Chemical, mechanical and visual cues in the vertical migration behavior of the marine planktonic copepod Acartia hudsonica

Recent experimental evidence in both marine and freshwater systemsindicates that predators can induce vertical migration behaviorin individual zooplankters, yet the specific cues by which zooplankterssense their predators appear to vary. In situ manipulation experimentswere carried out with enclosed populations of the marine planktoniccopepod Acartia hudsonica to re-examine the potential role ofchemical cues in the behavior of A.hudsonica, and to test explicitlyfor the role of mechanical or visual stimuli in triggering verticalmigration behavior in this species. Adult female copepods wereinduced to vertically migrate (descend) when exposed to fishmimics during the day, but no such response occurred when thecopepods were exposed to Fish mimics during the night. Moreover,copepods exhibited no changes in vertical distribution whenexposed to water which, having recently held a natural predator(the threespine stickleback, Gasterosteus aculeatus), was presumedto be laden with predator-produced chemical exudates. Predator-mediatedmechanical or visual cues, or a hierarchy of both, are responsiblefor eliciting vertical migration behavior in adult female A.hudsonica.These results, together with those of other investigations demonstratingthe inducing role of chemical exudates, indicate that the stimulieliciting vertical migration in zooplankton can be expectedto vary between species.     

Predator-induced vertical behavior of a ctenophore

Although many studies have focused on Mnemiopsis leidyi predation, little is known about the role of this ctenophore as prey when abundant in native and invaded pelagic systems. We examined the response of the ctenophore M. leidyi to the predatory ctenophore Beroe ovata in an experiment in which the two species could potentially sense each other while being physically separated. On average, M. leidyi responded to the predator’s presence by increasing variability in swimming speeds and by lowering their vertical distribution. Such behavior may help explain field records of vertical migration, as well as stratified and near-bottom distributions of M. leidyi.     

Environmental factors influencing the vertical migration of planktonic rotifers in a hypereutrophic tarn

The diel vertical migration of planktonic rotifers in a small, hypereutrophic tarn was investigated on four occasions in 1983. When the tarn was isothermal the rotifers were distributed throughout the water column. After stratification, the rotifers were confined to the top 1–2 m of oxygenated water. On all four dates the rotifers were aggregated at specific depths in the water column. On some occasions, the pattern of aggregation changed as the animals performed distinct diurnal migrations. Keratella cochlearis, K. quadrata and Polyarthra vulgaris usually followed the reverse migrations of the phytoplankton. In contrast, the movements of Anuraeopsis fissa were less pronounced and were associated with variations in the depth of the oxycline.     

Hydrocarbon contamination decreases mating success in a marine planktonic copepod

The mating behavior and the mating success of copepods rely on chemoreception to locate and track a sexual partner. However, the potential impact of the water-soluble fraction of hydrocarbons on these aspects of copepod reproduction has never been tested despite the widely acknowledged acute chemosensory abilities of copepods. I examined whether three concentrations of the water-soluble fraction of diesel oil (0.01%, 0.1% and 1%) impacts (i) the swimming behavior of both adult males and females of the widespread calanoid copepod Temora longcornis, and (ii) the ability of males to locate, track and mate with females. The three concentrations of the water-soluble fraction of diesel oil (WSF) significantly and non-significantly affect female and male swimming velocities, respectively. In contrast, both the complexity of male and female swimming paths significantly decreased with increasing WSF concentrations, hence suggesting a sex-specific sensitivity to WSF contaminated seawater. In addition, the three WSF concentrations impacted both T. longicornis mating behavior and mating success. Specifically, the ability of males to detect female pheromone trails, to accurately follow trails and to successfully track a female significantly decreased with increasing WSF concentrations. This led to a significant decrease in contact and capture rates from control to WSF contaminated seawater. These results indicate that hydrocarbon contamination of seawater decreases the ability of male copepods to detect and track a female, hence suggest an overall impact on population fitness and dynamics.     

Zonal distribution and seasonal vertical migration of copepod assemblages in the Scotia Sea

Large, biomass-dominant Southern Ocean copepod species have been much studied, but small and mesopelagic species also play major rôles in these ecosystems. However, little is known of some basic aspects of their ecology. To address this, the abundances of 23 copepod species and genera were analysed from 72 stations sampled during the Discovery Expeditions in the 1920s to 1950s. Stratified net samples, usually to a depth of 1000?m, provided year-round coverage in the Scotia Sea from the Subantarctic Front to the Weddell-Scotia Confluence. Small copepods (Microcalanus pygmaeus, Ctenocalanus spp., Oncaea spp. and Oithona spp.) formed ～75% of total copepod abundance in the top 1000?m across all major zones. Oithona spp. composed ～40% of copepod numbers in the Polar Front area and to its south: further north their importance declined. All mesopelagic taxa except for the warmer-water species Metridia lucens and Pleuromamma robusta, extended throughout the entire study area, with smaller regional differences than for the shallower-living species. The species showed a continuum of temperature ranges, and there was no evidence that the Polar Front was a major biogeographic boundary to their distribution. Indeed, several important species, including Oithona spp. (mainly Oithona similis), Ctenocalanus spp., Metridia lucens and Rhincalanus gigas reached maximum numbers in this area. Total copepod abundance was thus higher in the vicinity of the Polar Front than in any other region. Only two copepod families made pronounced seasonal vertical migrations: Eucalaniidae (Eucalanus longiceps and R. gigas) and Calaniidae (Neocalanus tonsus, Calanoides acutus, Calanus simillimus and Calanus propinquus). Some evidence for a winter descent was found for Ctenocalanus spp. and some deeper-living groups: Euchaeta spp. and the Metridiidae, although their migrations were not so great as for the eucalanids and calanids.     

Extraordinary prolongation of the life cycle in a freshwater planktonic copepod

The limnetic copepod Cyclops scutifer Sars shows an extraordinarily prolonged life cycle in a temperate lake near Oslo, Norway. Developmental sequences become one, two, and three years old, and there are circumstantial evidence of a four year old fraction. Prolongation of the cycle is mainly caused by two consecutive periods of diapause, the first as small copepodids during the second winter, the other as large copepodids during the third winter. There is a marked concentration of diapausing individuals in a small area of the bottom at the deepest part of the lake. There is evidence that this concentration is caused by a horizontal migration to areas with optimal oxygen conditions. The adaptive value of a prolongation of the life cycle is assumed to be an increase in the reproductive potential caused by a spreading out of the reproductive period by three year classes succeeding each other throughout the summer.     

拓林湾浮游桡足类生态研究

2000年7月至2001年7月的周年调查结果表明,粤东柘林湾浮游桡足类29属57种,其中,强额拟哲水蚤Paracalanus crassirostris和短角长腹剑水蚤Oithona brevicornis为优势种,合计占浮游桡足类总个体数的66.7%.柘林湾是一个浮游桡足类相对丰富的海湾,年均总个体数达5.4×10³ind.·m^-3.浮游桡足类的种类数和总个体数均表现为湾外大于湾内的平面分布格局,周年变化基本上为单峰型,高峰期位于5~10月,最低谷位于冬季1月。     

枯林湾浮游桡足类生态研究

2000年7月至2001年7月的周年调查结果表明,粤东柘林湾浮游桡足类29属57种,其中,强额拟哲水蚤Para-ca;amis crassorpstris和短角长腹剑水蚤Ootjpma brevicomis为优势种,合计占浮游桡足类总个体数的66.7%.柘林湾是一个浮游桡足类相对丰富的海湾,年均总个体数达5.4×103ind.@m-3.浮游桡足类的种类数和总个体数均表现为湾外大于湾内的平面分布格局,周年变化基本上为单峰型,高峰期位于5～10月,最低谷位于冬季1月.     

Photoreactivation of UV-induced damage to embryos of a planktonic copepod

UV irradiation damaged the embryos of the planktonic copepodCalanus sinicus. The hatching rate was reduced, and the hatchedlarvae were deformed by the UV irradiation at unweighted intensitiessimilar to those occurring naturally. However, the UV-induceddamage was reduced by simultaneous irradiation with the visiblelight from a fluorescent lamp. This photoreactivation may playan important role in reducing the mortality of this speciesin the marine environment.     

胶州湾浮游桡足类时空分布

根据2003年1月至12月在胶州湾所获得的浮游生物样品,已鉴定浮游桡足类28种,幼虫、幼体6类.分析了该海区浮游桡足类的分布﹑时空变化及其与生态环境因子的关系,同相关历史资料进行了比较,结果表明,浮游桡足类的种类组成单纯,生态属性以暖温带、近岸低盐种类为主.浮游桡足类的丰度分布具明显的月份变化,高峰在7月份,为181.61个/m3,最低在12月份,为23.53个/m3,全年平均为71.42个/m3.浮游桡足类丰度的平面分布不均匀,最大丰度在5号站,为132.62个/m3,最小丰度在8号站,为40.45个/m3,丰度平面分布的变化趋势基本是湾北部海域大于湾南部海域.浮游桡足类丰度的时空分布,主要种类的季节更替,近20a来的变化趋势基本相同,高峰出现时间的差异,是受温度年季变化差异因素的影响.浮游桡足类丰度的时空分布与海水温度和盐度密切相关,与温度的关系更重要于与盐度的关系.并且用胶州湾的调察资料证实了浮游桡足类对浮游植物的依存关系,浮游植物为浮游桡足类的生长、繁衍提供了饵料.     

Sex differences in habitat distribution of a planktonic copepod, Eudiaptomus gracilis

The spatial distribution of adult males and females in a population of the copepod Eudiaptomus grachs ; was studied throughout one year The sexes were markedly segregated in spring and under ice in late winter This skewed distribution was mainly due to a strong concentration of females in deep water in the lake centre Males were more evenly distributed but dominated in relative terms strongly over females near the surface and the littoral zone Among females, those carrying eggs were most concentrated in deep regions Also during summer, females in the lake centre showed a marked abundance peak in deep water but the distribution of egg-carrying females did not differ from other females During autumn and early winter, differences in the distribution of the sexes were minor The distribution of the sexes is discussed in relation to predators, temperature, food, and mates Female copepods are susceptible to fish predation when carrying eggs Fish may contribute to the over-representation of females in deep regions by eating or scaring away this category of vulnerable prey from littoral areas and from the surface waters The fish predation hypothesis does not accurately predict the seasonal occurrence of the skewed distribution, however Feeding rate of fish is most likely low under ice Reproductive advantages in the warmer deep water may have contributed to female choice of habitat in late winter In spring and late winter proportionally fewer females near the surface and shore carried eggs, but they earned more spermatophores This indicates that these females were more receptive to matings Phytoplankton biomass was higher near the surface Thus, males may have gamed mating advantages and more food by avoiding deep water in the centre of the lake     

Cryptic ecological diversification of a planktonic estuarine copepod, Acartia tonsa

The recent discovery of cryptic species in marine holoplankton, organisms that 'drift' in oceanic currents throughout their life cycle, contrasts with their potential for long-distance passive dispersal and presumably high gene flow. These observations suggest that holoplankton species are adapting to surprisingly small-scale oceanographic features and imply either limited dispersal or strong selection gradients. Acartia tonsa is a widespread and numerically dominant estuarine copepod containing deep mitochondrial lineages within and among populations along the northwestern Atlantic coast. In this study, we intensively investigated A. tonsa populations in Chesapeake Bay with the goals of testing species status for the deep lineages and testing for their association with environmental features over space and time. Phylogenetic analyses of DNA sequences from mitochondrial cytochrome c oxidase I (mtCOI) and the nuclear ribosomal internal transcribed spacer (nITS) resolved two concordant monophyletic clades. Deep divergence between the two clades (13.7% uncorrected sequence divergence for mtCOI and 32.2% for nITS) and genealogical concordance within sympatric populations strongly suggest that the two clades represent reproductively isolated cryptic species. Based on restriction fragment length polymorphisms of mtCOI, representatives from the two clades were found consistently associated with contrasting salinity regimes (oligohaline vs. meso-polyhaline) with an overlap between 2 and 12 PSU in samples from 1995 to 2005. Finding these patterns in one of the best-known estuarine copepods reinforces the conclusion that marine biodiversity is underestimated, not only in terms of species numbers, but also with respect to niche partitioning and the potential importance of ecological divergence in marine holoplankton.     

Feeding by an omnivorous planktonic copepod aetideus divergens Bradford

Aetideus divergens Bradford is representative of a large group of marine planktonic calanoid copepods which are omnivores or mixed feeders. Because very little quantitative information is available on the feeding behavior of these copepods, laboratory feeding experiments have been carried out with adult female A. divergens presented with various sizes and concentrations of diatoms and freshly hatched nauplii of Artemia. The copepod fed most efficiently on the largest size of diatom and on Artemia nauplii, but was peculiarly inefficient at feeding on small diatoms, even when they were available at very high concentrations. In this respect, the copepod differs from filterfeeding copepods, such as Calanus pacificus Brodsky. A possible explanation of this difference depends upon Aetideus being less capable of handling very small food particles than Calanus. Aetideus divergens and its congeners usually occur at subsurface depths not far below the mixed layer and seem to be adapted for feeding on large particles, possibly large phytoplanktonic organisms and fecal pellets, which sink out of the mixed layer.     

Ontogenetic niches of a planktonic copepod in Lake Biwa studied on a fine temporal scale

Eodiaptomus japonicus was collected in the north basin of Lake Biwa, Japan, on six dates from 11 to 25 June 1987. Temporal changes in its vertical distribution and reproduction indices were small, but those in its abundance were large. Mortality was high in the naupliar stage I and from copepodid stage III to adult stage. The latter fact and low proportion of females in adulthood suggest heavy predation by fishes which prefer larger prey.Eodiaptomus japonicus showed ontogenetic vertical migration within the epilimnion. The direction of the migration was upward in the early naupliar stages and downward in the late naupliar and early copepodid stages. Both migrations resulted in raising mortality in the corresponding or succeeding stages, probably expressing the behavioral constraints ofE. japonicus.     

Bacteria associated with a marine planktonic copepod in culture. II. Degradation of fecal pellets produced on a diatom, a nanoflagellate or a dinoflagellate diet

Copepods (A cartia tonsa Dana) were allowed to feed on culturedalgal species simulating the yearly boreal phytoplankton succession,where the spring is characterized by diatoms, the summer bynanoflagellates and the autumn by dinoflagellates. Degradationof freshly produced fecal pellets in suspension was followedover time by volume recording and estimation of carbon loss.The fecal pellets produced on a diatom diet were very denseand showed a significantly slower degradation than those producedon nanoflagellate or dinoflagellate diets. This indicates thatthe algal texture, i.e. the mechanical robustness given by inertstructures, determines the degradation rate of the pellets.The degradation rate was also very dependent on the algal concentrationfor the grazer (565 µg Cl^–1 T₁     

Transgenerational effects alleviate severe fecundity loss during ocean acidification in a ubiquitous planktonic copepod

Ocean acidification (OA) caused by anthropogenic CO₂ emission is projected for thousands of years to come, and significant effects are predicted for many marine organisms. While significant evolutionary responses are expected during such persistent environmental change, most studies consider only short‐term effects. Little is known about the transgenerational effects of parental environments or natural selection on the capacity of populations to counter detrimental OA effects. In this study, six laboratory populations of the calanoid copepod Pseudocalanus acuspes were established at three different CO₂ partial pressures (pCO₂ of 400, 900 and 1550 μatm) and grown for two generations at these conditions. Our results show evidence of alleviation of OA effects as a result of transgenerational effects in P. acuspes. Second generation adults showed a 29% decrease in fecundity at 900 μatm CO₂ compared to 400 μatm CO₂. This was accompanied by a 10% increase in metabolic rate indicative of metabolic stress. Reciprocal transplant tests demonstrated that this effect was reversible and the expression of phenotypic plasticity. Furthermore, these tests showed that at a pCO₂ exceeding the natural range experienced by P. acuspes (1550 μatm), fecundity would have decreased by as much as 67% compared to at 400 μatm CO₂ as a result of this plasticity. However, transgenerational effects partly reduced OA effects so that the loss of fecundity remained at a level comparable to that at 900 μatm CO₂. This also relieved the copepods from metabolic stress, and respiration rates were lower than at 900 μatm CO₂. These results highlight the importance of tests for transgenerational effects to avoid overestimation of the effects of OA.     

Modelling physico-chemical factors affecting occurrences of a non-indigenous planktonic copepod in northeast Pacific estuaries

Estuarine ecosystems along the Pacific coast of North America are vulnerable to invasions by non-indigenous planktonic copepods, with documented invasions by at least nine species introduced via ship’s ballast. One of these, the calanoid copepod Pseudodiaptomus inopinus, now occurs in a relatively wide geographical area in coastal estuaries of Washington and Oregon States. Although it appears to be well established in the region, plankton surveys conducted in 1992, 1996, 2000, and 2004 in estuaries from southern Vancouver Island in British Columbia, Canada, to northern California, United States indicate that it has not expanded its range. This static distribution suggests that P. inopinus has reached a distributional limit, and it may thus be a good organism for applying models for predicting planktonic invasions, by characterizing estuaries with and without populations of the copepod. In this study, we applied both parametric, linear (discriminant function analysis, logistic regression) and nonparametric, non-linear (classification trees) techniques to develop models for occurrence of P. inopinus, to identify parameters that may lead to successful invasions and to identify specific estuaries or regions that might be at risk of invasion by this species. Both model types had similar results, identifying relatively simple salinity- and stratification-based models as good predictors of P. inopinus. While different models selected slightly different sets of variables and thresholds, all models identified relatively low salinity and stratification of water column temperature and salinity as important predictors of P. inopinus presence. The models also identified several “false positives” that mainly occurred in more inland waters of Puget Sound—estuaries that did not have P. inopinus, but had the conditions that support it, and which may be at risk for future invasions by this species.     

Swimming and feeding behaviour of the planktonic copepod Clausocalanus furcatus

The objective of this study was to quantify motion and feeding behaviour of the small calanoid Clausocalanus furcatus, which is a common and abundant species in oligotrophic environments. Adult females were video recorded at 60 fields s^-1 using video equipment which allowed us to follow each free-swimming individual continuously in 3 1 vessels. At 20C under dark conditions, C.furcatus moved continuously along convoluted small loops at a mean speed of 10 mm s^-1 (corresponding to 10 body lengths s^-1). This motion was occasionally interrupted by sudden somersaulting performed at very high speed (up to 17 mm s^-1). The copepods only occasionally sank. There was no evidence that C.furcatus created feeding currents. Dinoflagellate cells offered as food appeared to be perceived by direct encounter at high speed, being instantaneously captured and ingested or rejected. The capture rates were correlated with the frequency of somersaulting. By moving fast and by associating a high turning rate with a high frequency of crossing the previous tracks, C.furcatus searched 22-26% of the explored volumes. The motion and feeding behaviour of C.furcatus show that the foraging tactic of this species is to explore small volumes of water rapidly. This strategy appears, so far, to be unique among small planktonic copepods.      

Fluid mechanosensory stimulation of behaviour from a planktonic marine copepod, Euchaeta rimana Bradford

This research provides the first reported thresholds for thebehavioural response of an individual planktonic copepod. Usinga novel technique to create near-field fluid disturbances, wedirected microlitre volumes of water towards the antennularysetae. In response to an increasing strength of this purelymechanical signal, the animal varied its behaviour from a rapidflick to a capture response and finally an escape reaction.This work provides a basis for addressing the criteria copepodsuse to interpret biologically generated signals to elicit anappropriate behavioural response and offers insight into howthese signals are differentiated from the random fluid motionin their environment.     

Seasonal fluctuations in fecundity and hatching success in the planktonic copepod Centropages typicus

A mismatch of {small tilde}2–3 months was observed betweenreproductive rates and population abundances in the planktoniccopepod Centropages typicus, with the highest production atrelatively low female abundance and low production at high abundance,during the course of a 2 year study in 1989 and 1990 in neriticwaters of the Gulf of Naples. During this period, egg mortalitywas at times severe, with values as high as 59% in February1989. The seasonal trend in percentage hatching success didnot match seasonal fluctuations in breeding intensity, and wasnot correlated with variations in environmental variables suchas temperature and chlorophyll a. The results of experimentsusing the fluorescent dye Hoechst 33342 showed that unhatchedeggs had been fertilized and that in most cases developmenthad proceeded to an advanced stage before death of the embryo.The causes of high egg mortality are uncertain, but here wegive evidence, for the first time, that egg mortality may notonly be due to infertility caused by failure to remate.