus glacialis CI–CVI, Calanus finmarchicus CI–CVI, Calanus hyperboreus CV–CVI, Acartia longiremis CI–CV, Metridia longa N3-N6 CI-CIII CVIf, Eukrohnia hamata, larvae of echinodermata, mollusca, cirripedia, appendicularia, and polychaeta in the northwestern and southeastern HS transects. For the HB transect, the RDA analyzed allowed us to distinguish three regions (HB west, central, and east) with different environmental gradients and zooplankton assemblages, in particular higher concentration of Pseudocalanus spp. nauplii and CI–CVI, as well as benthic macrozooplankton and meroplankton larvae in western HB. In HS, Calanoid species (mainly C. finmarchicus and C. glacialis) were mostly observed at the north shore stations associated with the weakly stratified Arctic–North Atlantic waters coming from southwestern Davis Strait (inflow). In general, the RDA models tested among the HBS regions were very consistent with its general surface circulation pattern for summer conditions in terms of environmental variables and distinct zooplankton assemblages. Overall, zooplankton biomass and diversity indices (H′, J′, and S) were lower in the most stratified environment (i.e., HB) than in the deeper (FB) and more dynamic (HS) regions. The results of this work clearly show that the spatial differentiation and structure of the zooplankton communities are strongly influenced by the hydrodynamic conditions in the HBS that, trough their actions on temperature, salinity, stratification, mixing conditions and depth strata, lead to the spatial differentiation of these communities.

Winter studies on zooplankton in Arctic seas: the Storfjord (Svalbard) and adjacent ice-covered Barents Sea

Zooplankton was sampled in the Storfjord and ice-covered Barents Sea during March 2003. Environmental conditions represented a typical winter situation with low air temperatures, close pack ice, and extremely low chlorophyll concentrations. Polar water dominated the hydrographic regime in the upper layers. Zooplankton distribution reflected spatial variability of hydrography. The copepods Pseudocalanus spp., Oithona similis, Microsetella norvegica together with gastropod larvae were most numerous. Biomass averaged for the entire water column varied from 3.3 to 14.3 mg dry mass m−3, Calanus glacialis and Parasagitta elegans contributed most, followed by C. finmarchicus, Oithona similis, and Pseudocalanus spp. Various holoplankters showed reproductive activity, especially cyclopoid copepods and chaetognaths. A few C. glacialis females laid eggs in situ, but when fed diatom cultures rapidly increased their egg production. Meroplankton including larvae of nudibranchia, bivalvia, ophiuroida, polychaeta, and bryozoa were also present. Our data demonstrate that the pelagic community of the seasonally ice-covered Barents Sea was not in a “sleeping” state at the end of the winter, but in addition to dormant stages, a portion of mainly omnivorous and several carnivorous species was reproducing.

Zooplankton trends in Massachusetts Bay, USA: 1998-2008

Zooplankton community analyses in Massachusetts Bay (Gulf of Maine, USA) from 1998 to 2008 with 102 μm mesh nets revealed seasonal and interannual variability in zooplankton abundance, with maxima in summer and minima in winter. Zooplankton was dominated by copepod nauplii, copepodites and adults, mostly of the small cyclopoid copepod Oithona similis. Time-series analyses revealed a multi-year decline in total zooplankton abundance from 2000 to 2008, especially due to declines in Oithona similis and Pseudocalanus spp. This decline was not exhibited by barnacle nauplii and Calanus finmarchicus. There were no significant relationships between surface or mean water column temperature and salinity for any zooplankton group except for significantly higher abundances of C. finmarchicus at higher surface salinity. There was a significant positive correlation between total zooplankton abundance and integrated chlorophyll. The decline in zooplankton abundance since 2000 was not obviously related to diversion of sewage effluent from the Boston Harbor outfall to Massachusetts Bay, or to natural hydrographic variability. The zooplankton decline in Massachusetts Bay highlights the importance of multi-year sampling to characterize interannual variability. Comparisons of our results with those of other programs in the Gulf of Maine are complicated by differences in sampling net meshes, but our results shared some similarities with other studies during years when these studies overlapped with ours. In particular, small copepods declined in abundance beginning around 2000-2001, Calanus finmarchicus was abundant and salinities were high during 2002 through 2004, and zooplankton and chlorophyll levels declined from 2000 through 2004.

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.

Individual-based modeling of feeding ecology and prey selection of larval cod on Georges Bank

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 376:227-243 (2009) - DOI: https://doi.org/10.3354/meps07796 Individual-based modeling of feeding ecology and prey selection of larval cod on Georges Bank Trond Kristiansen1,4,*, R. Gregory Lough2, Francisco E. Werner1,5, Elisabeth A. Broughton2, Larry J. Buckley3 1Marine Sciences Department, University of North Carolina, Chapel Hill, North Carolina 27599-3300, USA 2Northeast Fisheries Science Center, NMFS, NOAA, Woods Hole, Massachusetts 02543, USA 3University of Rhode Island/NOAA CMER Program, Graduate School of Oceanography, Narragansett, Rhode Island 02882, USA 4Present address: Institute of Marine Research, PO Box 1870 Nordnes, 5817 Bergen, Norway 5Present address: Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey, United States *Email: trond.kristiansen@imr.no ABSTRACT: Understanding larval fish survival dynamics is essential to determining variability in future adult population structure. Realistic modeling of larval fish feeding ecology depends on incorporating both the biotic and abiotic conditions that affect predator–prey interactions. We used an individual-based model (IBM) to test which variables drive Atlantic larval cod Gadus morhua feeding preferences. The IBM included a bioenergetics component that incorporated metabolic parameters and growth and a mechanistic prey selection component that depended on larval development and behavior, prey size and behavior, depth, light, and physical oceanographic conditions. We applied our model to Georges Bank and incorporated high-resolution field data on environmental conditions and prey abundance to analyze larval cod feeding ecology. Based on simulated selectivity indices, we found that cod prey selection was determined by differential encounter of prey due to the abundance of suitably sized prey, their visibility, and larval cod ability to capture these prey items. The model suggested that Pseudocalanus spp. were the dominant prey species for larval cod because of their abundance in the water column and their large image area. Centropages spp. were also modeled to be an important part of larval diet, but no copepodite stages of this taxon were found in gut samples. Lack of Centropages spp. in the gut samples indicated that they are more elusive in their behavior than Pseudocalanus spp. Overall our results suggest larval cod feeding ecology on Georges Bank is a consequence of the physical and biological conditions rather than active prey selection. KEY WORDS: Feeding ecology · Individual-based model · Cod · Larval fish · Georges Bank · Gadus morhua · Prey selection Full text in pdf format PreviousNextCite this article as: Kristiansen T, Lough RG, Werner FE, Broughton EA, Buckley LJ (2009) Individual-based modeling of feeding ecology and prey selection of larval cod on Georges Bank. Mar Ecol Prog Ser 376:227-243. https://doi.org/10.3354/meps07796 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 376. Online publication date: February 11, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Mesozooplankton prey preference and grazing impact in the western Arctic Ocean

Abstract The role of mesozooplankton as consumers and transformers of primary and secondary production in the Beaufort and Chukchi Seas was examined during four cruises in spring and summer of both 2002 and 2004 as part of the western Arctic Shelf–Basin Interactions (SBI) program. Forty-seven grazing experiments using dominant mesozooplankton species and life stages were conducted at locations across the shelf, slope, and basin of the Chukchi and Beaufort Seas to measure feeding rates on both chlorophyll and microzooplankton and to determine mesozooplankton prey preferences. Mesozooplankton biomass was at all times dominated by life stages of four copepod taxa: Calanus glacialis , Calanus hyperboreus , Metridia longa , and Pseudocalanus spp. Significant interannual, seasonal, regional, between species and within species differences in grazing rates were observed. Overall, the dominant zooplankton exhibited typical feeding behavior in response to chlorophyll concentration that could be modeled using species and life-stage specific Ivlev functions. Microzooplankton were preferred prey at almost all times, with the strength of the preference positively related to the proportion of microzooplankton prey availability. Average mesozooplankton grazing impacts on both chlorophyll standing stock (0.6±0.5% d −1 in spring, 5.1±6.3% d −1 in summer) and primary production (12.8±11.8% d −1 in spring, 27.6±24.5% d −1 in summer) were quite low and varied between shelf, slope, and basin. Coincident microzooplankton grazing experiments [Sherr, E.B., Sherr, B.F., Hartz, A.J., 2009. Microzooplankton grazing impact in the Western Arctic Ocean. Deep-Sea Research II] were conducted at most stations. Together, microzooplankton–mesozooplankton grazing consumed only 44% of the total water-column primary production, leaving more than half directly available for local export to the benthos or for offshore transport into the adjacent basin.

Seasonal variability in copepod ingestion and egg production on the Faroe shelf

Copepod community ingestion rates of Calanus finmarchicus, Temora longicornis, Acartia longiremis and Pseudocalanus spp., and egg production rates of C. finmarchicus and T. longicornis, were studied in relation to phytoplankton composition, abundance and biomass on the Faroe shelf during a one-year cycle. The phytoplankton community during winter was mainly composed of small flagellates and the copepods of Pseudocalanus spp. As the spring bloom progressed, diatoms increased in abundance and dominated the biomass throughout summer. C. finmarchicus increased in numbers in early spring, while T. longicornis and A. longiremis dominated the community during summer and autumn. While no response in ingestion rates was observed for A. longiremis and Pseudocalanus spp. with increasing diatom biomass, both ingestion rates and egg production of C. finmarchicus and T. longicornis, generally increased, showing a dependence upon diatoms for production. The daily ingestion for C. finmarchicus females was 7% and 22% of body biomass during the pre-bloom and bloom period, respectively, while for T. longicornis females it was 33% and 56% and for A. longiremis females 22% and 33%, respectively. C. finmarchicus accounted for more than 80% of the total copepod ingestion in May, but in mid- and late summer, T. longicornis and A. longiremis dominated, and represented 80–90% of the total copepod ingestion. The proportion of reproductively mature C. finmarchicus increased as the phytoplankton biomass increased. Most of the time there was good agreement between herbivorous ingestion rates and calculated carbon demand for the observed egg production. However, both species showed a peak in egg production prior to the phytoplankton spring-bloom.

Seasonal abundance, reproduction and development of four key copepod species on the Faroe shelf

The copepod community on the Faroe shelf is dominated by Calanus finmarchicus, Temora longicornis, Acartia longiremis and Pseudocalanus spp. The species composition, abundance and development of the copepod community varied considerably during the season 2004. These variations reflected to a large extent the different life strategies of the copepods. Both nauplii and copepodites of C. finmarchicus were most abundant during spring and early summer. The two neritic copepods T. longicornis and A. longiremis were present in low numbers during spring but dominated the copepod community later during the productive period. Pseudocalanus spp., on the other hand, occurred throughout the year, but showed no clear numerical response in abundance to the spring bloom. The egg production measurements of C. finmarchicus and T. longicornis showed some pre-bloom egg production, but as the spring bloom started the egg production rate increased significantly, especially for C. finmarchicus. There seemed to be a substantial loss of nauplii and copepods from the shelf ecosystem during the productive season. It was, however, not possible to determine whether this was mainly due to mortality or advective loss.

Spatio-temporal distribution and production of calanoid copepods in the central Baltic Sea

The aim of our study was the exploration of species-specific distribution and production patterns of dominant copepods in the Central Baltic Sea (Bornholm Basin). Spatio-temporal distribution, egg and secondary production were studied by means of net-sampling and egg production experiments from April to August 1999. Vertical and horizontal distribution patterns appeared to be linked with each other and were primarily species-dependent. Both Acartia spp. and Temora longicomis preferentially inhabited the upper 30 m of the water column and the shallower marginal regions of the Bornholm Basin. In contrast, the C4-5 and C6 of Pseudocalanus spp. preferentially inhabited the halocline region (50-70 m) and the deep central part of the area. Observed differences in horizontal distribution among these three copepods appear to result from different depth preferences and depth-dependent water circulation patterns. Egg production rates (EPR) clearly exhibited seasonal differences with maximum EPR in May and minimum EPR in July. Mean EPR was significantly different between species, being highest in Acartia spp. and lowest in Pseudocalanus spp. The variability in EPR was related to differences in hydrography and modelled food environment.

Growth and development of copepodite stages of Pseudocalanus spp.

Quantitative expressions are presented describing the effects of temperature and food concentration on the growth and development of the copepodite stages of Pseudocalanus spp. The calculations were made on the basis of experimental data from the literature for two geographically separate populations of Pseudocalanus from Puget Sound (Washington, USA) and from the southern North Sea. Relationships were obtained between the growth parameters for Pseudocalanus sp. from Puget Sound and temperature in the 8–15.5 � C range and food concentrations from 10 mg Cm � 3 to excess, as well as for Pseudocalanus elongatus from the southern North Sea at high food concentrations and in the 4–15 � C temperature range. Also computed was the total development time of P. elongatus for the final four copepodid stages as a function of food concentration from 50 mg Cm � 3 to excess and temperature from 5 to 20 � C. Empirical models computed here may be used

Horizontal and vertical distribution patterns, retention rates, and population dynamics of zooplankton on Western Bank, Scotian Shelf

We assess the importance of retention rates and local production to the concentration of zooplankton on Western Bank, Scotian Shelf, during September and October 1998. We do so using (i) particle retention rates derived from an array of 25 current meters and inferences from hydrographic structure; (ii) observations on the horizontal and vertical distribution of zooplankton and ichthyoplankton; and (iii) a simple projection-matrix model of the population dynamics of two copepod species, Centropages typicus and Pseudocalanus spp. Zooplankton biomass and adult stages of copepods were more abundant in surface waters on the bank (p &lt; 0.05) at broad (25 km) spatial scales. Zooplankton was correlated with ichthyoplankton abundance at this scale (r &gt; 0.5, p &lt; 0.001), a result of local production of both zooplankton and fish on the bank. The time-dependent anticyclonic circulation around Western Bank was variable, and particle retention rates were 18 and 33% for 20 days at 12.5 and 28.5 m, respectively. The population model showed that both C. typicus and Pseudocalanus spp. are capable of increasing their population size despite advective loss and mortality rates approaching 10%·day-1. We conclude that local production exceeding advective loss rates can explain the high concentrations of zooplankton on Western Bank.

Advanced recruitment and accelerated population development in Arctic calanoid copepods of the North Water

Abstract The timing of copepodite recruitment and population development of copepods in spring and early summer (April–July) were compared between the North Water polynya and Barrow Strait, a non-polynya region in the Canadian Archipelago. In the North Water, young copepodites (CI–CIII) of calanoid herbivores were concentrated in the cold and chlorophyll-rich water at the base of the Arctic surface layer, while later stages (CIV–CV) invaded the warmer surface layer. The phytoplankton bloom and the recruitment of the first cohort of copepodites of Calanus hyperboreus , C. glacialis , and Pseudocalanus spp started in May–June, some 1.5–3 months earlier than in Barrow Strait. Consistent with a precocious summer recruitment, population stage structure of these species in early spring (April–May) was more advanced in the North Water than in Barrow Strait. The recruitment in June of CI of the omnivore Metridia longa was advanced by at least 5 weeks in the polynya relative to Barrow Strait. We found no evidence for an acceleration of the population development of the small Microcalanus pygmaeus , Oithona similis or Oncaea borealis in the polynya. Once the recruitment of young copepodites had started, recruitment success (i.e. % of young copepodites in the population) increased primarily with Chl a concentration for C. hyperboreus , with both sea-surface temperature and Chl a for C. glacialis , and with temperature only for Pseudocalanus spp. Hence, depending on the species, both greater food availability and higher temperature resulting from reduced ice cover contributed to improve reproductive success in herbivorous copepods in the North Water relative to Barrow Strait. A climate-induced reduction of ice cover duration is predicted to favour the population growth of the predominant large calanoid copepods and Pseudocalanus on Arctic shelves.

Variations in Egg Production Rates by Pseudocalanus Spp. In a Subarctic Alaskan Bay During the Onset of Feeding by Larval Fish

Weekly estimates of female abundance and daily egg production rates were made for Pseudocalanusspp. during 1987 and 1988 in Auke Bay, southeastern Alaska. The sampling, which included measurements in primary production, was done during April and May when larval fish initiate feeding on copepod nauplii. The objective of the study was to examine the relative importance of female abundance and daily egg production rates for Pseudocalanus spp. in determining production of nauplii during the study period. In both years primary production rates exceeded 500 mg C·m―2·d―1. At this level of primary production Pseudocalanus spp. should not have been food-limited in either year. The average egg production rates per individual female during the 2 years were identical: 2.6 eggs·female―1· d―1. The average populations of female Pseudocalanus were 4,765 and 7,656 individuals·m―2 in 1987 and 1988, respectively. The larger populations of female Pseudocalanus spp. in 1988 resulted in higher overall egg production and better feeding conditions for larval fish. Thus, during the period when larval pollock began feeding on nauplii, female copepod abundance was more important than temporal differences in egg production rates in determining production of nauplii. A complete understanding of the copepod-larval fish relationship in Auke Bay will require explanation of the causes for interannual variability in abundance of adult female Pseudocalanus spp.