The role of copepods in the planktonic ecosystems of mixed and stratified waters of the European shelf seas

The European shelf seas can be divided into regions which have tidally mixed waters and thermally stratified waters. The tidally mixed near shore environments support zooplankton communities dominated by smaller copepods and having large meroplankton contributions. These small copepods (Centropages spp., Temora spp., Acartia spp., Paral Pseudo/Microcalanus spp.) together with the microzooplankton component form a different and more complex food web than the larger copepod/diatom link associated with thermally stratified waters. The copepods Calanus finmarchicus and C. helgolandicus account for over 90% of the copepod dry weight biomass in stratified waters. Although occurring in lower numbers in mixed waters they can still make significant contributions to the biomass. A 31 year time series from the European shelf shows the inter- and intea-annual variability of these species. The basic biology and food web that these two systems support, and the transfer of energy, can result in marked differences in quantity and quality of particulates available as food for fish larvae. Calanus dominated systems allow the primary production to be directed straight through the trophic food chain (diatoms/Calanus/fish larvae) while the near shore communities of smaller copepods limit the amount of energy being transferred to the higher trophic levels. Eighty-two Longhurst Hardy Plankton Recorder hauls were used as the data base for this study. In all cases the zooplankton was dominated by copepods both in numbers and biomass accounting for > 80% of total zooplankton dry weight in the Irish Sea, Celtic Sea, shelf edge of the Celtic Sea and the northern and southern North Sea in Spring.     

The Biogeochemistry of Sediments from the Madeira Abyssal Plain — Preliminary Results

The organic biogeochemistry of surface sediments from the Madeira Abyssal Plain has been investigated. Total organic carbon contents, organic carbon to nitrogen ratios, concentrations of hydrolysable amino acids, hydrolysable carbohydrates and lipids have been determined. In one case, the detailed lipid compositions were also investigated. The sedimentary geochemistry appears to have been strongly influenced by the recent (ca. 1000 yrs.) deposition of a turbidite. Normally labile lipids are present in high concentrations through the turbidite and the numbers of the most abundant metazoan meiofauna (nematodes) closely correlates with the concentrations of the former. Concentrations of hydrolysable amino acids and carbohydrates, relative to total organic carbon, also decrease through the turbidite layer, but in the case of the carbohydrates tend to be higher in the underlying pelagic sediments. Deeper sediments are more oxidised than those at the surface. The concentration profile for manganese in one of the examined cores suggests that this anomaly arises through the action of manganese-reducing bacteria that are present in pelagic sediments underlying the turbidite.     

Day/night differences in the grazing impact of marine copepods

Day/night differences in the removal rate of phytoplankton can occur as a result of increased copepod grazing rates at certain times of the day and diel vertical migration of animals. We conducted shipboard grazing experiments and fine-scale vertical zooplankton sampling to resolve these behaviors. Day/night feeding differences were compared in the center of several warm-core Gulf Stream rings, under conditions of no lateral water mass exchange, in the mesohaline portion of Chesapeake Bay and when following drogues in the Chesapeake Bay plume. Day/night variations in copepod biomass in the surface mixed layer were greater in neritic waters as compared to the open ocean stations. Day/night differences in weight-specific copepod filtration rates varied less than biomass. At the neritic stations copepod grazing was often higher at night, whereas at the oceanic stations day/night grazing rates were similar or daytime grazing rates were highest. The night/day ratio of zooplankton grazing impact on the phytoplankton community (the product of zooplankton biomass and their weight-specific grazing rate) averaged 4.8 in the Chesapeake Bay plume and 1.6 in warm-core Gulf Stream rings. Our results suggest that at lower food levels, there often are less day/night differences in the removal rate of phytoplankton by the copepod community.     

The estimation of individual dry weight and standing crop of harpacticoid copepods

Individual dry weights have been calculated for ten species of harpacticoid copepods including epibenthic and interstitial forms. The data have been used to calculate a linear relationship between body length and weight enabling the individual dry weight of any harpacticoid of known body length to be estimated. The length-weight relationship has been used to estimate the standing crop of harpacticoids from three different sediment types. In all cases the estimated values were within 20% of the actual standing crop as determined directly by weighing.     

Site-to-site variability in abundance of meiobenthic copepods along a tidal gradient over 24 hours

As part of a larger study on the effects of juvenile fish predation on meiobenthic copepods, we collected meiofauna every two hours for 24 hours at three muddy sites along a transect through vegetated marsh, to unvegetated intertidal to unvegetated subtidal habitats. The vegetated marsh (Spartina alterniflora) site harbored significantly more copepods over the combined sampling period than the other two sites. Some species were distributed along the entire transect, but several species were much more abundant at one site than the others. For example, Microarthridion littorale was most abundant at the intertidal site, and Enhydrosoma propinquum was most abundant at the unvegetated sites. The most abundant subtidal species included Pseudobradya pulchella and Paronychocamptus wilsoni. Three species were most abundant in the vegetated marsh (Stenhelia (D.) bifidia, Nannopus palustris, and Diarthrodes aegidius). Maximum total copepod abundance occurred during the daytime low tide at all three sites. Of the four species more abundant in the light than at night, three were subtidal. Most of the time there were no detectable differences between high and low tide abundances, suggesting that there was little exchange of individuals between habitats as tidal levels changed. Without samples from additional transects or the ability to obtain samples for all possible combinations of light and tide levels, we could not detect significant interactions between these two environmental factors. Based upon the species composition of copepods in the gut contents of motile fish predators, the existence of distinct copepod species assemblages at sites along the transect may allow inferences about where fish had fed.Contribution No. 695 from the Bell W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina.     

The distribution of calanoid copepods in the plankton of Wisconsin Lakes

Zooplankton communities from 499 lakes were examined for calanoid copepod species. Limnocalanus macrurus and Senecella calaloides are confined to Lakes Michigan, Superior and one inland lake each. Eurytemora affinis has recently become established in the coastal waters of Lakes Michigan and Superior. Epischura lacustris is present in the summer plankton of a wide variety of lake types. Aglaodiaptomus leptopus is sensitive to fish predation and confined to small lakes without fish. Leptodiaptomus ashlandi is restricted to Lakes Michigan and Superior, but L. sicilis is also found in some inland lakes. Leptodiaptomus minutus is a boreal species found mostly in lakes of the far north. Skistodiaptomus oregonensis is the most commonly occurring calanoid and seems well adapted to lakes of the meso-to low eutrophic types. Skistodiaptomus pallidus is also generally distributed throughout the state, but less common than oregonensis and adapted to more eutrophic lakes. Leptodiaptomus siciloides and A. clavipes are western species, adapted to eutrophic lakes, which are expanding their ranges eastward, aided by cultural eutrophication.     

Propagation of planktonic copepods: production and mortality of eggs

Data on fecundity and egg mortality of neritic copepods were collected in various seasons, areas and under various hydrographical conditions. On a seasonal basis variations in fecundity (F) were related to temperature rather than to the abundance of phytoplankton (P). However, a strong correlation between F and P was evident when water column stability varied horisontally or temporally (i.e. at a tidal front or subsequent to a storm). Estimated specific egg-mortalities were variable and occasionally very severe, up to 9.1 d^–1, implying that down to 10^–4% of the eggs survive to hatching. The implications for phenology and distribution of copepods are discussed.     

Effects of sediment loading on food perception and ingestion by freshwater copepods

Seasonal influx of suspended sediments to lakes is common in many aquatic systems, particularly during periods of high flow. Suspended particles not only affect visibility and net primary productivity, as light penetration is reduced, but may also affect the ability of herbivorous zooplankton to locate and ingest food. In Swan Lake, an oligotrophic lake in northwestern Montana, the dose association between zooplankton population development and seasonal maxima in turbidity levels suggests that the community present during peak turbidity is minimally impacted by suspended sediments. This report presents the results of laboratory investigations into the effect of suspended sediments on feeding by the copepod Diaptomus ashlandii, the dominant zoo‐plankter in Swan Lake. Ingestion rate for copepods feeding on ³²P labeled algae was significantly reduced in the presence of suspended particles at all turbidity levels tested (5 to 200 NTU's) compared to ingestion rate in the absence of suspended particles (0 NTU's).     

Aspects of the study of the life cycles of Antarctic copepods

Different approaches to the study of life cycle strategies of Antarctic copepods are described in an attempt to shed new light on our present knowledge. To date, most studies were carried out on abundance, horizontal and vertical distribution and stage composition during different seasons and in various regions. Hence, the seasonal pictures had to be compiled from different years and sampling regions. The physiological method includes measurements on e.g. egg production, feeding, respiration and excretion rates, C:N and O:N ratios, lipid and protein contents. However, both physiological and biochemical data are still rare. Results of field observations are given in this paper for investigations conducted within the last 15 years in the eastern Weddell Sea, while data of physiological parameters are based on a broader geographical region. In the eastern Weddell Sea, eight copepod species account for about 95% of copepod abundance and for more than 80% of copepod biomass. Within the calanoids, the small species Microcalanus pygmaeus dominates by numbers with 66%, while the large species Calanoides acutus and Calanus propinquus comprise together 52% of the biomass. Species abundance is lowest in winter and highest in summer/autumn, however, seasonal changes in the abundance of M. pygmaeus are small and this species occurs in similar quantities throughout the year. All copepod species show a distinct seasonal vertical distribution pattern and they occur in upper water layers in summer, in contrast to the other seasons. However, the depth layers of maximum concentration differ between species. The ontogenetic vertical migration is most pronounced in C. acutus and relatively weak in C. propinquus. The age structure also shows seasonal differences with the youngest population observed in summer for C. acutus, C. propinquus, Ctenocalanus citer or autumn for Metridia gerlachei, whereas the M. pygmaeus population is oldest during summer. The youngest copepodite stage and the males are not always present in C. acutus and C. propinquus. In contrast, all developmental stages and both sexes occur throughout the year in M. gerlachei, M. pygmaeus and C. citer. Gonad maturation in the dominant calanoid species proceeds well before the onset of phytoplankton production in the eastern Weddell Sea. However, the highest portion of females with ripe gonads and hence highest egg production rates coincide with the productive period in spring and summer. In autumn, ovaries of the three larger species C. acutus, C. propinquus and M. gerlacheiare all spent. In contrast, the percentage of ripe females of the two smaller species, C. citer and M. pygmaeus, stays high in autumn. Egg production rates are highly variable within one region and species. Many copepods accumulate large depots of lipid, mainly wax esters. In contrast, five species (C. propinquus, C. simillimus, Euchirella rostromagna, Stephos longipes and Paralabidocera antarctica) almost exclusively synthesise triacylglycerols and not wax esters. The lipid content exhibits distinct seasonal patterns, and is highest in autumn. A seasonal difference is also obvious in metabolic activities with lowest rates during the dark season. The adaptation to the pronounced seasonality in the Southern Ocean differs greatly between copepod species, and most Antarctic copepods stay active during the dark season. Calanoides acutus seems to be the only true diapause species. Calculations of summer developmental rates and winter mortality rates of the large species C. acutus and C. propinquus suggest that both species have a 1-year life cycle with few females overwintering and probably spawning a second time. In contrast, a 2-year life cycle is more likely in R. gigas. However, life cycle durations of all species studied are still uncertain and regional differences are very probable.     

Harpacticoid copepods associated with the seagrass Halophila ovalis in the Ashtamudi Estuary,south-west coast of India

A temporal study of harpacticoid copepod populations associated with the seagrass Halophila ovalis was undertaken in the Ashtamudi Estuary, south-west coast of India. A total of 19 species representing 8 families was recorded in this assemblage. Harpacticoids formed 7.52% of the total phytal meiofauna. At the species level, harpacticoids exhibit parallel assemblages with phytal zones, found in other localities.     

Foraging tactics and prey-selection patterns of omnivorous and carnivorous calanoid copepods

The foraging tactics and prey-selection patterns of omnivorous and carnivorous calanoid copepods are reviewed. Calanoid foraging tactics are envisioned as falling along several closely coupled continua reflecting swimming behavior, feeding behavior, and dietary habit. The consequences of these foraging tactics on prey-selection patterns are explored in the context of a graphical model. It is hypothesized that the prey-selection patterns of calanoid copepods are determined, to a large extent, by calanoid foraging tactics and the size relationships of predator and prey.     

Diet and trophic position of two mackerel species in the archipelago of Madeira,Portugal

The Atlantic chub mackerel Scomber colias and the blue jack mackerel Trachurus picturatus are two abundant species in the Macaronesia region which includes the archipelago of Madeira, Portugal. Both are key species in the trophic web, being important prey for several local top predators, such as seabirds and marine mammals. Nonetheless, little is known about their feeding ecology in oceanic environments. In this study, the authors describe the seasonal variation in the diet of S. colias and T. picturatus in the oceanic region of Madeira throughout a year. Visual inspection of stomach contents revealed that S. colias fed on a broader range of prey groups than T. picturatus, but for both species, zooplankton (particularly calanoid copepods) and fish were the most important food items. The diet of S. colias included a higher proportion of fish, namely Atlantic saury Scomberesox saurus and S. colias, than that of T. picturatus, that included mostly the longspine snipefish Macroramphosus scolopax. T. picturatus consumed a higher proportion of decapods and other copepods. Seasonal variation was found in the diet of both species, with zooplanktonic species being more important in colder months (February to April) for S. colias and during warm months (May to October) for T. picturatus. Their diet in other seasons was dominated by fish. Although they consume similar prey, carbon and nitrogen stable isotope analysis of muscle of S. colias and T. picturatus showed little overlap in their diets, and T. picturatus showed higher δ¹⁵N and a narrower isotopic niche.     

三江平原湿地小叶章群落磷素积累动态与生物量动态分析

采用野外定位观测结合室内分析的方法,对三江平原典型小叶章湿地两种类型小叶章生长季磷的积累及植物生物量的季节动态进行研究,以揭示三江平原湿地中磷在植物中积累的季节动态变化及其与植物生物量积累之间的关系,进一步认识磷在湿地系统中通过植物吸收迁移转化的机制。结果表明,两种小叶章群落地上、地下生物量以及植物体磷储量有明显的季节动态变化,但二者季节变化特征不同。此外,植物体地上、地下部分磷素积累量和生物量在整个植物体所占的比重两种类型也存在一定差异,这与植物所处的生境及其生态适应有一定关系。分析两种小叶章群落的生长速率(AGR)以及磷素的积累速率(Vp),表明在生长初期,磷是植物生长的重要营养元素。两种小叶章的AGR、Vp的变化曲线相似,说明对于这两种小叶章群落,生境不是磷积累速率的主要影响因素。     

Implication of the feeding limb morphology for herbivorous feeding in some freshwater cyclopoid copepods

1. The mouthparts of five species of adult planktonic cyclopoid copepods (Cyclops vicinus, C. abyssorum, Acanthocyclops robustus, Mesocyclops leuckarti and Thermocyclopscrassus), in particular the distance between setae and setules of the maxilliped (which can indicate the ability to retain small particles), were compared using electron and light microscopy. 2. The mesh‐sizes of the food‐collection grid formed by these setae and setules ranged between 4.6 and 13.2 μm; the area covered by the grid ranged between 6000 and 32 000 μm². 3. Mesh‐size was not simply correlated with body size. Cyclops abyssorum and M. leuckarti have the coarsest meshes and T. crassus the finest, while C. vicinus and A. robustus were intermediate. 4. The results suggest that cyclopoid copepods are able to retain particles in the size range of nanoplankton and that differences in mesh‐sizes between species may explain differences in the ability to subsist and reproduce on a diet of small algae.     

Mediterranean marine copepods: basin-scale trends of the calanoid Centropages typicus

The Mediterranean Sea is located in a crossroad of mid-latitude and subtropical climatic modes that enhance contrasting environmental conditions over both latitudinal and longitudinal ranges. Here, we show that the large-scale environmental forcing is reflected in the basin scale trends of the adult population of the calanoid copepod Centropages typicus. The species is distributed over the whole Mediterranean basin, and maximal abundances were found in the north-western basin associated to oceanic fronts, and in the Adriatic Sea associated to shallow and semi enclosed waters. The peak of main abundances of C. typicus correlates with the latitudinal temperature gradient and the highest seasonal abundances occurred in spring within the 14–18°C temperature window. Such thermal cline may define the latitudinal geographic region where C. typicus seasonally dominates the >200 μm-sized spring copepod community in the Mediterranean Sea. The approach used here is generally applicable to investigate the large-scale spatial patterns of other planktonic organisms and to identify favourable environmental windows for population development.     

Observations on the taxonomic composition and vertical distribution of cyclopoid copepods in the central Red Sea

The taxonomic composition and vertical distribution of cyclopoid copepods, including very small species, in the central Red Sea were analyzed. Samples were taken in a multiple opening and closing net with 0.1 mm mesh size to a depth of 450 m. Most species belong to the genus Oncaea (13 identified and 6 unidentified forms). Nearly one half of these are smaller than 0.4 mm in length. Nine cyclopoid species and three groups of very similar species and forms of Oncaea predominate. In the upper 450 m of the water column, each of these species or groups account for more than 1 % of all cyclopoid specimens. In the epipelagic zone (0–100 m) Oithona simplex predominates, accounting for 20 % of the total. In the upper mesopelagic zone Paroithona sp. and one of the unidentified Oncaea forms are most numerous from 100 to 250 m, and two groups of Oncaea are most abundant from 250 to 450 m. The dominance of single species among cyclopoids is less pronounced than that reported for calanoids in the mesopelagic zone of the central Red Sea.     

Species-specific changes in the phenology and peak abundance of freshwater copepods in response to warm summers

SUMMARY 1. Climate warming is now widely recognised as a major factor influencing ecological processes in terrestrial, marine and freshwater habitats. Here, we investigated how a recent period of warm springs and summers has affected the population dynamics of various cyclopoid copepods in a central European lake. We compared (i) the duration of the period when the species were present in the water column, and (ii) their annual peak density in a period dominated by cool summers (1980–91) and one dominated by warm summers (1992–99). 2. The copepods under investigation were (i) Thermocyclops oithonoides, (ii) Mesocyclops leuckarti and (iii) Acanthocyclops robustus. These species differ in their thermal demand and seasonal phenology. Therefore, we hypothesised that enhanced summer warming would produce species‐specific responses. 3. The active phase of the copepods was usually prolonged both in spring and autumn. The earlier emergence of T. oithonoides (May in the warm years, July in the cool years) was probably related to high water temperature in late spring. The later onset of winter diapause in all species may have been coupled to raised temperature in late summer and autumn. 4. The annual peak abundance of the two thermophiles M. leuckarti and T. oithonoides increased significantly in the warm period. In the latter case, the increase was probably because of the early start to population growth. In contrast, M. leuckarti probably responded primarily to mid‐summer heat waves, in that its development time was likely to be short. We speculate that the increase in population size of both species resulted from the development of an additional generation (three instead of two cohorts per year). In contrast to these thermophiles, the coexisting A. robustus, which is adapted to a broader temperature range, did not respond noticeably to the warming trend. 5. In general, the nature of these responses to summer warming varied substantially among species, and depended on the detailed seasonal patterning of the warming. Our findings thus support the hypotheses that single species are sensitive indicators of climate change, and that the seasonal timing of warming is crucial in the context of climate–ecosystem relationships. 6. Moreover, our results add to the body of evidence that climate warming produces shifts in the seasonal phenology of aquatic and terrestrial organisms.     

Locomotion in copepods: pattern of movements and energetics of Cyclops

The cost of swimming in copepods has generally been estimated through the application of fluid dynamics theory to data on velocity and acceleration obtained by means of movies. It has also been estimated through the changes in fat content of copepods after sustained swimming (i.e. vertical migration). However, the range of estimated costs of locomotion is exceedingly large (from 0.1% to 95% of total metabolism). This communication studies the pattern of swimming movements and the work done by Cyclops, using high speed cinematographic techniques. The contribution of swimming to the energy expenditure of the individual is estimated, and consideration of the possible role of rubber-like proteins in the cuticle of copepods is made.