Flux of radioactive cadmium through the sea-skater Halobates (Heteroptera: Gerridae)

Uptake of ¹⁰⁹Cd in freshly caught sea-skaters Halobates nereis and H. flaviventris was measured under the influence of abiotic parameters as salinity and stable Cd concentration. After 6 d of accumulation a concentration factor of 8 over the seawater level was reached with no indication for an equilibration. The calculated biological half-life of ¹⁰⁹Cd amounted to 9.3 d. Cadmium uptake from food (wingless Drosophila sp. flies reared on cadmium enriched agar) can be considerable. A large pond-skater Limnogonus fossarum, measured for comparative purposes, accumulated cadmium, but at a much lower rate. The results are discussed with respect to observed natural cadmium concentrations in open ocean sea-skater populations.     

Flux of 141Ce through a euphausiid crustacean

The role of the Mediterranean euphausiid Meganyctiphanes norvegica in the cycling of radiocerium (¹⁴¹Ce) was examined. When uptake of ¹⁴¹Ce occurs directly from the water, a dynamic population equilibrium is reached at a concentration factor of about 250. Molting was responsible for up to 99% loss of total body burden at first molt, and about 45% of the remaining activity at second molt, thus denying true longterm equilibrium to individual animals. Fecal pellets did not contain measureable ¹⁴¹Ce activity when the euphausiids accumulated the isotope from water, thus proving that surface adsorption was the key accumulating process from water. When radiocerium was taken in through ingestion of labelled Artemia, about 99% of the body burden was voided as fecal pellets. Excretion by this route was accelerated when euphausiids were fed non-radioactive Artemia during loss phase. Radioactive counts of the pellets confirmed that all ingested ¹⁴¹Ce was lost through defecation. When ¹⁴¹Ce was ingested as labelled phytoplankton, a substantial fraction of the total body burden occurred in the molts, which indicated that the phytoplankton lost ¹⁴¹Ce to the water and the radioactivity was subsequently adsorbed to outer surfaces of the euphausiids. Molts, fecal pellets, and freshly-killed euphausiids lost ¹⁴¹Ce to the water exponentially, the rates being similar to the exponential portions of the loss curves for live, non-molting individuals. It is suggested that M. norvegica, and probably other pelagic zooplankters, can greatly accelerate radiocerium transport to the ocean floor by packaging the isotope as fecal pellets. In coastal areas subject to low-level radioactive waste disposal, ¹⁴¹Ce might be ionic (or at least soluble) to a great extent, in which case euphausiids could take up the isotope rapidly and accelerate its vertical transport via molting.     

Population dynamics and production of euphausiids

Seasonal changes in abundance, size and aspects of the population structure of Meganyctiphanes norvegica (M. Sars) and Nyctiphanes couchi (Bell) are described from samples taken with the Continuous Plankton Recorder at 10 m depth over a 2 yr period (1966 and 1967) in the North Atlantic Ocean and the North Sea. M. norvegica lived for a maximum of just over 2 yr, and adults of both year-classes spawned during a limited breeding season in the spring or summer. N. couchi spawned over a prolonged breeding season, giving rise to a complex of cohorts with overlapping size ranges. It was concluded that 3 or 4 cohorts were spawned in each year and that the maximum life span was probably greater than 1 yr, although maturity may be attained in less than a year. Estimated annual production at 10 m depth for M. norvegica ranged from 0.80 to 18.74 mg m^-3yr^-1 and for N. couchi from 0.67 to 8.23 mg m^-3yr^-1. P:B ratios ranged from 1.3:1 to 6.3:1 for M. norvegica and 4.0:1 to 5.5:1 for N. couchi.     

Drach's molt staging system adapted for euphausiids

A method is introduced to determine intermolt stages in Antarctic and boreal euphausiids. The system is based on the classical scheme elaborated by Drach and Tchernigovtzeff. In addition to the definitions of these authors several features unique to euphausiids are described and combined to establish a system of at least 12 easily distinguishable stages. The method can be used to investiate specific cyclical physiological changes as well as answer questions regarding general growth physiology.     

Zoogeography and diversity of euphausiids around southern Africa

Published and unpublished records of euphausiid distributions around southern Africa are examined for zoogeographic pattern and the results compared with patterns generated from intertidal data sets. Two basic groups of euphausiids are discerned from cluster analysis, corresponding to neritic and oceanic assemblages. Superimposed upon these are Indian Ocean (Agulhas Current) and Atlantic Ocean (Benguela Current) groups. Patterns of diversity and zoogeography generally conform to the large-scale hydrological features in the area. Diversity is higher in the oceanic than in neritic regions. Maximum diversity is recorded off Cape Point, where Indian, Atlantic and southern Ocean waters interact. Diversity is otherwise higher along the east coast, and particularly low in the nearshore waters of the Benguela Current. While particular species of euphausiids can be associated with Agulhas Current and Angola Current waters, westcoast communities lack any distinctive species, and this is discussed. Although the patterns of zoogeography observed for euphausiids are generally similar to those observed for rocky shore communities, there are clear differences between them that reflect their respective habitats and the influence that large-scale water movement has on each.     

Flux of different forms of 106Ru through a marine zooplankter

The dynamics of accumulation and loss of different physico-chemical forms of ¹⁰⁶Ru were measured in the euphausiid Meganyctiphanes norvegica. The accumulation of ¹⁰⁶Ru was directly related to the concentration of the radioisotope in solution, as evidenced by similar concentration factors for euphausiids in the low and high activity ¹⁰⁶Ru chloride solutions. The chemical form of the radioisotope in solution had a pronounced effect on the uptake, with ¹⁰⁶Ru chloride fractions being accumulated at a faster rate than ¹⁰⁶Ru nitrosyl-nitrato complexes. Euphausiids lost ¹⁰⁶Ru, previously accumulated from the ¹⁰⁶Ru chloride complexes, at a faster rate than ¹⁰⁶Ru which had been accumulated from ¹⁰⁶Ru nitrosyl-nitrato forms. Also, in the case of the ¹⁰⁶Ru chloride complexes, the loss rate was inversely proportional to the time allowed for isotope accumulation. The process of molting greatly accelerated the loss of ¹⁰⁶Ru from euphausiids, with first molts shed during the loss phase accounting for 70 to 80% of the total ¹⁰⁶Ru body burden. When euphausiids accumulated ¹⁰⁶Ru from the food chain, the initial-loss rate was rapid due to large amounts of the radioisotope associated with fecal pellets; however, no relationship was found between loss rate and the number of food rations received. Molts from these individuals did not contain ¹⁰⁶Ru, thus, loss from euphausiids obtaining this radioisotope through the food chain is mainly due to fecal pellet deposition and other excretion or exchange processes.     

Trophic strategies of euphausiids in a low-latitude ecosystem

Vertical distribution, diet, and morphology of adults were examined in 27 species of euphausiids occurring in the upper 1000 m in the eastern Gulf of Mexico. Vertical distribution patterns were similar to those found in the central ocean gyres and oceanic equatorial waters of the Atlantic, Indian and Pacific Oceans. Most species migrated vertically from their daytime depths of 300 to 600 m to the upper 300 m at night. Exceptions were the non-migrating species of Stylocheiron, which remained in the epipelagic zone day and night, and Nematobrachion boopis, which remained in the mesopelagic zone. Based on gut-contents analysis, the Gulf euphausiids were largely zooplanktivorous, with cyclopoid and calanoid copepods being the most common items in stomachs. ostracods were especially common in the stomachs of Thysanopoda spp. and phytoplankton in the guts of Euphausia spp. Nearly every species' diet contained a considerable amount of olive-colored debris, which may have been marine snow generated in the epipelagic zone. Cluster analysis grouped the euphausiids into nine diet guilds. Euphausiids with a generalized morphology (i.e., spherical eyes, uniform thoracic appendages) tended to group together and demonstrated little variety in stomach contents among species. Euphausiids with a specialized morphology (i.e., bilobed eyes, elongate thoracic appendages) showed considerable variety in stomach contents among species, and several species had diets that were highly specific. Many of the species that had similar gut contents fed on prey of different sizes, as indicated by the width of the calanoid copepod mandibles found in stomachs. Principal-components analysis of seven morphological characters yielded species groups that were similar, but not identical, to those generated by cluster analysis of stomach contents data. We inferred from this that morphological characters partly determine diet, but that behavior is also important. Using the 20 most abundant species and 3 niche parameters, we attempted to identify the degree of separation among euphausiids based on the level of overlap in vertical distribution and diet composition, and on differences in mean prey size. Overlap of <60% in vertical distribution or diet composition was considered to indicate distinction of that parameter. Of 190 total species pairs, only 4 pairs did not demonstrate niche separation in at least one of these categories. We found that differences in these niche parameters were greatest among species with a specialized morphology and least among species that were morphologically generalized.     

Morphology of the gastric mill in ten species of euphausiids

SEM observation revealed the detailed morphology of the gastric mill in ten species of euphausiids, Bentheuphausia amblyops, Thysanopoda acutifrons, Meganyctiphanes norvegica, Pseudeuphausia latifrons, Euphausia superba, Tessarabrachion oculatum, Thysanoessa longipes, Nematoscelis microps, Nematobrachion boopis, and Stylocheiron maximum. The well-developed gastric mill of euphausiids consists of a pair of cluster spines and a pair of lateral teeth displaying great diversity in morphology. It is suggested that there are three categories of gastric mill and filterpress (gland filter) within euphausiids. One is the well-developed gastric mill with filter-press of B. amblyops; a second is the well-developed gastric mill of M. norvegica, T. oculatum, E. superba, P. latifrons and T. longipes; and the third is the gastric mill without lateral teeth of T. acutifrons, N. microps, N. boopis and S. maximum.     

Biology of euphausiids in the subarctic waters north of Iceland

The seasonal abundance, maturity, spawning, and population dynamics of Thysanoessa inermis (Krøyer, 1846), T. longicaudata (Krøyer, 1846), and Meganyctiphanes norvegica (M. Sars, 1857) were studied in the subarctic waters north of Iceland from February 1993 to February 1994. The material was sampled at approximately monthly intervals along a transect of eight stations extending from 66°16′ to 68°00′N at 18°50′W. Information on temperature and chlorophyll a concentrations is also presented. Spring warming of the water began in March to April and maximum temperatures were recorded in August (3.8?°C). The spring bloom of the phytoplankton started in late March and highest chlorophyll a concentrations were measured during middle to late April (7.0?mg chlorophyll a m^?3). T. inermis was the dominant species in the samples, constituting 77% of juvenile, male and female euphausiids present. The greatest abundance of juvenile, male and female T. inermis and M. norvegica was observed during autumn and winter, with lower abundance in spring and summer. T. longicaudata showed only limited changes in seasonal abundance. Male T. inermis had spermatophores in their ejaculatory ducts from February to May, while mature females had spermatophores attached during April and May. T. longicaudata males bore spermatophores from February to July, whereas females only bore spermatophores in April and May. M. norvegica males had spermatophores from February to April, while the single female with spermatophores was caught in February. Euphausiid eggs were first recorded during the latter part of April; the highest numbers of eggs were observed in the samples taken in late May. Maximum numbers of nauplii of both Thysanoessa spp. and M. norvegica were recorded in late May. The main spawning of the euphausiids coincided with the phytoplankton spring bloom. Most male T. inermis took part in breeding at 1 yr of age while most females appeared not to mature until 2 yr of age. T. inermis has a life span of just over 2 yr, T. longicaudata appears to live just over 1 yr. Limited data did not allow the life span of M. norvegica to be determined.     

Day/night vertical distribution of euphausiids in the eastern tropical Pacific

Between March 23 and April 4, 1981, samples were taken in the eastern tropical Pacific. The day/night vertical distribution of euphausiid species and biomass are described and contrasted in detail on two eastern tropical Pacific stations, the DOME station, in a region of continuous upwelling and the BIOSTAT station, in a nonupwelling area. The effects of various biological parameters, such as temperature, salinity and oxygen concentrations on the distributions of the species are examined. The numbers of euphausiids m^-2 on both stations were highest during the day, indicating that avoidance of the sampler was not a problem. During the day the largest concentration of adult euphausiids was between 300 and 350 m whereas the juveniles were concentrated between 170 and 80 m on both stations. Very few individuals were found within the oxygen minimum layer, but low concentrations of some species were found below the oxygen minimum down to 1 000 m. At night the euphausiid concentration migrated upward into the mixed layer (20 to 30 m) at BIOSTAT and to the base of the mixed layer at the DOME. Significant differences in the night depths of the species were found on both stations. The oxygen minimum layer appeared to act as a barrier to the vertical distribution of all species. Only two species were found in water with an oxygen concentration of <0.1 ml O₂ l^-1. Twentyone species of euphausiids were found on the two stations but the adult population was dominated by only two or three species on both stations. The reproductive state of the species suggested that some species reproduced earlier on the DOME than on BIOSTAT. Analysis of the depth distribution by cluster analysis showed that the most abundant species occupied different depths during the night and day at BIOSTAT but the two most abundant species were concentrated at the same depth at the DOME station although portions of each species population occupied different pelagic zones.     

Diagnostic value of the thelycum in euphausiids. II. Oceanic species,genus Nematoscelis

The thelycum morphology of 7 species of the genus Nematoscelis, based upon observations with the scanning electron microscope, is described. The thelycum of N. megalops and N. difficilis did not differ either with respect to general morphology of the thelycum, or in spermatophore insertion. In the other 5 species, N. tenella, N. gracilis, N. atlantica, N. lobata, N. microps, the main thelycum structure consists of a central lobe of various forms, to which a filamentous spermatic mass is attached. Preliminary observations on the position of the genital pores of two species are reported briefly.     

Vertical distributions of euphausiids and fish in relation to light intensity in the Northeastern Atlantic

The relationship between the vertical distributions of euphausiids and fish and light intensity has been studied directly by using a photometer in conjunction with an acoustically controlled rectangular midwater trawl. Samples were taken at a position centered on 47°N; 17°W on 15 and 16 May 1978. Five species of euphausiid and six species of fish have been analysed, both groups contained migrant and non-migrant species. The population of each of these species occurred throughout a light regime spanning at least three orders of magnitude of intensity; none of them was restricted to, or followed, and isolume. There were no sexual or size differences in the distributions of the euphausiids, but the population of Argyropelecus hemigymnus was probably stratified during the day, with smaller individuals occurring shallower than large ones. The results are discussed in relation to previous observations and to the theories of photic regulation of distributions and migrations.     

Comparative lipid dynamics of euphausiids from the Antarctic and Northeast Pacific Oceans

To better understand the feeding and reproductive ecology of euphausiids (krill) in different ocean environments, lipid classes and individual lipid components of four different species of euphausiids from Northeast Pacific (temperate species) and Southern Ocean (Antarctic species) were analyzed in animals from multiple life stages and seasons. The dominant krill species in the Northeast Pacific Euphausia pacifica and Thysanoessa spinifera, were compared to the two major Antarctic species, Euphausia superba and E. crystallorophias. Analysis comprised total lipid and lipid classes together with individual fatty acid and sterol composition in adults, juveniles, and larvae. Antarctic krill had much higher lipid content than their temperate relatives (10–50 and 5–20% of dry mass for Antarctic and temperate species, respectively) with significant seasonal variations observed. Phospholipids were the dominant lipid class in both temperate krill species, while neutral storage lipids (wax esters and triacylglycerols for E. crystallorophias and E. superba, respectively) were the major lipid class in Antarctic krill and accounted for up to 40% of the total lipid content. Important fatty acids, specifically 16:0, 18:1ω9, 20:5ω3, and 22:6ω3, were detected in all four krill species, with minor differences between species and seasons. Detailed lipid profiles suggest that krill alter their lipid composition with life stage and season. In particular, larval Antarctic krill appear to utilize alternate food resources (i.e., sea-ice associated organisms) during austral winter in contrast to juveniles and adults (i.e., seston and copepods). Lipid dynamics in krill among krill in both systems appear closely linked to their life cycle and environmental conditions including food availability, and can provide a more complete comparative ecology of euphausiids in these environmentally distinct systems.     

Experimental studies on elimination of zinc-65, cesium-137 and cerium-144 by euphausiids

The elimination of 3 radionuclides from Euphausia pacifica was measured over a 5 month period. The biological half-lives for ⁶⁵Zn, ¹³⁷Cs, and ¹⁴⁴Ce, calculated after the euphausiids had ingested radioactive Artemia nauplii, were found to be 140 days, 6 days, and 7.5 h, respectively. The percentages of body burdens lost in molts were greatest for the fission products, ¹⁴⁴Ce (21%) and ¹³⁷Cs (7%), and least for ⁶⁵Zn (1%). Elimination of the isotopes in the feces could not be followed because of the difficulty in collecting fecal material for analysis; however, 1 sample collected 2 months after the beginning of the elimination experiment had no measurable radioactivity. Loss of ⁶⁵Zn from molts and time to disintegration of the molts were found to be temperature dependent over a 5° to 15°C range, and the sinking rate of molts was both temperature and salinity dependent. Calculations showed that, in areas in the North Pacific outside the influence of upwelling, percentage ⁶⁵Zn loss from sinking molts (before disintegration of the molts) was likely to be the same throughout the year, since the molts would be exposed to about the same mean temperature in the water column in all seasons. Even though temperature structure in the upper layers changes with season, mean temperatures change very little when calculated over the sinking distance of intact molts. Intact molts would sink to slightly over 400 m in the absence of turbulence, and would lose 87% of their ⁶⁵Zn by the time they reached this depth. Sinking molts thus might contribute substantially to the vertical transport of ⁶⁵Zn in the sea. If loss of ⁶⁵Zn in fecal pellets is assumed to be small under our experimental conditions, and molting loss is only 1% of ⁶⁵Zn body burden, the major mechanism of ⁶⁵Zn loss from euphausiids feeding on non-radioactive food must be isotopic exchange with the water. Approximately 96% of the initial body burden was eliminated over a period of 5 months.Supported by USAEC research contract AT (45-1)1830, PHS grant ES00026, and a Richland Graduate Fellowship to S. W. Fowler.     

Predation on euphausiids by cod,Gadus morhua,in winter in Icelandic subarctic waters

The euphausiids consumed by cod (Gadus morhua Linnaeus, 1758) taken in November 1983 and February–March 1984 on feeding grounds in the subarctic shelf area north-west, north-east, and south-east of Iceland have been examined. A total of 2 714 euphausiids occurred in the 1 029 stomachs with food which were analysed; of these 1 640 (60%) could be identified to species. Thysanoëssa inermis (Krøyer, 1846) and Meganyctiphanes norvegica (M. Sars, 1857) were most numerous, constituting 58 and 40%, respectively, of the euphausiids which could be identified. The other euphausiids were, in declining numbers of abundance, T. raschii (M. Sars, 1864), T. longicaudata (Krøyer, 1846), and Nematoscelis megalops G. O. Sars, 1883. The mean number of euphausiids occurring per stomach showed considerable variation between both sampling areas and time of sampling. In each area, the mean number of M. norvegica occurring per stomach was similar at both sampling times, while for T. inermis it was greater in February–March than in November. The mean number of euphausiids occurring per stomach increased with increasing size of cod, being 1 to 2 and 4 to 6 in 10 to 30 cm and 50 to 70 cm cod, respectively. An examination of the diel variation in the occurrence of the euphausiids in the stomachs indicated two peaks, one in the morning before sunrise and another in the evening around and after sunset.     

Growth and cadmium uptake in barley under cadmium stress

Effect of various additions of cadmium (5 to 3125 microg g(-1) air dried soil) was studied on growth and Cd uptake in barley grown in pots containing two soil types- a loamy sand and a sandy loam, during different stages of growth. While lower doses (5 to 25 microg g(-1)) led to an increase, the higher doses resulted in a substantial decrease in barley growth. The plant Cd content increased with an increase in soil applied Cd. A decrease in translocation ratio prevailed at higher soil applied Cd, indicating the existence of an exclusion mechanism.     

Influence of complexation on lead(II) and cadmium(II) percolation through a clay liner

Wastes are usually stocked in waste disposals without any pre-treatment. Runoff waters lead to the formation of leachates containing mineral and organic pollutants. In order to prevent groundwater contamination, a double barrier is placed on the landfill bottom. The first one is an active barrier made up of a draining system and a geomembrane, and the second one, consisting of a clay liner allowing pollutant retention, is considered as a passive system. The aim of this work is to evaluate the complexation impact on the organic and inorganic retention. Percolations on columns filled with clay are performed, which allow a better knowledge of the transfer of metallic pollutants, complexed or not, through a model porous media, considering charge and conditional stability of complexes.     

石灰氮对镉污染土壤中镉生物有效性的影响

以石灰作对比,在大田条件下研究了不同石灰氮用量对镉污染土壤中镉生物有效性的影响。结果表明,一定量石灰或石灰氮处理均能显著提高酸性土壤的pH值,降低污染土壤中有效态镉质量分数及水稻茎叶和糙米中的镉质量分数。与不施改良剂的对照相比,石灰施用量达到1 200 kg.hm-2时土壤pH值显著提高,土壤有效态镉质量分数降低12.6%（P〈0.05）,水稻茎叶和糙米中镉质量分数分别降低25.5%（P〈0.05）和28.3%（P〈0.05）;石灰氮施用量达到600 kg.hm-2时,土壤pH值显著高于对照,土壤有效态镉质量分数较对照降低10.9%（P〈0.05）,水稻茎叶和糙米中镉质量分数分别降低36.8%（P〈0.05）和33.0%（P〈0.05）。等量条件下（600 kg.hm-2）石灰氮对降低土壤镉有效性及水稻累积镉的效果相对优于石灰处理。因此,石灰氮与石灰一样可用于酸性重金属污染土壤的修复与改良,是一种极具潜力的土壤改良剂。     

模拟降水对碱性盐化土壤中镉的淋滤及形态变化的影响

采用人工模拟方式,试验研究了不同pH值的降水对碱性盐化土壤中镉的连续淋滤效果,分析了淋洗后土壤中镉的形态变化特征。结果表明,在不同pH值降水对土壤中镉的淋滤过程中,12h内基本上达到高峰,12h后镉的淋滤量较低,随着时间的延续镉的淋洗量基本保持不变;降水有利于土壤中的镉释放,且pH值越低,镉的释放量越高。土壤盐化对降水淋洗镉的效果有一定影响,氯化物的存在,有利于镉的淋滤,淋滤量增加值在18%～94%之间,随着淋洗液pH值的增加,镉的淋滤量增加幅度减少;与对照组土壤样品相比,淋洗液pH降低利于增大硫酸盐型盐化土壤中镉的淋滤量,当pH值为中性时,镉的淋滤量减少;苏打型盐化土壤镉的淋洗效果与硫酸盐型土壤相似。模拟降水淋洗后,土壤中镉的形态发生明显变化,与淋洗前相比,土壤中镉的可交换态、碳酸盐结合态、有机结合态的质量分数降低,随着淋洗液酸性的增加,降低幅度增大;镉的铁锰氧化态相对质量分数在淋洗后有所增加。     

The fatty acids of antarctic phytoplankton and euphausiids. Fatty acid exchange among trophic levels of the Ross Sea

The fatty acids of 3 samples of Euphausia superba, 7 samples of E. crystallorophias, and 12 samples of phytoplankton collected in the Ross Sea, Antarctica, during Eltanin Cruise 51 were examined. The fatty acid profiles of the samples of E. superba resembled each other closely. The fatty acid profiles of the E. crystallorophias samples were also similar to each other but different quantitatively from those of E. superba. Phytoplankton fatty acid patterns varied with the geographical location and species composition of the samples. The fatty acids of euphausiids were compared to those of the phytoplankton from the corresponding locations. Rather similar fatty acid patterns in phytoplankton and E. superba corroborate the herbivorous nature of this euphausiid. On the other hand, phytoplankton and E. crystallorophias showed quite different fatty acid patterns. The differences were mostly due to the presence of waxes among the lipids of E. crystallorophias. It is not clear whether these waxes are of dietary origin or are synthesized endogenously.