Diel vertical migration in Mesocyclops edax: implications for predation rate estimates

The diel migration patterns of Mesocyclops edax and its preyin a small lake were followed in two studies separated by approximatelyone year. Gut contents of the predators were examined and selectivityindices calculated at each depth at 0100 h during 1980. Thethree principal zooplankton prey found in the guts of M. edaxwere Keratella, Kellicottia, and Bosmina. The predator and allthree major prey species exhibited unique and different dielvertical distribution and migration patterns. The complex natureof the spatio-temporal variation in prey density to which M.edax is exposed, demonstrates the dangers of using selectivityindices without knowledge of the distribution patterns of bothpredator and prey. An increase in vertebrate predation pressurefrom one year to the next is thought to be responsible for anincrease in the abundance of small zooplankton species, thedisappearance of two out of three of the large zooplankton species,and the onset of a pronounced nocturnal migration pattern inthe third large species. ¹Present address: Biology Department, Williams Hall #31, LehighUniversity, Bethlehem, PA 18015, USA     

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 variations in gut pigment content, diel vertical migration and estimates of grazing impact for copepods in the southern Benguela upwelling region in October 1987

The gut fluorescence technique was used to estimate ingestionand filtration rates of the adult female copepods Paracalanusparvus, Cenlropages brachiatus and Calanus austrails, and copepoditestages 3, 4 and 5 of C.australis in the southern Benguela upwellingregion. During the study period chlorophyll concentrations withinthe upper 20 m of the water column were high, 5 µg I^–1in mid-shelf waters and 15–30 µg I^–1 in innershelf waters. Copepod gut pigment content was low and constantduring the day then increased sharply during the first 2 h aftersunset. Gut pigment content was 2–6 times higher duringthe night compared with daytime values. Small non-migratingcopepods (Paracalanus parvus) showed the smallest diel differencein gut pigment content and large migrating copepods (Centropagesbrachiatus and Calanus australis) the largest difference. Eggproduction rates were 20 and 50% of maximum at the mid-shelfand inner shelf stations respectively, suggesting food-limitation.Comparison of ingestion rates calculated from egg productiondata with ingestion rates calculated from gut pigment data suggestedthat the copepods were feeding omnivorously at the inner shelfstations but herbivorously at the mid-shelf stations. Assumingthat all of the phytoplankton was available as food, the nearshorecopepod assemblage grazed {small tilde}1% of the standing cropeach day, and the mid-shelf assemblage grazed 5% day^–1.Because of errors and uncertainties associated with the gutfluorescence technique, the feeding impact could be underestimatedby 2–4-fold. We discuss several approaches which couldlead to more precise estimates of feeding rates. ³Present address: Marine Sciences, SUNY, Stony Brook, NY, 11794-5000,USA     

Diel vertical migration of the planktonic copepods at an upwelling station north of Taiwan, western North Pacific

A total of 178 copepod species were identified in an upwellingarea of the Mienhua Canyon off northern Taiwan, western NorthPacific during a spring cruise in 1995. Paracalanus aculeatus,Oncaea venusta and Clausocalanus furcatus were the three dominantspecies, comprising 43% of the total copepod numbers. Most copepodspecies performed normal diel vertical migration, descendingduring daytime and ascending at night to different depth zonesand with different rates. Some dominant copepod species, suchas P. aculeatus, C. furcatus, Temora discaudata and Canthocalanuspauper, apparently congregated in the surface water (between0 and     

Diel feeding periodicity, daily ration and vertical migration of juvenile Cape hake off the west coast of South Africa

Feeding periodicity, daily ration and vertical migration of juvenile Cape hake Merluccius capensis are investigated from midwater and bottom trawl collections taken during a 42-h period between 29 February and 2 March 1992 at a fixed position off the west coast of South Africa. Feeding of 10-20 cm hake intensified during the night when they ascended into subsurface layers to prey on recruits of anchovy Engraulis capensis. Larger hake remained close to the bottom, were partially cannibalistic and exhibited no diel feeding periodicity. M. capensis appear to migrate vertically and feed asynchronously in midwater, as individuals, and not as a population, returning to the bottom when satiated. Based upon the exponential rate of decline in stomach fullness throughout the day, the evacuation rate by hake <20 cm was estimated as 0.054 h⁻¹; 90% evacuation of anchovy prey required an estimated 43 h. Using the Elliott & Persson and Eggers methods, the daily ration was estimated as 5.51 and 4.15% of wet body weight respectively. The effect of the foraging behaviour of M. capensis on the appropriateness of acoustic sampling for estimates of their abundance is discussed.     

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 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.     

Diel vertical migration of major fish-species in Lake Victoria, East Africa

Understanding of migration patterns is essential in the interpretation of hydro-acoustic stock assessment data of partly demersal partly pelagic fish stocks. In this paper we provide this kind of information for some species that were common in the Mwanza Gulf of Lake Victoria in the 1980s, before and after the upsurge of introduced Nile perch (Lates niloticus). Detritivorous haplochromines and Nile tilapia (Oreochromis niloticus), both stay near the bottom during day and night. Feeding seems to occur predominantly during the day. The zooplanktivorous haplochromines and dagaa (Rastrineobola argentea) dwell near the bottom by day and migrate towards the surface during the night. They seem to follow their prey, zooplankton and lake-fly larvae. Piscivorous nembe (Schilbe intermedius) show similar migration patterns to zooplanktivorous fishes, but their behaviour cannot be unambiguously explained by pursuit of prey. Nile perch to some extend migrate into the column at night, though the majority remains near the bottom. Feeding takes place during day and night.     

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.     

Diel vertical migration of zooplankton: optimum migrating schedule based on energy accumulation

Zooplankton perform diel vertical migration (DVM) to avoid predators at the upper water layer, but often stay in the upper water layer throughout the day seeking food in spite of the presence of predators. This difference in migrating behavior has been explained by differences in environmental conditions or genetic differences. We examined theoretically how nutritious conditions of zooplankton individuals relate to determining different migrating behavior. A simple optimization model, maximizing the population growth rate, demonstrates that zooplankton individuals change their migrating behavior depending on the amount of accumulated energy. Such energy accumulation and its investment in reproduction are repeated every reproductive cycle. Therefore, unless the reproductive cycle is synchronized among individuals, different migrating behaviors will be observed within a population even if no genetic differences exist. Our model demonstrates that such coexistence of the two migrating behaviors is possible in natural Daphnia populations, and suggests that internal conditions of zooplankton individuals may be important as a factor for determining migrating behavior of zooplankton. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diel vertical migration of zooplankton following optimal food intake under predation

A model is developed to investigate the trade-offs between benefitsand costs involved in zooplanktonic diel vertical migration(DVM) strategies. The ‘venturous revenue’ (VR) isused as the criterion for optimal trade-offs. It is a functionof environmental factors and the age of zooplankter. Duringvertical migration, animals are assumed to check instantaneouslythe variations of environmental parameters and thereby selectthe optimal behavioral strategy to maximize the value of VR,i.e. taking up as much food as possible with a certain riskof mortality. The model is run on a diel time scale (24 h) infour possible scenarios during the animal’s life history.The results show that zooplankton can perform normal DVM balancingoptimal food intake against predation risk, with the profileof DVM largely modified by the age of zooplankter.     

Diel periodicity and selectivity in the feeding rate of the predatory copepod Mesocyclops edax

The diel periodicity and selectivity in the feeding behaviorof the predatory cyclopoid copepod Mesocyclops edax was investigatedat 3 h intervals over two 24 h sampling periods in nature. Gutcontent analyses revealed an increase in gut fullness at 11.30and 20.30 in July, and at 20.30 in August. The increase in gutfullness at these times could not be explained by an increasein prey density, changes in predator-prey overlap or differencesin prey vulnerability. We suggest that M.edax exhibits a truediel periodicity in the intensity of its predatory activities,although the alternative hypothesis of a diel periodicity ingut passage time cannot be ruled out. Vanderploeg and Scavia'sE^* selectivity index indicated a preference for rotifer andcladoceran prey over copepods.     

Diel vertical migration thresholds of Karenia brevis (Dinophyceae)

Light and nutrient availability change throughout dinoflagellate diel vertical migration (DVM) and/or with sub-population location in the water column along the west Florida shelf. Typically, the vertical depth of the shelf is greater than the distance a sub-population can vertically migrate during a diel cycle, limiting the ability of a sub-population to photosynthetically fix carbon toward the surface and access nutrients sub-surface. This project investigated changes of Karenia brevis (C.C. Davis) G. Hansen et Moestrup intracellular carbon, nitrogen, internal nitrate (iNO₃), free amino acid (FAA), and total lipid concentrations in high-light, nitrate-replete (960 μmol quanta m⁻² s⁻¹, 80 μM NO₃), and high-light, nitrate-reduced (960 μmol quanta m⁻² s⁻¹, <5 μM NO₃) mesocosms. The nitrate-reduced mesocosm had a slowed cell division rate when compared to the nitrate-replete mesocosm. Minimum intracellular carbon, nitrogen, iNO₃, FAA, and total lipid concentrations during the largest surface sub-population aggregations led to the conclusion that daughter cells resulting from cell division received unequal shares of the parental resources and that this inequality influenced migration behavior. Nutrient reduced daughter cells were more strongly influenced by light and phototaxis for carbon production than their replete same cell division sister cells during vertical migration thus rapidly increasing the fulfillment of constituents through photosynthesis. Vertical migration was consistent with an optimization scheme based on threshold limits through utilization or formation of photosynthate. We propose a simplified conceptual model describing how K. brevis is transported along the benthos of the west Florida shelf from off-shore to on-shore. Dynamic carbon thresholds are also suggested for future DVM modeling efforts on K. brevis populations transported between nitrogen replete and nitrogen reduced environmental conditions.     

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 freshwater fishes – proximate triggers,ultimate causes and research perspectives

1. Diel vertical migrations (DVM) are typical for many cold‐water fish species such as Pacific salmons (Oncorhynchus spp.) and coregonids (Coregonus spp.) inhabiting deep lakes. A comprehensive recent overview of DVM in freshwater fish has not been available, however. 2. The main proximate trigger of DVM in freshwater fish is the diel change in light intensity, with declining illumination at dusk triggering the ascent and the increase at dawn triggering the descent. Additional proximate cues are hydrostatic pressure and water temperature, which may guide fish into particular water layers at night. 3. Ultimate causes of DVM encompass bioenergetics efficiency, feeding opportunities and predator avoidance. None of these factors alone can explain the DVM in all cases. Multi‐factorial hypotheses, such as the ‘antipredation window’ combined with the thermal niche hypothesis, are more likely to explain DVM. It is suggested that planktivorous fish move within a layer sufficiently well illuminated to capture zooplankton, but too dark for predators to feed upon the migrating fish. In complete darkness, fish seek layers with a temperature that optimises bioenergetics efficiency. The strength of each factor may differ from lake to lake, and hence system‐specific individual analyses are needed. 4. Mechanistic details that are still poorly explored are the costs of buoyancy regulation and migration, the critical light thresholds for feeding of planktivorous and piscivorous fish, and predator assessment by (and size‐dependent predation risk of) the prey fish. 5. A comprehensive understanding of the adaptive value of DVM can be attained only if the behaviour of individual fish within migrating populations is explicitly taken into account. Size, condition and reproductive value differ between individuals, suggesting that migrating populations should split into migrants and non‐migrants for whom the balance between mortality risk and growth rate can differ. There is increasing evidence for this type of partial DVM within populations. 6. Whereas patterns of DVM are well documented, the evolution of DVM is still only poorly understood. Because experimental approaches at realistic natural scales remain difficult, a combination of comprehensive data sets with modelling is likely to resolve the relative importance of different proximate and ultimate causes behind DVM in fish.     

Diel vertical migration and feeding rhythm of Daphnia longispina and Bosmina corexoni in Lake Toya, Hokkaido, Japan

Diel vertical migration (DVM) and diel feeding rhythm of two cladocerans, Daphnia longispina and Bosmina coregoni were investigated at the pelagic area of Lake Toya (Hokkaido, Japan) in May, August and October 1992. Both species performed nocturnal DVM. The amplitude of DVM, however, became smaller from May to October. Such seasonal variations in DVM could not be explained by light penetration and/or water temperature. The two species had a clear feeding rhythm; they fed at night in May and October but also after sunrise in August. These feeding rhythms appeared to be related to the light-dark cycle, but were not necessarily associated with their DVM. We suggest that the diel feeding rhythm and DVM are regulated independently by light cues.     

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 migration and vertical distribution of Cladocera in Lake D. Helvecio (Minas Gerais,Brazil)

Six genera of Clad ocera (Diaphanosoma, Daphnia, Ceriodaphnia, Moina, Bosmina, Bosminopsis), each of them usually with only one species were found in Lake D. Helvecio, a natural valley lake located in the eastern part of Brazil. Diurnal migratory movements of the organisms observed in this lake showed a different pattern in different species. Closely related species, which explore the same food source, live in different layers, thus avoiding interspecific competition. The migratory behaviour of the species was studied mainly in relation to temperature and oxygen distribution in the lake. Thus, analyses were made in the summer (January, 1978) when a strong stratification occurs with the establishment of a thermocline and an oxycline. Comparisons were made also with the data obtained in winter (July, 1978), when a complete mixing of water occurs.     

Vertical relationships between chlorophyll, production and copepods in the eastern tropical Pacific

Data consisting of high resolution profiles of in situ chlorophyll,copepods and primary production have been measured with a towedBatfish and profiling pumping system at two sites named ‘BIOSTAT’(9°45'N, 93°45'W) and ‘DOME’ (7°19'N,83°25'W) sites during March 1981. Primary production profileswere generated from Batfish profiles using a chlorophyll/lightmodel and incubated pump samples, the latter with high verticalresolution of 3–5 m. The BIOSTAT site had a subsurfacechlorophyll maximum situated at {small tilde}50 m, and a productionmaximum at a depth of 40 m Copepods had a mean depth centroidcorresponding to the production maximum although their distributionwas more uniformly dispersed from 0 to 40 m. The latter observationindicated that copepods occurred at depths of high productionpotential and low biomass rather than high total productionand high biomass as found at 40 m depth. The DOME site had amixed surface layer of chlorophyll (0–20 m) while copepodswere located at the base of the chlorophyll layer and primaryproduction maximum located at the surface (0–10 m). Theareal daily production measured at the BIOSTAT and DOME siteswere 0.27 and 0.80 mg C m^–2day^–1 respectively.     

Diel cycles of reproduction and vertical migration in the marine cladocerans Pseudevadne tergestina and Penilia avirostris

The marine cladocerans Pseudevadne tergestina and Penilia avirostrisuse different strategies to avoid visual predators. Pseudevadnetergestina exhibited a pronounced diel cycle in reproduction,but did not perform diel vertical migration. Parthenogeneticfemales with fully developed embryos were absent during theday in both fishless enclosures and in the natural environment.This observation suggests that the diel cycle was due to nocturnalrelease of neonates and not the result of selective predationby fish. The need to use the compound eye to locate food wouldforce P. tergestina to remain in the illuminated surface waterduring the day and release their offspring in darkness thusdecreasing their visibility to fish. The diel cycle in reproductionin P. avirostris was not as pronounced as that in P. tergestina,but females with mature embryos were still more common at nightthan during the day. As a grazer of phytoplankton, P. avirostrisperformed diel vertical migration and retreated to dark, deeperwaters during the day, avoiding visual predators.