Number Of Nauplii Research Articles

A Bayesian Mixture Model for Estimating Intergeneration Chronic Toxicity

Understanding toxic effects on biological populations across generations is crucial for determining the long-term consequences of chemical pollution in aquatic environments. As a consequence, there is considerable demand for suitable statistical methods to analyze complex multigeneration experimental data. We demonstrate the application of a Bayesian mixture model (with random-effects) to assess the effect of intergeneration copper (Cu) exposure on the reproductive output of the copepod, Tigriopus japonicus, using experimental data across three generations. The model allowed us to appropriately specify the nonstandard statistical distribution of the data and account for correlations among data points. The approach ensured more robust inferences than standard statistical methods and, because of the model's mechanistic formulation, enabled us to test more subtle hypotheses. We demonstrate intergeneration Cu exposure effects on both components of reproductive output (1) the ovisac maturation rate, and (2) the number of nauplii per ovisac. Current and parent generation Cu exposures negatively affected current generation reproductive output However, in terms of reproductive output, there was also some evidence for adaptation to parental Cu exposures, but with an associated cost under Cu concentrations different from the parental exposure. Bayesian mixture and random-effects models present a robust framework for analyzing data of this kind and for better understanding chemical toxicity.

Toxicity of estuarine sediments using a full life-cycle bioassay with the marine copepod Robertsonia propinqua

Estuarine sediment contamination is a growing significant ecological issue in New Zealand. Methods of assessing toxicity and ecological impacts in a cost effective way are currently limited. Further to that is a need to develop bioassays that generate data quickly and cost effectively and have ecological relevance to the wider community. A chronic full life-cycle bioassay to assess the toxicity of New Zealand estuarine sediments using the marine harpacticoid copepod Robertsonia propinqua has been investigated. Sediment samples were collected from the Bay of Plenty region and included two polluted and one reference site. Sources of pollutants in the contaminated field sites originated from a variety of sources and generally include nutrients, pesticides and herbicides and the pollutants zinc, copper, lead and polycyclic aromatic hydrocarbons (PAHs). Conversely, the reference site was exposed to low levels of contaminants due to the relatively undeveloped catchment. Adult male and female copepods were exposed to field collected sediments for 24 days under flow-through conditions at 21 °C and 12 h L:D cycles. Five endpoints were recorded: male and female survival, fecundity (number of gravid females per replicate at the end of the test), clutch size per female, number of eggs per sample and juvenile survival (number of nauplii and copepodites per replicate at the end of the test). Adult mortality was observed in all sediment samples but the number of males, gravid females, clutch size per female and number of eggs produced were not affected by either the contaminated or reference sediment samples. However, the contaminated sediments did reduce reproductive output (i.e. nauplii and copepodite production). Therefore, we conclude that reproductive endpoints provide a good measure of sediment-associated contaminant effects compared with adult R. propinqua survivorship. It may be that a change in focus from chemical thresholds without ecological relevance or lethal dose threshold methods, to more subtle but ecologically significant elements of faunal life, such as reproductive success, are a more sensitive and a long term ecologically informative method.

Reduction of hydrocarbon contamination on viability of Acartia pacifica benthic resting eggs

The potential effect of hydrocarbon contamination on the hatching success of benthic resting eggs of Acartia pacifica in Xiamen Bay was investigated experimentally. The number of nauplii emerging from the sediment samples decreased with increasing Fuel Oil #0 concentration. The estimated rate of mortality increased markedly with the increase of Fuel Oil #0 concentration. Successive fuel Oil #0 concentrations from 50 mg/kg to 5000 mg/kg reduced the number of hatched nauplii by 3.8%–100%. The mortality of A. pacifica resting eggs due to Fuel Oil #0 contamination did not significantly increase as time progressed at each concentration level. The LC50 values of resting eggs, changing from 237.12 to 279.59 mg/kg, remained at an almost stable level in two months. The number of A. pacifica nauplii that hatched from the sediment at 10°C was higher than those from the sediment at 30°C, which indicates that the toxicity of Fuel Oil #0 on A. pacifica resting eggs increases with increasing temperature.

Heavy metal exposure reduces hatching success of Acartia pacifica resting eggs in the sediment

The potential effects of three heavy metals (Cu, Pb, and Cd) on hatching success of Acartia pacifica resting eggs in the sediment of Xiamen Bay were experimentally investigated. The number of A. pacifica nauplii hatched from the sediment sharply decreased with the increase of metal concentration and exposure time from 3 to 30 d. An increase of the Cu concentration from 34.8 to 348 mg/kg, reduced the number of hatched nauplii by 46.6%–100%. An increase of the Pb concentration from 75.2 to 752 mg/kg, reduced the number of hatched nauplii by 21.4%–78.9%. An increase of the Cd concentration from 0.68 to 6.8 mg/kg, reduced the number of hatched nauplii by 31.6%–94.7%. The number of nauplii also significantly decreased with the increase of mixed-metal concentration and exposure time in the mixed-metal test. Trimmed Spearman-Karber analysis gave sediment metal 72-h LC 50 values of 1.25 mmol Cu/kg, 1.73 mmol Pb/kg, and 0.054 mmol Cd/kg, which suggested that Cd was the most toxic to A. pacifica resting eggs in the three tested metals. The results indicate that heavy metals with higher concentrations can reduce recruitment of A. pacifica nauplii from benthic resting eggs to planktonic population.

Effect of algal and animal diets on life history of the freshwater copepod Eucyclops serrulatus (Fischer, 1851)

We studied the survivorship and reproduction of the cyclopoid Eucyclops serrulatus using four diet types: algae Chlorella vulgaris and Scenedesmus acutus separately and each together with the rotifer Brachionus havanaensis. We used equal biomass (3.9 mg C l−1) of C. vulgaris and S. acutus while B. havanaensis was offered at a density of 0.5 ind. ml−1. Regardless of the food type, the average lifespan of female E.␣serrulatus varied from 30 to 50 days, and those of males from 22 to 27 days. When Chlorella was offered alone as food, the female lifespan was 40% lower than when fed together with B. havanaensis. The number of nauplii per female (gross reproductive rate, GRR) was higher on Scenedesmus alone than on Chlorella alone or Chlorella and Scenedesmus offered with Brachionus. Thus, GRR was not significantly influenced by the presence of rotifer in mixed diet. Net reproductive rate (R o) and the rate of population increase (r) were similar at all the four food types. This implies that the diet-related differences of GRR did not ultimately translate to the differences in R o or r, due to the survivorship patterns of the adult females.

Necrotizing hepatopancreatitis (NHP) infected Penaeus vannamei female broodstock: Effect on reproductive parameters, nauplii and larvae quality

Necrotizing hepatopancreatitis (NHP) is a disease of cultured Penaeus vannamei caused by a gram-negative intracellular bacterium rickettsia-like organism. NHP was first reported in Texas in 1985, as being responsible for mortalities in shrimp ponds in Central and South America. The growth and proliferation of NHP within the hepatopancreatic epithelial cells is associated with anorexia, lethargy, abdominal muscle atrophy, softened exoskeleton, growth retardation and mortalities ranging from 20% to 95%. Although NHP can cause high mortalities in commercial ponds, it has been considered a problem only in broodstock ponds and maturation laboratories due to an increase in broodstock mortalities in Colombia. In order to evaluate additional negative effects at this level, we investigated the effect of NHP infection upon the reproductive behavior of females and the effect of maternal infection on nauplii and larval quality. Broodstock from NHP affected ponds were transferred to a maturation laboratory. After copula, females were transferred to individual spawning tanks. After spawning, females were sacrificed for histopathology and PCR analysis, while the eggs were placed in individual tanks for hatching. Females were classified into three groups according to their histopathological findings: NHP negative ( n = 23) had no NHP lesions, positive for NHP with lesions grade 1 ( n = 20) and NHP positive females with lesions grade 2 ( n = 12). For each group, we analyzed the number of eggs, hatching percentage and number of nauplii per female. Our results show that females with NHP lesions grade 2 presented a significant reduction in the number of eggs and nauplii ( P < 0.05) as compared with NHP negative females and females grade 1 NHP disease. No significant differences were found in hatching percentage among the three groups. Triglyceride levels in nauplii II were significantly higher in NHP negative females than in females with grade 2 NHP ( P < 0.05), whereas there was no difference between NHP negative and grade 1 females. No significant differences were found for glucose and cholesterol levels in nauplii among the three groups. No differences were found in survival at zoea I, mysis I, PL-1 and PL-10 for the three groups. However, after a salinity stress test, the PL-10 survival decreased significantly in larvae from NHP positive females. Also a significant decrease in PL-10 length was also observed in the progeny of these females (grades 1 and 2). This study demonstrated that NHP disease in female shrimp spawners affects both maturation and larviculture causing a decrease in the number of eggs and nauplii per female, a reduction in the levels of triglyceride in nauplii II and decreasing larvae growth and resistance to osmotic stress test at PL-10 stage.

Comparison of the Reproductive Performance of Similarly‐Sized Wild and Captive Farfantepenaeus paulensis

AbstractThe reproduction of wild‐caught Farfantepenaeus paulensis in captivity has been successfully achieved since 1983. However, year‐round supply of wild broodstock is costly and unpredictable. This study compares the reproductive performance of animals of similar size (females from 32–33 g and males from 19–21 g) but from different sources: estuary‐caught juveniles reared indoors for 9 mo and wild‐caught adults from shallow coastal waters. Groups of 20 males and 30 unilaterally eyestalk‐ablated females were maintained for 60 d in four maturation tanks under controlled environmental conditions. A higher number of eggs per spawning event (78,414 ± 34,491) and total egg production (4,469,600) were observed for the wild females. Nevertheless, captive females produced a higher number of nauplii (1,788,259) due to their higher percentage of fertilized spawns. Therefore, within the size range of this study, the reproductive performance of estuary‐caught F. paulensis juveniles over‐wintered indoors was found to be equivalent to that of wild‐caught females from shallow coastal waters.

Effects of four synthetic musks on the life cycle of the harpacticoid copepod Nitocra spinipes

A full life-cycle (≤26 days exposure) toxicity test with the harpacticoid copepod Nitocra spinipes was used to study the effects of one nitro musk (musk ketone) as well as three polycyclic musks (Tonalide™, Celestolide™ and Galaxolide™). A subchronic individual life-table endpoint, the larval development rate, was recorded after 7–8 days exposure of juveniles and was significantly decreased in copepods exposed to sublethal concentrations of musk ketone, Celestolide™ and Galaxolide™. However, none of the Tonalide™ concentrations had any effect on larval development. The lowest Galaxolide™ concentration (0.02 mg/l), which affected juvenile development, was about 100 times below the adult 96-h-LC 50-value of 1.9 mg/l (95% confidence interval: 1.4–2.7 mg/l). However, none of the four musks had any agonistic or antagonistic activity in the ecdysteroid-sensitive Drosophila melanogaster B II-cell line. This indicates that the decrease in larval development rate was due to pharmacological effects rather than steroid receptor-mediated endocrine disruption. A modified Euler–Lotka equation was used to calculate a population-level endpoint, the intrinsic rate of natural increase ( r m), from individual life-table endpoints, i.e. mortality rate, time of release of first brood, sex ratio, the fraction of ovigerous females among all females as well as the number of nauplii per ovigerous female. The second highest musk ketone concentration (0.1 mg/l) was the only treatment, which significantly affected r m (*** P<0.001). At the highest musk ketone (0.3 mg/l) and Celestolide™ (0.3 mg/l) concentrations, all copepods were dead at the end of the exposures. This shows that a sensitive individual life-table endpoint is protective over the population-level endpoint r m. Though we think that it is necessary to obtain population-level endpoints from standardised toxicity test, for ecologically successful risk characterisation of synthetic musks as well as other chemicals. The results from the present study show that it is possible to obtain population-level data from the full life-cycle test with N. spinipes. However, there seems to be little risk that synthetic musks are harmful to copepods at present environmental concentrations.

Estimating genetic and environmental components of variance using sexual and clonal Artemia

Reproductive and life span traits were measured for two obligately parthenogenetic ( Artemia parthenogenetica) and three sexual (two A. franciscana and one A. sinica) brine shrimp populations. For each population, clonal lineages or single mating pairs were followed through one life cycle. The relative contributions of environmental and genetic components to total phenotypic variation for 10 life-history traits in response to environmental stress (0, 10, 25 ppb Cu) were estimated. Within treatment variation (CV W) was 39% higher for sexual populations than parthenogenetic populations, with significant ( p<0.05) differences in total number of offspring and number of nauplii. CV A (the change in variance due to rearing in different environments), when averaged for all traits and all populations, increased variability by 9.9%. CV A was 44.2% higher for sexual than parthenogenetic populations, with significant differences in number of broods, total number of offspring, and number of nauplii. The average genetic component of variation for the 10 traits was 23.44%, ranging from 5.26% for number of cysts to 44.87% for number of nauplii. For all traits, the environmental component of variance is greater than the genetic component measured, but every trait has a genetic component, which can potentially be acted upon by selection.

Spawning Frequency Analysis of Wild and Pond‐Reared Pacific White Shrimp Penaeus vannamei Broodstock under Large‐Scale Hatchery Conditions

AbstractSecond generation Penaeus vannamei broodstack, pond‐reared and wild populations, were compared for spawning frequency and several variables associated with reproductive performance. For this purpose, 470 pond‐reared and 237 wild‐caught individually tagged females were stocked with males of the same origin in ten maturation tanks in a commercial hatchery, and several productivity variables were recorded over time. Results of the analysis indicate that wild shrimp had higher mating and spawning frequencies compared to pond‐reared broodstock. The number of nauplii per spawn was higher for wild shrimp, but fertilization and hatching rates were higher for pond‐reared spawners. A larger proportion of nonmating females were found in pond‐reared shrimp; whereas, wild females had a higher potential for multiple matings. The spawn quality (fertilization and hatching rates, percentage of viable spawns, and number of nauplii) in consecutive matings did not decline substantially. The present study indicates that selection of females with multiple spawning capabilities can be an important commercial strategy to improve nauplii production over the short term. Pond‐reared broodstock can be an adequate source for applying this strategy because of their year‐round availability and an overall acceptable reproductive performance.

Tetraselmis suecica cultured in different nutrient concentrations varies in nutritional value to Artemia

Artemia were fed the marine microalga Tetraselmis suecica that had been previously cultured with increasing nutrient concentrations of 0.5, 1, 2, 4, 8 and 16 mg atom N 1 −1 under cyclostat regime with a daily semi-continuous renewal of 50% of the culture. The different nutritive qualities of the Tetraselmis suecica cultures generated were reflected in dramatic changes in Artemia survival, dry weight, total length, percentage of gravid females, percentage of spawning and number of nauplii per spawning. All these parameters were positively correlated to nutrient concentration up to 8 mg atom N 1 −1, decreasing with 16 mg atom N 1 −1. After 19 days of culture, the best results were obtained when Artemia were fed Tetraselmis suecica grown at a nutrient concentration of 8 mg atom N 1 −1. In these cultures, the Artemia had a survival rate of 85%, an average length of 8.3 mm, a dry weight of 0.61 mg, a percentage of gravidity of 27%, a percentage of spawning 19%, with a production of 86 nauplii per spawning and a food conversion rate (FCR) of 2.37. The lowest results for all culture parameters were obtained with the lowest nutrient concentration tested. The production of nauplii per spawning was the parameter most influenced, being the best index to test the nutritional quality of the microalgae. The wide variability in the growth parameters of Artemia induced by the changes in the initial inorganic nutrient concentration of the trophic chain could be very useful for physiological studies and for the production of Artemia and nauplii of high nutritive value for the culture of finfish or crustacean larvae in their early developmental stages.

Lethal and sublethal effects of the sediment-associated PCB aroclor 1254 on a meiobenthic copepod

Acute toxicity tests were performed on field-collected copepods (Microarthridion littorale) using the sediment-associated polychlorinated biphenyl (PCB) Aroclor 1254 (i.e., PCB concentrations in bulk sediments in the bound and/or unbound states). Three replicates of 50 adult copepods (25 males + 25 females) were exposed to five levels of PCB-contaminated sediments for 96 h and compared to untreated controls and solvent controls. LC50 concentrations were nearly twice as high for females (251 mg/kg) as for males (117 mg/kg). To determine the effects of the PCB on reproductive output of the copepods, copulating pairs of Microarthridion littorale were allowed to reproduce in concentrations of Aroclor 1254-contaminated sediments below LC50 values. Two experimental trials with 10 and 15 replicates, each with one pair of Microarthridion littorale in copu-lus, were conducted for 12 d, the normal time needed for females to produce one set of nauplii and carry a second clutch of eggs. In both experiments, a significant decrease in number of nauplii was found with Aroclor contamination. Although NOECs were not determined, high concentrations (83 mg/kg) of the sediment-associated Aroclor 1254 were required to affect mortality significantly, whereas lower levels (4 mg/kg) impaired reproduction.

Influence of three bacteria strains on the population dynamics ofTisbe holothuriae (Copepoda, Harpacticoida)

The influence of three bacteria strains (Helgo 21, NCMB 308 and NCMB 13) on the life cycle ofTisbe holothuriae Humes 1957 was investigated under constant experimental conditions (19–20°C and 38‰ S). For each of the first six experiments, females (F1), whose life history was followed, were obtained from a common mother (F0). Experiment no 7 was carried out with adult females (F2) obtained during exp. 4. Females were bred in 50-ml dishes and transferred to a fresh container as soon as they produced a new egg-sac. Offspring (F2: exp. 1–6; F3: exp. 7) from successive egg-layings were counted as soon as they moulted into adults. Larval mortality was estimated by enumeration of the adults issuing from a known number of nauplii that had been fed different bacteria strains. Some difficulties arose in obtaining adults with NCMB 13: it appeared to be necessary to provide this first generation with a small quantity of TetraMin (commercial fish food) in order to initiate reproduction and obtain a second generation. However, in exp. 4, F2 adult females fed NCMB 13 became ovigerous and fertile without needing TetraMin. This result is interpreted as denoting an indispensable period of adaptation to the diet, which probably requires important changes at the enzymatic level. One experiment was carried out with Helgo 21; another one with NCMB 308; two with NCMB 13 (with a unique additional meal of TetraMin to allow reproduction), two with NCMB 13 during larval development, then only tetraMin during adult stage, and one with NCMB 13 alone (with females issued from exp. 4). Data obtained regarding longevity, duration of reproduction period, number of egg-sacs and number of adult descendants show an important variability between bacteria strains. Lower results were almost always obtained with Helgo 21 and NCMB 308. An interesting result lies in the maximum number of egg-sacs: low with Helgo 21 and NCMB 308 (5), but very ample with NCMB 13 (11 in one experiment). In experiment 7, carried out with animals bearing a large coefficient of inbreeding (0.375), the results concerning the maximum number of egg-sacs are good (10) as are the mean number of descendants per female (294: the highest number of the seven experiments). These results indicate that genetic factors involved in the reduction of descendants in ageing laboratory cultures can be suppressed to a certain extent by nutritional factors. The poor results obtained with Helgo 21 and NCMB 308 alone must be considered with caution: after a period of adaptation with an alimentary complement, these strains could perhaps permit an interesting production of copepods.

Life history responses of Amphiascus tenuiremis (Copepoda, Harpacticoida) to mimicked predation

Potential demographic effects of life stage or gender specific predation on population size and composition were investigated using populations of a laboratory-reared benthic harpacticoid copepod, Amphiascus tenuiremis cf. Mielke, 1974. Control populations initially contained 100 cope- podites, 100 adult males and 100 adult females. In the experimental treatments, one of these com- ponents was reduced by 90 or 50 % to mimic 30 or 17 % once-in-time predation impact Number of nauplii, copepodites, adult males, adult females and total population size was recorded for each population after 21 d (1 generation) Abundance increased in all populations, and at both levels removal of females (female treatment) resulted m significant decreases in final total abundance Cope- podite and male removal had no significant effect on total population size Final population composi- tion was also affected by treatment In the 90 % removals final abundances of nauplii were significantly lower in female removal treatments At the 50 % removal level, final number of nauphi and cope- podites was lower in female treatments only. Number of males was significantly lower in male treat- ments at both levels of removal, as was number of females in female treatments. Female specific predation had the greatest effect on these copepod populations. Total population size decreased because number of nauplii (which comprised 75 to 80 % of each population) was significantly decreased. High reproductive potential, as indicated in up to 28-fold increases in population size over 1 generation, intimated that the observed changes in population size and composition would not be enduring. Predation, imitated herein by removal, would play a small role in determining population structure of A. tenuiremis.

Reproduction of Eyestalk‐AblatedPenaeus stylirostrisFed Various Levels of Total Dietary Lipid

AbstractEffects of total dietary lipid (TDL) on reproduction ofPenaeus srylirostriswere compared using a series of diets ranging from 7.8% to 13.9% TDL. In addition, a commercial feed was compared to the experimental feeds, and a single fresh diet component (squid as 40% of diet) was compared to a multiple fresh component portion (squid, bloodworms, shrimp, and brine shrimp as 40% of diet). The control diet consisted of the four fresh components in equal proportions.Significant differences among diet treatments during 87 days of evaluation were observed for mean percent hatch, number of nauplii per spawn, and percent females mating per night. A new parameter, protozoea I length, was evaluated also and appeared to be a sensitive measure of treatment differences. In general, the all‐fresh component diet (control) and diets with multiple fresh components performed better than those with a squid‐only component. Among the three diets varying only in total lipid content, the middle level (11.1% TDL) treatment means were significantly higher (P&lt; 0.05) than the highest lipid treatment (13.9% TDL) based on number of nauplii per spawn, percent females mating per night, and protozoea length. The middle level treatment means were also higher than the low lipid level tested (7.8% TDL) for these parameters, but only protozwa length was significantly higher (P&lt; 0.01).In the best treatment (100% Fresh), there were 189,000 ± 10,300 eggs per spawn (mean ± SE), 103,000 ± 10,400 nauplii per spawn, 51.3 ± 4.3 percent hatch (N =64), and 7.0 ± 0.7 percent females mating per night (N= 174). The High Lipid treatment, in which the poorest results were obtained, produced 164,000 ± 11,100 eggs per spawn, 39,000 ± 9,400 nauplii per spawn, 23.0 ± 4.8 percent hatch (N =40) and 3.9 ± 0.5 percent females mating per night (N= 174). Results indicate that dietary lipid levels affect reproduction and that 10% to 11% total lipid produced better results than 7.8% and 13.9%.

The reproductive performance of wild and pondreared Penaeus semisulcatus de Haan

A controlled comparison of the reproductive performance of individually tagged wild (P0) and first generation pond-reared (P1) Penaeus semisulcatus is presented. Eyestalk ablated and nonablated females matured and spawned in 3-m 3 maturation tanks. Females which had undergone unilateral eyestalk ablation showed: (1) a slower growth rate (g/day); (2) a trend towards shortening of the molt cycle; (3) a significantly smaller number of eggs and nauplii per spawn; and (4) significantly increassed spawn frequency and increased rate of egg and nauplii production. The fertility and hatchability of spawns from ablated females were not different from those of spawns from nonablated females. All of these trends were observed for both P0 and P1 spawners. The average spawn from a P1 female had fewer eggs than the average spawn from a P0 female. Fertility and hatchability of spawns from both generations were variable and no significant difference was found in the number of nauplii in an average spawn. No significant differences were found between the two generations in the average number of spawns, eggs and nauplii produced per day. Thus the reproductive potential of P1 broodstock was not different from that of P0 females induced to mature and spawn in captivity.

On the biology ofParamphiascella fulvofasciata (Copepoda, Harpacticoida)

The benthic harpacticoid copepodParamphiascella fulvofasciata Rosenfield & Coull was collected from holdfasts ofLaminaria hyperborea from a subtidal area of Helgoland (North Sea). All developmental stages ofP. fulvofasciata are raptorial feeders. The feeding of the nauplii is advanced by a marginal setule-crest of the labrum which prevents food-particles from being swept away. The oral appendages of the copepodites circumscribe a frustal space ventral to the mouth which facilitates uptake of food-particles. The nauplii are not able to swim and perform stalking movements with their antennal endopodites. Good swimming ability as well as digging-in-behaviour and negative phototaxis of the copepodites indicate epi- as well as inbenthic mode of life. Several life-cycle characters are described. Precopula lasts ca. one day. The mean egg-number is 27, and mean egg-diameter is 87 × 75 µm. The number of nauplii per egg (double)-sac amounts to 25–30. Developmental time at 19°C is 6–9 days (nauplii) and 20–24 days (copepodites). The whole developmental period lasts 28 days. The maximal lifespan in the laboratory is 193 days. Sex-ratio is almost balanced. Females produce egg-sacs more than 3.5 times during their life period. Seasonal effects on reproductive activity have not been detected in laboratory cultures.

Feeding rates and gross growth efficiencies in Hyasaraneus L. larvae (Decapoda: Majidae) Reared in the laboratory

Rates of food uptake were measured for individually reared larvae of the spider crab Hyas araneus L. feeding on freshly hatched Artemia nauplii at constant 12°C. Food particles and fragments thereof were registered quantitatively by means of automatic image analysis. Feeding rates ( FR) of crab larvae were given as number of nauplii and amounts of dry weight, carbon, nitrogen, hydrogen, and energy (estimated from C) consumed per day. In both zoeal stages FR increased during postmoult and intermoult, remained high during early and intermediate premoult, and decreased again during late premoult. No clear pattern was found in the course of daily FR of the megalopa. Gross growth efficiencies ( K 1) showed a dramatic decrease from postmoult to early premoult (>60 to <20%) in both zoeal stages. Daily consumption expressed as % body weight also decreased significantly in these instars. Average daily FR were highest in the zoea II, lowest in the megalopa, and intermediate in the zoea I. Since development of the megalopa took the longest time, the total amount of food consumed by this instar was equal to consumption in both zoeal stages combined. K 1 (C-based) was approximately the same in the zoeal instars (24.3 and 25.2), but lower in the megalopa (19.4%), averaging 21.5% for total larval development from hatching to the first crab stage.

Characteristics of suspensions of Kuwait oil and Corexit 7664 and their short-and long-term effects on Tisbe bulbisetosa (Copepoda: Harpacticoida)

A technique for preparing seawater suspensions of Kuwait oil and Corexit was developed. The resulting hydrocarbon concentrations were analysed by gas-chromatography and spectrofluorometric methods and the stability of the suspensions with time was determined. It was established that the suspensions have an effective stability from Days 3 to 15 after preparation, since in this period the concentration varies within a relatively narrow range. Adult female Tisbe bulbisetosa appeared to be quite tolerant of this type of hydrocarbon suspension, in short-term experiments, especially considering that the concentrations used in the bioassays were about 200 times higher than those measured in a relatively polluted area of the lagoon of Venice. Long-term effects on number of eggs produced, number of nauplii and hatching success for females of the third and fourth generations, subject to continuous exposure, were negligible compared with controls.

Dynamique des populations de Tisbe holothuriae (Crustacea: Copepoda) en �levage sur trois r�gimes artificiels diff�rents

The influence of three different artificial diets (“Tetramin”, “Bioter food” and “Renutryl”) on the life cycle of Tisbe holothuriae Humes, 1957 has been investigated under constant experimental conditions (19°C; 38‰ S). Females (F2) whose life history has been followed, were obtained from a common mother (F1). They were bred in 50 ml dishes and transferred into a fresh container as soon as they produced a new egg-sac. Offspring (F3) resulting from successive egg-layings were counted as soon as they moulted into adults. Larval mortality was estimated in two ways: (1) by enumeration of adults issuing from a known number of nauplii; (2) by comparison of the average number of eggs from egg-sacs of F2 with the average number of adult offspring F3. The life-span of F2 females, including the larval stages, varies between 23.6 days (Renutryl diet) and 33.4 days (Tetramin diet). The first egg-sac appears about 12 days after hatching, whatever diet is used. The first copulation immediately follows the last moult, about 8 days after hatching. The reproductive period lasts for 6.5 (Renutryl) to 10.4 days (Bioter). The average number of successive egg-sacs laid is minimal with Renutryl (3.7) and maximal with Tetramin (5.1), but actual egg production is higher with Renutryl (86 eggs/sac) than with Bioter (67) or Tetramin (58). Nevertheless, as a result of varying larval mortality with the different diets, eventual numbers of adult F3 obtained are significantly higher with Bioter (310) than with Tetramin and Renutryl (216 and 188, respectively). The offspring F3 sex-ratio varies in successive broods and with the nature of the food offered: more females are produced with Bioter or Renutryl than with the Tetramin diet. Then net reproduction rate, R0, is higher with Bioter, because of the low larval mortality, high fertility, and high ratio of females resulting from this diet. The intrinsic rate of natural increase (rm) is similar with Renutryl and Bioter diets (0.298 and 0.301, respectively), a lower value (0.260) occurs with the Tetramin diet. These different values are discussed and compared with previous data for Tisbe species fed natural diets.