Vertical, lateral and longitudinal movement of zooplankton in a large river

1. The spatial distribution and movement patterns of zooplankton in large rivers are little known compared with those in lake environments. We conducted a series of studies in the Ohio River (U.S.A.) during the low flow period to assess diel vertical (DVM), longitudinal and lateral movement of crustacean zooplankton. 2. The dominant large zooplankter, the copepod Eurytemora affinis, showed a consistent vertical migration pattern of daytime ascent and night‐time descent during all sampling periods – the reverse of the most common migratory pattern of zooplankton in lakes. The cladoceran Bosmina migrated in a similar way in two of the three sampling periods. Surveys taken longitudinally in the river showed similar trends for both taxa. 3. During the lateral surveys, E. affinis was significantly more abundant in the shallow littoral zone during the night than in the daytime. The combination of vertical and lateral movement patterns along with the diel distribution of zooplanktivorous fish suggest that these movements are a predator‐avoidance mechanism. 4. Sampling programmes in large rivers should consider that larger zooplankton such as E. affinis may not be randomly distributed in the river channel and behaviours such as diel vertical migration may be just as evident in river habitats as in lakes.     

Vertical distribution of<Emphasis Type="Italic"> Daphnia longispina</Emphasis> in a shallow subarctic pond: Does the interaction of ultraviolet radiation and<Emphasis Type="Italic"> Chaoborus</Emphasis> predation explain the pattern?

The adaptive significance of vertical migration by planktonic organisms is often explained in terms of reducing the risk of predation. Observational evidence, however, indicates that migratory patterns may also be triggered by solar ultraviolet (UV) radiation. Such a strategy would allow animals to escape from UV-induced damage into deeper water layers. In this study, we examine the relation of several biotic (invertebrate predators, algae) and abiotic (temperature, radiation) factors to the vertical distribution of Daphnia longispina in a 50-cm-deep, fishless pond in subarctic Finnish Lapland. Samples were taken from three depths, on both sunny and overcast days, and at different hours of day. Our results show that, on sunny days, the vertical distribution of Daphnia responds to ultraviolet radiation, whereas on overcast days, predator avoidance (phantom midge, Chaoborus obscuripes) is a better predictor of Daphnia distribution. Juvenile and adult Daphnia showed a similar distribution pattern.     

Individual food niche specialization in stream-dwelling charr

Food niche variation within a population of white-spotted charr, Salvelinus leucomaenis, was investigated by means of mark and recapture to examine the simplification that conspecific individuals are ecologically equivalent. Food diversity measured on the basis of living form of dietary organisms demonstrated variability in food niche in incidence, degree, and stability. As inferred from body size distribution and fish movement, niche variation was inexplicable by social rank hierarchy or foraging habitat rotation, and occasional niches were deemed to be realized individually. Higher annual growth rate shown by those with a larger niche width indicated the adaptive significance in niche variation. Assuming trade-off between feeding efficiency and predation risk, phenotypic plasticity was suggested to determine the food niche specialization of individuals to maximize lifetime fitness.     

Seasonal Vertical Migration and Aestivation of <Emphasis Type="Italic">Rhyacodrilus hiemalis</Emphasis> (Tubificidae,Clitellata) in the Sediment of Lake Biwa,Japan

The vertical distribution of the tubificid worm Rhyacodrilus hiemalis Ohtaka, the numerically dominant species of oligochaete in the littoral of Lake Biwa, was studied with special reference to seasonal vertical migration in the lake sediment. Monthly collections of lake sediment cores were made using PVC tubes. Core sections of sample sediments ranged from 76 to 117 cm. The vertical distribution of the worms showed no diurnal variation; therefore diel vertical migration was not evident. Seasonal downward migration started in April, and upward migration started in October. From December to March, almost all worms remained in the near-surface sediment layer (surface to 30 cm deep), while from July to September almost all worms remained deeper than 30 cm. However, few individuals migrated deeper than 90 cm. No discontinuous layers were found in grain size composition, water content, loss on ignition, particulate carbon, nitrogen or phosphorus. In deep sediment there was no free oxygen, as evidenced by negative ORP values. For 4 months in summer, R. hiemalis aestivated, probably utilizing anaerobic respiration. It appeared that R. hiemalis moved deeper in the sediment in response to sediment temperature, because sediment temperatures in the deep layers seemed to converge at around 20–21 °C in the summer months. The life history traits of seasonal vertical migration and summer aestivation perhaps arose as an adaptation to the climatic conditions accompanying the geographical origin of R. hiemalis, and they also serve to minimize predation risk during summer when most invertebrate predatory fishes are active.     

Distribution of antarctic zooplankton around Elephant Island during the austral summers of 1988, 1989, and 1990

Year to year variation and vertical distributions of epipelagic Zooplankton around Elephant Island and King George Island were examined with samples collected with bongo nets and a 1 m² MOCNESS during the austral summers (Jan–Feb.) of 1988, 1989 and 1990. Copepods were the major components of epipelagic Zooplankton (in numbers) with dominance of Metridia gerlachei (1988 and 1989) and small calanoids and cyclopoids (1990). Euphausiids and salps were the next most abundant groups. The percent composition of euphausiids decreased from 1988 to 1990 while that of salps increased. The abundance of salps exceeded euphausiids and major taxa of copepods in 1990. Local patches of polychaetes and amphipods were also found. Statistically significant annual variations with increased numbers in 1990 were found by analyses of variance in total abundance, abundances of copepods, salps, chaetognaths and amphipods, but abundances of euphausiids, polychaetes and fishes showed no significant annual variations. When the study area was divided geographically, horizontal variability in abundance within each year showed no significance in total abundance, abundances of copepods, euphausiids, amphipods and fishes, but significance in salps, polychaetes and chaetognaths. Results of site clustering based on covariances of abundances of eleven major taxa were well matched, though not perfect, with the distribution of surface water temperatures which could be used as a tracer of source water masses suggesting that spatial variation was related to hydrodynamic conditions. Factor analyses showed that annual and spatial variations in abundance were mainly caused by only two taxa, Metridia gerlachei and salps (mostly Salpa thompsoni). These two taxa were responsible for about 60% and 30% of total variance, respectively, and were useful indicators of the interannual variation. That is, 1988 and 1989 were the years of M. gerlachei, and 1990 was the year of salps. From vertically stratified MOCNESS samples, it was shown that the major taxa in this study area were active vertical migrators. While most samples obtained by relatively shallow tows (uppermost 100 m depth) were composed of exclusively one or two taxa, those from relatively deep tows (down to 200 m) showed various patterns of vertical stratification suggesting that the patterns of vertical migration were species specific. Species specific ontogenetic vertical migration associated with elevated habitat temperatures also seemed to be responsible for the annual variation in zooplankton distribution in the upper water column.     

Diel pattern of pelagic distribution and feeding in planktivorous fish

Summary The spatial distribution of juvenile roach (Rutilus rutilus), rudd (Scardinius erythrophtalamus), bream (Abramis brama) and bleak (Alburnus alburnus) was registered by echosounding during two years in small Bavarian lakes. The gut contents of the fish were analysed in order to reconstruct their rhythmicity of food intake. Fish were found in the pelagic zone only during the night, feeding before midnight with maximal rate. The vertical position of the fish was dependent on the water transparency following a light intensity in the order of 10^-3 Lux. The diel migration between littoral and pelagic zones was a mainly horizontal one with a vertical component. Both the speed of increase of fish density in the open water and of the vertical movement was correlated to the speed of change of light intensity. Shoals broke up into single fish during the offshore migration. The span of presence in the pelagic zone was identical with the duration of the dark period. During winter no diel migration nor periodical feeding took place.     

The effects of haloclines on the vertical distribution and migration of zooplankton

While the influence of horizontal salinity gradients on the distribution and abundance of planktonic organisms in estuaries is relatively well known, the effects of vertical salinity gradients (haloclines) are less well understood. Because biological, chemical, and physical conditions can vary between different salinity strata, an understanding of the behavioral response of zooplankton to haloclines is crucial to understanding the population biology and ecology of these organisms. We studied four San Francisco Bay copepods, Acartia (Acartiura) spp., Acartia (Acanthacartia) spp., Oithona davisae, and Tortanus dextrilobatus, and one species of larval fish (Clupea pallasi), in an attempt to understand how and why zooplankton respond to haloclines. Controlled laboratory experiments involved placing several individuals of each species in two 2-m-high tanks, one containing a halocline (magnitude varied between 1.4 and 10.0 psu) and the other without a halocline, and recording the location of each organism once every hour for 2-4 days using an automated video microscopy system. Results indicated that most zooplankton changed their vertical distribution and/or migration in response to haloclines. For the smaller taxa (Acartiura spp., Acanthacartia spp., and O. davisae), this behavior took the form of accumulating in or below the halocline, while the effects on the larger species (C. pallasi and T. dextrilobatus) were more subtle. C. pallasi yolk sac and 3- to 6-day-old larvae seemed to pause or remain in the halocline during their diel migration, while 14- to 17-day-old larvae appeared to avoid the halocline by remaining in deeper, more saline water. There were very few statistically significant effects of haloclines on the vertical distribution of T. dextrilobatus. Subsequent mortality experiments with Acartiura spp., Acanthacartia spp. and T. dextrilobatus indicated that the behavioral changes seen in the halocline studies were not associated with any salinity-induced mortality per se, although more subtle affects of physiological stress could not be ruled out. These results point to a high degree of flexibility in vertical migration behavior within a given species as well as large variation between species. Such behavioral flexibility is likely to be very important in allowing planktonic organisms generally, and estuarine organisms in particular, to maintain or alter position relative to currents, food, and predators.     

The development and vertical distribution of populations of gas-vacuolate bacteria in a eutrophic,monomictic lake

The role of gas vacuoles in the vertical stratification of planktonic bacteria is analysed. Measurements made with certain gas-vacuolate bacteria in laboratory culture suggest that only colonial forms could sink or float fast enough to form population maxima in lakes by vertical migration from other depths. It is suggested that in the case of individual cells the importance of the buoyancy provided by gas vacuoles is to minimise sinking rates and thereby to increase residence times of the organisms at depths where conditions support their growth.Changes in the vertical distribution of a number of gas-vacuolate bacteria were followed throughout the year in a monomictic, eutrophic lake (Crose Mere, Shropshire). All were restricted to the anaerobic hypolimnion which developed in summer. The various species formed maxima at different depths and times. With some of them (e.g. species of Thiopedia, Pelonema and Brachyarcus) growth was necessary to explain their development. In others (e. g. species of Pelodictyon and two colourless bacteria) vertical migrations might also have contributed to their development.     

Vertical migration of Chaoborus flavicans in a Scottish loch

The pattern of diel vertical migration of Chaoborus flavicans larvae in a shallow Scottish loch varies according to the instar and, in third and fourth instars, according to the season. The planktonic phase of the migration is not exclusively concerned with predation, the larvae feeding at least equally actively in the benthos. Although there is no conclusive evidence as to the role of vertical migration in Chaoborus flavicans, it has some of the characteristics of an epideictic display. Upward and downward locomotion can be induced experimentally in a plankton wheel by manipulating light intensity alone. However, the responses are complex and there is a great deal of individual variation, suggesting that additional factors are involved.     

Diel variation in the vertical distribution of fish and plankton in Lake Kinneret: a 24-h study of ecological overlap

Diel vertical migration (DVM) behaviour is a predator avoidance mechanism observed within many zooplankton species in the presence of zooplanktivorous fish. A 24-h survey was carried out in June 1998 to investigate diel variation in the vertical distribution of fish, zooplankton and phytoplankton (chlorophyll) in Lake Kinneret, Israel. Fish revealed diel variation in vertical distribution but had no spatial overlap with zooplankton, and consequently no apparent influence on zooplankton dispersal. Zooplankton revealed some diel variation in distribution being affected by thermocline and oxycline position and movement of the internal the internal seiche wave. Cyclopoid species closely follow the movement of the seiche wave implying that, due to their greater motility, they are following conditions that are suitable to them. The Cladocera species and small rotifers only partly, which may be part of their phototaxic behaviour. Physical forces like convection, horizontal and vertical forcing probably have a role in contributing to a homogeneous distribution of the plankton by preventing stratification or interfering with the more motile zooplankton which may be attempting to migrate.     

Vertical distribution of the zoobenthos in southeastern Lake Michigan with evidence of seasonal variation*

SUMMARY. The vertical distribution of the zoobenthos in southeastern Lake Michigan was investigated monthly from May to November 1976. The organisms could be divided into two categories: one in which the majority of the population occurred in the upper 1 cm of substrate (Pontoporeia, naidids, chironomids, cyclopoids, harpacticoids, cladocerans, turbellarians, ostracods, rotifers, sphaeriids and gastropods) and one in which the majority of the population occurred deeper (immature tubificids without hair setae, Stylodrilus heringianus, enchytraeids, nematodes, and tardigrades). The vertical distribution of these infaunal forms showed a marked seasonal variation. They were found in the superficial sediments in the spring, but deeper in the sediments in the autumn. This trend coincided with the seasonal occurrence of a detrital layer that overlay the sandy substrate in the spring but was absent in the autumn.     

Diel vertical migrations of zooplankton in a shallow, fishless pond: a possible avoidance-response cascade induced by notonectids

1. Day (noon) and night (midnight) vertical distributions of zooplankton and phytoplankton in the water column (1.5 m) of a Vermont pond were determined on two consecutive days from 470 mL water samples taken at three depths (0.1, 0.5 and 1.0 m) at three sites. There was little variation across depths in temperature, dissolved oxygen concentration and phytoplankton. All individuals of each zooplankton species (a small copepod, Tropocyclops extensus and six rotifers) were counted. 2. A three-way ANOVA on the zooplankton data showed no effect of date or time of day on the abundance of any species. Significant diel shifts in vertical distribution (depth × time-of-day interactions) were found for T. extensus (nauplii, as well as copepodites and adults) and Polyarthra remata, but not for Hexarthra mira, Keratella cochlearis, Anuraeopsis fissa, Ascomorpha ovalis and Plationus patulus. Tropocyclops extensus showed a pronounced, typical diel vertical migration, avoiding the surface and occurring most abundantly near the bottom during the day. Polyarthra remata showed an equally pronounced, reverse diel vertical migration, avoiding the bottom and being most abundant near the surface during the day. 3. The diurnal descent of Tropocyclops is interpreted as an avoidance response to Buenoa macrotibialis, a notonectid which feeds on this copepod at the surface during the day but not at night. The diurnal ascent of Polyarthra is thought to be an avoidance response to Tropocyclops, which strongly suppresses this rotifer in field enclosures and laboratory vessels. Thus, these out-of-phase migrations may be coupled and represent a behavioural cascade initiated by Buenoa. 4. At night, Tropocyclops and Polyarthra both were uniformly distributed across depths. This is believed to reflect the absence of appreciable depth-related variation in temperature, algal food resources (biovolume of cryptomonads and chrysophyte flagellates) and predation risk at this time. 5. The five rotifer species that did not exhibit diel vertical migrations may be less susceptible to Tropocyclops predation than Polyarthra.     

Automated Recording of Vertical Negative Phototactic Behaviour in Daphnia magna Straus (Crustacea)

Diurnal vertical migration is a well-known phenomenon in the circadian activity rhythms of zooplankton. Our goal was to test whether negative phototaxis in Daphnia magna clone BEAK (provoked by artificially induced light stress, alternating light and dark phases in 2 h intervals), and its interference with the endogenous rhythm of diurnal vertical migration, can be automatically registered with a biomonitor. For the first time the vertical swimming behaviour of D. magna was recorded quantitatively based on non-optical data recording in a fully automated biotest system, the Multispecies Freshwater Biomonitor in a new experimental setup consisting of a column of three recording units (3-level chambers). Circadian vertical migration was clearly recorded in the 3-level chambers and the rhythm was more clear with 5 than with 1 organism per chamber. The organisms clearly responded to induced light stress with negative phototaxis, however best in larger chambers. The artificially induced rhythm was influenced by the endogenous rhythm. This approach may facilitate long-term observations of vertical swimming activity of zooplankton in the future.     

Diel vertical migration of the copepod <Emphasis Type="Italic">Thermocyclops inversus</Emphasis> (Kiefer, 1936) in a tropical reservoir: the role of oxygen and the spatial overlap with <Emphasis Type="Italic">Chaoborus</Emphasis>

The effect of water transparency, dissolved oxygen concentration and the invertebrate predator Chaoborus brasiliensis on the day–night vertical distribution of the copepod cyclopoid Thermocyclops inversus was investigated in a shallow tropical reservoir, Nado Reservoir, Belo Horizonte, Brazil. Diel cycles were carried out over a period of 12 consecutive months, between October 1999 and September 2000. The different developmental stages of T. inversus exhibited diel vertical migration (DVM) and displayed a clear ontogenetic trend, with the amplitude of DVM increasing with the age of the organism, and ranging from 0.4 m to 0.8 m for nauplii, 0.4 m to 1.2 m for copepodite, and 1.1 m to 2.1 m for adults. We observed that seasonal changes in dissolved oxygen and C. brasiliensis directly influenced the vertical distribution of the copepod population in this reservoir. Furthermore, it was showed that the diurnal vertical migration is an important predator avoidance behavior since it diminished the spatial overlap between prey and its potential predator. This finding supports the hypothesis that the vertical migration is a defense mechanism against predation. Thus, T. inversus is able to remain in the anoxic layers during day light hours, and at night they move upwards avoiding hypolimnetic waters to escape from predation by Chaoborus.     

Behavioural and genetic differences in populations of Daphnia subjected to different levels of predation

1. Predictions based on a genetic control mechanism for vertical migration were tested by monitoring the vertical migration behaviour of electro-phoretically distinct clones of Daphnia longispina and Daphnia magna collected from ponds with different levels of predation. 2. The number of predator species in a pond (a measure of predation) had a significant effect on the vertical migration behaviour of the clones found within that pond, and a phenogram constructed on the basis of the percentage dissimilarity between the genotypes of the clones indicated that clones from the same site were more closely related genetically than clones from different sites. 3. There were significantly different vertical migration behaviour patterns between clones from different sites and between-site variation in behaviour was significantly greater than that found within a site. 4. Clones differed in the average depth they maintained in the waterbody regardless of the pond from which they were collected, but clones from the same site did have similar behavioural profiles suggesting a tendency to show the same behavioural patterns. 5. These findings, which support predictions based on a genetic control mechanism, are discussed in relation to phenotypically plastic mechanisms of vertical migration control widely reported in the literature.     

Vertiquant: A Device for Automatically Recording Vertical Migration of Plankton

Vertical migration is a key subject in understanding zooplankton ecology and its influence on aquatic ecosystems. This paper introduces a device for automatically recording vertical plankton migrations to study proximate factors regulating the stimulus, timing and amplitude of these movements under controlled laboratory conditions. The instrument records the light scattered by organisms at their respective depths and processes the signals in real time to a graphic representation of the organisms vertical distribution. Organisms of different taxa from a size of <40 μ, to > 10 000 μm were used for these experiments. Daphnia migrations in response to UV light are used to demonstrate the basic functions of the instrument.     

VIIRS captures phytoplankton vertical migration in the NE Gulf of Mexico

In summer 2014, a toxic Karenia brevis bloom (red tide) occurred in the NE Gulf of Mexico, during which vertical migration of K. brevis has been observed from glider measurements. The current study shows that satellite observations from the Visible Infrared Imaging Radiometer Suite (VIIRS) can capture changes in surface reflectance and chlorophyll concentration occurring within 2 h, which may be attributed this K. brevis vertical migration. The argument is supported by earlier glider measurements in the same bloom, by the dramatic changes in the VIIRS-derived surface chlorophyll, and by the consistency between the short-term reflectance changes and those reported earlier from field-measured K. brevis vertical migration. Estimates using the quasi-analytical algorithm also indicate significant increases in both total absorption coefficient and backscattering coefficient in two hours. The two observations in a day from a single polar-orbiting satellite sensor are thus shown to be able to infer phytoplankton vertical movement within a short timeframe, a phenomenon difficult to capture with other sensors as each sensor can provide at most one observation per day, and cross-sensor inconsistency may make interpretation of merged-sensor data difficult. These findings strongly support geostationary satellite missions to study short-term bloom dynamics.     

Feeding selectivity of a tropical Chaoborus population

SUMMARY. The Chaoborus population of Lake Lanao, Philippines, was sampled weekly over a 65-week period. Specimens representing all four instars, all times of the year, and two points in the daily migration cycle were dissected for determination of gut contents. Major items in the diet of Lanao Chaoborus include Bosmina, Diaphanosoma, and the copepodid and adult stages of cyclopoid and calanoid copepods. Items that are available but seldom eaten include nauplii and rotifiers except Keratella. Feeding rate averages 2.5% of body weight per day in instars 3–4. Predator size affects but does not fully explain prey selection. Electivity values are much higher for Bosmina and Diaphanosoma than for copepods, even though these food items overlap in size. Bosmina, which has the highest electivity value of any prey, is virtually identical in size to the calanoid nauplius, which has one of the lowest electivity values. This and other similar data suggest that prey of the same size differ greatly in palatability or vulnerability. There is a marked variation in feeding rate and food composition from day to night. The smallest Chaoborus feed more during the day than at night, but the opposite is true for Chaoborus of moderate to large size. Large Chaoborus switch from a daytime emphasis on copepod copepodids and adults to a nighttime emphasis on Cladocera. Diurnal variation between instars in food composition cannot be explained simply on the basis of the vertical distributions of predators and prey. An interaction of vertical distribution with prey density and predator selectivity does explain the overall Chaoborus feeding pattern, however. During the day, larger Chaoborus move deep into the water column where food is scarce. Their daytime feeding rate is lower due to low prey density at great depths. Low prey density is partially compensated by relaxation of preference. At night, upward migration of large Chaoborus into an area of high prey density permits a resumption of marked selectivity and high feeding rates. Small Chaoborus do not descend deep into the water column during the day, as their lower hunting efficiency apparently requires higher food density and use of visual cues to sustain adequate feeding rates. Prey density thus affects both the vertical distribution and feeding selectivity of the Chaoborus population.     

Modification of the diel vertical migration of Bythotrephes longimanus by the cold-water planktivore, Coregonus artedi

1. The weak diel vertical migration observed in the large cladoceran Bythotrephes longimanus seems contradictory to the predator‐avoidance hypothesis that predicts large zooplankton should have long migration amplitudes. However, cold‐water planktivores, especially Coregonus spp., are a main source of mortality for Bythotrephes and hence a deeper migration would result in a greater overlap with these hypolimnetic planktivores. We hypothesized that Coregonus artedi (cisco) modifies the normal vertical migration pattern of Bythotrephes, such that the latter stays higher in the water column during the day and thus migrates less extremely at night. 2. The vertical distribution of Bythotrephes during the day was determined from single visits to six lakes in Ontario, Canada, all of which contain warm‐water, epilimnetic planktivores but differing in whether they contain cisco. One lake of each fish type was sampled day and night every 2–3 weeks over the ice‐free season to examine daytime depths and migration amplitude. 3. The vertical migration of Bythotrephes differed in the presence and absence of cisco. In the lakes with cisco, there were significantly fewer Bythotrephes in the hypolimnion and they were higher in the water column during the day. Migration amplitude was smaller in the cisco than in the non‐cisco lake. These observations were not attributable to differences in physical factors, and, although not conclusively attributable to cisco, are consistent with an effect of cisco. 4. We suggest that diurnal depth selection by Bythotrephes in lakes containing cisco is a trade‐off between the risk of predation by warm‐ versus cold‐water predators, balanced by the benefits of increased temperature and feeding rates near the surface. Even in lakes without cisco, however, the vertical migration of Bythotrephes was less than expected, suggesting that diurnal depth selection is a balance between the risk from warm‐water planktivores and access to sufficient light to feed effectively.     

Etude des migrations verticales journalières du phytoplancton à l'aide d'enceintes placées dans un Rang peu profond

Two enclosures without a bottom were placed in a shallow non-stratified pond. One of these enclosures (B) had a transparent plastic wall and was open at the top. The second enclosure (N) was painted in black and covered over. The vertical distribution and daily migration of Ceratium hirundinella, Trachelomonas spp., Gomphosphaeria naegeliana and Aphanizomenon flos-aquae were studied. Investigations were carried out during a 24 h period both in the pond and inside the two enclosures. Vertical migration was shown by the four algae, even within the water column N. Differences between the behaviour patterns of the different algae are described.