Life cycle of Epischura baicalensis Sars (Copepoda, Calanoida) in Lake Baikal

Epischura baicalensis Sars is a dominant pelagic species of Lake Baikal zooplankton. This is endemic to Lake Baikal and inhabits the entire water column. It produces two generations per year: the winter–spring and the summer. These copepods develop under different ecological conditions and vary in the duration of life stages, reproduction time, maturation of sex products and adult males and females lifespan. The total life period of the animals from each generation is one year. One female can produce 10 egg sacks every 10–20 days during its life time. The ratio of males and females is 1:1. One of the most essential features of the ecology of E. baicalensis is the alteration of its mass inhabited areas during a year, as well as in day time. This is due to the need for various conditions for gonad maturation, reproduction, nourishing and protection from being consumed by planktivors.     

Observations on colony formation by the cosmopolitan phytoplankton genus Phaeocystis

Few marine phytoplankton have heteromorphic life cycles and also often dominate the ecosystems in which they occur. The class Prymnesiophyceae contains a notable exception: the genus Phaeocystis includes three species that form gelatinous colonies but also occur within their ranges as solitary cells. Phaeocystis antarctica and P. pouchetii are exclusively high latitude taxa, and are notable for regionally tremendous blooms of the colony stage. P. globosa occurs circumglobally, yet its colony blooms primarily are confined to colder waters within its range. Three additional species are warm water forms that have been reported only as solitary cells or loose aggregations that bear little resemblance to the organized colonies of the other taxa. Interpretation of existing data indicates that resource availability (light, temperature and nutrients) by itself is not sufficient to explain this distinction between cold-water colony-forming taxa and warm water solitary cell taxa, nor why colony development in P. globosa is essentially a spatially restricted phenomenon within a much broader geographic range. Colony development by P. globosa in situ has been observed at temperatures ≥20 °C, but only rarely and generally under conditions of seasonally or anthropogenically elevated nutrient supply. Data presented here demonstrate colony development at 20–22 °C in natural plankton communities from oligotrophic waters that were pre-screened through 63 μm mesh (i.e. lacking mesozooplankton and large microzooplankton), but not in unscreened communities containing microzooplankton and >63 μm zooplankton. Reduction of colony proliferation at higher temperatures by mesozooplankton grazing remains as an intriguing possibility that is consistent with available evidence to help explain differences in latitudinal extent of in situ colony development. These data are interpreted within a theoretical framework regarding the potential advantages and disadvantages of the two life cycle stages.     

Colonization of a new man-made river (Marchfeldcanal, Lower Austria) by benthic copepods

The role of copepods in the colonization and emigration processes of benthos and drift of an irrigation canal were studied. During the 3 first years of existence of the canal, fifteen species of copepods were recorded (1 diaptomid, 11 cyclopoids, 3 harpacticoids). Copepod succession in the canal was initially represented by lentic species, then by predatory species like Macrocyclops albidus that developed with the proliferation of filamentous algae and epibionts during the first two years. Primary consumers appeared from the beginning of the flowing conditions but started to dominate only from the third year. Smaller species associated with the bed sediments like the harpacticoid species Nitocra hibernica, were late colonizers. The latter as well as Paracyclops fimbriatus and Eucyclops serrulatus were the dominant copepod species in the canal. Total copepod density in the benthos ranged from 15,800 to 68,000 ind./m², with a mean of 7.6% of the total zoobenthos. Copepods constituted up to 25% of the total faunal drift density, ranging from 50 to 140 ind./m³. Their highest abundance was observed around midnight. A three-fold increase of the discharge temporarily affected the drift density, but did not change the diel rhythm of the drift. Cyclopoid copepods namely P. fimbriatus (54.77%), copepodid cyclopoids (20.76%) and E. serrulatus (16.11%) formed the main part of the drift samples. The harpacticoid Nitocra hibernica was a minor participant in the drift processes.     

Distribution and diet of larval and juvenile Arctic cod (Boreogadus saida) in the shallow Canadian Beaufort Sea

The distribution and diet of larval and juvenile Arctic cod (Boreogadus saida) were studied during summer 2005 in the coastal Canadian Beaufort Sea. A total of 275 individuals were captured and the highest abundance was observed at station depths of 20–30 m. This corresponds well with the location of the frontal zone where the Mackenzie River plume water and open sea water meet. Diet examinations were performed on 220 Arctic cod, which were found undamaged from sampling. We observed a gradual decrease in prey number per fish and increase in prey size as larvae grew which corresponded to a shift from Rotifera and nauplii towards larger copepodid stages. However, at all sizes, the larvae remain generalists and feed on a broad range of organisms. Environmental changes due to climate warming could have a two-fold impact on fish larvae feeding in the studied region. First, the potential for increased primary production may lead to increased zooplankton production that may impact the feeding and nutrition positively. On the other hand, greater discharge of turbid water from the Mackenzie River may reduce light penetration in the water column that may negatively influence the ability of visual predators to successively forage.     

The gonad morphology and maturation in Arctic Calanus species

Gonad morphology and maturation of the dominant Arctic copepod species Calanus glacialis and C. hyperboreus were studied using a combination of observations on whole animals (“whole-body analysis”) and histological sections to describe basic reproductive processes. The comparison with C. finmarchicus shows that the internal organisation of the gonads is the same in the Calanus species: from the dorsally laying ovary, two anterior diverticula extent into the head region and two posterior diverticula extend into the abdomen. In the diverticula, the oocytes increase in size and development stage in a dorso–ventral direction. There were no physiological differences between the oocytes in the diverticula and oviducts in any of the three species. During gonad development, the morphological modifications of the gonads mainly refer to an increase in number, developmental stage and size of the oocytes both in diverticula and oviducts. During spawning the most ventral layer of oocytes is released, and then the adjacent dorsal layer begins final maturation. Thus, the final maturation processes occur simultaneously as it is essential to produce clutches.     

Modelling Pseudocalanus elongatus stage-structured population dynamics embedded in a water column ecosystem model for the northern North Sea

This paper outlines an approach to couple a structured zooplankton population model with state variables for eggs, nauplii, two copepodites stages and adults adapted to Pseudocalanus elongatus into the complex marine ecosystem model ECOHAM2 with 13 state variables resolving the carbon and nitrogen cycle. Different temperature and food scenarios derived from laboratory culture studies were examined to improve the process parameterisation for copepod stage dependent development processes. To study annual cycles under realistic weather and hydrographic conditions, the coupled ecosystem–zooplankton model is applied to a water column in the northern North Sea. The main ecosystem state variables were validated against observed monthly mean values. Then vertical profiles of selected state variables were compared to the physical forcing to study differences between zooplankton as one biomass state variable or partitioned into five population state variables. Simulated generation times are more affected by temperature than food conditions except during the spring phytoplankton bloom. Up to six generations within the annual cycle can be discerned in the simulation.     

Distribution, reproduction and development of Calanus species in the Northeast water in relation to environmental conditions

The vertical and horizontal distribution of mesozooplankton biomass and its composition, together with the reproduction and development of the three dominant herbivorous copepods Calanus finmarchicus, C. glacialis and C. hyperboreus, were studied in the Northeast Water between the end of May and end of July, 1993. Biomass varied between 0.15 and 10.6 g m⁻² and was lower on the shallow banks. Highest biomass was found on the shelf slope and in the entrances to Belgica and Westwind Troughs. There was no seasonal trend during the study period. Among the zooplankton taxa, copepods were dominant, with 84% biomass of all other taxa, followed by chaetognaths with 14%. The large Calanus species made up 91% of copepod biomass. The most abundant species, C. glacialis, inhabited areas of low current speeds on Belgica and Ob Bank, C. hyperboreus dominated shelf slope and trough stations, while C. finmarchicus was most abundant in the Return Atlantic Current along the shelf slope and also eastern Belgica Trough. C. glacialis was the only Calanus species spawning during this period, but young copepodites of the other species were also abundant. Egg production of C. glacialis was at a maximum by our arrival and continued to at least mid August. According to the results from starvation experiments, its egg production was fuelled by food uptake, but was decoupled from phytoplankton chlorophyll until July, indicating ice-algae and microzooplankton as an alternative food source. Only when the polynya approached its maximum extent was a close relationship to phytoplankton established. Due to both spatial and temporal heterogeneity of the occurrence of young copepodite stages it was impossible to follow the growth of cohorts of developmental stages. Herbivorous carbon requirements estimated from egg production rates were mostly less than one third of the phytoplankton stock. From egg production and the distribution of young stages, the outer Westwing Trough seems to be the centre of biological activities. This may be related to the formation of young ice in winter in this area, which was found to carry a large mass of under-ice algae. High biomass but low production in Belgica Trough indicate this as an advective and expatriated community of C. finmarchicus and C. hyperboreus, where grazing is negligible, at least during early summer.     

Additions to Mexican freshwater copepods with the description of the female Leptodiaptomus mexicanus (Marsh)

A survey on 10 temporary and permanent water-bodies, located at more than 2000 m above the sea level in the central part of Mexico resulted in the presence of 17 cyclopoid and five calanoid copepods. From the total taxa found, seven are new to the country: Leptodiaptomus assiniboiaensis (Anderson), Microcyclops dubitabilis Kiefer, Ectocyclops rubescens Brady, Eucyplops cf. bondi Kiefer, Eucyclops cf. prionophorus Kiefer, Eucyclops pseudoensifer Dussart, and Eucyclops cf. solitarius. The female of Leptodiaptomus mexicanus, a species known only from a single male found near Mexico City in 1929, is here described for the first time. Copepod fauna for each of the systems was highly diverse, with up to 12 species co-occurring in temporary ponds. This study revealed a mixture of north and south American taxa in the area.     

Production of Acartia omorii (Copepoda: Calanoida) in Ilkwang Bay, southeastern coast of Korea

Production of the marine calanoid copepod Acartia omorii was measured from 2 October 1991 to 8 October 1992 at a station in Ilkwang Bay on the southeastern coast of Korea. A. omorii (nauplii + copepodites + adults) were present in the plankton throughout the year, with seasonal variation in abundance. Biomass of A. omorii was averaged at 0.44 mgC m^− 3, with peaks in February and July, and relatively low biomass in late summer and fall. Egg production rate ranged from 2.4 to 151.9 μgC m^− 3 day^− 1, which was equivalent to 95–6075 eggs m^− 3 day^− 1. Fecundity of an adult female was averaged at 38 eggs female^− 1 day^− 1. Instantaneous growth rates of copepodites were higher than those of nauplii stages. Annual production of A. omorii ranged from 33.5 mgC m^− 3 year^− 1 to 221 mgC m^− 2 year^− 1, showing a seasonal variation of daily production rate with peaks in February and July. The daily production rate of A. omorii was significantly correlated with chlorophyll a concentration. These results suggest that standing stocks and/or productivity of phytoplankton are the major influencing factors, rather than water temperature for the seasonal variation of production of A. omorii in Ilkwang Bay.     

Estimation of copepod production in a flooded savanna of Venezuela

This is the first contribution to the copepod production in Venezuelan tropical savannas. Total abundance, biomass, production and mean P/B ratio of nauplii, copepodids and adults were determined in interdaily samples from a flooded, embanked savanna during February and March (end of dry season), and May (beginning of rainy season). Highest values of biomass and total production were recorded during dry season (61.5 mg m⁻³, 153.8 mg m⁻³ day⁻¹, respectively), compared to the rainy season (5.6 mg m⁻³, 45.9 mg m⁻³ day⁻¹). The last values are related to a low population density found during rainy season. Highest production were observed in copepodids at the end of the dry season. Significant differences of production between nauplii and copepodid stages, as well as between nauplii and adults, were also found.     

Egg production of the copepod Acartia hongi in Kyeonggi Bay, Korea

Many studies of copepod egg production have shown that food availability and temperature are major factors that influence copepod growth. However, coastal environments are complicated ecosystem and the relationships between growth of copepods and influencing factors are not always clear in nature. We conducted a study along an inner–middle–outer bay transect where variations in environmental parameters would be expected to affect the biomass and egg production rate of A. hongi from February 2001 to December 2001. In this study, we investigated the abundance and biomass with developmental stages and egg production rates of A. hongi in relation to various environmental factors. The copepod A. hongi occurred continuously throughout the year, with a peak abundance in May. In general, the variation in egg production rates showed a similar tendency with the variations in chlorophyll-a throughout the study period. This suggests that phytoplankton biomass is an important factor that affects the egg production of A. hongi. In addition, during the warm season, the egg production of A. hongi was also influenced by the ciliates abundance in the middle and outer bay. Consequently, the egg production of A. hongi is generally affected by food availability in Kyeonggi Bay.     

Small scale retentive structures and Dinophysis

Despite its rarity, Dinophysis acuminata is in terms of economic impact, the first toxic algal species along the coasts of Western Europe. It is observed at low levels (< 20 cell l^− 1) all the year round but toxic events occur mainly in late spring and summer. D. acuminata ecophysiology is largely unknown due to the inability to culture it. Therefore, standard biomass models based on inorganic nutrition are largely inadequate. Presently, any progress in describing the conditions of population growth of this species will be a step forward to prediction of harmful events at the coast. This species has been observed at increased, albeit low cell densities in retentive eddies located in pycnocline layers. A concentration build-up of one species results from the balance between growth and loss processes, one of the latter being dispersal. The scales of interest for a D. acuminata population are of the order of 10 nautical miles on the horizontal and duration of 10 days, for a reported achievable growth rate of 0.6 day^− 1. A three dimensional (3D) hydrodynamical model of the Bay of Biscay has been elaborated to reproduce hydrological structures over the last decade. We attempt here to relate the existence of retentive structures revealed from simulations under realistic forcing conditions and the toxic coastal events recorded in the 10-year time series of the French plankton monitoring network database. The eddies in the coastal area appear to be directly related with the Dinophysis coastal events and they may be a potential effective tool to predict those.     

Character phylogenies in Candacia and Paracandacia (Copepoda, Calanoida) and the inevitably paraphyletic nature of many nominal taxa above subspecies level

Examination of the phylogenetic structure of the family Candaciidae shows the genus Paracandacia to comprise a strongly modified branch emerging from the clade commonly denoted as Candacia. This has been confirmed by studying selected character phylogenies. It is argued that the resulting paraphyletic nature of Candacia auct., though in a cladistic context undesirable on theoretical grounds, has to be accepted as inevitable. Recent studies on molluscs and arthropods, viz., have demonstrated that the continuous origin of paraphyletic taxa from previously monophyletic ones is nothing but a naturally occurring process, intrinsically embodied in the course of evolution.     

A probabilistic damage tolerance concept for welded joints Part 2: a supplement to the rule based S–N approach

The first part of this paper presented the required statistics and stochastic models for reliability analysis of the fatigue fracture of welded plate joints. This present Part 2 suggests a probabilistic damage tolerance supplement to the design S–N curves for welded joints. The goal is to provide the practising engineer with simple tools that predict the reliability against fatigue fracture during service life. The impact of the chosen fatigue design factors (FDF) and the uncertainty in the applied stresses is revealed. The effect of an in-service inspection programme is also predicted. The results are presented as dimensionless matrices and suggested for use in support of decision-making at the design stage, without any advanced fracture mechanics modelling and stochastic simulation. One important advantage of this format is that the probability levels are presented regardless of actual weld class and target service life (TSL). This is obtained by introducing the FDF as a key parameter to the results. This parameter is defined as the ratio of predicted fatigue life over TSL. FDF is always calculated in the S–N approach which is mandatory in fatigue life prediction. Various welded details (classes) will have the same reliability level for the same FDF. This is true at the end of TSL and at earlier stages, i.e. fractions of TSL. The absolute value of TSL is immaterial for a given FDF. In the case of in-service inspection, the inspection interval is also given without dimensions as a fraction of TSL.

Only the influence of future scheduled inspections is treated. Updating based on actual inspection results is not included as the scope of work is inspection planning at the design stage. Results for some frequent cases occurring in practice are readily derived and presented.     

Review of empirical and semi-empirical Y factor solutions for cracked welded tubular joints

The practical use of fracture mechanics has been established for use on large turbine and electric generator rotor components used in the atomic power generation and the aircraft industry. Application areas in the offshore industry have also been identified. Fracture mechanics is currently used at the design stage of offshore facilities. It provides the basis for fatigue life prediction, steel selection and tolerance setting on allowable weld imperfections. Fracture mechanics is also used during the operational stage of a structure to make important decisions on inspection scheduling and repair strategies and as a tool for establishing limits on operational conditions. Linear elastic fracture mechanics relies on the use of the stress intensity factor concept. The stress intensity factor is a very important fracture mechanics parameter. Therefore, the accuracy of any fracture mechanics model for the prediction of fatigue crack growth in offshore structures for example will depend very much on the accuracy of the stress intensity factor solution used. Several empirical and semi-empirical solutions have been developed over the years with varying degrees of accuracy. This paper presents a review of some of these methods and attempts to assess their accuracy in predicting Y factors for welded tubular joints by comparing predicted results with experimental data obtained from fatigue tests conducted on large scale welded tubular joints. The experimental results were conducted under simulated service conditions, using a jack-up offshore standard load history (JOSH). A comparison between the experimental and predicted results shows that there may be other factors, which influence fatigue crack growth under variable amplitude conditions. Some of these factors have been identified and discussed in this paper.     

Haplostoma dudleyae sp. nov. (Cyclopoida: Ascidicolidae), parasitic in Eudistoma olivaceum from the Indian River in southern Florida

Haplostoma dudleyae sp. nov. is described and illustrated on the basis of females found in a compound ascidian (Eudistoma olivaceum) collected from the Indian River in southern Florida, USA. Each parasitized zooid has a single female copepod. The egg sacs of the female are paired and, when laid, are almost U-shaped and folded against the dorsal side of the body. Haplostoma dudleyae and two other species (H. canui Chatton and Harant, 1924, and H. humesi Ooishi, 1995) constitute a subgroup within the genus Haplostoma.     

Environmental causes of the fluctuations of red shrimp (Aristeus antennatus) landings in the Catalan Sea

The fluctuations of catches of the deep-sea shrimp Aristeus antennatus (Risso, 1816) were analysed in the 6 ports of Catalonia where production is concentrated, based on monthly landings from 1988 to 2004. The 6 selected ports produced 300 t of red shrimp in 2004, or 80% of the total production in Catalonia. The series for each port showed clear interannual variability, with peaks of production in the early 1990s and more recently from 2001 to 2003. The time periods of the monthly data series, estimated by frequency analysis based on Fourier transform, varied around 7–8 years in the four central ports and 12–13 years in the two northern ports. Additionally, the different curves were not in phase: even in nearby ports, the maximum production is observed in different years. Since the North Atlantic Oscillation (NAO) index is an excellent proxy for long-term series of environmental variables, we aimed to explore relationships between the fluctuation of the NAO index and A. antennatus landings in the Catalan Sea. The correlation between the mean annual NAO index and the annual catches in each port was positive and significant with some time lags (from 1 to 3 years). The existence of clear patterns linking the NAO with marine ecological processes has been demonstrated in many studies, but the underlying ecological mechanisms are far from being well understood. The variations in environmental parameters linked to the NAO may act on biological organisms at different levels (individual, population) through physiology (metabolic and reproductive processes) or through trophic relationships, including ecological cascade effects. We propose that NAO-induced environmental variability may enhance food supply to A. antennatus and hence strengthen the reproductive potential of particular year classes, which result in increased catches 1 to 3 years later, although other possible effects of environmental variability on the population dynamics of this species are worth investigating.     

Seasonal variability of the Black Sea chlorophyll-a concentration

The optimal spectral decomposition (OSD) method is used to reconstruct seasonal variability of the Black Sea horizontally averaged chlorophyll-a concentration from data collected during the NATO SfP-971818 Black Sea Project in 1980–1995. During the reconstruction, quality control is conducted to reduce errors caused by measurement accuracy, sampling strategy, and irregular data distribution in space and time. A bi-modal structure with winter/spring (February–March) and fall (September–October) blooms is uniquely detected and accurately documented. The chlorophyll-a enriched zone rises to 15 m depth in winter and June, and deepens to 40 m in April and 35 m in August. The June rise of the chlorophyll-a enriched zone is accompanying by near-continuous reduction of upper layer maximum chlorophyll-a concentration.     

Species of Thaumatomastix (Thaumatomastigidae, Protista incertae sedis) from the Arctic sea ice biota (North-East Water Polynya, NE Greenland)

The sea ice biota of polar regions contains numerous heterotrophic flagellates very few of which have been properly identified. The whole mount technique for transmission electron microscopy enables the identification of loricate and scaly forms. A survey of Arctic ice samples (North-East Water Polynya, NE Greenland) revealed the presence of ca. 12 taxa belonging to the phagotrophic genus Thaumatomastix (Protista incertae sedis). Species of Thaumatomastix possess siliceous body scales and one naked and one scale-covered flagellum. The presence in both Arctic samples and sea ice material previously examined from the Antarctic indicates that this genus is most likely ubiquitous in polar sea ice and may be an important component in sea ice biota microbial activities.