Diel reproduction and vertical distributions of the marine cladocerans, Evadne tergestina and Penilia avirostris, in contrasting coastal environments

Evadne tergestina and Penilia avirostris were sampled duringseveral diel cycles in the well-mixed, turbid Inland Sea ofJapan and the more stratified, less turbid Gulf of Mexico shelf.Parthenogenetic female Evadne contained embryos with pigmentedeyes only at night, and apparently released neonates near dawnor in the morning. There was no significant diel vertical migrationin the Gulf of Mexico, and a ‘reverse’ migrationin the Inland Sea. Female Penilia could contain mature embryosat any time, but were most likely to do so at night. Peniliadid not migrate dielly, and in the Gulf of Mexico was concentratedin a nepheloid layer near the bottom.     

Spatial and temporal variations of Penilia avirostris and Evadne tergestina (Crustacea,Branchiopoda) in a Tropical Bay,Brazil

We analysed monthly samples collected in Guanabara Bay, with a conical net of 200 m mesh during 1985. The bay was divided into three areas: an outer region (area A), influenced by oceanic waters; an inner region (area C), influenced by fluvial inflow; and a transition region (area B) with intermediate features. Penilia avirostris and Evadne tergestina were observed in the three areas, with greatest densities, however, in the outermost region, which had the highest salinities and lowest temperatures. Penilia avirostris was more abundant in summer (March), a period with the greatest relative densities of nanoplankton. Evadne tergestina was also abundant in summer, but its peak fell in November, a period with a relative increase in microphytoplankton density in the bay. The two species disappeared in winter: Penilia avirostris was absent from May to August, whereas Evadne tergestina disappeared in August and September.     

Feeding, growth and food conversion of the marine cladoceran Penilia avirostris

Ingestion and clearance rates, feeding behaviors and life historyvariables of the marine cladoceran Penilia avirostris were evaluatedover a range of food concentrations encountered in nature (0.01–3.0mm³ 1^–1 of Isochrysis galbana). Ingestion rates increasedand clearance rates decreased with increasing food concentration.No maximum feeding thresholds were observed over the range ofalgal concentrations offered. Weight-specific ingestion ratesdecreased with increasing body weight. Feeding behaviors suchas mandibular activity, abdominal claw rejections of cloggedfeeding structures and feeding appendage activity decreasedat a food level of 0.3 mm³ l^–1 of l. galbana. Peniliaavirostris had very poor survivorship at extremely low (0.01mm³ l^–1 and high (3.00 mm³ l^–1) food levels. Mortalitywas hardly affected at food levels of 0.03–1.0 mm³ l^–1Reproduction did not occur at food levels of     

The trophic role of the marine cladoceran Penilia avirostris in the Gulf of Trieste

The herbivory of the marine cladoceran Peniliaavirostris was studied in the Gulf of Trieste(Northern Adriatic) from June 1993 to December1994 using the gut fluorescence method. P. avirostrisoccurred from June to December, butreached its greatest abundance in the summer months.A significant correlation between the gut pigmentcontent and chlorophyll a concentration in thesurface layer was established. Observations with anepifluorescence microscope revealed that the guts werefilled with fluorescing nanoplankton and picoplankton(cyanobacteria). Quantitative estimates indicated thatP. avirostris grazed less than 5% of theavailable chlorophyll a in more than half of allmeasurements, but removed most of the availablechlorophyll a in the surface layer during someperiods in September. It can therefore be concludedthat P. avirostris, together with planktonicprotists, plays an important role within the microbialloop.     

Increasing prevalence of the marine cladoceran Penilia avirostris (Dana, 1852) in the North Sea

Rising sea surface temperatures in the North Sea have had consequential effects on not only indigenous plankton species, but also on the possibility of successful colonisation of the area by invasive plankton species. Previous studies have noted the introduction and integration into the plankton community of various phytoplankton species, but establishment of zooplankton organisms in the North Sea is less well-documented. Examining continuous plankton recorder (CPR) survey data and zooplankton results from the Helgoland Roads study, the autumn of 1999 witnessed the occurrence of the marine cladoceran Penilia avirostris in large numbers in the North Sea. The rapid appearance of the species corresponded with exceptionally warm sea surface temperatures (SSTs). Since 1999, the species has become a regular feature of the autumnal zooplankton community of the North Sea. In 2002 and 2003, the species occurred in greater abundance than recorded before. It is suggested that increased autumn SSTs have proved favourable to P. avirostris, with warmer conditions contributing to the success of the species resting eggs and aiding colonisation.Communicated by H.-D. Franke     

Production of Penilia avirostris in Kingston Harbour, Jamaica

The cladoceran Penilia avirostris is one of the more abundantand widespread members of the crustacean zooplankton in nearshoretropical and subtropical waters. Its abundance, biomass, fecundity,development rate and production were estimated in Kingston Harbour,Jamaica, during an 18 month period. Mean annual abundance ofPenilia was 1821 m^–3, while biomass (excluding eggs/embryos)was 2.87 mg ash-free dry-weight (AFDW) m^–3 (43.1 mg AFDWm^–2), accounting for 13% of the copepod community biomass.Fecundity increased with body size. There was no clear seasonalpattern of abundance, size or fecundity, nor were physical orbiological variables correlated to these variations. Developmenttime averaged 20.5 h for juveniles and 41.4 h for adult femalesduring incubations; there was no clear evidence of a diel patternto molting. Growth rate appeared to be exponential, with correspondingsomatic growth rates, averaging 0.27 day^–1 for juveniles,and 0.34 day^–1 for somatic plus reproductive growth inadult females. Annual production was estimated as 173 kJ m^–2year^–1,     

Penilia avirostris DANA in the Indian Ocean (Cladocera)

The records of the marine cladoceran Penilia avirostris DANA in the Indian Ocean are discussed as a further contribution to studies on the features of its world distribution. The review has pointed out different aspects of the life cycle of the species and the influence of biological and environmental factors upon the mechanisms of the cycle itself. Production of P. avirostris is considered on a trophic basis. Observations carried out elsewhere are also discussed.     

Natural ingestion rates and grazing impact of the marine cladoceran Penilia avirostris Dana in Tolo Harbour, Hong Kong

The gut fluorescence method was used to study algal grazingby Penilia avirostris in a semiestuarine embayment. Grazingimpact estimated from ingestion rate and animal abundance revealedthat only {small tilde}1% of the algal biomass was grazed perday by the cladocerans.     

Diel vertical migration of zooplankton in the Northeast Atlantic

Acoustic Doppler current profiler (ADCP) data collected duringAugust–September 1991 reveal the diel migration of zooplanktonin the northeast Atlantic (50–60     

Diel vertical migration: modelling light-mediated mechanisms

Light is generally regarded as the most likely cue used by zooplanktonto regulate their vertical movements through the water column.However, the way in which light is used by zooplankton as acue is not well understood. In this paper we present a mathematicalmodel of diel vertical migration which produces vertical distributionsof zooplankton that vary in space and time. The model is usedto predict the patterns of vertical distribution which resultwhen animals are assumed to adopt one of three commonly proposedmechanisms for vertical swimming. First, we assume zooplanktontend to swim towards a preferred intensity of light. We thenassume zooplankton swim in response to either the rate of changein light intensity or the relative rate of change in light intensity.The model predicts that for all three mechanisms movement isfastest at sunset and sunrise and populations are primarilyinfluenced by eddy diffusion at night in the absence of a lightstimulus. Daytime patterns of vertical distribution differ betweenthe three mechanisms and the reasons for the predicted differencesare discussed. Swimming responses to properties of the lightfield are shown to be adequate for describing did vertical migrationwhere animals congregate in near surface waters during the eveningand reside at deeper depths during the day. However, the modelis unable to explain how some populations halt their ascentbefore reaching surface waters or how populations re-congregatein surface waters a few hours before sunrise, a phenomenon whichis sometimes observed in the field. The model results indicatethat other exogenous or endogenous factors besides light mayplay important roles in regulating vertical movement.     

Diel vertical migration arising in a habitat selection game

Predator and prey react to each other, adjusting their behavior to maximize their fitness and optimizing their food intake while keeping their predation risk as low as possible. In a pelagic environment, prey reduce their predation mortality by adopting a diel vertical migration (DVM) strategy, avoiding their predator during their peak performance by finding refuge in deep layers during daylight hours and feeding at the surface during the night. Due to the duality of the interaction between prey and predator, we used a game theory approach to investigate whether DVM can be a suitable strategy for the predator as well as the prey. We formulated three scenarios in plankton ecology in order to address this question. A novel finding is that mixed strategies emerge as optimal over a range of the parameter space, where part of the predator or prey population adopts a DVM while the rest adopt one or other “sit and wait” strategies.     

Diel vertical migration of Arctic zooplankton during the polar night

High-latitude environments show extreme seasonal variation in physical and biological variables. The classic paradigm of Arctic marine ecosystems holds that most biological processes slow down or cease during the polar night. One key process that is generally assumed to cease during winter is diel vertical migration (DVM) of zooplankton. DVM constitutes the largest synchronized movement of biomass on the planet, and is of paramount importance for marine ecosystem function and carbon cycling. Here we present acoustic data that demonstrate a synchronized DVM behaviour of zooplankton that continues throughout the Arctic winter, in both open and ice-covered waters. We argue that even during the polar night, DVM is regulated by diel variations in solar and lunar illumination, which are at intensities far below the threshold of human perception. We also demonstrate that winter DVM is stronger in open waters compared with ice-covered waters. This suggests that the biologically mediated vertical flux of carbon will increase if there is a continued retreat of the Arctic winter sea ice cover.     

巢湖微囊藻和浮游甲壳动物昼夜垂直迁移的初步研究

2002年10月进行了巢湖微囊藻和几种优势浮游甲壳动物的昼夜垂直变化的研究,结果表明:微囊藻具有明显的昼夜垂直变化现象。白天上层水中的微囊藻密度显著高于下层水中,夜晚逐渐下沉使得下层水中的密度相对高于上层水。微囊藻与叶绿素a、水温、溶解氧和pH等均呈显著的正相关(p<0.01)。几种优势浮游甲壳动物的昼夜垂直迁移存在较大的差异。短尾秀体溞和角突网纹溞白天在下层水(1.5m和2.5m)中的密度较高,夜晚则倾向于在上层水(0m和0.5m)中活动。相反,卵形盘肠溞白天在上层水中密度较高,象鼻溞则在11:00和15:00时各水层中的密度显著高于夜晚。汤匙华哲水蚤和广布中剑水蚤白天倾向于在下层水中活动,夜晚则逐渐迁移到上层水中。许水蚤在夜晚和凌晨3:00时各水层中的密度显著高于白天。中华窄腹剑水蚤昼夜垂直变化不明显。微囊藻与短尾秀体溞密度呈显著的负相关,而与象鼻溞和卵形盘肠溞呈显著的正相关(p<0.01)。     

Modelling the population dynamics of Penilia avirostris (Branchiopoda,Ctenopoda) in a tropical bay

An ecological model for the simulation of the population dynamics of the cladoceran Penilia avirostris in Guanabara Bay, a tropical Brazilian bay, was developed. The simulated curve gave a good fit, in time and intensity, to the exponential increase and decrease in densities of P. avirostris during the March-July 2000 period. The densities of embryos, young individuals, males, and parthenogenic and gamogenic females were the state variables. Parameters of the model were varied within the range of field and literature data. Predation was considered as the main factor affecting mortality, the death rate being a function of the density of chaetognaths, the dominant invertebrate predator in Guanabara Bay. Input of resting eggs into the model as a “seed” source of embryos provided a good fit to the exponential increase of Penilia density. The observed sharp decreases and collapses of the population could not be explained by mortality or a shift from parthenogenic to gamogenic reproduction only. To provide an explanation, it was necessary to introduce an output forcing function, which probably represents physical factors such as water mass exchanges by tide- and wind-driven currents.     

Diel vertical migration of adult Pacific cod Gadus macrocephalus in Alaska

The diel vertical migration (DVM) of Pacific cod Gadus macrocephalus was examined using depth and temperature data from 250 recaptured archival tags deployed on G. macrocephalus in the eastern Bering Sea and in the Gulf of Alaska near Kodiak Island. DVM of two types, deeper during daytime (type I) and deeper during night‐time (type II), occurred frequently (15–40% of all days) in G. macrocephalus released at all sites. Most individuals displayed both diel types, with each type of behaviour lasting up to 58 contiguous days, and day and night depth differences averaging c. 8 m. Despite high among‐individual variability, the occurrence of DVM varied significantly with the release site, season (i.e. day‐of‐year) and bottom depth, with the trend in seasonal occurrence nearly opposite for type I compared to type II DVM. No significance could be attributed to G. macrocephalus fork length, sex or ambient (tag) temperature. Trends in the magnitude of G. macrocephalus depth change were observed, with increased movement often occurring during night‐time, dawn and dusk, and at release sites where the bathymetry was more complex. Both type I and type II DVMs were attributed to foraging on prey species that also undergo DVM, and increased vertical movements of G. macrocephalus during crepuscular and night‐time periods were attributed to more active foraging during dim‐light conditions when G. macrocephalus can potentially exploit a sensory advantage over some of their prey.     

Embryonic development time of Penilia avirostris Dana, 1852 in a tropical bay in Brazil.

Development time of embryos in the brood pouch of the cladoceran Penilia avirostris Dana, 1852, was estimated by collecting zooplankton daily for 15 days in surface water of Guanabara Bay, Brazil. Each day the maturity stage of embryos of 90 parthenogenic females was noted. Total development time (egg to birth) varied from 2 to 3 days, the immature phase (stages I to IV) being generally longer (2 days) than intermediate and mature phases (1 day, stages V to XII). Similar results were obtained from Bottrell's equation, which takes water temperature into account.     

Diel vertical migration and feeding of chaetognaths in coastal waters of the eastern Mediterranean

This study investigates the diel vertical distribution and the diet of the most important chaetognath species found in the 0–50 m surface layer of a coastal area in the eastern Mediterranean during a 24-hour period in July 2004. Among the recorded chaetognaths, Sagitta enflata was the most abundant species (41.6%), followed by S. minima (32.5%) and S. serratodentata (20.8%). Those three species exhibited a “twilight migration” pattern, with only small differences among them. Vertical separation was found between S. enflata and S. minima. Both species preyed mainly on cladocerans, although copepods were the most abundant group in the zooplankton assemblage. The chaetognath species followed partially the diel vertical migration of their prey. S. enflata showed high feeding intensity at different times in both day and night, while S. minima fed more intensively at midday (12:00) and at dusk (20:00), and S. serratodentata in the morning (08:00). It seems that in order to coexist in an area of low productivity the chaetognath species follow the basic ecological rules of space, time and food-type separation, in order to reduce the inter- and intra-specific competition. The high preference of S. minima and especially of S. enflata for the cladocerans made them probably the most important predators of cladocerans during summer.     

Diel vertical migration of a pelagic amphipod in the absence of fish predation

The pelagic amphipod, Hyalella montezuma, migrates vertically into the surface waters at twilight in Montezuma Well, Arizona, USA despite the absence of fish predators or thermal stratification. We suggest that a persistent, dense, neustonic algal assemblage may provide a food resource incentive for the twilight ascent.     

Diel vertical migration in zooplankton: rapid individual response to predators

While diel vertical migration in zooplankton has been shownrecently to be a predator avoidance behavior, the mechanismby which predators induce and maintain such behavior has beendebated. We report results of an in situ predator manipulationexperiment during which enclosed populations of the marine planktomccopepod Acaraa hudsonica rapidly changed their vertical distributionand diel migration behavior depending on presence or absenceof the planktivorous fish Casterosteus aculeatus These resultspoint unambiguously to phenotypic behavioral plasticity of individualplanktonic prey, not, as previously hypothesized, population-geneticlevel behavioral changes caused by selective fish predation,as the mechanism underlying changes in diel vertical migrationin this copepod.