Diel vertical distribution of zooplankton in Lake Naivasha,Kenya

Diurnal and diel vertical distribution of limnetic zooplankton species in relation to temperature and dissolved oxygen profiles was examined at a central station in Lake Naivasha. During calm days thermal stratification developed gradually from late morning to reach maximum formation at mid-day. Dissolved oxygen concentrations showed similar vertical profiles to temperature. These stratifications were, however, short lived and were broken up in late afternoons by the wind induced poly-holomictic nature of the lake. During the day most zooplankters aggregate at the top 3–4 metre zone of the water column coincident with maximum photosynthetic activity. The pattern of diel vertical distribution of zooplankton in Lake Naivasha is undefinedly even. The absence of significant diel changes in the distribution of the limnetic zooplankton may be related to the absence of permanent physico-chemical boundaries and lack of predation pressure in the open water.     

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)。     

Diurnal changes in the vertical distribution of cladocerans in a biomanipulated lake

The diel vertical migration of cladoceran zooplankton in LakeVesijärvi was studied after a distinct improvement of the waterquality following mass removal of fish. Four out of seven speciesshowed diurnal changes in vertical distribution. The two speciesdominating at 0–10 m, Bosmina crassicornis and Daphniacucullata, migrated reverse, while hypolimnetic Bosminalongispina and Ceriodaphnia quadrangula ascended at night.The migration did not cross the thermocline, suggesting thatzooplankton had a minor role in restricting the availability ofphosphorus for phytoplankton. The reverse migration in theepilimnion was likely connected to the feeding behaviour of thedominating planktivores. During night, smelt (Osmeruseperlanus (L.)) migrated from the hypolimnion to the surface tofeed on daphnids, while roach (Rutilus rutilus (L.)) thatinhabited the 5–15 m depth, was day-active and fed mainly on Bosmina. In the hypolimnion, the cladocerans used the low oxygenconcentration as a refuge and at night migrated to layers moreprofitable for feeding. This suggests that the predation by fishwas the ultimate factor of the vertical migration, but otherenvironmental factors determined its magnitude.     

Diel vertical migration by males,females, copepodids and nauplii in a limnetic population of diaptomus (Copepoda)

Diel vertical migration (DVM) by the sexes and life history stages of the copepod Diaptomus novamexicanus (Herrick) was investigated during two summers in a subalpine lake (Castle Lake, California, USA). Migratory behavior was quantified repeatedly by 1300 and 21–2200 hr sampling in the epilimnion. Population density and vertical distribution were estimated routinely at 1300 hr and at 2200 hr on selected dates. Males had greater night to day biomass differentials and ratios than females. The sexes showed comparable DVM participation (% of total biomass migrating) and amplitudes of migration (distance of ascent). Copepodids displayed higher participation, night/day ratios and amplitudes than younger copepods, but adult participation differed only from that of nauplii. Active participation in high amplitude ascents thus increased with age and was greatest in adult males. Analysis suggests that such relative behaviors probably occur in most limnetic Diaptomus, and that the magnitude of ascent into the epilimnion is associated with daytime vertical distribution.     

On the combined analysis of proximate and ultimate aspects in diel vertical migration (DVM) research

Although evolutionary ecologists agree that proximate and ultimate aspects are two sides of one coin, they are seldom interested in studies on physiological and behavioural mechanisms at the base of ecological phenomena. Nevertheless, these mechanisms are objects of selection and evolved to realise adaptive significances. This paper is a plea to bring both fields closer together, and, by means of an example of Diel Vertical Migration of Daphnia, some proximate and ultimate aspects are discussed. It is argued that light changes, not fish kairomone, is the primary cause for an individual to swim downwards at dawn and upwards at dusk. However, what is called a causal factor might differ when ecosystems or individuals are studied. In addition, causality in ecology is not simple, and has the character of a `set of necessary conditions'. To illustrate the importance of proximate analyses in DVM, two basic response mechanisms are discussed: Photobehaviour system 1 and 2. The physiological character of these systems leads to a fixed type of migration or to a phenotypically induced DVM, respectively. The adaptive significance of the first might be a reduction of the hazardous effects of UV radiation and of the second a lowering of mortality due to visually hunting predators.     

Variability and possible adaptive significance of day-time vertical distribution ofLeptodora kindtii (Focke) (Cladocera) in a shallow eutrophic lake

The day-time vertical distribution of different size classes ofLeptodora kindtii in Tjeukemeer was studied during two contrasting years: 1978 and 1979. During the first year (1978) the predation pressure exerted by the planktivorous fish was rather high, whilst this was ca. 15 times lower during 1979. The diel vertical migration of different size classes ofLeptodora, was studied twice during 1979. Both studies support the predator avoidance hypothesis and also emphasize the idea that diel vertical migration is a dynamic rather than a fixed behaviour trait within a population.     

The effect of Cyanophyta upon zooplankton in a eutrophic tropical lake (Lake Valencia,Venezuela)

The effect which Cyanophyta have upon the zooplankton varies according to the form of the alga (mucilaginous colonies or filaments) and its abundance. Periodical blooms of Microcystis aeruginosa were not detrimental for the zooplankton, in spite of the fact that copepods, cladocerans and rotifers consume small colonies. High concentrations of Lyngbya limnetica and Oscillatoria limnetica in Lake Valencia, Venezuela, proved to be inhibitory for cladocerans. A total absence of cladocerans was detected when filaments increased.     

浮游动物昼夜垂直迁移机理的主要假说及其研究进展

对有关浮游动物昼夜垂直迁移(DVM)机理的实验、假说以及理论模型方面的研究进.展进行了综述。昼夜垂直迁移通常指常规迁移(傍晚上升,拂晓下降),其行为过程不仅影响浮游动物的垂直分布,而且也间接地影响其水平分布及生活史特征,对浮游动物在一定水域的种群维持和补充具有重要的意义。与垂直迁移机理有关的假说主要有光驱动假说、逃避捕食者假说、能量和资源利用假说等,其中逃避捕食者假说已得到大量的实验证实。其理论模型研究一般在两个时间尺度上进行,一个是短期的行为机制研究,另一个从长期的生活史策略的角度考虑。随着实验技术的进步和理论及建模工具的发展,这两个时间尺度的研究正逐渐统一到一个框架下进行。     

Diel patterns of feeding and vertical migration in daphnids and diaptomids during the clear water phase in Lake Geneva (France)

In lacustrine environments, little attention has been paid to small-scale interactions between zooplankton diel vertical migration (DVM) and feeding rhythms. Moreover, most of the information on in situ diel feeding and migratory rhythms is based on low sampling frequencies. The kinetics and the degree of coupling of these processes are thus only roughly known. Here, we present a study conducted on a diel cycle in Lake Geneva to establish the temporal and spatial relationships between DVM and grazing activity of the dominant planktonic crustaceans. Our methodological approach is based on reliable and frequent (every 30 minutes) sampling, and on gut fullness analysis. We test the hypothesis of temporal and spatial segregation in DVM and feeding activity of sympatric taxa to counteract resource competition. We also evaluate the variation in DVM and feeding activity between taxa, size and sexes. In Lake Geneva, the Daphnia complex of different species and size (D. hyalina × galeata) and the diaptomid (Eudiaptomus gracilis) have distinct DVM and diel feeding patterns which lead to temporal and spatial segregation. Differences arise from the amplitude and kinetics of DVM and diel feeding rhythms. A strong day/night contrast in depth distribution and feeding activity was observed for the large daphnids while the small daphnids and the diaptomids had lower amplitudes of DVM and weaker diel changes in feeding activity. Large Daphnia exhibited a bimodal feeding pattern coupled with dynamic interchange of individuals between the epi- and hypolimnetic layers at dusk and dawn. In contrast, little coupling between DVM and feeding patterns was found for the diaptomid. These distinct behaviours can be viewed as specific adaptive strategies developed by calanids and daphnids to limit interspecific competition and to compromise between avoidance of starvation in deep waters and avoidance of visual predators in surface layers. Our study supports the hypothesis of exogenous control of Daphnia DVM by the relative change in light intensity at dusk and dawn, but also suggests that small Daphnia (not large ones), are controlled by absolute light variations when this major stimulus is lacking. Our results also support the hypothesis that selective predation by fish is responsible for the observed differences in DVM and diel feeding patterns of sized-daphnids and diaptomids. Other factors explaining the coupling of DVM and feeding patterns are hunger, vertical temperature gradient and for daphnids, size. Thus, ecological plasticity in crustacean DVM and feeding patterns results from the interactive effect of multiple abiotic and biotic driving forces. Finally, our study also shows that large Daphnia have a marked contribution to the acceleration of downward nutrient fluxes in Lake Geneva, via their diurnal rhythm in feeding and vertical migration. Ecological implications of the study for lake management and sampling design of zooplankton grazing studies are also presented.

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Résumé Dans les écosystèmes lacustres, les interactions à fine échelle temporelle entre les patrons diurnes de migration verticale et de broutage du zooplancton sont peu étudiées. En outre, jusq'à présent, les études ont généralement été réalisées selon des chroniques temporelles assez lâches. La cinétique et le degré d'interaction entre les patrons journaliers de migration verticale et de broutage sont donc encore mal connus. La présente étude, conduite au Lac Léman (Lac de Genéve) au cours d'un cycle nycthéméral, tente de préciser les liaisons spatiales et temporelles existant entre les migrations journalières et la consommation de phytoplancton chez les taxons de Crustacés les mieux représentés. Notre approche méthodologique repose sur une maille temporelle d'échantillonnage fine et sur l'analyse de la fluorescence du contenu stomacal. Nous testons l'hypothèse d'une ségrégation spatio-temporelle visant à réduire la compétition entre les taxons sympatriques et reposant sur des différences entre les patrons journaliers respectifs de migration et d'alimentation. Nous évaluons pour ces rhythmes d'activité les différences entre les espèces, les classes de tailles et les sexes. Au lac Léman, le complexe de différentes espèces et tailles de daphnies (Daphnia hyalina × galeata) et le diaptomide (Eudiaptomus gracilis) présentent des patrons journaliers de migration et d'alimentation distincts, assurant une ségrégation spatio-temporelle. Les différences proviennent de variations dans la cinétique et l'amplitude des migrations et dans les niveaux d'alimentation. Les grandes daphnies affichent un fort contraste jour/nuit dans leur répartition verticale et leur état de réplétion, tandis que les petites daphnies et les diaptomides présentent une faible amplitude de migration et de variations circadiennes de réplétion. Les grandes daphnies ont un rythme alimentaire bimodal couplé avec un relais dynamique des organismes entre l'épilimnion et l'hypolimnion au crépuscule et à l'aube. Chez le diaptomide, les interactions sont au contraire faibles entre les patrons de migration verticale et de réplétion. Ces différents comportements peuvent être perçus comme des stratégies adaptives spécifiques développées par les daphnies et les diaptomides pour limiter la compétition interspécifique et aboutir à un compromis satisfaisant entre l'évitement de la famine en eaux profondes et de la prédation par les poissons dans les eaux superficielles. Notre étude conforte l'hypothèse d'un contrôle exogène de la migration verticale de Daphnia par les changements relatifs de la lumière au crépuscule et à l'aube. En l'absence de ce stimulus, la répartition verticale des petites daphnies semble par contre contrôlée par les variations absolues de lumière. Nos observations confortent également l'hypothèse que la prédation sélective par les poissons est responsable des différences observées dans les patrons de migration des grandes daphnies et ceux des petites daphnies et des diaptomides. Les autres facteurs pouvant influencer les patrons de migration et d'alimentation des crustacés du Lac Léman sont la famine, le gradient thermique vertical et, chez les daphnies, la taille. En définitive, la plasticité écologique des patrons journaliers de migration et d'alimentation résulte des effets interactifs de daphnies ont un rôle très important dans le transfert des nutriments dans les couches profondes durant l'été, via leurs migrations verticales et les variations circadiennes d'activité alimentaire. Les implications écologiques pour l'aménagement lacustre et la planification des études portant sur le broutage du zooplancton sont aussi présentées.

     

Diel and seasonal distribution of perch in Lake Constance: a hydroacoustic study and in situ observations

A near-shore belt 50 km in length was surveyed parallel to the shoreline of Lake Constance, central Europe, with a single-beam echosounder five times between July 1993 and February 1994. The species and age composition of fish in the survey area was investigated by gillnet fishing and SCUBA-diving. In summer, the horizontal distribution of perch was patchy. Population density declined from east to west, and highest densities occurred in one shallow bay and close to ports and jetties at steeper shores. During daytime, perch stayed in the sublittoral zone between 3 and 15 m depth and between 2 and 6 m above the thermocline. Within this layer age classes were separated spatially: the relative number of young-of-the-year perch declined with depth whereas the relative number of adult perch (2+ and older) increased with depth. At dusk the fish migrated to the littoral zone, where they spent the night resting on the bottom. In winter, under almost homothermal conditions, perch of all ages were located between the 35 and 70 m depth contours, where they performed pronounced diel vertical migrations. They rested on, or close to, the bottom during daytime and ascended up to 20 m below the surface at night. During this season, horizontal distribution of perch was much more homogeneous than in summer.     

Vertical distribution of phytoplankton in Lake Xolotlán (Managua)

A study of the vertical distribution of phytoplankton was carried out at the end of the rainy season (October–November), when wind activity is lower and the probability for phytoplankton stratification is enhanced. Samples were taken every other day at 0, 0.5, 1.0 m and, thereafter, for every meter up to the bottom. The number of individuals and their biomass were determined for each sampling depth and expressed as wet weight and chlorophyll-a, respectively. The results indicate that there were no significant differences (ANOVA one way, P<0.05) with regard to the vertical distribution of phytoplankton biomass over the 15 m of the water column. This result reflects the polymictic condition of Lake Xolotlán (Managua).     

Diel vertical migration of the loosejaw dragonfishes (Stomiiformes: Stomiidae: Malacosteinae): a new analysis for rare pelagic taxa

The diel vertical migration (DVM) of three genera of the stomiid subfamily Malacosteinae (Photostomias, Aristostomias and Malacosteus) was analysed from capture records of nearly 300 specimens in the Atlantic Ocean. To account for broad temporal and geographic scales encountered in this study, local time of capture was transformed to a corrected time representing position in a solar day. Species of Photostomias and Aristostomias undertake asynchronous DVMs characterized by a residence in the mesopelagic zone during the day and separate migrating and non‐migrating subpopulations at night. Species of Photostomias displayed an asynchronous DVM pattern characterized by a residence in the lower mesopelagic zone (>500 m) during the day and a segregated distribution at night. Specimens of Photostomias guernei captured at night in the mesopelagic were nearly identical in size to those captured in the epipelagic; however, day epipelagic specimens were stratified by size. In species of Aristostomias, few specimens were caught in the mesopelagic zone during the day and only small specimens were captured in the mesopelagic zone at night, indicating that sampling depth may not have been adequate to capture the bulk of mesopelagic daytime residents and the entire size range of the non‐migrating night‐time residents. In contrast, Malacosteus niger was distributed below 600 m, did not regularly migrate to the epipelagic zone and was stratified across the 700 m isobath. From these data, relationships between DVM patterns, morphology and foraging ecology are inferred and biases and applications of this method are discussed.     

Caridina nilotica in Lake Victoria: abundance, biomass, and diel vertical migration

Caridina nilotica (Decapoda: Atyidae) in offshore waters of Lake Victoria were investigated with both day and night sampling over a period of two years. Offshore populations are mainly planktonic rather than benthic, and the animals exhibit diel vertical migrations into near-surface waters at night. These changes in diel abundance as well as the size-frequency distribution of the migrating shrimp suggest that the migratory behavior is in response to visual planktivory, because only the very smallest individuals (2–4 mm) remain in surface waters during the day. During October 1992, abundances were estimated both by vertical net sampling and by underwater video transect methods. Concordance was established between abundances estimated by the two methods. Only about 9% (night) to 14% (day) of the Caridina population appeared to be epibenthic. We suggest that the behavior of the animal is consistent with the hypothesis that it is not a strict detritivore as previously reported; rather it may engage in facultative planktivory, especially at night.     

Vertical distribution and diel migration of flagellated phytoplankton in a small humic lake

The vertical distributions and migrations are described of the most abundant flagellated phytoplankton species from the summer community of a small forest lake in southern Finland. The lake showed a steep and stable thermal stratification with a shallow oxygenated epilimnion. Horizontal variation of phytoplankton distribution within the lake was tested on two scales and found to be statistically significant only in the case of Mallomonas reginae. The vertical distribution of flagellated phytoplankton was assessed by reference to the distribution of a non-motile, neutrally buoyant species Ankyra judayi. Statistically significant, active vertical positioning was demonstrated for all the flagellates examined with the exception of Spiniferomonas bourrellyi. Diel vertical migrations were apparent for all species showing active positioning and the pattern of an evening descent and a morning ascent was ubiquitous. The extent and timing of diel migrations varied between species. The most extensive migrations were by Cryptomonas marssonii which crossed a temperature gradient of 14 °C and penetrated far into the anoxic hypolimnion. Several categories of competitive advantage can be gained by species undertaking such diel vertical migrations.     

Diurnal vertical migration of Daphnia hyalina Leydig, 1860 (Crustacea: Cladocera) in Lake Bled (Slovenia) in relation to temperature and predation

Diurnal vertical migration (DVM) of Daphnia hyalina in Lake Bled was most intense during summer stratification. The extent of DVM varied with the size of the animal and its reproductive state. Migration distances were shortest in immature specimens and longest in ovigerous females. During daytime, ovigerous females stayed deeper in the water column than females without ova or immatures. The daytime temperature of water at the median depth of the ovigerous females did not exceed 10 °C, even in the warmest season. At night they migrated upward to an environment which was warmer by as much as 9 °C.Laboratory observations indicate that specimen's size and water temperature determine the velocity of passive sinking, such that morning descent of the different groups of Daphnia can be explained by passive sinking alone.Our hypothesis is that the distribution of different groups of D. hyalina in Lake Bled is influenced by two types of predators: fish (Perca fluviatilis L. and Rutilus rutilus (L.)) and larvae of Chaoborus flavicans (Meig.), the latter appearing in the epilimnion during the night. Fish predation has a key-role at the beginning of thermal stratification. Supposing that in spring the gene pool of Daphnia consists of a mix of different genotypes, distributed at different depths during the day, fish predation combined with a presence of fish chemicals favored genotypes with a lower day-depth during the spring/summer period.     

Thermal structure,heat content and stability of two lakes in The National Park of Rio Doce Valley (Minas Gerais,Brazil)

The thermal structure, heat content and stability were studied in Lakes Dom Helvécio and Carioca during an annual cycle. It was found that the maximum heat content, stability and work of the wind in Lake Dom Helvécio correspond to two, four and four times, respectively, the values for the Lake Carioca. These difference can be attributed to morphometric differences in the lakes. A long-term record of heat content and stability for lake Carioca is also presented. Diel variations were studied in summer and winter. The tropicality of the lakes is discussed and compared with other lacustrine systems.     

Diel and seasonal patterns of food intake and prey selection by Coregonus sp. in re-oligotrophicated Lake Lucerne, Switzerland

Feeding intensity by whitefish Coregonus sp., in oligotrophic Lake Lucerne in Switzerland was high during dusk when the bulk of potential prey items were in the depth zone occupied by the fish. Diet composition was fairly uniform throughout the day but changed substantially over the seasons. The fish fed opportunistically; differences between seasons reflected changes in prey availability. During the intensive feeding and growing period (May-September), fish were found in the upper 20 m of the lake feeding primarily on cladocerans. Large and non-evasive species, Daphnia spp. and Bythotrephes longimanus , were the most numerous and frequent organisms in the diet during the major part of the growing season. Smaller ( Bosmina spp.) as well as evasive species (cyclopoid copepods) were consumed in large numbers when larger, non-evasive species were rare in the lake. The fish showed strong preference for the least abundant crustacean, B. longimanus , while the most abundant crustaceans, calanoid copepods, were rare in the diet. The fish not only selected particular species but, within each species, selected the larger individuals. Diel vertical migration of the prey items in this lake could be, at least in part, attributed to fish predation pressure. The observed selectivity patterns shown by the fish are explained in terms of prey visibility, escape ability, the overlap in distribution of predators and prey in time and space, the profitability of the prey and the present trophic state of the lake.     

Two hundred years of zooplankton vertical migration research

Vertical migration is a geographically and taxonomically widespread behaviour among zooplankton that spans across diel and seasonal timescales. The shorter-term diel vertical migration (DVM) has a periodicity of up to 1 day and was first described by the French naturalist Georges Cuvier in 1817. In 1888, the German marine biologist Carl Chun described the longer-term seasonal vertical migration (SVM), which has a periodicity of ca. 1 year. The proximate control and adaptive significance of DVM have been extensively studied and are well understood. DVM is generally a behaviour controlled by ambient irradiance, which allows herbivorous zooplankton to feed in food-rich shallower waters during the night when light-dependent (visual) predation risk is minimal and take refuge in deeper, darker waters during daytime. However, DVMs of herbivorous zooplankton are followed by their predators, producing complex predator–prey patterns that may be traced across multiple trophic levels. In contrast to DVM, SVM research is relatively young and its causes and consequences are less well understood. During periods of seasonal environmental deterioration, SVM allows zooplankton to evacuate shallower waters seasonally and take refuge in deeper waters often in a state of dormancy. Both DVM and SVM play a significant role in the vertical transport of organic carbon to deeper waters (biological carbon sequestration), and hence in the buffering of global climate change. Although many animal migrations are expected to change under future climate scenarios, little is known about the potential implications of global climate change on zooplankton vertical migrations and its impact on the biological carbon sequestration process. Further, the combined influence of DVM and SVM in determining zooplankton fitness and maintenance of their horizontal (geographic) distributions is not well understood. The contrasting spatial (deep versus shallow) and temporal (diel versus seasonal) scales over which these two migrations occur lead to challenges in studying them at higher spatial, temporal and biological resolution and coverage. Extending the largely population-based vertical migration knowledge base to individual-based studies will be an important way forward. While tracking individual zooplankton in their natural habitats remains a major challenge, conducting trophic-scale, high-resolution, year-round studies that utilise emerging field sampling and observation techniques, molecular genetic tools and computational hardware and software will be the best solution to improve our understanding of zooplankton vertical migrations.     

Where to stay by night and day: Size-specific and seasonal differences in horizontal and vertical distribution of Chaoborus flavicans larvae

1. Data on the distributions of pelagic and benthic Chaoborus flavicans larvae were gathered in 1994 and tested for their agreement with the predator avoidance hypotheses. The development of all Chaoborus life stages, as well as the horizontal and vertical distribution in the four larval instars, was followed from May until October. We expected the largest larvae to dwell deeper by day, thus avoiding predation by visually foraging fish.
2. In agreement with this prediction body size increased with daytime depth, and this was true both between and within instars. The migration amplitude consequently increased with larval instar.
3. There was also evidence for horizontal migration, mainly in the third but also in the fourth instar.
4. Along a horizontal transect with increasing depth, locations with many benthic larvae had fewer pelagic larvae. Oxygen concentration was a good predictor of maximum benthic larval depth for most of the season but failed to predict their distribution in autumn.