Young Copepodites Research Articles

Grazing pressure of the calanoid copepod Temora longicornis on a Phaeocystis dominated spring bloom in a Dutch tidal inlet

Between 30 March and 11 May 1990, total copepod abundance and the abundance, biomass and gut fluorescence of Temora longicornis were determined and related to the abundance and succession of phytoplankton development in a Dutch tidal inlet. Gut pigment values were highest in females and lowest in young copepodites, but weight-specific pigment concentrations were about similar. Pigment levels measured in the guts were relatively high at the beginning and end of the period of investigation when diatoms dominated the phytoplankton community, and low during the Phaeocystis dominated period, when ambient chlorophyll concentrations were highest. For the latter period, calculated ingestion rates in T. longicornis were low and estimated daily consumption amounted to less than 1% of the phytoplankton standing stock, suggesting a negligible grazing impact on the development of the Phaeocystis bloom. In spite of the low grazing on phytoplankton, T. longicornis biomass increased by one order of magnitude. The discrepancy between low grazing pressure and copepod development is explained by assuming that T. longicornis switched to heterotrophic food: a bloom of ciliates present during the Phaeocystis dominated period.

Sampling and filtration efficiency of two commonly used plankton nets. A comparative study of the Nansen net and the Unesco WP 2 net

The paper presents the results from a study in which two commonly used plankton nets, the Nansen net and the WP 2 net, were compared. The study was performed at six stations in the Baltic Sea and the samples were collected during seasons of both high and low particle abundance. The comparison included both qualitative and quantitative filtration capacity of the nets under different environmental conditions. Different mesh sizes were also tested. The results show that the Nansen net has an efficiency of 50–70% compared to the WP 2 net under favourable conditions. When conditions are unfavourable, i.e. during periods of high particle abundance or during long hauls, the efficiency may be as low as 25–30%. The mesh size of the nets proved to be of decisive importance for the qualitative composition of the samples. Most of the smaller size fractions such as rotifers, copepod nauplii and young copepodites passed through the 160 and 200 μm meshes. The 90 μm nets sampled these fractions well but with the drawback of retaining vast amounts of phytoplankton at certain times of the year.

Vertical distribution, and seasonal and diurnal migration of Calanus helgolandicus in the Celtic Sea

The vertical distribution and migration (seasonal, diel and ontogenetic) of Calanus helgolandicus are described from the shallow (100 m) shelf-seas to the south-west of the British Isles. In 1978 and 1979, the overwintering population of C. helgolandicus consisted primarily of Stage V copepodites and adults. By late winter/early spring the copepodites had moulted to adult females (>90%), which matured and bred the first cohorts of the year, prior to onset of the spring phytoplankton bloom in April/May. C. helgolandicus reached a peak of numerical abundance in August of 20x103 copepodites m-2 (over the depth range sampled -0 to 70 m), which was 200 times the population in winter. The seasonal peak of abundance occurred 4 mo after the peak of the bloom of phytoplankton in spring. The yearly development of the copepod was not always out of phase with the diatom bloom, as seen when the data from 1978 was placed in the context of a longer time-series collected at 10 m over 22 yr (1960–1981, inclusive). Large vertical migrations were observed in the younger copepodites (CI and II) in May from below to above the thermocline. In the remainder of the year, the CI and CII stages behaved differently and were located above the thermocline within the euphotic zone. The largest vertical displacements of biomass were seen in the summer months due to the migrations of the CV stages and adults, which had developed from the spring cohorts. It was contended that the seasonal and vertical migrations of C. helgolandicus are part of a more complex pattern of inherent behavior than has been reported previously and that, however difficult this is to discern in the natural populations, it always expresses itself.

The Faunal Assemblage Inhabiting Seasonal Sea Ice in the Nearshore Arctic Ocean with Emphasis on Copepods

Large numbers of invertebrates were collected from the lower layer of seasonal ice in the nearshore Beaufort Sea, off the northern coast of Alaska in spring 1980. Over 90 % of the individuals found belonged to meiofaunal taxa. Although density within the ice was low compared to that typically found in sediments, it was comparable to the highest previous estimate from sea ice. Densities were lowest in samples taken in April and reached a maximum of around 50 000 individuals m-2 in June. Nematodes were numerically dominant, but copepods and turbellanans were also abundant. Population structures of the 2 most numerous copepod species were examined and found to differ greatly. Cyclopina gracilis appeared to reproduce continuously during the study; both adults and young copepodites were always present. The population of Harpacticus sp. initially consisted only of juveniles; the growth of a single cohort was observed. Harpacticus sp. mated in the ice, but gravid females did not appear during the sampling period. Although the ephemeral seasonal sea ice habitat would seem to be very different from typical habitats of benthic copepods, these 2 species did not appear to possess any special strategies for living there.

Population Dynamics, Biomass and Biomass Production of Eudiaptomus gracilis (G. O. SARS) in Two Water Areas of Differing Trophic State of Lake Balaton (Hungary)

AbstractPopulation dynamics and production of Eudiaptomus gracilis (G. O. Sars) were investigated in two basins of differing water quality of Lake Balaton from February through December, 1977. One of the basins (Keszthely) is considered to be hypertrophic. the other (Tihany) moderately eutrophic. Plankton samples were collected at weekly intervals.The fecundity was 9.61 ± 3.39 at Tihany, and 16.53 ± 3.60 at Keszthely. The difference between the two basins was significant (P<0.1%). At Tihany the average number of eggs per m3 was lower by 36% relative to Keszthety.The number of nauplii differed only a little between the two basins with the exception of April, when at Tihany the amount of individuals was nearly two times as great as at Keszthely.In the case of younger copepodites (Stages I … III) the difference in individual numbers between the two areas of water was marked from February to June, while in other periods it proved to be small. At Tihany, the number of young copepodites was greater by 8%, on the average, than at Keszthely. The amount of larger copepodites (IV … V) relative to the total number of younger individuals of the population was by 63% resp. 77% smaller at Tihany and Keszthely.In the whole period of these studies the number of adults was less by 44% at Keszthely than at Tihany. Their amount relative to that of nauplii was smaller by 6% at Tihany and by 45% at Keszthely.At Tihany, the population biomass was at a constant high level during winter and spring (40 to 50 mg/m3), in summer values being lower (15 … 35 mg/m3). In the Keszthely‐Basin biomass showed more extreme changes, reaching a peak as high as 40 … 43 mg/m3 in April and November, but hardly exceeding 6 mg during July–August.During the period of investigation, total biomass in the Tihany‐Basin was 342 mg/m3, at Keszthely 204 mg/m3.Net biomass production‐two methods for estimation having been used – was higher in the Tihany‐Basin (17.25 and 33.83 KJ/m2), while in the Keszthely‐Basin it was considerably lower (13.06 and 9.50 KJ/m2).

Instar development rates of Diaptomus minutus (Copepoda: Calanoida) in a small lake in Quebec

A study of the life history of the calanoid copepod Diaptomus minutus Lilljeborg in C-22, a small lake of the Matamek River System, Quebec, demonstrated that instar duration times of the nauplii and younger copepodites in the major generation were considerably shorter than those reported elsewhere. It is hypothesized that these differences may be attributable to the abundance of nannoplankters characteristic of highly oligotrophic waters.