Copepodite Stages Research Articles

Effects of starvation on intermolt development in Calanus finmarchicus copepodites: a comparison between theoretical models and field studies

Campbell et al . (Deep Sea Research II, 48 (2001) 531) have shown that there was a localized starvation event affecting Calanus finmarchicus on the southern flank of Georges Bank in April 1997. Growth and molting rates of this dominant copepod were reduced. We have used the morphology of tooth development in field-collected samples to show that this starvation affected animals living continuously in the field, as well as those in Campbell et al .'s experimental tanks. Assuming a point of reserve saturation (PRS) response of Calanus to food limitation, and correspondence between PRS and advance from the postmolt jaw facies, the proportion of individuals with postmolt jaws should increase in all copepodite stages under starvation. Individuals that have developed past PRS should molt to the next stage, acquiring postmolt facies. Thus, the fraction of postmolt jaws should increase, while the fraction of jaws in later phases should decrease. This was observed for a drifter-marked station over five days. Numerical simulations of jaw phase distributions expected under full nutrition, and both total and patchy starvation were generated from individual-based models of development. Proportions of copepodites in postmolt phase do not increase with full nutrition. A simulation of a total starvation event showed a marked increase in postmolts during food limitation, but the increase was more extreme than the field data. A modification of the starvation simulation, representing patchy feeding conditions, matched the level of increase of postmolt individuals in all stages that was observed in the field samples.

Evidence for food limitation of Calanus finmarchicus production rates on the southern flank of Georges Bank during April 1997

We present here strong evidence that production rates of the copepod Calanus finmarchicus were limited by the lack of food on the southern flank of Georges Bank during April 1997. Indices of production include size, condition, RNA/DNA ratio, and the rates of molting, growth, and egg production of C. finmarchicus. Observations were made at a site in well-mixed water north of the tidal mixing front in a region of higher chlorophyll; a drifter site, occupied for 7 days, which was located in stratified water south of the front where chlorophyll concentrations were very low; and at several stations along an initial survey grid in the same region. At the drifter site, measurements of size, condition, molting rate, and egg production rate declined over time, and growth rates were enhanced when ambient water was enriched with mixed phytoplankton cultures. RNA/DNA ratios, molting rates, and growth rates were much lower than laboratory measurements at high food at the same temperatures, and egg production rates were lower than predicted under non-limiting conditions. The effects of food limitation were more severe in naupliar and early copepodite stages. In comparison, in the higher chlorophyll region, younger copepodites were larger and in better condition, and RNA/DNA ratios and egg production rates were higher and near maximum predicted values. We evaluate these results with respect to the question of food limitation on the bank and explore the implications for understanding variability in C. finmarchicus abundance and its potential role in the trophodynamics of fish larvae.

Rearing cohorts of Calanus finmarchicus (Gunnerus) in mesocosms

Cohort development and nutritional conditions of Calanus finmarchicus were studied in experimental seawater mesocosms in a Norwegian fjord. Artificially added cohorts developed from early naupliar stages to copepodite stage IV in 41-43 days at ambient temperature increasing from 4.3 to 6.8°C. A natural stock of C. finmarchicus, initially dominated by early copepodite stages, developed to CV, males and females. Total storage lipid increased exponentially until CV. Individual body carbon weight increased sigmoidally with age. Relationship of body carbon weight (W, μg) to prosome length (L, μm) determined for copepodites and adults (W=2.6×10 −10 L 3.45 , r 2 =0.92) showed a higher weight than from in situ studies. This investigation demonstrates (i) that cohorts of C. finmarchicus can be reared successfully in mesocosms, (ii) a good nutritional state of copepods in terms of body carbon content and lipid reserves, and (iii) that part of the final CV moulted to both males and females.

Distribution of the copepodite stages of Calanus finmarchicus from Lofoten to the Barents Sea in July 1989

The zooplankton biomass in the Barents Sea can vary by an order of magnitude from year to year. One reason for the large change is the varying transport of Calanus finmarchicus from the Norwegian Sea into the Barents Sea. How much of the population is stationary in the Barents Sea and how much is transported from the Norwegian Sea is unknown. Zooplankton samples were collected along the coast of North Norway from Lofoten and into the Barents Sea during the early juvenile fish survey in July 1989. The samples were evaluated with special emphasis on Calanus finmarchicus, which were sorted to copepodite stage. The probable drift route of the zooplankton and its origin were determined by examining the distribution of the different stages and the currents. The different stages were in very distinct bands, with the youngest stages in the south and the older stages in bands stretching east-west, with stage CV farthest north and east. When these patterns are compared with currents in 1989, the results support the theory that a large proportion of the C. finmarchicus stock is transported from the Norwegian Sea into the Barents Sea.

Escape behavior of Acartia hudsonica copepods during interactions with scyphomedusae

Calanoid copepods possess remarkable abilities to detect and escape from hydrodynamic disturbances, such as those created by approaching predators. At the same time, a number of studies in coastal ecosystems have suggested that gelatinous predators, including medusae in the Class Scyphozoa, exert top-down control on copepod populations. Although prey escape behavior plays a critical role in predation models, we have relatively little empirical data on how copepods respond to encounters with scyphomedusae. In this study, I used video to quantify encounter rates and escape behaviors of the copepod Acartia hudsonica during interactions with two scyphomedusae, Aurelia aurita and Cyanea sp., in two flow regimes. Escapes were complex, variable and effective. Fewer than 1% of encounters resulted in ingestion. Typically, A.hudsonica avoided contact by responding when predators remained several body lengths (4 to 10 mm) distant and stringing together many escape jumps at submaximum velocities (33 to 59 mm s -1 ). In addition, copepodite stages behaved passively-or failed to respond-following encounters with medusae more often than did adults. Because escape behavior exhibited by A.hudsonica was so variable, it is unlikely that medusae capture copepods using a single, quantifiable mechanism. A range of responses within populations and individuals may be the best strategy for zooplankton faced with strong predation pressure from a variety of predators.

A review of the biology and ecology of Calanus agulhensis off South Africa

Calanus agulhensis is the dominant large copepod on South Africa's Agulhas Bank, and is an important food item for pelagic fish. This paper reviews current knowledge and understanding of its biology and ecology and includes comparisons with other Calanus species. Its distribution is influenced by the prevailing hydrography, being advected from the eastern to the western Agulhas Bank and then north along the edge of the west coast shelf. Highest biomass of C. agulhensis is on the central Agulhas Bank in the vicinity of a cool ridge of upwelled water that is thought to enhance local retention. Daily vertical migration on the Agulhas Bank is linked to food concentration, with a strong correlation between the extent of migration of large stages (C4-female) and food abundance in the chlorophyll-rich layer. A diel feeding rhythm has been observed, independent of whether or not animals are migrating vertically. Females offered natural assemblages show a preference for the larger particles of the dominant size classes. Development time from egg to adult (20.3 d at 15.5°C) is fast compared with other Calanus species. The long N3 stage duration suggests that it is the first feeding stage. Isochronal growth is approximated, but the equiproportional rule is not adhered to. In the field, growth rate is influenced more by food than by temperature, particularly larger stages that are more frequently food-limited. This is probably because the small phytoplankton cells that dominate at warm temperatures are generally at low concentrations (<2 mg chlorophyll a m−3), insufficient for fast growth of large stages. Egg production following short periods (1–3 d) of starvation returns quickly to normal on the reintroduction of food, an adaptation that may be beneficial in the relatively stable food environment of the Agulhas Bank. Following long periods (9 d) without food, however, many females are unable to regain normal levels of egg production. At present, there is no information on the extent of omnivory in C. agulhensis, and little on the ecology of the naupliar and young copepodite stages. These may be fruitful areas for future research.

Comparative analysis of Calanus finmarchicus demography at locations around the Northeast Atlantic

Standardized time-series sampling was carried out throughout 1997 at seven locations around the Northeast Atlantic to investigate regional variations in the seasonal demography of Calanus finmarchicus. Sites ranged from an inshore location in the North Sea, where C. finmarchicus formed only a small component of the zooplankton ( 2000 mgC m-2 during spring and summer). The internal consistency of the demographic time-series from each site was investigated by three partial models of life-cycle processes. In general, the demography of late copepodites could be accounted for by a relatively simple forecast model of stage development and diapause. However, there was a large discrepancy between nowcast estimates of egg production based on female abundance, temperature, and chlorophyll, and hindcast simulations of the egg production required to account for the observed abundance of early copepodite stages. The results point to a gap in our understanding of seasonal variations in rates of egg production and/or survival of nauplii. Overall, the population sampled at Weathership M appeared to be reasonably self-contained, but all other sites were reliant on invasion of overwintered stock in spring. At least two generations were observed at all but one site, but the extent to which these were generated by discrete bursts of egg production varied between sites and seemed to be partly dependent on the proximity to an overwintering location.

Vertical distribution, life cycle, and developmental characteristics of the mesopelagic calanoid copepod Gaidius variabilis (Aetideidae) in the Oyashio region, western North Pacific Ocean

Vertical distribution, life cycle, and developmental characteristics of the mesopelagic copepod Gaidius variabilis Brodsky in the Oyashio region were investigated by combining analyses of field copepodite populations with laboratory-rearing data of egg hatching and naupliar development. Field samplings from five discrete depths between the surface and ≤2000 m were made approximately every month for 1 year. Most populations of G. variabilis occurred between 600 and 1000 m depth. A modest degree of reversed diel vertical migration behavior and some stage-specific depth-distribution patterns were noted. All copepodite stages were observed throughout the year, suggesting a year-round spawning of G. variabilis. From a prominent abundance peak of Copepodite Stage 1 (C1) seen in June to August, together with development times of eggs and nauplii obtained in laboratory-rearing experiments, the major spawning season was extrapolated to be April to June, the phytoplankton bloom season. Tracing the peak abundance of each copepodite stage (distinguishing males and females for C4 to C6), the generation times of males and females were deduced as 2 and 1 year, respectively. All between-stage increments in terms of wet-, dry-, and ash-free dry weights were greatest in C3/C4, and least in C5/C6 for both males and females. The increments in C3/C4 and C4/C5 were greater for males than for females, reflecting a longer stage duration of the males. These weights did not increase in C5/C6 males, possibly because feeding ceased in C6 males. These results for G. variabilis are compared with those for some mesopelagic copepods previously reported from other regions.

Population growth capacities and regulatory factors in monospecific cultures of the cladocerans Moina micrura and Diaphanosoma excisum and the copepod Thermocyclops decipiens from Côte d’Ivoire (West Africa)

The cladocerans Moina micrura and Diaphanosoma excisum and the copepod Thermocyclops decipiens were studied in microcosms (0.8 m 3) under semi-controlled experimental conditions at 25–29 °C for 32 days, by daily sampling after an initial monospecific inoculation. For each species, the time series began with an exponential population growth phase. M. micrura showed a higher daily population growth rate (mean = 1.19) than D. excisum (0.78) and T. decipiens (0.45). The growth phase of M. micrura coincided with bacterial and phytoplanktonic peaks while the growth phase of the two other species followed these peaks. After this phase, M. micrura quickly disappeared (day 10), while D. excisum biomass decreased but showed a second increase, followed by a stabilization sequence. T. decipiens biomass had a slower increase and stabilized after day 17. The passage to sexual reproduction in relation to crowding was the main regulating factor for M. micrura, whereas food limitation was important for D. excisum. For T. decipiens, population growth was limited by decreased recruitment to copepodite stages which could have resulted from cannibalism exerted by older stages.

Response of life history traits to food conditions in a cyclopoid copepod from an oligotrophic environment

The Cyclops sp. responses of life history traits (growth, development, and reproduction) to food conditions from oligotrophic Lake Toya were analyzed by rearing animals individually under four food regimes:three densities of the alga Cryptomonas tetrapyrenoidosa and nauplii of the calanoid copepod Eurytemora affinis as prey in an algal suspension. Cyclops sp. grew successfully from newborn nauplii to adults when algal density was ≥4 × 103 cells ml‐1 . Development time was shorter and body length larger in the high‐density (H) treatment (4 × 104 cells ml‐1 ) than in medium‐density (M) treatment (4 × 103 cells ml−1) until the early copepodite stages. In late copepodite stages, females tended to grow more slowly but tended to be larger in the M treatment than in the H treatment. However, stage‐specific growth rates were similar among treatments during development, suggesting a trade‐off between body size and development time. Although the egg production rate was higher in the M treatment than in the H treatment, it depended on female body size regardless of the food regime. Furthermore, the weight‐specific egg production rate was the same among treatments, indicating egg production was not affected by the algal concentrations tested. Addition of copepod prey influenced neither postembryonic development time nor body size, and egg production rates were comparable to those reared with an algal diet. These results reveal that even older copepodites and adults, which are generally thought to be predacious, do not necessarily require animal prey for growth and reproduction, and that Cyclops sp. can complete its life cycle on an algal diet alone. For female Cyclops sp., reduction of algal density resulted in slow development and large body size, which might be an adaptation to the oligotrophic environment, the original habitat of the copepod.

Food web interactions in a Calanus finmarchicus dominated pelagic ecosystem--a mesocosm study

The significance of nauplii versus copepodite stage V of Calanus finmarchicus grazing and their effects on the structure of the food web were investigated during two sampling periods of 7–8 days in March and April in experimental mesocosms held in a Norwegian fjord over a 2 month period. The mesocosms were manipulated by the addition of two different levels of inorganic nutrients (control versus enriched). During the ‘naupliar’ period in March, the phytoplankton was characterized by a diatom bloom while during the ‘copepodite’ period in April, it was in a post-bloom phase characterized by small-celled species, mainly Phaeocystis pouchetii. Phytoplankton, bacterial and protozooan biomass and production rates were measured in addition to copepod biomass. Copepod grazing was estimated by three different methods: (i) gut fluorescence; (ii) chlorophyll clearance from the water; and (iii) growth method measured as body carbon increase. The two latter methods gave similar results for nauplii, but all three gave different results for the copepodites. Independent somatic growth, based on changes in abundance and individual carbon content, and grazing estimates revealed an overall growth efficiency of 0.66 ± 0.20 (mean ± S.E.) for copepodites. Empirical carbon flow models were constructed, which indicated that the nauplii could not control either phytoplankton or protozoan growth in either the control or in the enriched system. Ignoring recycling and sedimentation, the fate of the primary production for the nauplii-dominated community was to be grazed by a diverse and abundant protozooplankton community. In the copepodite-dominated community, the copepods grazed >100% of the daily primary production, and also grazed heavily on a protozooplankton community of low biomass and diversity and presumably on detritus. The fate of the primary production in the two different copepod scenarios followed predicted routes for ‘low meso-zooplankton’ and for ‘high meso-zooplankton’ biomass systems, as suggested by Wassmann (Wassmann, 1998).

Relationship between specific dynamic action and protein deposition in calanoid copepods.

The link between specific dynamic action (SDA) and protein deposition was investigated in copepodites stage V of two calanoid copepod species, the neritic Acartia tonsa and the oceanic Calanus finmarchicus. This was done by measuring respiration before, during, and after a specific feeding period and measuring the incorporation of carbon into proteins. These were also measured on individuals incubated with cycloheximide, an antibiotic that inhibits protein synthesis. The cycloheximide treatment significantly diminished the magnitude of SDA in both A. tonsa and C. finmarchicus, and inhibited carbon incorporation into protein in both species. This provides evidence that the rate at which protein deposition takes place greatly affects the magnitude of SDA. The specific respiration rates of both starving and feeding copepods were generally higher in A. tonsa than in C. finmarchicus. This influenced SDA, the magnitude of SDA normalised to an 8 h feeding period being threefold higher in A. tonsa (78.7+/-25.7 nlO(2) µgC(-1)) than in C. finmarchicus (27.5+/-11.6 nlO(2) µgC(-1)). This difference may arise due to differences in energy allocation in the organisms of the copepodite V stage of the two species. In this stage C. finmarchicus deposits large quantities of storage lipids, predominately wax esters, whereas A. tonsa deposits proteins during somatic growth.

Vertical distribution, life cycle and body allometry of two oceanic calanoid copepods (Pleuromamma scutullata and Heterorhabdus tanneri) in the Oyashio region, western North Pacific Ocean

Diel and seasonal vertical distribution, life cycle and body allometry of Pleuromamma scutullata and Heterorhabdus tanneri were investigated in the Oyashio region during September 1996 through October 1997. Monthly samples were collected with 0.1 mm mesh closing nets towed through five discrete depths between the surface and  2000 m. Copepodite stages 1 through 6 of P.scutullata and 3 through 6 of H.tanneri were collected effectively with the nets. Day-night samplings during December 1996, April and October 1997 revealed both species ascend at night. Seasonal differences in the vertical distribution patterns of both copepods were insignificant, and P.scutullata was distrib- uted at a much shallower depth (250-500 m) than H.tanneri (600-850 m). By tracing the sequential changes in abundance peaks of each copepodite stage, both species are considered to produce one generation per year. The main reproduction season was estimated to occur in spring for P.scutullata and in winter for H.tanneri. The relationships between prosome length and wet weight, dry weight, and ash-free dry weight indicated that the increase in weight per molt was much greater in H.tanneri than in P.scutullata. These dissimilar features are discussed in relation to the dissimilar food habits of these two species and the production cycle of food organisms in the Oyashio region.

Effect of UVB radiation on the survival, feeding, and egg production of the brackish-water copepod, Sinocalanus tenellus, with notes on photoreactivation

We examined the effects of UVB radiation on hatching success of eggs, survival of various naupliar and copepodite stages, and feeding and egg production of adult females of the brackish-water copepod, Sinocalanus tenellus, by exposure to varying doses of UVB irradiance in the laboratory. Artificial UVB radiation resulted in an increased mortality of eggs, nauplii and copepodites with increasing UVB doses. UVB induced damage was stage-specific with eggs being most susceptible (LD50= 4.1 kJ m−2 ) and adult females being least susceptible (LD50= 16.7 kJ m−2). Effects on feeding and egg production of adult females were significantly evident at UVB doses higher than 11.0 kJ m−2 and 7.0 kJ m−2, respectively. We also examined the photorepair response of eggs and various developmental stages in simultaneous irradiation of UVB and enhanced PAR. With enhanced PAR there was a considerable recovery against UVB damage, being higher for younger animals than older ones. In nature, however, solar UVB radiation may rarely cause appreciable damage to S. tenellus population due to optically high attenuation properties of their habitat waters.

Temporal variation in body composition and lipid storage of the overwintering, subarctic copepod Neocalanus plumchrus in the Strait of Georgia, British Columbia (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 192:239-247 (2000) - doi:10.3354/meps192239 Temporal variation in body composition and lipid storage of the overwintering, subarctic copepod Neocalanus plumchrus in the Strait of Georgia, British Columbia (Canada) Melissa Evanson1,*, Elizabeth A. Bornhold2, Robert H. Goldblatt3, Paul J. Harrison3, Alan G. Lewis3 1Department of Zoology, University of Guelph, Guelph, Ontario N1G 2W1, Canada 2Ocean Science and Productivity, Institute of Ocean Sciences, 9860 West Saanich Rd, Sidney, British Columbia V8L 4B2, Canada 3Department of Earth and Ocean Sciences (Oceanography), University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada *E-mail: mevanson@uoguelph.ca ABSTRACT: Neocalanus plumchrus (Marukawa) was sampled between October 1996 and August 1997 in the upper 400 m of the water column in Strait of Georgia (49° 15' N, 123° 45' W), a large, partly enclosed basin in British Columbia, Canada. The overwintering vertical stage distribution of N. plumchrus is described together with the temporal variations in total body length, dry weight, lipid and body composition in copepodite stage V (CV) and adult females. Adult males and females were found at depths of less than 200 m from January to March. Regressions of total body length to total dry weight showed significant correlations for CVs and females. Carbon and nitrogen isotopic analysis (δ15N and δ13C) indicated no temporal increase, suggesting a lack of feeding in CVs (October to December) and females (January to March) at depth and a dependency on stored lipid reserves accumulated during times of high primary production in the euphotic zone. Total lipid content per individual copepod showed significant decreases from 0.5 to 0.2 mg during the time of adult female gonadal development between January and February. A decrease in total dry mass per copepod from 0.9 to 0.4 mg also occurred during this time period. Lipid composition showed preferential retention of long-chained fatty acids until the onset of egg release in March. Significant decreases in carbon and nitrogen from January to February and, to a lesser extent, between February and March were observed, corresponding to periods of gonad maturation and egg release, respectively. Significant increase in nitrogen content suggests the possibility of bacterial ingestion by late moulting CVs. The significant decrease in C:N ratio, from 8.7 to 4.1, suggests a depletion of lipid reserves and resultant reliance on proteins as an energy source for egg release. Variations in organic content verify that the CVs remain in a state of dormancy in which minimal lipid reserves are depleted, while the onset of maturation and reproduction is the major energy consumer. KEY WORDS: Neocalanus plumchrus · Lipid · Body composition · Vertical distribution · Temporal variation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 192. Publication date: January 31, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Short-term and long-term effects of the toxic dinoflagellate Alexandrium minutum on the copepod Acartia clausi

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 203:161-169 (2000) - doi:10.3354/meps203161 Short-term and long-term effects of the toxic dinoflagellate Alexandrium minutum on the copepod Acartia clausi M. Frangópulos1,*, C. Guisande1, I. Maneiro1, I. Riveiro1, J. Franco2 1Facultad de Ciencias del Mar, Universidad de Vigo, Apartado 874, 36200 Vigo, Spain 2Instituto de Investigaciones Marinas (CSIC), Eduardo Cabello 6, 36208 Vigo, Spain *E-mail: mfr@uvigo.es ABSTRACT: Several experiments were performed to determine the effects of cell toxin concentration, composition and toxicity of Alexandrium minutum on ingestion rate, egg production, hatching success and naupliar fitness of the copepod Acartia clausi. A combination of A. minutum and non-toxic algae (Prorocentrum micans, Tetraselmis suecica and Isochrysis galbana) was used as food. Copepods ingested a higher amount of A. minutum cells as the concentration of these toxic dinoflagellates increased, and also in response to decreasing total food concentration available for the copepods. A positive relationship was obtained between A. minutum cells ingested by copepods and total toxin concentration per copepod. Hatching success and naupliar production were lower when copepods ingested a higher amount of toxic dinoflagellates. This negative effect could has been due to the accumulated toxins in the egg and copepod tissues, and was higher when A. minutum had a higher cell concentration of GTX1. Finally, the results obtained from nauplii incubated with T. suecica and I. galbana showed that nauplii hatched from females fed non-toxic food (T. suecica and I. galbana) reached copepodite stage earlier than those nauplii hatched from females fed with a combined of toxic (A. minutum) and non-toxic (T. suecica and I. galbana) food. KEY WORDS: Dinoflagellate · Copepod · Toxins · PSP · Reproduction Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 203. Online publication date: September 18, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.

Investigations on the ecology of Calanus spp. in the Labrador Sea. I. Relationship between the phytoplankton bloom and reproduction and development of Calanus finmarchicus in spring

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 193:53-73 (2000) - doi:10.3354/meps193053 Investigations on the ecology of Calanus spp. in the Labrador Sea. I. Relationship between the phytoplankton bloom and reproduction and development of Calanus finmarchicus in spring E. J. H. Head*, L. R. Harris, R. W. Campbell** Department of Fisheries and Oceans, Ocean Sciences Division, Bedford Institute of Oceanograhy, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada *E-mail: heade@mar.dfo-mpo.gc.ca **Present address: Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada ABSTRACT: During mid-May-early June 1997 observations of hydrography, phytoplankton and nitrate concentrations, and abundance and stage distribution of Calanus finmarchicus populations were made in the Labrador Sea and south of Greenland. Egg production rates were also measured for isolated C. finmarchicus females. Surface nitrate and integrated phytoplankton concentrations indicated that, in the deep water, the phytoplankton bloom had ended in the north and east, was in progress in the north central Labrador Sea and near the basin margins, and had not yet become established in an area stretching from the central Labrador Sea to the south of Greenland. C. finmarchicus egg production rates and stage distributions at stations in the 3 areas designated as early, mid- and late/post-bloom zones, suggested that development rates of the overwintered G0 generation into mature adults (females and males) were probably low before the bloom, but accelerated during its development. Individual and areal rates of egg production were highest in the early bloom zone, whereas nauplii were more abundant in the bloom and late/post-bloom zones. Differences in naupliar abundance may have been related to food limitation, or predation. Following development through to the young copepodite stages (CI-III), which were most abundant in the late/post-bloom zone, morality rates were apparently lower and growth rates less dependent on high phytoplankton concentrations and perhaps more dependent on temperature. In the Labrador Sea, where the annual growth season is relatively short and C. finmarchicus produces only 1 generation per year, the timing of the spring bloom may have a significant impact on recruitment of the new year's generation. In areas where the bloom is early and intense, maturation of the overwintered adults will be rapid and egg-laying will occur when phytoplankton concentrations are high. Subsequent survival success of eggs through to later stages will also probably be relatively high and individuals from the new year's generation will have ample time to reach stages capable of overwintering. By contrast, if the bloom is late or of low intensity, adult maturation will be delayed and egg-laying may occur when phytoplankton concentrations are low. Under these conditions relatively few eggs may survive and individuals that do survive will have a shorter period in which to attain stages which can overwinter. KEY WORDS: Calanus finmarchicus · Reproduction · Spring bloom · Labrador Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 193. Publication date: February 28, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Life histories of Neocalanus flemingeri and Neocalanus plumchrus (Calanoida: Copepoda) in the western subarctic Pacific

Life cycles of large suspension-feeding copepods were investigated in the western subarctic gyre (Oyashio area). Two populations were recognized in Neocalanus flemingeri by body size, life cycle and timing of ontogenetic migration. Small forms (same size as original description; adult female ca. 3.6 mm in prosome length) have a 1-year life cycle and occurred at the surface between December and June. At least some individuals of large forms (adult female ca. 4.5 mm in prosome length) have a biennial life cycle with winter dormancy as Stage 4 copopodites (C4) and adult females. The young copepodites of the large form occur in the surface water later than the small forms, then grow to C4 with full deposition of lipid. The following year, the C4 individuals start grazing in January, and sink to deep layers at the same time as the small forms. The life cycle of Neocalanus plumchrus was identical to the original description made for the Alaskan gyre population, although the recruitment to the surface layer during copepodite stages occurred 2 weeks to a month later than in other areas of the subarctic Pacific. Temporal partitioning of surface habitat utilization between N. plumchrus and the small form of N. flemingeri was clearly established, but overlap was observed between N. plumchrus and the large form of N. flemingeri.

Factors affecting abundance of Triaenophorus infection in Cyclops strenuus, and parasite-induced changes in host fitness

Factors affecting the abundance of Triaenophorus crassus and Triaenophorus nodulosus procercoids in their copepod first intermediate host, Cyclops strenuus, and effects of infection on feeding behaviour, reproduction and survival of the host were studied experimentally. When exposed to the same number of coracidia, copepods harboured considerably less procercoids in the trials where ciliates or Artemia salina nauplii were given as alternative food items. The prevalence of infection was higher in adult copepods as compared with copepodite stage IV and stage V, and higher in stage V than in stage IV. The prevalences in adult females and males did not differ significantly from each other. The frequency of females carrying egg sacs was lower among infected than among exposed uninfected and unexposed copepods. The rate of feeding on Artemia nauplii remained at the same level in uninfected copepods, but decreased strongly in infected copepods during 7 days p.i. The survival of unexposed, exposed uninfected and infected copepods did not differ significantly from each other for the first 11 days post-exposure, but the mortality of infected copepods increased significantly after 3 weeks post-exposure. However, the rate of development and mortality of copepods might have been affected by the apparently arrested development of stage IV copepodites found in the experiment. Some of the contradictions between these results and earlier observations are suggested to be caused by the differences in the duration of exposure, intensity of infection and duration of observation post-exposure in the present study as compared with other experiments.

The reproductive cycle and life history of the Arctic copepod Calanus glacialis in the White Sea

Seasonal variations in the gonad development and sex ratio of copepodite stage V (CV) and adults were examined from February to November in order to understand the reproductive cycle and the life history of Calanus glacialis in the White Sea. Gonad maturation, sexual differentiation and moulting to adults take place during the 2nd year of development. Energy accumulation takes place in the spring and summer of the 2nd year. The following autumn/winter is the major period of CV maturation, which occurs independent of food supply. Maturation of males precedes that of females by 2–3 months. The maximum proportions of CV and adult males are found in the population in October and November. The onset of female maturation is observed in February and March, ca. 2 months prior to the spring phytoplankton bloom. Reproduction takes place between April and June. Its termination in the second half of June coincides with the warming of the surface water layer where egg laying takes place. Variations in the gonad morphology throughout the year suggest long life spans and iteroparity of females of C. glacialis in the White Sea. Many of them survive for several months after reproduction and are able to overwinter again. Therefore, females with different life histories co-occur in the population in winter: “young” females recently moulted from the overwintering CVs, and “old” females which have spawned at least once in their life, after which they return to overwintering conditions. In contrast, males have shorter life spans of 3–4 months resulting in a sex ratio skewed toward females at all seasons.