Stages CIV Research Articles

Modelling the complete life cycle of an arctic copepod reveals complex trade-offs between concurrent life cycle strategies

Calanus hyperboreus is a large-bodied, biomass dominant species that performs a crucial ecosystem energy transfer by converting the spring phytoplankton bloom into lipid reserves that fuel the higher trophic levels of the Gulf of St. Lawrence (GSL) pelagic ecosystem, including the critically endangered North Atlantic right whale (Eubalena glacialis). Given that the GSL, the southernmost core habitat of C. hyperboreus, is undergoing rapid warming, developing a population model allows us to synthesize existing knowledge of the species, and to examine the species response to environmental conditions. To simulate the multi-year life cycle in the northwest GSL, model equations are implemented for ingestion, assimilation, respiration, egg production, stage development, mortality, and vertical migration behaviors including dormancy entry and exit. The 1-D particle-based model predicts the evolution of individual stage, structural mass, lipid, age, sex, abundance, and egg production, as well as the seasonal evolution of the population structure in the northwest GSL. Individual lipid-based thresholds inform the timing of ontogenetic vertical migration. Life cycle targets defined from a literature review are used to guide model parameterization and assess its performance. The simulated population structure, phenology, and size at stage are generally consistent with observations. Under 10 years of repeat year forcing, the model simulates a quasi-stable overwintering population composed of late stages CIV, CV and CVI. Observations suggest that stage CIV is the first overwintering stage in the GSL, and point to the occurrence of iteroparous females. Using the model, the relative success of diverse dormancy and reproductive phenotypes are explored. Second reproduction females reproduce earlier in winter than first reproduction females, with implications for the ability of the new generation to match the spring bloom and accumulate sufficient lipid to overwinter as stage CIV. Without iteroparity, the time window of reproduction contracts and the population is reduced, underscoring the role of a flexible multi-year life cycle in population success.

North Atlantic right whale Eubalaena glacialis prey selection in Cape Cod Bay

North Atlantic right whales Eubalaena glacialis have been observed feeding in Cape Cod Bay (CCB) for over 8 decades, making CCB the most consistent known feeding habitat under shifting ocean and climate conditions. Determining the composition of the right whales’ prey resource in a stable feeding habitat during a period of environmental change will inform conservation efforts throughout their habitat range. We compared zooplankton sampled in the paths of skim-feeding right whales to the bay-wide zooplankton resource in CCB over 23 yr. The dominant zooplankton taxa in CCB were Pseudocalanus complex, Calanus finmarchicus, and Centropages spp. during the winter/spring seasons. The succession of these 3 dominant taxa—Centropages spp. to Pseudocalanus complex (day of the year [DOY] mean ± SD: 34 ± 3) to C. finmarchicus (DOY 92 ± 3)—has provided right whales with a stable, multi-month food resource in a small portion of their greater North Atlantic habitat. We found that right whales targeted aggregations of non-dominant prey groups: Pseudocalanus complex and Centropages spp. aggregations when Centropages spp. dominated the bay-wide zooplankton community; Pseudocalanus complex patches and C. finmarchicus patches when Pseudocalanus dominated; and primarily C. finmarchicus copepodite stage CIV and CV aggregations when CIII dominated bay-wide abundances. Over the time series, we found that Centropages spp. abundance increased and C. finmarchicus decreased only at the beginning of the season. CCB remains a critical foraging habitat for right whales due to the phenological cycle of their prey and limited inter-annual changes in prey abundance.

Ocean acidification causes fundamental changes in the cellular metabolism of the Arctic copepod Calanus glacialis as detected by metabolomic analysis

Using a targeted metabolomic approach we investigated the effects of low seawater pH on energy metabolism in two late copepodite stages (CIV and CV) of the keystone Arctic copepod species Calanus glacialis. Exposure to decreasing seawater pH (from 8.0 to 7.0) caused increased ATP, ADP and NAD+ and decreased AMP concentrations in stage CIV, and increased ATP and phospho-L-arginine and decreased AMP concentrations in stage CV. Metabolic pathway enrichment analysis showed enrichment of the TCA cycle and a range of amino acid metabolic pathways in both stages. Concentrations of lactate, malate, fumarate and alpha-ketoglutarate (all involved in the TCA cycle) increased in stage CIV, whereas only alpha-ketoglutarate increased in stage CV. Based on the pattern of concentration changes in glucose, pyruvate, TCA cycle metabolites, and free amino acids, we hypothesise that ocean acidification will lead to a shift in energy production from carbohydrate metabolism in the glycolysis toward amino acid metabolism in the TCA cycle and oxidative phosphorylation in stage CIV. In stage CV, concentrations of most of the analysed free fatty acids increased, suggesting in particular that ocean acidification increases the metabolism of stored wax esters in this stage. Moreover, aminoacyl-tRNA biosynthesis was enriched in both stages indicating increased enzyme production to handle low pH stress.

Contrasting Life Traits of Sympatric Calanus glacialis and C. finmarchicus in a Warming Arctic Revealed by a Year-Round Study in Isfjorden, Svalbard

The calanoid copepod Calanus glacialis dominates the mesozooplankton biomass in the Arctic shelf seas, but its smaller North Atlantic sibling Calanus finmarchicus is expanding northwards and may potentially replace it if the climate continues to warm. Here we studied the population structure, overwintering strategies, gonad maturation and egg production of C. glacialis and C. finmarchicus over a period of 15 consecutive months in a high-Arctic fjord with sub-Arctic ocean climate and no sea ice formation in winter. The relative proportions of C. glacialis and C. finmarchicus varied throughout the study period, but with an overall dominance of C. glacialis. The overwintering population of C. glacialis was dominated by copepodite stage CIV (74%) while C. finmarchicus overwintered mainly as CV (65%), reflecting a primarily two- and one-year life cycle, respectively. Adult males and females of C. glacialis appeared as early as October with a peak during December-January, two months earlier than in C. finmarchicus, with a corresponding one-month earlier peak in recruitment for C. glacialis. While C. glacialis reproduced prior to the bloom with egg production peaking during the bloom, C. finmarchicus started egg laying during the bloom and continued to reproduce throughout the summer. Seasonal changes in the population structure suggest that C. finmarchicus born early in spring are able to develop to CV during summer and overwinter successfully, while offspring born later in the season do most likely not reach the CV overwintering stage. The ability to reproduce early and the flexibility to alter between 1- and 2-year life cycles give C. glacialis an advantage over C. finmarchicus in high-Arctic unpredictable environments with short-pulsed primary production regimes. Our data indicate that C. glacialis and C. finmarchicus occupy similar environmental niches, but different timing in reproduction reduces the competition. If sea temperatures remain within their temperature-tolerance ranges, both C. glacialis and C. finmarchicus seem to benefit from warming due to accelerating growth and higher survival of the recruits as long as C. glacialis has access to a colder refuge by descending to deeper depths.

Seasonal and interannual variability in abundance and population development of Calanus finmarchicus at the western entrance to the Barents Sea, 1995–2019

Data on copepodid abundance and stage composition of Calanus finmarchicus was collected with seasonal resolution (5–6 times a year) from four stations along an oceanographic transect across the western Barents Sea Opening over 25 years (1995–2019). The stations were located in the Norwegian Coastal Current (NCC), inflowing Atlantic water (two stations), and near the Arctic polar front south of Bear Island. Mean copepodite abundance in the water column for the four stations increased from a level around 1000–10,000 individuals m−2 in winter to 30,000–100,000 individuals m−2 in summer (maximum 670,000 m−2). The overwintering (G0) population was dominated by copepodite stage 5 (CV) (40–70%) but with a relatively high fraction also of stage CIV (25–35%) in January. During winter, there was a progressive development of CVs into adult males and females, with mean abundances from 1500 to 4000 adult females m−2 in April and May for the stations in the NCC and Atlantic water. Young copepodids of the new spring generation (G1) appeared with relatively high abundances in April at the NCC station and in May at the Atlantic water stations. The data showed a gradient of later development from south to north, reflected both in the maturation of the overwintering generation and in the development of the spring generation. Back-calculations based on temperature-dependent development time suggested peak spawning around late April to mid-May for the Atlantic water stations, and a month or so earlier (in March) for the NCC station, during an early phase of the spring phytoplankton growth. The spring generation developed as a distinct cohort but with large interannual variability in numbers. In Atlantic water, the composition of the copepodid developmental stages in August resembled the situation in June, although it was slightly more advanced. This is interpreted to reflect development of a second generation (G2) spawned upstream sometime in June or early July. The June data suggests that only a small fraction of the G1 cohort develops into adults that spawn and form the G2. There was a tendency of increased summer abundance of C. finmarchicus in the inflow region of the southwestern Barents Sea after about 2005. This may be related to the wind regime with more eastward wind-stress at the Barents Sea opening in recent ‘high Calanus’ years compared to ‘low Calanus’ years in the early 2000s.

Could offspring predation offset the successful reproduction of the arctic copepod Calanus hyperboreus under reduced sea-ice cover conditions?

Life cycle and reproduction of Calanus hyperboreus were studied during a year of record low ice cover in the southeastern Beaufort Sea. Stages CIV, adult females and CV dominated the overwintering population, suggesting a 2- to 3-year life cycle. Within two spring-summer months in the upper water column females filled their energy reserves before initiating their downward seasonal migration. From February to March, vigorous reproduction (20–65 eggs f−1 d−1) delivered numerous eggs (29 000 eggs m−2) at depth and nauplii N1-N3 (17 000 ind. m−2) in the water column. However, CI copepodite recruitment in May, coincident with the phytoplankton bloom, was modest in Amundsen Gulf compared to sites outside the gulf. Consequently, C. hyperboreus abundance and biomass stagnated throughout summer in Amundsen Gulf. As a mismatch between the first-feeding stages and food was unlikely under the favourable feeding conditions of April-May 2008, predation on the egg and larval stages in late winter presumably limited subsequent recruitment and population growth. Particularly abundant in Amundsen Gulf, the copepods Metridia longa and C. glacialis were likely important consumers of C. hyperboreus eggs and nauplii. With the ongoing climate-driven lengthening of the ice-free season, intensification of top-down control of C. hyperboreus recruitment by thriving populations of mesopelagic omnivores and carnivores like M. longa may counteract the potential benefits of increased primary production over the Arctic shelves margins for this key prey of pelagic fish, seabirds and the bowhead whale.

Contribution of Calanus species to the mesozooplankton biomass in the Barents Sea

AbstractCopepods from the genus Calanus are crucial prey for fish, seabirds and mammals in the Nordic and Barents Sea ecosystems. The objective of this study is to determine the contribution of Calanus species to the mesozooplankton biomass in the Barents Sea. We analyse an extensive dataset of Calanus finmarchicus, Calanus glacialis, and Calanus hyperboreus, collected at various research surveys over a 30-year period. Our results show that the Calanus species are a main driver of variation in the mesozooplankton biomass in the Barents Sea, and constitutes around 80% of the total. The proportion of Calanus decreases at low zooplankton biomass, possibly due to a combination of advective processes (low C. finmarchicus in winter) and size selective foraging. Though the Calanus species co-occur in most regions, C. glacialis dominates in the Arctic water masses, while C. finmarchicus dominates in Atlantic waters. The larger C. hyperboreus has considerably lower biomass in the Barents Sea than the other Calanus species. Stages CIV and CV have the largest contribution to Calanus species biomass, whereas stages CI-CIII have an overall low impact on the biomass. In the western area of the Barents Sea, we observe indications of an ongoing borealization of the zooplankton community, with a decreasing proportion of the Arctic C. glacialis over the past 20 years. Atlantic C. finmarchicus have increased during the same period.

Contrasting physiological responses to future ocean acidification among Arctic copepod populations.

Widespread ocean acidification (OA) is modifying the chemistry of the global ocean, and the Arctic is recognized as the region where the changes will progress at the fastest rate. Moreover, Arctic species show lower capacity for cellular homeostasis and acid-base regulation rendering them particularly vulnerable to OA. In the present study, we found physiological differences in OA response across geographically separated populations of the keystone Arctic copepod Calanus glacialis. In copepodites stage CIV, measured reaction norms of ingestion rate and metabolic rate showed severe reductions in ingestion and increased metabolic expenses in two populations from Svalbard (Kongsfjord and Billefjord) whereas no effects were observed in a population from the Disko Bay, West Greenland. At pHT 7.87, which has been predicted for the Svalbard west coast by year 2100, these changes resulted in reductions in scope for growth of 19% in the Kongsfjord and a staggering 50% in the Billefjord. Interestingly, these effects were not observed in stage CV copepodites from any of the three locations. It seems that CVs may be more tolerant to OA perhaps due to a general physiological reorganization to meet low intracellular pH during hibernation. Needless to say, the observed changes in the CIV stage will have serious implications for the C.glacialis population health status and growth around Svalbard. However, OA tolerant populations such as the one in the Disko Bay could help to alleviate severe effects in C.glacialis as a species.

Potential misidentifications of two climate indicator species of the marine arctic ecosystem: Calanus glacialis and C. finmarchicus

Calanoid copepods of the genus Calanus represent an important, nutrient-rich food source for a multitude of Arctic marine organisms. Although morphologically very similar, their life histories and ecological roles differ. Because the distribution of Calanus glacialis and C. finmarchicus corresponds to Arctic and Atlantic water masses, respectively, they are regularly used as climate indicators. A correct identification of these species is therefore necessary in many ecological, environmental and climatological studies. In this study, we aimed at validating the traditionally used morphological characteristics (combining prosome length and copepodite stage) for separation of species of Calanus by using molecular tools (PCR–RFLP of the 16S mtDNA). A total of 418 specimens of copepodite stages CIV, CV and CVI(af) from three Arctic fjords have been identified both morphologically and genetically. We find that the morphological identification systematically overestimates the abundance of C. finmarchicus at the expense of C. glacialis. Hence, parts of the C. glacialis populations are found to be structurally smaller and the within population size range thus larger than previously assumed. Consequently, using the traditional morphological species delimitation poses a serious problem in the use of these two species as indicators of Atlantic versus Arctic water masses and thus as climatic indicators. Furthermore, it obscures our understanding of the life history differences between the two species and of their relative importance as food for a number of ecologically and economically important species in the Arctic.

Some biological features and productive characteristics of Oithona similis (Copepoda) in the Sea of Okhotsk and western Bering Sea

The biological peculiarities of Oithona similis were described based on the materials from 29 complex surveys that were conducted by the TINRO Center in the Sea of Okhotsk and the western Bering Sea from 1986 to 2005 and the production of the species was estimated. In this area, O. similis produces four generations a year, viz., one in the spring, one in the fall, and two in the summer. The peak of spawning in May and June coincides with the maximum development of phytoplankton. Somatic production of O. similis in both seas becomes higher during the summer season. In this species, the largest increment in body weight begins with the copepodite stage CIV, when basic nutrients are accumulated. The average specific daily production of O. similis in the epipelagic zone of the Sea of Okhotsk and Bering Sea was 0.0092 and 0.01 in the spring, 0.043 and 0.031 in the summer, and 0.023 and 0.014 in the fall, respectively. The total somatic production of this species reached 28.318 million tons in the Sea of Okhotsk and 4.811 million tons in the Bering Sea. The Sea of Okhotsk is more favorable for the development of O. similis.

Life strategy and diet of Calanus glacialis during the winter–spring transition in Amundsen Gulf, south-eastern Beaufort Sea

The copepod Calanus glacialis plays a key role in the lipid-based energy flux in Arctic shelf seas. By utilizing both ice algae and phytoplankton, this species is able to extend its growth season considerably in these seasonally ice-covered seas. This study investigated the impacts of the variability in timing and extent of the ice algal bloom on the reproduction and population success of C. glacialis. The vertical distribution, reproduction, amount of storage lipids, stable isotopes, fatty acid and fatty alcohol composition of C. glacialis were assessed during the Circumpolar Flaw Lead System Study. Data were collected in the Amundsen Gulf, south-eastern Beaufort Sea, from January to July 2008 with the core-sampling from March to April. The reduction in sea ice thickness and coverage observed in the Amundsen Gulf in 2007 and 2008 affected the life strategy and reproduction of C. glacialis. Developmental stages CIII and CIV dominated the overwintering population, which resulted in the presence of very few CV and females during spring 2008. Spawning began at the peak of the ice algal bloom that preceded the precocious May ice break-up. Although the main recruitment may have occurred later in the season, low abundance of females combined with a potential mismatch between egg production/development to the first feeding stage and phytoplankton bloom resulted in low recruitment of C. glacialis in the early summer of 2008.

Zooplankton boom and ice amphipod bust below melting sea ice in the Amundsen Gulf, Arctic Canada

Early summer in the Arctic with extensive ice melt and break-up represents a dramatic change for sympagic–pelagic fauna below seasonal sea ice. As part of the International Polar Year-Circumpolar Flaw Lead system study (IPY-CFL), this investigation quantified zooplankton in the meltwater layer below landfast ice and remaining ice fauna below melting ice during June (2008) in Franklin Bay and Darnley Bay, Amundsen Gulf, Canada. The ice was in a state of advanced melt, with fully developed melt ponds. Intense melting resulted in a 0.3- to 0.5-m-thick meltwater layer below the ice, with a strong halocline to the Arctic water below. Zooplankton under the ice, in and below the meltwater layer, was sampled by SCUBA divers. Dense concentrations (max. 1,400 ind. m−3) of Calanus glacialis were associated with the meltwater layer, with dominant copepodid stages CIV and CV and high abundance of nauplii. Less abundant species included Pseudocalanus spp., Oithona similis and C. hyperboreus. The copepods were likely feeding on phytoplankton (0.5–2.3 mg Chl-a m−3) in the meltwater layer. Ice amphipods were present at low abundance (<10 ind. m−2) and wet biomass (<0.2 g m−2). Onisimus glacialis and Apherusa glacialis made up 64 and 51% of the total ice faunal abundance in Darnley Bay and Franklin Bay, respectively. During early summer, the autochthonous ice fauna becomes gradually replaced by allochthonous zooplankton, with an abundance boom near the meltwater layer. The ice amphipod bust occurs during late stages of melting and break-up, when their sympagic habitat is diminished then lost.

Life cycle of Oithona similis (Copepoda: Cyclopoida) in Kola Bay (Barents Sea)

The annual population dynamics (nauplii, old copepodites CIV–CV and adults) and seasonal variations in reproductive parameters of the cyclopoid copepod Oithona similis were investigated on the basis of the data 1999–2006 in Kola Bay, a large subarctic fjord in the Barents Sea. Population density of O. similis ranged from 110 to 9,630 ind m−3 and averaged 1,020 ± 336 ind m−3. The relative abundance of adults was high during winter (~60%). At the end of winter (mid-March), the population included a large percentage of later-stage copepodites (stage CIV 23% and stage CV 57%). There were two periods of mass spawning, in late June and September. Autumn and summer generations strongly differed in abundance, average prosome length (PL), clutch size (CS), egg diameter (D), egg production rates (EPR and SEPR) and female secondary production. Average PL decreased with increasing water temperature, while D and CS were strongly correlated with PL but unaffected by temperature. Annual average EPR and SEPR were 0.55 ± 0.18 eggs female−1 day−1 and 0.0011 ± 0.003 day−1, respectively. Female secondary production averaged 0.8 ± 0.3 μg C m−3 day−1 (range 0.001–3.58). There were positive relationships between abundance, EPR, SEPR, production and water temperatures. Reproductive parameters appeared to be controlled by hydrological factors and food conditions.

Feeding ecology and predation impact of the recently established amphipod, Themisto libellula, in the St. Lawrence marine system, Canada

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 373:53-70 (2008) - DOI: https://doi.org/10.3354/meps07716 Feeding ecology and predation impact of the recently established amphipod, Themisto libellula, in the St. Lawrence marine system, Canada Alexandra Marion1,2, Michel Harvey2,*, Denis Chabot3, Jean-Claude Brêthes1 1Institut des Sciences de la Mer (ISMER), Université du Québec à Rimouski (UQAR), 310 Allée des Ursulines, Rimouski, Québec G5L 3A1, Canada 2Direction des Sciences Océaniques et Environnementales, Ministère des Pêches et des Océans, Institut Maurice-Lamontagne, CP 1000, Mont-Joli, Québec G5H 3Z4, Canada 3Direction des Sciences Halieutique et de l’Aquaculture, Ministère des Pêches et des Océans, Institut Maurice-Lamontagne, CP 1000, Mont-Joli, Québec G5H 3Z4, Canada *Corresponding author. Email: Michel.Harvey@dfo-mpo.gc.ca ABSTRACT: Themisto libellula was virtually absent from the St. Lawrence marine system (SLMS) before 1990. Since then, it has become an abundant, full-time resident of this system. Hyperiid amphipods of the genus Themisto are principally carnivorous and represent an essential link in the trophic pathway from secondary production to higher trophic levels. Sampling of T. libellula was carried out in the lower St. Lawrence Estuary (LSLE) and the northwest Gulf of St. Lawrence (NWGSL) in the fall of 1998, 2003 and 2004 to study the feeding dynamics and predation impact of this species on mesozooplankton and macrozooplankton communities. Our results showed that T. libellula was an opportunistic predator with a circadian feeding cycle; activity was higher during the second part of the night and the sunrise period. Stomach content analyses showed that these amphipods consumed chiefly copepods, in particular, the copepodite stages CIV and CV of Calanus finmarchicus. Euphausiids, chaetognaths, amphipods and mysids constituted other important prey. Digestion time was estimated at 13 h. The daily ingestion rate of T. libellula was estimated using 2 approaches: (1) stomach fullness index and (2) mean number of prey removed per unit of time and converted to prey biomass using the stage-species dry masses of each prey item. We found that the daily ingestion rate of T. libellula ranged from 6.32 to 16.82% of body dry mass per day in both study areas (LSLE and NWGSL). Concerning predation impact, T. libellula consumed between 0.14 and 1.79% of the combined mesozooplankton and macrozooplankton standing stock per day and between 0.43 and 2.48% of the C. finmarchicus standing stock. Themisto libellula may thus exert a significant control on the mesozooplankton and macrozooplankton communities in the SLMS through direct predation. KEY WORDS: Hyperiid amphipod · Themisto libellula · Feeding ecology · Ingestion rate · Digestion time · Predation impact · Gulf of St. Lawrence Full text in pdf format PreviousNextCite this article as: Marion A, Harvey M, Chabot D, Brêthes JC (2008) Feeding ecology and predation impact of the recently established amphipod, Themisto libellula, in the St. Lawrence marine system, Canada. Mar Ecol Prog Ser 373:53-70. https://doi.org/10.3354/meps07716Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 373. Online publication date: December 23, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Seasonal changes in digestive enzyme (trypsin) activity of the copepods Pseudocalanus minutus (Calanoida) and Oithona similis (Cyclopoida) in the Arctic Kongsfjorden (Svalbard)

Seasonal activities of the digestive enzyme trypsin were measured between August 1998 and May 1999 to study different nutritional strategies of the two copepods Pseudocalanus minutus and Oithona similis in the Arctic Kongsfjorden (Svalbard) using a highly sensitive fluorescence technique. Stage-, depth- and season-specific characteristics of digestive activity were reflected in the trypsin activity. P. minutus females and stage V copepodids (C) had highest trypsin activities in spring during reproduction (197.5 and 145.7 nmol min−1 ng C−1, respectively). In summer stages CIII–V and in autumn stages CIV and V had high activities (80–116 nmol min−1 ng C−1) in the shallow layer ( 100 m) in summer and autumn were low in stages CIII and CIV (29–60 nmol min−1 ng C−1) and in winter in all stages in both layers (20–43 nmol min−1 ng C−1). Based on low trypsin activity, males most likely did not feed. In O. similis, the spring phytoplankton bloom did not significantly affect trypsin activity as compared to the other seasons. O. similis CV and females had high trypsin activities in summer in the deep stratum (304.5 nmol min−1 ng C−1), which was concomitant with reproductive processes and energy storage for overwintering. In autumn, stage CV and female O. similis had significantly higher activities than stage CIV (130–152 versus 78 nmol min−1 ng C−1), which is in accordance with still ongoing developmental and reproductive processes in CVs and females. Comparisons of both species revealed different depth-related responses emphasizing different nutritional preferences: the mainly herbivorous P. minutus is more actively feeding in the shallow layer, where primary production occurs, whereas the omnivorous O. similis is not as much restricted to a certain depth layer, when searching for food. P. minutus had lower levels of trypsin activity during all seasons. In contrast to P. minutus, higher enzyme activities in males of O. similis suggest that they continue to feed and survive after fertilization of females.

Body mass and lipid dynamics of Arctic and Antarctic deep-sea copepods (Calanoida, Paraeuchaeta): ontogenetic and seasonal trends

Ontogenetic and seasonal trends in body dry mass (DM) and total lipid content were studied in polar species of the predatory calanoid copepod genus Paraeuchaeta. Analyses included the Arctic representatives Paraeuchaeta glacialis, P. norvegica, P. barbata, and P. polaris as well as the Antarctic congener P. antarctica and one sample of P. cf. biloba. A total of 567 samples including 7007 individuals collected during four Antarctic and six Arctic research cruises was processed to provide seasonal coverage from spring to fall for both areas investigated, the Antarctic Weddell Sea and Arctic Fram Strait. All epipelagic species, i.e. P. glacialis, P. norvegica, and P. antarctica, showed a continuous increase in body DM from early copepodite stage CI onwards to stage CV. On average, body mass tripled with every moult. In females, body mass tripled again during the last moult to adulthood, whereas adult males, which have reduced mouthparts and do not feed at all, did not significantly increase their body mass after moulting from the CV stage. In contrast, early stages, i.e. nauplii to copepodids CII, of the bathypelagic species P. barbata remained at similar DMs. The deepest living species P. polaris was characterised by relatively large juvenile stages but small adult females, resulting in a rather small increase in body mass during ontogenetic development. Total lipid content decreased from maximum values of 60–70% of DM in eggs and early copepodite stages to <20–30% DM in stage CIII. Starting with stage CIV, lipids were again accumulated leading to high values of 40% to >50% DM in adult females. Distinct differences were detected with regard to seasonal trends of body mass and lipid content between epipelagic and bathypelagic species: Copepodids CIV, CV and adult females of epipelagic species exhibited highest body masses and lipid contents in fall, whereas for the deeper-living P. barbata maximum values occurred in spring. These discrepancies are discussed in relation to reproductive patterns and differences in abiotic and biotic environmental factors between the epipelagic and bathypelagic zones.

Relative production of Calanoides acutus (Copepoda: Calanoida) and Euphausia superba (Antarctic krill) at South Georgia, and its implications at wider scales

Antarctic krill are often described as the major species in Southern Ocean food webs, but there have been no direct site-specific comparisons between their production and that of copepods that dominate mesozooplankton biomass. Here, we compare biomass, growth and production of Euphausia superba (Antarctic krill) and the copepod Calanoides acutus at South Georgia, in the Atlantic sector of the Southern Ocean. Average acoustically derived krill biomass across the 5 study years was 2.6 g C m–2, 4 to 5 times that of Stages CIV and CV of C. acutus. Mean length of krill was 41 ± 4 mm, and the average growth rate was 0.10 mm d–1, giving an average mass-specific growth rate of 0.0084 d–1. This equated to a daily gross production of krill of 0.022 g C m–2 d–1. Gross production of Stages CIV and CV of C. acutus was similar, around 0.026 g C m–2 d–1. These stages of C. acutus represent about 25% of the total copepod biomass around South Georgia, so total copepod production here may exceed that of krill by a factor of 4 during the productive summer months. Biomass of copepods and krill in other parts of the Southern Ocean differ by similar orders of magnitude, whilst growth rates are likely to remain within the range measured in this study. Therefore, our finding has relevance outside the local South Georgia system. All of the krill production is likely to be rapidly consumed by higher predators within the surface layers, whilst it is estimated that around 17% of copepod production may be sequestered at depth during winter diapause.

Zooplankton population dynamics: measuring in situ growth and mortality rates using an Optical Plankton Counter

An application to assess in situ population dynamics rates is introduced based on the measurements of size-structured zooplankton population. This method differs from those based on species and stages by taking advantage of allometrically-scaled rates, automated sampling devices and net tows. For the first test of this method, we conducted 3 surveys in a nearly enclosed sub-Arctic fjord in northern Norway, from early May to mid June 1998, the period of the spring bloom. Bio-volume spectra in the size range between 10 -1 and 10 3 mm 3 individual body volume, from small mesozooplankton to euphausiids, were derived from the Optical Plankton Counter measurements. From 3 bio-volume spectra measured on Days 1, 21, and 35, we calculated in situ individual growth and mortality rates using the theory based on biomass spectra. The net samples corroborate the basic fact that Calanus finmarchicus and euphausiids absolutely dominate in 2 different size ranges. In this spring bloom period, the first generation of Calanus finmarchicus at copepodite stage CIV dominated the size range between 0.3 and 0.58 mm 3 , and had a growth rate within 0.02 and 0.17 d -1 . C. finmarchicus at copepodite stage CV and euphausiid larva dominated the size range from 0.58 to 4 mm 3 . Their growth rates increased from 0.2 d -1 at the size of 0.71 mm 3 to the peak of 0.59 d -1 at the size of 1.9 mm 3 , and then decreased to 0.22 d -1 at the size of 4 mm 3 . In the size range above 4 mm 3 , euphausiid juveniles and adults were absolutely dominant. The growth rate estimated from the bio-volume spectra varied between 0.11 and 0.19 d -1 at the size range from 4 to 400 mm 3 . In the size range between 0.3 and 0.58 mm 3 , the mortality rate varied between -0.03 and -0.05 d -1 . The mortality rate reached -0.38 d -1 in the range from 0.71 to 10 mm 3 . In the size range between 10 and 40 mm 3 the rate decreased from -0.31 to -0.11 d -1 , and in the size range above 40 mm 3 the rate increased to -0.27 d -1 . The comparison with estimates from net tow samples and literature data indicates that the biomass spectrum theory affords a valuable method for estimating in situ individual growth and population mortality rates by providing high resolution in size classes and a greater degree in accuracy. It is also less labor-intensive and time-consuming than other methods. A test of this method in an advective environment needs further study.

Growth and development of Calanus helgolandicus reared in the laboratory

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 238:125-138 (2002) - doi:10.3354/meps238125 Growth and development of Calanus helgolandicus reared in the laboratory Catherine Rey-Rassat1,*, Xabier Irigoien2,**, Roger Harris2, Robert Head2, François Carlotti3 1Université Pierre et Marie Curie (Paris VI), Station Zoologique, ESA 7076, CNRS/INSU, BP 28, 06230 Villefranche-sur-mer, France 2Plymouth Marine Laboratory, Prospect Place, Plymouth PL1 3DH, United Kingdom 3Laboratoire d¹Océanographie Biologique, CNRS, Université Bordeaux 1, UMR 5805, 2 rue du Professeur Jolyet, 33120 Arcachon, France *E-mail: catherinerey@aol.com or rey@obs-vlfr.fr **Present address: AZTI, Herrera Kaia portualdea z/g, 20110 Pasaia (Gipuzkoa), Spain ABSTRACT: Two Calanus helgolandicus cohorts were reared under laboratory conditions (150 l tanks) at 15°C with the dinoflagellate Prorocentrum micans as food, at high (278 µgC l-1, Cohort H) and low concentrations (77.5 µgC l-1, Cohort L), respectively. The study focused on the copepodite stages and for each stage, development time, total and structural growth rates, ingestion rate and gross growth efficiency were estimated. The growth rate of each stage was estimated using 2 methods, the classical one (Method I) and a new method (Method II), which considers the initial weight of the 2 successive stages rather than their mean weights. The initial weight corresponds to that estimated at the day (tini) when 50% of the individuals in the cohort entered the stage. Using the new method, the increase in lipid deposition through copepodite stages (increase of the C:N ratio from 4.3 up to 4.7 and 6.9 in Cohorts L and H, respectively) and the effect of food concentration on the growth rate from early CI to CV are clearly shown in the values of the growth rates (the CV growth rate in terms of carbon was 0.063 d-1 in Cohort L and 0.115 d-1 in Cohort H). Both of these features are not apparent for the key stage CV when using the classical method (0.041 d-1 in Cohort L and 0.035 d-1 in Cohort H). Female weight increase after moulting, by up to ~60% in Cohort L and ~40% in Cohort H, is also demonstrated by the new method. Using Method II on field data is however limited to some specific cases in which the cohort development is synchronous; this might be particularly the case for some large copepods. Food supply influences the development time of stages CIV and CV, and differences are also found in the development time of each stage indicating a non-isochronal development. Food concentration also influences the gross growth efficiency (GGE) of all copepodite stages, with significantly higher GGE at the low food concentration. GGE varies with stage, mostly at low food concentration (for GGE in terms of carbon: 0.135 to 0.502 in Cohort L and 0.147 to 0.308 in Cohort H). Finally, we propose an index that can be used to indicate the position of an individual within its stage. KEY WORDS: Calanus helgolandicus · Copepodite · Growth rate · Development · Ingestion · Efficiency · Food concentration · Method Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 238. Online publication date: August 08, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Distribution and feeding of the carnivorous copepod Paraeuchaeta norvegica in habitats of shallow prey assemblages and midnight sun

Paraeuchaeta norvegica was found to be widely distributed in the Norwegian Sea. They were least abundant in north-western areas, but otherwise no clear horizontal patterns appeared with respect to latitude, longitude or water mass. Females and males had similar vertical distributions. The highest concentrations of adults occurred at 400–500 m depth; they largely avoided the upper 50–100 m, even at night. Stages CIV and CV lived shallower in the water column than the adults, with the highest concentration between 100 and 300 m. Stages CII–CIII were most abundant at 50–100 m, while CI was distributed slightly deeper (maxima at 100–200 m). Potential prey were most abundant in the upper 100 m; i.e. shallower than P. norvegica. Numbers of fecal pellets produced by freshly collected adult females were relatively low (estimated at 0.7 pellets per individual on average for the entire sea), with maximal numbers for individuals captured in shallow waters. This suggests food limitation during summer, when food is concentrated in upper waters, and short and light nights limit nocturnal access to the shallow food resources. Pellets mainly contained copepod remains.