Effects of small-scale turbulence on development time and growth of Acartia grani (Copepoda: Calanoida)

To test the effects of small-scale turbulence on developmentand growth of marine copepods, a series of 10 1 labortory microcosmswere used to follow the development, under turbulent and calmconditions, of a cohort of Acartia grani, a common coastal planktoniccopepod of temperate zones Aside from possible indirect effectsdue to differences in food availability, turbulence significantlyshortened development times and modified growth rates Theseinfluences seem to vary throughout its life history, late naupliiand early copepodites being more affected.     

Existence and significance of Acartia grani resting eggs (Copepoda: Calanoida) in sediments of a coastal station in the Alboran Sea (SE Spain)

The seasonal abundance of copepod eggs in bottom sediments ofMalaga harbour was documented during an annual cycle betweenJune 1989 and June 1990. The concentration noted ranged from6.6.10⁶ to 0.1910⁶ m^–2. The number of adults in thewater column and eggs recovered from the bottom sediments fluctuatedmarkedly with season. The highest egg abundance in sedimentswas found coincidentally with the early population growth season,although the values remained high until the adults disappearedfrom the water column. During the winter, the number of eggsdecreased until the development of the next copepod population.When bottom sediments were incubated in the laboratory, a largenumber of Acartia nauplii hatched, which showed that eggs laidin the autumn remain viable at the bottom until late spring,thus providing a large pool of potential recruits for the planktonicpopulation. ¹Present address: Departamento de Biologa Animal, Vegetal yEcologa, Facultad de Ciencias Experimentales, Universidad deMan Paraje Las Lagunillas s/n, 23071 Man, Spain     

Description of the developmental stages in Acartia bifilosa Giesbrecht (Copepoda: Calanoida)

The developmental stages and increase in length of Acartia bifilosa,a dominant planktonic copepod in Kyeonggi Bay, Yellow Sea, Korea,were investigated in a laboratory. Adults laid eggs at a rateof 2.5 eggs day^–1 female^–1 and up to 97% of eggshatched. The eggs were 92 µm in diameter and larger thanthe eggs of other Acartia species. The body segmentation wasrecognizable at the fifth nauplius stage and sex distinctionwas possible at the fourth copepodite stage. Thesix naupliusstages took -7.5 days and the five copepodite stages -8.5 days.Sexually mature males and females appeared at the 16th day,and by the 20th day the adults laid eggs that hatched and grewsuccessfully into the nauplius stages. The detailed morphologicalcharacteristics of each developmental stage are presented anddiscussed in relation to A.dausi.     

Interactions between red tide microalgae and herbivorous zooplankton: effects of two bloom-forming species on the rotifer <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> (O.F. Muller)

Experiments were carried out to investigate interspecific interactions between the rotifer Brachionus plicatilis and two harmful algal bloom (HAB) species using single and mixed culture methods. B. plicatilis populations and the growth of two algae were compared at different algal cell densities. The results demonstrate that B. plicatilis obtained sufficient nutrition from Alexandrium tamarense to support net population increase. When exposed to a density of 8 × 10⁴ cells ml⁻¹ A. tamarense, the number of B. plicatilis increased faster than it did when exposed to other four algal densities (16 × 10⁴, 24 × 10⁴, 32 × 10⁴, and 40 × 10⁴ cells ml⁻¹). Cell densities of A. tamarense decreased due to the grazing of B. plicatilis. In contrast, Heterosigma akashiwo had an adverse effect on the B. plicatilis population and its growth was largely unaffected by rotifer grazing. In this case, the B. plicatilis population decreased and H. akashiwo grew at a rate similar to that of a control without addition of rotifers. Mixed culture experiments showed that A. tamarense could partly counteract the effect of H. akashiwo in limiting the rate of population increase of rotifer. In addition, the effect of different initial cell densities on interspecific competition between A. tamarense and H. akashiwo in mixed culture(s) was also investigated. The results show that A. tamarense competed very successfully when the inoculation proportions of A. tamarense and H. akashiwo were 40:5 and 40:30. Handling editor: D. Hamilton     

A new species of Acartia (Copepoda, Calanoida) from the Yellow Sea

A new species (Acartia hongi) of Acartia (family Acartiidae)predominating in the Korean coastal waters of the Yellow Seais described. This species closely resembles Acartia bifilosa,from which it can be easily distinguished by the co-occurrenceof the following morphological characters: the absence of rostralfilaments in both genders; the terminal spine on the femalefifth leg toothed only on the inner side; the first exopodalsegment of the male right fifth leg with a long seta; the distalsegment of the male left fifth leg with a rod-like appendage.Its distribution was discussed in comparison with two siblingspecies, Acartia omorii and Acartia hudsonica.     

Enhanced excretion rates induced by small-scale turbulence in Acartia (Copepoda: Calanoida)

Several experiments have been performed on three congenericspecies of the calanoid copepod Acartia to determine the effectsof small-scale turbulence on metabolic rates. Both inorganicnitrogen and phosphorus excretion rates significantly increased     

Effects of small-scale turbulence on feeding rate and gross-growth efficiency of three Acartia species (Copepoda: Calanoida)

Experiments designed to test the effects of small-scale turbulenceon the feeding rates and gross-growth efficiency of calanoidcopepods have been performed within a wide range of controlledfood concentrations. Turbulence significantly enhanced feedingrates only at food concentrations lower than the ingestion saturatinglevel. Gross-growth efficiency (the quotient carbon-egg production/carbon-foodingested) of the different Acartia species studied showed differentpatterns of response to turbulence, in agreement with the hydrodynamiccharacteristics of their habitat. Furthermore, experiments conductedon Acartia clausi at two different intensities of turbulenceindicate a shift in the response, with enhancement of feedingat low intensities of turbulence and negative interference athigher intensities.     

Development of Acartia clausi (Copepoda,Calanoida) cultured at different conditions of temperature and food

The pelagic copepod Acartia clausi Giesbrecht was bred 3 times from nauplius stages I and II to maturity at 5, 10, 15 and 20 °C and 4 different rations of autotrophic and heterotrophic food. The rate of development of copepods increased with increasing temperature and food level. At the highest food level the stage duration was almost constant through most stages, but development was not quite isochronal. Particularly at lower food concentrations stage duration became progressively longer with increasing stage of development. The relation between development time and temperature is described by Blehrádek's functions at different food levels. These relations predict a generation time of about 50 days at spring bloom conditions and only slightly less during summer due to food limitation. Comparison with estimates in the field from the literature suggests hat food is often limiting during summer conditions.     

Discrimination between Acartia (Copepoda: Calanoida) species using their diffraction pattern in a position, rotation invariant digital correlation

Digital images of Acartia discaudata, A. clausi, A. margalefiand A. tonsa were processed to obtain their diffraction pattern.To discriminate between species and sex all diffraction patternswere correlated with a spatial filter, invariant to positionand rotation, for each Acartia male and female. This filterwas made up using a combination of different images of eachspecies and sex. Considering the great similarity between thecopepod species used in this work and between the male and femaleof each species the results obtained are very good. It is concludedthat the method used to discriminate between species of thiscongeneric group can be very useful for the development of anautomated system for the identification of copepods.     

Development of Acartia bifilosa (Copepoda: Calanoida) eggs in the northern Baltic Sea with specialreference to dormancy

Development of eggs produced by Acartia bifilosa in summer andautumn was studied in the northern Baltic Sea. Resting eggsof the species have previously been found in sediments, andthe aim of this study was to reveal the type of dormancy inthe eggs. Eggs were incubated at temperatures ranging from 1.5to 18°C. The effect of continuous darkness on hatching wasalso tested. Hatching success in the experiments varied between56 and 97%. Egg development was similar in summer and autumn,indicating that A. bifilosa does not produce diapause eggs inthe area. Furthermore, dormancy was not induced at any of thetemperatures tested, nor by darkness. Results are compared withthose of Castro-Longoria and Williams (Castro-Longoria and Williams,1999b, J. Plankton Res., 21, 65–84) who studied A. bifilosain the English Channel, where both production of diapause eggsand arrest of development in the subitaneous eggs at low temperaturesoccurred. The possible causes of the difference in dormancystrategies in the two areas are discussed.     

First report of the presence of Acartia margalefi (Copepoda: Calanoida) in Southampton Water and Horsea Lake, UK

Acartia margalefi is recorded for the first time in Britishwaters, where it is found to be an important copepod in themesozooplankton community structure of Southampton Water andHorsea Lake. Within the genus Acartia. this species occurs allthrough the annual cycle. Abundance is higher in the upper estuary,where the range of temperature and salinity is relatively widerover the year. It is clear that A.margalefi is an estuarinespecies which can tolerate a significant range of temperature.     

Coexistence and competition within Acartia (Copepoda,Calanoida) congeners from Lebanese coastal water: niche overlap measurements

Annual succession and ecological niche formation among six dominant coexisting species of the genus Acartia were studied between 1979 and 1989. The coexisting species: A. discaudata, A. clausi, A. grani, A. italica, A. josephinae and A. latisetosa formed dense populations at different periods in Jounieh harbour (Central Lebanon, eastern Mediterranean). Using numerical data analysis, I defined and measured niche hyperspaces and niche overlaps of these species. Although both spatial and temporal segregation occurred between congeners, the amount of niche overlap was estimated in relation to the availability, use, and abundance of natural resources. The hydrobiological factors prevailing in the port were considered resource states. They include eight parameters: water temperature and salinity, dissolved oxygen, mineral phosphate, nitrate, chlorophyll-a concentration, plankton biomass, and species diversity of the plankton community. Some competition occurred between the co-existing species and an attempt is made to estimate this. As a result of this competition different ecological niches have developed for each species. Niche overlaps, their hyperspaces, and niche breadth between the congeners are estimated and computed using several indices, such as those based on Levin's and Lloyd's formulae. Two groups of Acartia congeners are defined: a group of spring affinity formed by A. clausi, A. discaudata, and A. grani and a second group involving A. italica, A. josephinae and A.-latisetosa, showing a spring-summer tendency. These coexisting species exhibited certain strategies in their opportunistic behaviours, in order to adapt to a highly variable marine environment, such as the one found in Jounieh port.     

Molecular phylogeny of the Calanoida (Crustacea: Copepoda)

The order Calanoida includes some of the most successful planktonic groups in both marine and freshwater environments. Due to the morphological complexity of the taxonomic characters in this group, subdivision and phylogenies have been complex and problematic. This study establishes a multi-gene molecular phylogeny of the calanoid copepods based upon small (18S) and large (28S) subunits of nuclear ribosomal RNA genes and mitochondrial encoded cytochrome b and cytochrome c oxidase subunit-I genes, including 29 families from 7 superfamilies of the order. This analysis is more comprehensive than earlier studies in terms of number of families, range of molecular markers, and breadth of taxonomic levels resolved. Patterns of divergence of ribosomal RNA genes are shown to be significantly heterogeneous among superfamilies, providing a likely explanation for disparate results of previous studies. The multi-gene phylogeny recovers a monophyletic Calanoida, as well as the superfamilies Augaptiloidea, Centropagoidea, Bathypontioidea, Eucalanoidea, Spinocalanoidea and Clausocalanoidea. The phylogeny largely agrees with previously-published morphological phylogenies, including e.g., enlargement of the Bathypontioidea to include the Fosshageniidae.     

First record of the calanoid copepod Acartia omorii (Copepoda: Calanoida: Acartiidae) in the southern bight of the North Sea

The occurrence of the calanoid copepod, Acartia omorii, is reportedfor the first time in the coastal waters of the Southern bightof the North Sea, off Calais harbour. Acartia omorii males andfemales were consistently found in four plankton samples. Thecollected specimens were compared with A. omorii individualscollected from the type locality (Tokyo Bay, Japan). The captureof A. omorii, a species native to Japanese coastal waters, isin agreement with the recent observation of the Japanese macroalgaeUndaria pinnatifida within Calais harbor and the hypothesisof passive transport in ship’s ballast water.     

Comparison of Coulter Counter and 14C measurements of Acartia tonsa (Copepoda,Calanoida) grazing on Chlamydomonas sp. (Volvocales)

Both the Coulter Counter and ¹⁴C method were used to measure the grazing (clearance rates) of the marine calanoid copepod Acartia tonsa on different concentrations of a Chlamydomonas sp. culture. In most cases, clearance rates measured by the Coulter Counter method were higher than those measured by the ¹⁴C method by factors of 2 to 3. We explore several possibilities for the differences obtained between the two methods. We suggest that loss of radioactivity through grazer egestion might be the main reason for the discrepancy between methods. Food concentration did not affect the comparability of both methods' measurements.     

Ecology of the zooplankton of a meromictic antarctic lagoon with special reference to Drepanopus bispinosus (Copepoda: Calanoida)

The zooplankton of Burton Lake, a meromictic lagoon with a tenuous connection to Crooked Fjord near Davis, Antarctica, was studied during the summer of 1981, when the lake was still ice-covered. Sampling occurred through a 10 cm diameter ice-hole. A plankton pump was used to investigate vertical changes in population density. A newly designed collapsible net was hauled vertically through the entire oxylimnion (6.5 m thick) to examine temporal changes in population structure and in the species composition of the zooplanktonic community. Four metazoan species occurred in the zooplankton: Drepanopus bispinosus and Paralabidocera antarctica (Copepoda), Rathkea lizzioides (Anthomedusae) and a cydippid ctenophore. Except for R. lizzioides, the lower limit of the vertical distributions occurred precisely at the oxycline at a depth of 8.15 m. The densities of both R. lizzioides and the ctenophore were low throughout the depth range 5.0–7.25 m and considerably higher above and below this stratum. The density of R. lizzioides increased greatly in a downward direction starting about 35 cm above the oxycline, and many individuals were capable of making excursions of about 10 cm downward past the chemocline into anoxic water. D. bispinosus had a more even vertical distribution than the medusa and ctenophore, but densities were higher in that portion of the oxylimnion lying below 6.0 m than above. The vertical distributions of R. lizzioides and D. bispinosus were stable over 24 h, but vertical migration occurred in that portion of the ctenophore population located above the low-density stratum. P. antarctica occurred in very small numbers. The ctenophore was uniformly distributed horizontally, but significant horizontal differences (among four stations) in mean vertical density occurred in adult D. bispinosus and R. lizzioides. The lowest density of D. bispinosus occurred at the station with the highest density of R. lizzioides. In early summer (11 December 1981), the mean densities of zooplankters within that portion of the oxylimnion overlying the anoxylimnion were D. bispinosus 550 m⁻³, ctenophore 410 m⁻³ and R. lizzioides 230 m⁻³. Throughout summer the absolute density and relative community proportion of R. lizzioides fell continuously, and these measures showed a comparable decline for adult D. bispinosus (almost entirely females). At the same time there was a consistent increase in the numbers of immature D. bispinosus. The density and community percentage of the ctenophore remained high (c. 480 m⁻³ and 44%, respectively) throughout December and early January, but declined thereafter. D. bispinosus is univoltine. Mature males appear in late autumn and mating occurs mainly in early winter, when significant numbers of mature females first appear. The species overwinters as adults, and ovigerous females first appear in midwinter. Males are short-lived and are already rare by the end of winter. Stage I nauplii are present in early spring, and naupliar development continues throughout spring and into early summer in company with an almost entirely female adult population. Stage I copepodites first appear in December and reach peak numbers in January. The last of the adult females from the previous winter disappear by late summer, but development of the immature copepodites continues into autumn. Females may store sperm for up to six months. Highly significant dry weight-length regressions were obtained for D. bispinosus. Mean clutch size for this species remained constant at about 24–25 eggs. The mean summer standing crop of total zooplankton was almost 80 mg (dry weight) m⁻³. This value is high compared with those of most other marine waters. The structure and composition of the zooplanktonic community of the lagoon were quite distinct from those of the fjord with which water was exchanged during January and February. The summer standing crop of the lagoon was substantially greater than that of the fjord in terms of both unit surface area and unit volume of water. A tentative food web for the lagoon is presented.     

Distribution and biogeography of the Paradiaptominae (Copepoda: Calanoida: Diaptomidae)

The Paradiaptominae, a subfamily of the large Diaptomidae family, is a small group of freshwater calanoids of which 24 species in four genera have been described. They are endemic to Africa with the exception of four species, Metadiaptomus asiaticus (Asia and Mongolia), M. gauthieri (Africa and Madagascar), Paradiaptomus greeni (India and Sri Lanka) and Neolovenula alluaudi (Canary Islands, North Africa, Baltic and Mediterranean countries). The North African species Metadiaptomus chevreuxi extends its range into Iraq and Iran. The Paradiaptominae are widely distributed in semi-permanent water bodies in the drier areas of Africa although most individual species have a restricted distribution. Only a few species have the ability to colonise permanent waters and these species are usually located at higher altitudes. The Paradiaptominae have not been recorded from the wet equatorial lowland areas of Africa. It seems likely that they are Gondwanian in origin as evidenced by their distribution (Africa, Madagascar, India and Sri Lanka). Neolovenula alluaudi (Mediterranean) shares morphological characters tenuously linked to the other species in the group and may either have a different origin or have branched off at an early stage in evolution of the group.     

Morphological differences between subitaneous and diapause eggs of Boeckella triarticulata (Copepoda: Calanoida)

1. Many calanoid copepods produce subitaneous eggs that hatch immediately and diapause eggs that remain dormant for long periods of time. Boeckella triarticulata (Copepoda: Calanoida) produces diapause eggs that hatch asynchronously over an extended period of time and appear identical under light microscopy to those that hatch immediately.
2. We compared the internal morphology of subitaneous and diapause eggs of B. triarticulata that had been prepared for transmission electron microscopy by four methods.
3. Subitaneous eggs had a thin, single-layered shell whereas diapause eggs had a thick, three-layered shell that appeared consistent over 3 months of diapause. Boeckella triarticulata appears to enter diapause at the multicellular stage.
4. Consistent morphological differences between subitaneous and diapause eggs of B. triarticulata suggest that these two egg types also have distinct differences in physiology, and are not merely extremes of a continuum from subitaneous to diapause eggs.     

Feeding of Acartia tonsa Dana (Copepoda,Calanoida): predation on nauplii of Canuella perplexa T. et A. Scott (Copepoda,Harpacticoida) in the sluice-dock at Ostend

Feeding experiments in which the zooplankton fraction of the Sluice-dock smaller than 200 μm is offered to Acartia tonsa, the dominant calanoid of this biotope, show that it feeds on the nauplii of Canuella perplexa, the dominant benthic harpacticoid. The ecological implications of this carnivorous feeding, occurring in the presence of natural phytoplankton concentrations, are briefly discussed.     

Seasonal variations in carbon and nitrogen content of Acartia clausi (Copepoda,Calanoida) in the Gulf of Trieste (Northern Adriatic Sea)

A yearly study was made on total and cephalothorax lengths, dry weight, carbon and nitrogen contents and C:N ratio of the species Acartia clausi (Copepoda, Calanoida) which is always abundant, particularly in spring, in the net zooplankton community of the Gulf of Trieste (Northern Adriatic Sea). The samples of net zooplankton were carried out every month at the permanent station located 200 m offshore and preserved for about one year in 4% buffered formalin to insure weight loss stabilization. A. clausi was separated from other zooplankton specimens; washed and dried. For each monthly sample the average total and cephalothorax lengths and the average dry weight of adult organisms of A. clausi were measured. The mean carbon and nitrogen contents, as a percentage of dry weight, were determined by using a CHN analyser. Linear regression models were computed on the log-transformed data in order to check the relationships between dry weight, total and cephalothorax lengths, carbon and nitrogen contents and C:N ratio of A. clausi. The best of the various established correlations, was between dry weight and carbon content. Our study pinpointed a high seasonal variability of the C:N ratio, mainly due to seasonal fluctuations in the nitrogen content.