The mortality of the planktonic copepod <Emphasis Type="Italic">Oithona similis</Emphasis> Claus, 1866 (Copepoda: Cyclopoida) in the Barents and White Seas

The mortality rates of the copepodite IV-copepodite V and copepodite V-adult individuals pairs in the populations of one of the most common species of planktonic copepod, Oithona similis, were estimated for the first time in the Barents and White seas. The average parameters were 0.060 and 0.082/day, respectively, in the Barents Sea and 0.166 and 0.120/day in the White Sea. In the Barents Sea, the mortality rates of O. similis significantly increased with an increase in water temperature and in the White Sea a significant decrease occurred with an increase in salinity. It was concluded that the mortality rate of this species is determined first by abiotic factors and that biotic factors are of secondary significance.     

Postembryonic development of Drescheriella glacialis Dahms & Dieckmann (Copepoda,Harpacticoida) reared in the laboratory

Summary All 6 naupliar and 5 copepodite stages of Drescheriella glacialis, a tisbid from Antarctic fast ice, are described. A key for the identification of the naupliar stages is given. Sexual dimorphism makes its first appearance in the copepodid IV. The setae configuration of the exopod of the second antenna in copepodid I is considered to be an ancestral state, and subsequent ontogenetic reductions are proposed to be apomorphic processes.     

Patterns in stage duration and development among marine and freshwater calanoid and cyclopoid copepods: a review of rules,physiological constraints,and evolutionary significance

Studies of development time of marine and freshwater copepods have taken separate tracks. Most studies on marine copepods report development time of each individual development stage, whereas studies on freshwater copepods report only development time, from egg to nauplius and nauplius to adult. This bias allows comparison of total development time but prevents detailed comparisons of patterns in stage-specific developmental schedules. With respect to egg to adult development time, three general relationships are known: developmental rates are dependent upon temperature and food concentration but independent of terminal body size; freshwater calanoids develop significantly slower than marine calanoids; freshwater cyclopoids develop at the same rate as marine calanoids. Two rules describe stage-specific developmental rates: the equiproportional rule and the isochronal rule. The first rule states that the duration of a given life history stage is a constant proportion of the embryonic development time; the second rule states that the time spent in each stage is the same for all stages. This review focuses on the second rule. From the 80+ published studies of copepod stage-specific developmental times, no species follows the isochronal rule strictly: Acartia spp. come closest with isochronal development from third nauplius (N3) to fourth copepodite (C4). The only pattern followed by all species is rapid development of the first and/or second naupliar stages, slow development of the second and/or third nauplius and prolonged development of the final copepodite stage. Once adulthood is reached, males are usually short-lived, but females can live for weeks to months in the laboratory. Adult longevity in the sea is, however, on the order of only a few days. The evolution of developmental patterns is discussed in the context of physiological constraints, along with consideration of possible relationships between stage-specific mortality rates and life history strategies. Physiological constraints may operate at critical bottlenecks in development (e.g. at the first feeding nauplius, N6, and the fifth copepodite stage). High mortality of eggs may explain why broadcast eggs hatch 2–3 times faster than eggs carried by females in a sac; high mortality of adults may explain why adults do not grow rather they maximize their reproductive effort by partitioning all energy for growth into egg production.     

Lipid composition of copepodite stages and adult females of Calanus glacialis in Arctic waters of the Barents Sea

Summary The composition of lipid classes and their component fatty acid are described for copepodite stages III, IV, V, and adult females of Calanus glacialis sampled from Arctic waters of the Barents Sea during summer. Was esters were the principal component of the lipid in all copepodite stages examined, averaging 73% over all the stages. The proportion of triacylglycerols varied from 1.5% to 10.5% of total lipid among copepodite stages. The lipids of adult females contained lower levels of wax esters and higher levels of triacylglycerols than copepodite stages III, IV and V. Fatty alcohols of wax esters from copepods sampled in June and July were dominated by 20:1 (n-9) and 22:1 (n-11) alcohols with the proportion of 20:1 (n-9) increasing from stages III to adult female. 14:0 and 16:0 alcohols were the principal fatty alcohols of wax esters of a sample comprising mainly of copepodites stage III taken in August. 16:1 (n-7), 20:1 (n-9) and 20:5 (n-3) were the major fatty acids in the was esters of animals captured in June and July whereas 18:1 (n-9) predominated in the August sample. The polar lipids of the copepodite stage III from August also contained lower levels of polyunsaturated fatty acids than from all stages of copepods from June and July. The data are discussed in relation to life cycle strategies and trophic aspects of Calanus glacialis in the Arctic pelagic community of the Barents Sea.     

Abundance,population structure and vertical distribution of dominant calanoid copepods on the eastern Weddell Sea shelf during a spring phytoplankton bloom

The main emphasis of this study was to analyse the short-term development of abundance, population structure and vertical distribution of the dominant calanoid copepods during a phytoplankton bloom in the coastal area of the eastern Weddell Sea in December 2003. Microcalanus pygmaeus was by far the most abundant calanoid species. Metridia gerlachei, Ctenocalanus citer, Calanoides acutus, Calanus propinquus and the ice-associated Stephos longipes were also present in considerable proportions. The observed changes in the population characteristics and parameters of these species are described in detail and discussed in the context of the spring phytoplankton bloom. A conspicuous event occurring during the final stage of the study was the development of a strong storm. While the results suggest that this storm did not have any considerable influence on the populations of all other investigated copepod species, it very likely caused pronounced changes in the S. longipes population present in the water column. Before the storm, S. longipes was found primarily in the upper 100 m of the water column, and its population was dominated by adults (mean proportion = 41%) and the copepodite stage I (mean proportion = 30%). After the storm, the abundance increased considerably, and the copepodite stage I contributed by far the largest proportion (53%) of the total population indicating that the early copepodite stages probably had been released from the sea ice into the under ice water layer due to ice break-up and ice melt processes caused by the storm.     

The effects of temperature on metabolic rates of different life stages of Calanus glacialis in the Barents Sea

Summary The effects of temperature on rates of respiration, excretion and gut evacuation were examined for copepodite stages and adult female Calanus glacialis collected in areas close to the ice-edge during the arctic summer in the Barents Sea. The various life history stages responded differently to acute temperature changes above the in situ temperature (ca.-1.7°C). Respiration rates of early copepodite stages (C I to C IV) were very variable whereas excretion rates declined with increasing temperature in the range from-1.7°C to +5°C. Rate of oxygen consumption of adult females were independent of temperature between-1.7° and +5°C, but increased as temperature increased from +5° to 10°C. Rates of excretion of copepodite stage V and adult females were independent of temperature in the range from-1.7° to +2°C, whereas excretion of copepodite stages III and IV was negatively related to temperature in the range from-1.7° to +5°C. In C IV, C V and adult females the instantaneous rate of gut evacuation increased with increasing temperature. The different response patterns of metabolic rates of small copepodite stages, copepodite stage V and adult females C. glacialis to acute temperature changes suggest that the capacity for adjustment of ammonia excretion is better developed in C V's and adult females than in the younger life stages.     

Dynamics of coexisting Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus populations in a high-Arctic fjord

We studied the population dynamics of Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus in Billefjorden, Svalbard (78°40N). All three species reproduced in the fjord with different timing. The maximum abundance of Calanus spp. copepodite stages peaked on the 11th of July (29,000 ind m^–2). C. glacialis was the dominant species accounting for 60–80% of the total Calanus abundance. C. finmarchicus appear to thrive in the fjord despite the low temperatures (–1.86°C to 5°C) and accounted for 20–30% of the total population. C. hyperboreus contributed less to the total abundance (5–20%). A 1-year life cycle is suggested for C. finmarchicus and C. hyperboreus in the fjord, C. glacialis has a 1- to 2-year life cycle. Highest mortality rates were observed for copepodite stage CV in C. finmarchicus and C. glacialis (0.09 and 0.075 d^–1, respectively) and for females in C. hyperboreus (0.149 d^–1). Mortality of copepodite stages was substantially lower in C. glacialis than in the other species. This is particularly obvious in the early and numerous copepodite stages (CI + CII) during the period of recruitment to these stages. This suggests that differences in secondary production in Arctic pelagic ecosystems are controlled partly by population loss rates.     

The occurrence of Rhincalanus gigas,Calanoides acutus,and Calanus propinquus (Copepoda: Calanoida) in late May in the area of the Antarctic Peninsula

Summary The Antarctic copepod species Rhincalanus gigas, Calanoides acutus and Calanus propinquus were studied in the area of the Antarctic Peninsula in May 1986. Research was focussed on vertical distribution and stage composition of the populations. Rhincalanus gigas occurred in greatest densities in the upper layers of the water column, and copepodite stages CI and CII and nauplii dominated the population. Gut content analyses suggest that R. gigas was actively feeding. Copepodite stage CV dominated the Calanoides acutus population. At two deep basin stations (water depth>1000 m) the C. acutus population occurred below 500 m, whereas at shallower stations the majority was found above 300 m. Most specimens had empty guts. Calanus propinquus occurred in low densities, mainly in the upper water layers, and copepodite stage CV dominated. Most individuals of stage V had food in their guts. Our results suggest that C. acutus had ceased feeding and was overwintering in a resting stage (diapause), while C. propinquus and R. gigas were still active, the latter species having finished a late autumn spawning.     

Ecological investigations of the zooplankton community of Balsfjorden,northern Norway: Generation cycle,seasonal vertical distribution,and seasonal variations in body weight and carbon and nitrogen content of the copepod Metridia longa (Lubbock)

Metridia longa (Lubbock) has an annual life cycle in Balsfjorden (69°21'N:19°06'E) with spawning occurring from early to mid-May. Development through copepodite stages I-V takes place during summer. At the end of August copepodite stage V accounted for >80% of the population. Overwintering (October-March) was mainly performed by adults. At noon throughout the year copepodite stage V and adults were found within the bottom 30 m of the fjord. The majority of stage IV occurred within the bottom 80 m, while copepodite stages I-III were mainly concentrated within the surface 50 m. Body length, weight, carbon and nitrogen content, and $\text{C}\text{N}$ ratio were determined for copepodite stage V, adult males and females throughout the year. While body length was constant, weight and C and N content varied with season. Lowest $\text{C}\text{N}$ ratios (4–6) were found in copepodite stage V in July and in adults in late winter. Highest $\text{C}\text{N}$ ratios (16–20) were measured in adults from October through early winter. These results are discussed in relation to the life cycle of M. longa and the primary production cycle of the fjord. It is argued that M. longa overwinters in an active state compared with Calanus finmarchicus (Gunnerus) from the same locality.     

The predator-prey relationship of perch,Perca fluviatilis,larvae and zooplankton in two Scottish lochs

Synopsis Food consumption of perch larvae and the impact of this on zooplankton were examined in two adjacent shallow Scottish lochs. Maximum annual abundance of zooplankton occurred in mid-May at L. Kinord with minimum values in mid-June. Copepods were prominent in spring but were followed by a multi-species community of cladocerans and rotifers in summer. At L. Davan zooplankton biomass remained high through summer with cladocerans dominating andDaphnia longispina the most frequent species. Availability of food items was a principal factor governing feeding behaviour of larvae. Copepodite stages were initially the most common item in the diet in L. Kinord in 1976 and 1977 and rotifers the principal food in June 1977, reflecting the dominance of these items in the zooplankton. Cladocerans were dominant in the plankton community in L. Davan and constituted the greater part of food intake. Overlying this general pattern there was an increase in the size of food items taken by larvae with time and also a definite pattern of food selection for copepods, with initially selection for smaller copepodite stages and later for larger stages and adults. On most occasions larvae selected forCyclops strenuus abyssorum andPolphemus pediculus and selected againstDaphnia longispina. The reduction in the total zooplankton biomass attributed to perch larvae was minimal, with the exception of mid-June at L. Kinord in 1976. However, predation on particular species and copepodite stages was occasionally intense and may have impacted the zooplankton populations.     

Postembryonic development of Tisbe gracilis (T. Scott) (Copepoda, Harpacticoida)

All six naupliar and five copepodite stages of Tisbe gracilis (T. Scott, 1895) are described. A key for the identification of the nauplius stages is given. The oral appendages of all copepodite stages are described. Sexual dimorphism is visible from the copepodite IV stage on.     

Vertical distribution and seasonal numerical abundance of the Calanidae in oceanic waters to the south-west of the British Isles

The vertical distribution and seasonal abundance of the copepodite and adult stages of Calanus finmarchicus, C. helgolandicus, C. tenuicornis, Neocalanus gracilis, Nannocalanus minor and Calanoides carinatus from a series of Longhurst Hardy Plankton Recorder hauls taken in the oceanic waters, off the continental shelf, to the south-west of the British Isles are described. The sampling area was selected because the geographical distributions of the major Calanidae copepods of the north-east Atlantic Ocean are shown to overlap in this region. It marks the southern boundary of the distribution of C. finmarchicus, the central area of C. helgolandicus and the approximate northern limit of distribution of C. tenuicornis, N. gracilis, N. minor and C. carinatus. These four southern species occasionally penetrate further north (60° N) in the open ocean but do not breed at these northern latitudes. In autumn and winter, when C. finmarchicus and C. helgolandicus were overwintering below 400 m primarily as Stage V copepodites, N. gracilis occurred in the upper 200 m of the water column in a breeding condition; all copepodite stages were present. This copepod reproduced throughout the year in this regions while C. tenuicornis was observed to breed primarily in spring and summer. The geographical and vertical distributions of the Calanidae are related to the observed seasonal temperatures of the North Atlantic and the breeding strategies of species are compared.     

Gut contents and diel feeding rhythm in dominant copepods in the ice-covered Weddell Sea,March 1992

Zooplankton was sampled at a diurnal station during the drift of the Ice Station Weddell-1 in the western Weddell Sea in March 1992. Gut contents of Metridia gerlachei, Calanoides acutus, Calanus propinquus and Rhincalanus gigas were studied. Calanoides acutus was trophically inactive, but 18%, 33% and 45% of Calanus propinquus, R. gigas and M. gerlachei, respectively, contained food in their guts. Diel changes in gut levels and percentage of individuals with full guts with maximum during the dark period were observed in M. gerlachei copepodite stage V and females. The possible reasons for observed differences in foraging patterns of the four copepod species are discussed.     

Feeding,metabolism and body composition of the Antarctic copepod Calanus propinquus Brady with special reference to its life cycle

Summary In the Weddell Sea, several biochemical and physiological characteristics of copepodite stage III to adult females of Calanus propinquus from the surface layer (0–100 m) and the deep layer (500–1,000 m) were compared at a time of high phytoplankton abundance (February) and a month later, when chlorophyll concentration was much lower and older copepodite stages had migrated to their overwintering depth. Daily rations of surface animals, estimated by the gut fluorescence method, varied from 0.8% to 7.8% body carbon (increasing with phytoplankton concentration). Respiration rate (calculated from measurements of electron-transport-system activity) and lipid and protein body content of animals inhabiting the surface layer decreased from February to April. Deep water animals (stage V and adult females) were characterized by high lipid and protein content; their respiration and excretion rates were much lower than in surface copepods. Our calculation showed that they could survive without an additional source of energy for 8–9 months. Based on our own and published data on bio-chemistry and physiology the possibility of a two-year life cycle is suggested.     

Metacyclops minutus (CLAUS, 1863) - Population Dynamics and Life History Characteristics of a Rapidly Developing Copepod

The cyclopoid copepod Metacyclops minutus, a typical species of temporary pools, shows an unusual life cycle in a small pond in South Germany. The species is present from April/May to December during which period it forms at least 8 generations. Winter and early spring, when the pond is frozen to the bottom, are spent in the bottom mud as C4 or C5 instars. M. minutus shows an extraordinarily low degree of sex size dimorphism (female: male body length ratio) and no significant differences in. copepodite development time between the two sexes. This, together with the exceptionally short durations of embryonic- and postembryonic development enables reproduction to start without delay and rapid population growth after harsh conditions. By these means M. minutus is the first species to reproduce after periods of extremely low water level; later, when conditions in the pond become more stable, M. minutus is surpassed in numbers by a coexisting, filterfeeding and parthenogenetically reproducing cladoceran Moina brachiata.     

The year cycle of Eudiaptomus vulgaris (Schmeil, 1896) (Copepoda,Calanoida) in a small,acid water body during 1973. Development in the natural habitat and relationships between temperature and duration of development stages

The development of a population of Eudiaptomus vulgaris (Schmeil, 1896) in the Meeuwenven, a shallow acid guanotrofic moorland pool, has been described during one year. The population hibernates as copepodite 5 stages, adults and, to a small extent as naupliar stages N1, N2 and N3 (which could not develop further at low temperatures in autumn). In spring the population development starts at temperatures above 10°C and shows 3 or 4 pulses a year. An attempt has been made to explain seasonal changes in the size of adult males and females and in the sex ratio.In order to establish the duration of the various development stages, the animals have been cultured at different temperatures under illumination with 2000 Lux at a daylength of 14 hours. An adequate quantity of food from the natural habitat was available.Total egg development and total naupliar and copepodite development have been compared with the results of other workers, especially with those from Eckstein (1964), who studied Eudiaptomus vulgaris in the deep Schluchsee. The duration curves do not differ markedly with those of Eckstein and are strongly temperature dependent.The relation between the development times of the various stages with temperature can be generally expressed as parabolic regressions of the type D = a + b₁T + b₂T², the C₅ and adult stages being the only exception at higher temperatures. Comparison of the relative duration of the stages at different temperatures did show that younger stages can take a larger share of the total development time at lower temperatures, stage N6 being the most temperature-sensitive.     

Salinity tolerance of the copepod Apocyclops dengizicus (Lepeschkin, 1900), a key food chain organism in the Salton Sea,California

The copepod Apocyclops dengizicus is a key item in the food chain of the Salton Sea where the salinity is currently 45 g 1^–1. The salinity of the Salton Sea may reach 90 g 1 ^–1 within the next 20 years. This study examined the salinity tolerance of this copepod.Large copepodite and adult A. dengizicus were introduced into various salinities with and without acclimation. The 96 h LC₅₀ without acclimation was 101 g 1^–1. Mortality (at 96 h) without acclimation was low at salinities of 90 g 1 ^–1 or less.Copepod cultures were maintained, with successful reproduction of at least one new generation, at salinities of from 0.5 to 68 g 1 ^–1 for at least 120 days. Copepods maintained at higher salinities, up to 79 g 1 ^–1, remained alive up to 90 days, but a new generation was not produced. In laboratory studies of larval production and survivorship, few nauplii were released at salinities of 68 g 1 ^–1 or higher, and none survived to the copepodite stage.     

The effect of environmental variation on the reproductive development time and output of the high-shore rockpool copepod Tigriopus brevicornis

The extreme environmental changes observed in high-shore rockpools occupied by Tigriopus brevicornis, provide a significant physiological challenge that may have implications for the energetics and hence the life history characteristics of this species. The present study was designed to assess the effect of this environmental variation on the reproductive development time and output of T. brevicornis in terms of duration of the various stages in ovary and egg sac development and maturation as well as naupliar development time to the first copepodite stage and total numbers of copepodites produced.There was a significant difference in reproductive development time and output in the three test salinities with only successful development to copepodite I stage seen in normal seawater (35 psu). There was also a successful release of nauplii seen at the low salinity (5 psu), but no subsequent survival to the copepodite I stage, whilst there was not even a development of egg sacs in the high salinity test medium (70 psu). There was also a significant difference in reproductive development times in the three test temperatures with fastest ovary development in the high temperature (23 °C) and slowest development time in the lowest temperature (5 °C). However, it should be noted that the highest number of nauplii produced was actually in the mid temperature (12 °C), not the high temperature. Exposure to hypoxic and anoxic conditions had a significantly detrimental effect on reproductive development with slower development time through the reproductive stages and no individuals surviving to copepodite stage I from the hypoxic and anoxic test conditions, but good development from the normoxic conditions.The present study indicates that animals living in high-shore rockpools may incur a considerable energetic cost, due to the environmental changes that are characteristic of this habitat and the importance of resource allocation in these different physiological conditions is paramount to the species' survival.     

The effects of temperature and food on copepodite development,growth and reproduction in three species of Boeckella (Copepoda; Calanoida)

Three species of Boeckella (B. triarticulata, B. dilatata and B. hamata) were reared from copepodite I to adult at three naturally fluctuating food levels and three temperatures in a 3 × 3 × 3 factorial design. Development times, lengths, times to produce the first clutch, clutch sizes, egg voumes, interclutch times, infertile clutches, total egg production, total reproductive time and mortality were measured. Development times for the three species were surprisingly similar but mortality differed among the treatments. The three species differed in their reproductive strategies. B. triarticulata, the largest species, produced a few large clutches. B. dilatata, the smallest species, produced many small clutches and invested the most energy per egg. B. hamata produced larger clutches than B. dilatata but not as many. B. hamata was the most tolerant of low, food levels and exhibited the most plasticity across the treatments. Thus, greater plasticity in life history characters is associated with survival in a wider-range of conditions.     

Variation nycthémérale de la répartition verticale et de l'efficacité de collecte du zooplancton en lagune Ebrié (Côte d'Ivoire)

Vertical distribution and night and day collecting efficiencies of both nets and a Schindler trap, were studied in two shallow (4 m) unstratified bays of the Ebrié Lagoon. Some of the organisms migrate (Mysidacae, copepodite and adult stages of Acartia clausi and Pseudodiaptomus hessei) and others do not (all the nauplii, copepodite and adult stages of Oithona brevicornis, rotifers, mollusca larvae). The first are found more or less near the bottom at noon and are evenly distributed throughout the water at the beginning of the night. Mysidaceae and P. hessei strongly exhibit this pattern, none (Mysidacea) or very few specimens being collected in the water during the day. For A. clausi, depth concentration increases from C1 to adult. Net and trap estimated night densities are higher than the day ones for migrating organisms, except for C1 or A. clausi. The Night/Day ratios are equal to 28 (net) and 25 (trap) for P. hessei, 5 and 13 for the adults of A. clausi and lies between 2 and 5 for the different copepodite stages of this last species. The possible causes and consequences of the vertical distribution are discussed, the interference of turbulence on vertical distribution being outlined.