Variability of Acartia clausi in the Black Sea

There are two morphotypes of A. clausi in the Black Sea. The diversity in the spine ornamentation of the last prosomal and urosomal segments generally has been decreasing in both morphotypes during the period of this study (1976–1990). Seasonal data showed increased variability in April.     

Gut pigment destruction by the copepod Acartia clausi

The extent of chlorophyll (Chi) a degradation into colorlessproducts by the copepod Acartia clausi was determined by measuringgut fluorescence prior to fecal pellet production. The efficiencyof pigment degradation of animals fed at different concentrationsof Thalassiosira weiss-fiogii varied between 30.56 and 94.05%,and the quantity of pigments lost during gut passage was directlyrelated to total ingestion. The role of feeding history in pigmentdestruction was tested. The fraction of ingested Chi a degradedby copepods acclimated to a high food concentration (15 ng Chla ml^–1) was greater than the fraction degraded by thoseacclimated to a low food concentration (1.5 ng Chl a ml^–1).The percentage of ingested Chl a that A.clausi transformed intofluorometrically undetected compounds was not constant. At present,knowledge of the pigment destruction process indicates thatChi a and Chi --derived pigments are not considered useful quantitativetracers of the feeding activity of copepods. The results ofthis study suggest a reassessment of the application of thegut fluorescence method to evaluate grazing activity of thecopepod A.clausi     

Comparison of the metabolism of Acartia clausi and A. tonsa: influence of temperature and salinity

In the Marseilles region (French Mediterranean coast), A. clausi is one of the most abundant copepod species of the Gulf of Fos while A. tonsa constitutes the almost exclusive copepod species of the Berre lagoon, a neighbouring semi-closed brackish area communicating with the gulf. As different ecophysiological capabilities to stand the various temperature, salinity and food conditions could explain why these two species do not coexist in the same environment, comparative experiments were performed on metabolism and feeding. The respiration and ammonia excretion of the two species were measured in different combinations of temperature (10, 15 and 20 degrees C) and salinity (15, 25 and 35 per thousand). For each temperature, at the salinity of 35 per thousand, respiration rates were less in A. clausi than in A. tonsa, the contrary being observed at the lowest salinity. At any temperature ammonia excretion was greater at the intermediate salinity in A. tonsa and least in A. clausi. In Acartia tonsa, Q(10) of respiration and excretion were minimum at the lowest salinity, while in A. clausi they were unaffected by salinity variation. The O:N atomic ratio (from respiration and ammonia excretion rates) was significantly more elevated in A. clausi (mean 21.2; range 13.6-28.7) than in A. tonsa (mean 11.3; range 4.2-25) suggesting a more proteinic oriented metabolism in the later. Feeding experiments where Dunaliella tertiolecta30 per thousand) or lagoon (<16 per thousand) salinity. The relationships between ingestion and food concentration in the two species were not significantly different. These different results are compared to other ecophysiological information concerning these Acartia species (survival tolerances, osmotic regulation, feeding behaviour) and are discussed in relation with the characteristics of their niches in the studied region.     

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.     

Seasonal variation in egg morphology and hatching success in the calanoid copepods Temora longicornis, Acartia clausi and Centropages hamatus

We report here on the seasonal changes in ultramicroscopic morphologyof the eggs of the calanoid copepod Temora longicornis. Duringa field study between 1996 and 1998 in the Menai Strait, easternIrish Sea, T. longicornis produced two types of eggs; hatchingor subitaneous eggs were spawned during autumn–winter,whereas a high proportion of non-hatching eggs (up to     

Seasonal cycles in population abundances and egg production rates in the planktonic copepods Centropages typicus and Acartia clausi

Laboratory studies on the seasonal cycling of egg productionrates for Centropages typicus and Acartia clausi did not reflectseasonal changes in densities for these species at sea. Maximumegg production rates occurred from autumn to spring when populationabundances at sea were low. In late spring, an increment inpopulation numbers was followed by a drastic decline in eggdeposition which continued into summer. The percentage lossdue to mortality, calculated using egg data and total numberof copepodid stages CIII and CIV recorded at sea {small tilde}2weeks later, indicated greatest mortality (80–99%) fromeggs to copepodids during periods of high breeding intensity.These results suggest that high and low density phases in populationnumbers may be the outcome of variations in reproductive potentialand survival rates of eggs and immature stages rather than reproductivepotential per se.     

Population genetics of drifting (Calanus spp.) and resident (Acartia clausi) plankton in Norwegian fjords

Kaartvedt distinguished between drifting and resident planktonand hypothesized that the latter were distinguished by theirability to maintain their horizontal position in desired habitats(Kaartvedt, 1993). In this study, we examined the populationgenetic consequences of these two lifestyles for copepods infour fjords of western Norway (Lurefjorden, Masfjorden, Sognefjordenand Sørfjorden) and one fjord in eastern Norway (Oslofjorden).Based on DNA sequence variation of a region of mitochondrial16S rRNA, we contrasted population genetic diversity and structurein drifting populations of Calanus spp. with that of residentpopulations of Acartia clausi. With the exception of Sørfjorden(where Calanus spp. were rare), two or three species of Calanusco-occurred in significantly different proportions in the fjords.Based on a 350 base-pair region of mitochondrial 16S rRNA, Calanusspp. varied in molecular genetic diversity, with the highestvalues for C.helgolandicus. There was no evidence of significantgenetic structure of fjord populations for either C.finmarchicusor C.helgolandicus; the population structure of C.glacialiscould not be evaluated as the species was only abundant in Lurefjorden.Acartia clausi was abundant in all five fjords sampled for thisstudy. Molecular genetic diversity of A.clausi, based on a 220bp region of mt 16S rRNA, was within the range of Calanus spp.values. Populations of A.clausi showed significant genetic structure(i.e. haplotype frequencies differed markedly) among the fjords.The results of this study indicated that little exchange (geneflow) occurs between populations of A.clausi in different fjords,and suggested that the populations are long-term residents ofa fjord. In contrast, most Calanus spp. fjord populations maybe replaced periodically, as they drift with currents flowingto and from coastal and fjord environments.     

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.     

Organic Matter,Carbon, Nitrogen and Phosphorus Contents of the Mesozooplankton,Mainly Acartia clausi,in a Tropical Brackish Lagoon (Ebrié Lagoon,Ivory Coast)

Mesozooplankton samples were collected over a period of one year in five stations of the Ebrié lagoon and analysed for organic, carbon, nitrogen and phosphorus contents. When zooplankton was dominated by A. clausi, body composition was relatively stable compared with the broad variability of environmental factors (mainly salinity, food abundance and composition), although a negative hypothetic influence of salinity may have occurred. Body composition was comparable when zooplankton was dominated by Pseudodiaptomus hessei and freshwater species, but contents were significantly lower for assemblages dominated by more exclusively marine species (Paracalanus spp., Oithona spp., marine cladocerans, chaetognates, etc.).     

The longevity of three generations of normal and pollution-impacted Acartia clausi (Copepoda) populations in the Saronicos Gulf (Greece)

The longevity of two populations of the planktonic copepod Acartia clausi in the Saronicos Gulf was estimated. One group lived in a heavily polluted area, the other group in a relatively clean area. Three annual generations were studied. A comparison was also made between fed and unfed animals. A temperature of 14°C appeared to be the most favourable for the survival of Acartia; however, the optimum survival temperature depended also upon the generation to which the Acartia belonged. The acclimatization temperature has a strong influence on survival. Acartia in its natural environment thrives best and has maximum longevity at colder temperatures. The pollution-adapted Acartia population survived longer under laboratory-controlled conditions than the population living in a non-polluted area.     

Abundance and spatial distribution of Artemia salina in Lake Abert,Oregon

In 1981–1982 Abert Lake had an area of 200 km², with a mean depth of 2.5 m and a total dissolved salt concentration of 82 gl^-1. The spatial distribution and abundance of the brine shrimp, Artemia salina, were monitored for 1981–1982. In 1981 during the midsummer months, with sampling primarily in the eastern side of Abert Lake, brine shrimp populations showed peak densities of 2–4 ind. 1^-1. In 1982, peak abundance occurred in early July and ranged between 5–8 ind. 1^-1. Lakewide estimates of brine shrimp derived from 14 collecting stations and assuming a uniform distribution over the lake resulted in estimates of lakewide abundance of 3 × 10¹¹ adults with a total biomass of 7 × 10⁶ kg. The major algal species in the lake was a benthic filamentous green alga (Ctenocladus circinnatus).     

Feeding selectivities and food niche separation of Acartia clausi, Penilia avirostris (Crustacea) and Doliolum denticulatum (Thaliacea) in Blanes Bay (Catalan Sea, NW Mediterranean)

Selectivity-size spectra, clearance and ingestion rates andassimilation efficiencies of Acartia clausi (Copepoda), Peniliaavirostris (Cladocera) and Doliolum denticulatum (Doliolida)from Blanes Bay (Catalan Sea, NW Mediterranean) were evaluatedin grazing experiments over a wide range of food concentrations(0.02–8.8 mm³ L^–1 plankton assemblages from BlanesBay, grown in mesocosms at different nutrient levels). Acartiaclausi reached the highest grazing coefficients for large algae>70 µm (longest linear extension), P. avirostris forintermediate food sizes between 15 and 70 µm, and D. denticulatumfor small sizes from 2.5 to 15 µm. Penilia avirostrisand D. denticulatum acted as passive filter-feeders. Acartiaclausi gave some evidence for a supplementary raptorial feedingmode. Effective food concentration (EFC) decreased linearlywith increasing nutrient enrichment for D. denticulatum andfollowed domed curves for A. clausi and for P. avirostris withmaximum values at intermediate and high enrichment levels, respectively.Clearance rates of crustacean species showed curvilinear responseswith narrow modal ranges to increasing food concentration. Clearancerates of D. denticulatum increased abruptly and levelled intoa plateau at low food concentrations. Mean clearance rates were13.9, 25.5 and 64.1 mL ind.^–1 day^–1, respectively.No clearance could be detected for A. clausi at food concentrations<0.1 mm³ L^–1 and for P. avirostris at food concentrations     

Toxicity of chromium to the marine planktonic copepodAcartia clausi,Giesbrecht

The toxicity of chromium to the marine planktonic copepodAcartia clausi, Giesbrecht was studied. The LC50 48 h values (concentration of chromium lethal to 50% of the test animals) vary with the experimental temperature, the form of chromium compound tested and the annual generation to which theAcartia specimens belong. The elevation of temperature resulted in a considerable increase ofAcartia's sensitivity to chromium. Cr⁶⁺ in the form of Na₂CrO₄ was more toxic toA. clausi than in the form of CrO₃ · Cr³⁺ in the form of Cr(NO₃)₃ 9 H₂O precipitated to the bottom and was not toxic toAcartia.Acartia specimens belonging to the summer generation were more sensitive to chromium than those belonging to the winter or autumn generation. The exposure ofAcartia to sublethal concentrations of chromium resulted in a reduction of its longevity proportional to the chromium concentrations used.Furthermore, whenA. clausi was exposed to sublethal chromium concentrations it showed a decrease of feeding capacity and increase of respiratory rates, which became more pronounced with increasing chromium concentrations.     

Escape behavior of Acartia hudsonica copepods during interactions with scyphomedusae

Calanoid copepods possess remarkable abilities to detect andescape from hydrodynamic disturbances, such as those createdby approaching predators. At the same time, a number of studiesin coastal ecosystems have suggested that gelatinous predators,including medusae in the Class Scyphozoa, exert top-down controlon copepod populations. Although prey escape behavior playsa critical role in predation models, we have relatively littleempirical data on how copepods respond to encounters with scyphomedusae.In this study, I used video to quantify encounter rates andescape behaviors of the copepod Acartia hudsonica during interactionswith two scyphomedusae, Aurelia aurita and Cyanea sp., in twoflow regimes. Escapes were complex, variable and effective.Fewer than 1% of encounters resulted in ingestion. Typically,A.hudsonica avoided contact by responding when predators remainedseveral body lengths (4 to 10 mm) distant and stringing togethermany escape jumps at submaximum velocities (33 to 59 mm s^–1).In addition, copepodite stages behaved passively—or failedto respond—following encounters with medusae more oftenthan did adults. Because escape behavior exhibited by A.hudsonicawas so variable, it is unlikely that medusae capture copepodsusing a single, quantifiable mechanism. A range of responseswithin populations and individuals may be the best strategyfor zooplankton faced with strong predation pressure from avariety of predators.     

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.