Contrasting Zooplankton Assemblages in Two Oxbow Lakes with Low Transparencies and Narrow Emergent Macrophyte Belts (Krapina River,Croatia)

The aim of this study was to examine the combined effect of water transparency and narrow macrophyte belts on zooplankton assemblages in two oxbow lakes (Krapina River, Croatia). Samples were collected in open water and among helophytes in the littoral zone from April until September 2008. Rotifers were the most abundant group of zooplankton in both lakes, and dominated in the Krapina oxbow lake 1 (KO1). Lake KO1 had significantly lower transparency, lower percentage macrophyte cover and higher chlorophyll a concentration than Krapina oxbow lake 2 (KO2). In lake KO1, variation in the horizontal distribution of cladocerans and rotifers in terms of their abundance seemed to be determined by competition between Bosmina longirostris and Keratella cochlearis, initiated by oscillation in transparency and detritus availability. In lake KO2, with higher transparency and higher percentage macrophyte cover, the abundance of small‐ and large‐bodied cladocerans increased in the littoral zone simultaneously with higher transparency, suggesting fish predation. Results of this study indicated that small differences in transparencies between the two lakes caused significant differences in horizontal distribution of the zooplankton assemblage. Even narrow helophyte belts offered a refuge to zooplankton, although lower transparencies reduced the effectiveness of macrophytes as a refuge from predators. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zooplankton,and related phytoplankton cycles,in a eutrophic lake

The seasonal cycles of zooplankton were determined for 18 consecutive months in a sewage-enriched lake in northern Canada and were related to algal availability and utilization, food consumption, temperature and the density of predators. Most of the common species (Daphnia pulex, Daphnia middenorffiana, Keratella cochlearis, Keratella quadrata, Polyarthra vulgaris) increased in abundance in May and June, reached a mid-summer maximum, and declined sharply in the fall. Phytoplankton densities increased sharply in May, peaked early in June and gradually decreased through the summer and fall. Since the quantity of algae in the guts remained constant during this period, algal availability and utilization had no direct impact on the seasonal cycles of any species. Furthermore, the amount of ingested material in D. pulex and D. middendorffiana was similar regardless of time of year, implying that the total quantity of food in the environment did not restrict development. Although temperature was the most important factor influencing variations in the densities of all species, predation by Cyclops spp. probably had little effect on the population dynamics of the fauna.     

Zooplankton swarms: characteristics,proximal cues and proposed advantages

This review focuses on monospecific swarms of four taxonomic groups of small crustaceans: three groups are marine copepods: oithonids (Oithona and Dioithona), Acartia species and Calanus species; and the fourth group includes freshwater cladoceran species in the Order Anomopoda. For each of these groups there is a substantial literature on swarming behavior from field studies and laboratory experiments. Swarming characteristics of each taxonomic group are reviewed, proximal cues for swarming are described, comparisons are made for proposed advantages of swarming, and future research directions are suggested. Swarming characteristics of Calanus spp. are distinctly different from those of the smaller crustaceans: the oithonids, acartiids and cladocerans. In a conceptual model proposed for the smaller crustaceans, swarming behavior is affected by their interactions with light cues, water currents and turbulence, behavior of their predators and prey, and abundance of other trophic levels.     

The effect of diapause emergence on the seasonal dynamics of a zooplankton assemblage

1. The role of seasonal phenology in the emergence of zooplankton from diapause in patterns of seasonal abundance in the water column was investigated in Oneida Lake, New York. Replicate emergence traps, placed in contact with the lake sediments at two locations (one at a shallow site and one at a deep site), were monitored between May and August.
2. Although six rotifer taxa showed a clear seasonal succession in the water column throughout the study period, all but one taxon emerged exclusively in spring. Three cladoceran and three calanoid copepod species, also present in the water column throughout the study period, again showed predominantly spring emergence. In contrast, three cyclopoid copepod species had distinct seasonal periods of emergence that corresponded, at least in part, to the timing of abundance peaks in the plankton.
3. These results for a single lake are largely consistent with patterns observed or inferred by other investigators for other lakes: variable dependence of abundance in the plankton on diapause emergence for species with long-lived diapausing eggs (i.e. rotifers, cladocerans and calanoid copepods), and much closer dependence for species with short-lived diapausing immature stages (i.e. cyclopoid copepods).     

Assessing the health of a zooplankton community in a small Precambrian Shield lake during recovery from experimental acidification

Acidified lakes recover chemically relatively quickly following the reduction or cessation of acidic inputs. Although fish, invertebrate, and phytoplankton communities are reported to begin to return to preacidification states in chemically-improving lakes, the process and extent of biological recovery are not well-documented. The experimental acidification of Precambrian Shield Lake 223 (27.4 ha surface area; 14.4 m maximum depth) in the Experimental Lakes Area in northwestern Ontario, provides an opportunity to compare the zooplankton community prior to acidification with that during progressive acidification and during chemical recovery. Acidified with sulfuric acid from pH 6.47 (ice-free season mean) in 1976 to pH 5.0 (1981 to 1983), Lake 223 has been allowed to recover in steps of pH 5.5 (1984 to 1987), pH 5.8 (1988 to 1990), and pH 6.11 (1991). Total zooplankton biomass showed no trend to increase or decrease during the acidification and recovery, but species composition changed. Compared with species composition at pH 6.13 early in acidification in 1977, the recovering community at pH 6.11 in 1991 had the previously-dominant cladoceran species present in very low numbers and had two newly-appearing cladoceran species. The community had lost one species of calanoid and gained none and lost two species of cyclopoids and gained two. It appeared to lose four species of rotifiers and gain seven. In nearby unmanipulated reference Lake 239 (56.1 ha; 30.4 m), species shifts were recorded but they involved rarer species, not dominants as in Lake 223. Although the zooplankton community in 1991 is in a new state with respect to species composition, static measures of total community biomass, contribution to biomass by the four main taxonomic groups, per cent smilarity to the preacidification community (for crustaceans), and biomass of herbivores do not indicate impairment of community health. Lowered species diversity for both crustaceans and rotifers partially returned to preacidification levels. Nevertheless, the rotifer community in 1991 was more dissimilar to the preacidification community than was the crustacean community, and carnivore biomass appeared to be depressed in Lake 223. The Lake 223 zooplankton community at pH 6.11 in 1991 appears to be in a state of flux.     

Zooplankton abundance and transport in a tropical white-water river

Zooplankton abundance and transport were studied in the Apure River of western Venuzuela over a 15-month period. Much of the lower portion of the drainage basin, which is an extensive savanna of low relief, is subject to seasonal flooding. Although more than 50 zooplankton species were recorded during the study, nine rotifer species accounted for more than 90% of total density (mean, 138 individuals · L^-1). Copepods were represented primarily by Mesocyclops decipiens. Most cladocerans were planktonic, but cladocerans were not abundant. Crustaceans comprised 46% of annual mean zooplankton biomass (1.9 gC·L^-1) but only 2% of zooplankton numbers. The annual transport of zooplankton biomass from the watershed was 29 300 kgC. Zooplankton abundance showed a strong, inverse relationship to discharge. Secondary branches (caños) of the braided channel appeared to be the primary source areas, but populations of some species also reproduced in the main channel at low water. As the river began to rise, caños were flushed and thus abruptly ceased to serve as source areas. Zooplankton transport fell sharply and remained low until the river inundated the floodplain. Secondary production in the floodplain was exported to the river as long as a connection existed. After drainage ceased from the floodplain, transport fell to very low levels until caños again became suitable habitat. Seasonal fluctuations in river level regulate the development of source areas suitable for zooplankton growth and control the export of plankton from the source areas. Plankton in the running waters reproduce only at low water.     

Impact of turbulence on riverine zooplankton: a mesocosm experiment

1. With increases in river discharge over time and space, zooplankton generally encounter increased turbulence, turbidity, hydraulic forces, downstream advection and food limitations, all of which should affect species diversity and densities. Of these factors, the role of turbulence on the distribution of zooplankton is least known along longitudinal and lateral dimensions in river networks. 2. We tested the factorial effects of turbulence and grazing level on Ohio River potamoplankton in spring and summer using twelve 1600‐L, outdoor mesocosms. Turbulence was calculated using the Froude number for equal depths but with current velocities of 0.064 and 0.32 m s^?1. Grazing levels corresponded to a high density treatment (=ambient river densities of rotifers, copepods and cladocerans) and a low density treatment (initially no zooplankton >64 μm). All tanks had the same water residence time, and hydraulic stress was minimized by circular flow patterns. 3. Zooplankton densities and population growth rates were significantly affected by turbulence level and season. In general, rotifer populations grew faster in high turbulence tanks (though Keratella and Brachionus populations flourished in both treatments in summer) and microcrustaceans thrived better in low turbulence environments. The larger, calanoid copepods handled more turbulent conditions much better than cyclopoids or nauplii. Zooplankton had no detectable effects on particulate organic carbon concentrations in either month (values were higher in spring), but rotifers reduced chlorophyll concentrations in both months. 4. The relative importance of turbulence in controlling potamoplankton is probably to vary not only on a longitudinal basis in river networks but also with both the hydrogeomorphic complexity of river reaches and the type and amount of river regulation. Plans for river rehabilitation and management should incorporate non‐turbulent habitats in large rivers as a means of enhancing zooplankton populations and providing an important food web component for planktivores.     

Daytime grazing and assimilation rates of planktonic copepods Acanthodiaptomus denticornis and Cyclops vicinus vicinus. Comparison of spatial and resource utilisation by rotifers and cladoceran communities in a eutrophic lake

The clearance rates of ¹⁴ carbon-labelled Chlamydomonas sp. by the copepodite and adult stages of the 2 dominant species of Copepoda were studied in eutrophic Lake Aydat. They varied from 30 to 3,007 µl ind^–1 h^–1 for Acanthodiaptomus denticornis (mean = 600 µl ind^–1 h^–1) and from 20 to 1,133 µl ind^–1 h^–1 for Cyclops vicinus (mean = 340 µl ind^–1 h^–1). Their maximum assimilation efficiencies were 58% and 50%, respectively. These populations collectively could consume the available food in 4 days during September (maximum daily grazing rate = 24%). Mean individual clearance rates could be ranked Acanthodiaptomus denticornis > Ceriodaphnia quadrangula > Chydorus sphaericus > Daphnia longispina > Cyclops vicinus vicinus > Bosmina longirostris > K. cochlearis > K. quadrata and Kellicottia longispina. Like cladocerans and rotifers, the copepods living in this eutrophic lake can feed at low oxygen concentrations.     

Zooplankton distribution in the coastal upwelling system along the Banc d'Arguin,Mauritania

In the framework of the Dutch Mauritania Expedition 1988, zooplankton was sampled in the beginning of the spring upwelling season at 44 stations along the Banc d'Arguin, Mauritania. Distribution patterns of oceanic and neritic copepod species and especially of the upwelling indicator Calanoides carinatus (Kröyer) were analysed in search for direct proof of circulation of ocean upwelling water over the inshore banks. The vertical temperature distribution at the stations pointed to upwelling in two different parts of the shelf area. According to the copepod data the two upwellings were of a different nature. A restricted area at the shelf edge near Cap Timiris appeared to represent a relatively stable coastal upwelling situation. Upwelled water present near Cap Blanc was found to have traveled quite recently over a considerable part of the shelf. In the central area between the two upwellings, Banc-water extended from the shelf into the ocean. The possible impact of the observed circulation of ocean water on productivity of the shelf benthic system is discussed.     

Zooplankton invasions: a brief review,plus two case studies from the northeast Pacific Ocean

Invasions of aquatic habitats by non-indigenous species (NIS), including zooplankton, are occurring at an alarming rate and are causing global concern. Although hundreds of such invasions have now been documented, surprisingly little is known about the basic biology and ecology of these invaders in their new habitats. Here we provide an overview of the published literature on NIS zooplankton, separated by life history (holoplankton vs. meroplankton), habitat (marine, estuarine, freshwater), and biological level of organization or topic (e.g. distribution and range extension, physiology, behavior, feeding, community impacts, ecosystem dynamics, etc). Amongst the many findings generated by our literature search, perhaps the most striking is the paucity of studies on community and ecosystem level impacts of NIS zooplankton, especially in marine and estuarine systems. We also present some results from two ongoing studies of invasive zooplankton in the northeast Pacific Ocean – Pseudodiaptomus inopinus in Washington and Oregon coastal estuaries, and Tortanus dextrilobatus in San Francisco Bay. Both of these Asian copepods have recently expanded their range and can at times be extremely abundant (10³ m^–3). We also examine some aspects of the trophic (predator–prey) ecology of these two invasive copepods, and find that they are likely to be important in the flow of material and energy in the systems in which they now pervade, although their impacts at the ecosystem level remain to be quantified. Finally, the findings of both our literature search and our two case studies of invasive zooplankton lead us to make several recommendations for future research.     

Zooplankton biomass dynamics in oligotrophic versus eutrophic conditions: a test of the PEG model

相似文献   

Zooplankton abundance and diversity in Central Florida grass carp ponds

The effect of the Asian grass carp (Ctenopharyngodon idella Val.) upon the zooplankton in three adjacent experimental ponds (0.139 ha each) was studied for one year. The ponds contained nine species of aquatic macrophytes. Grass carp were stocked into Pond 1 (65 per ha) and Pond 2 (611 per ha) three months after the study was started. At the time of stocking, physichochemical and biological parameters were similar among the ponds.Grass carp did not affect water quality and had little direct or indirect effect upon the zooplankton in the ponds. The abundance and species diversity of zooplankton (number of species, Shannon Index, and Simpson Index) were not significantly different (P < 0.05) between ponds prior to grass carp stocking. After stocking with grass carp, the number of species and species diversity were found to be significantly different (P < 0.05) between Pond 1 (low grass carp stocking rate) and Pond 2 (high grass carp stocking rate). Additionally, significant differences (P < 0.05) in populations between ponds were found for Lecane luna, Monostyla bulla, Lepadella ehrenbergii, Polyarthra sp., and Synchaeta sp. Temporal variation rather than grass carp was probably responsible for those differences. The number of zooplankton per group (Rotifera, Cladocera, and Copepoda) and species diversity were not significantly different (P<0.05) between ponds containing different stocking rates of grass carp.During the study, zooplankton were collected with a shallow-water sampler. No significant differences (P < 0.05) between collections were found for the sampler and a No. 20 mesh nylon zooplankton net.     

Zooplankton and salinity in the Rufiji River delta,Tanzania

A comparative analysis of the zooplankton from different salinities was carried out in the Rufiji River delta system, located on the mid Tanzanian coastline opposite Mafia Island (7° 45 S, 39° 20 W).Zooplankton samples were collected by vertical, oblique and horizontal surface tows (250 µm mesh) at three sites, namely at the river mouth (salinity = 20–25), in the estuary (salinity = 12–14), and in the upper reaches of the river (salinity = 0). Samples taken in the river mouth and estuary were collected at two times of the day, which coincided approximately with midday and sunset.A comparison of zooplankton diversity and abundance at the three sites showed that a much richer, more diverse fauna existed at the river mouth and estuary compared to the upper reaches. The zooplankton collected both at the mouth and in the estuary were very abundant at certain times of the day, although differences in faunal composition were found between the two sites.     

Microcrustacean communities in streams from two physiographically contrasting regions of Britain

ABSTRACT. Benthic microcrustaceans were sampled from forty-three streams in two physiographically contrasting regions of Britain: lowland southern England and upland Wales. Lowland streams had a significantly higher species richness than upland streams and, of the forty-three copepod and cladoceran species identified, only fourteen (33%) were found in both the lowlands and uplands. Canonical correspondence analysis revealed large differences in community structure between regions and between streams within regions. Differences within regions were related to pH, the distance downstream of a site and the presence of upstream impoundments. Variables underlying the large biological differences between regions are also discussed, including differences in chemistry (ionic content), physical parameters (e.g. flow), habitat availability and the influence of species biogeography. The importance of understanding species ecology and biogeography when assessing pollution impacts on stream communities is emphasized and a model is proposed for predicting the composition of microcrustacean communities in temperate European streams.     

Zooplankton structure in the Loosdrecht lakes in relation to trophic status and recent restoration measures

A five-year zooplankton study (1982–86) on three shallow and highly eutrophic lakes in the Loosdrecht area (The Netherlands) did not reveal any significant changes following the considerable reduction in external P-loading (from about 1.0 g to 0.3 g P m^–2 year^–1) since mid-1984.The recent annual fluctuations in the rotifer and crustacean densities are within the range of those found before the restoration measure became operative. A decrease in the average size of the crustaceans and an absence of large-bodied forms reflects an increased fish predation rather than a change in the quality or quantity of their sestonic food ( < 150 µm) which continues to be dominated by filamentous cyanobacteria and Prochlorothrix hollandica, a prochlorophyte discovered in these lakes recently.     

Zooplankton distribution and diversity in a frontal area of the Aegean Sea

This study was carried out in the northern Aegean Sea during late summer and spring. The aim was to examine the spatial and temporal distribution of the zooplankton community across a dynamic frontal area and to investigate how the oceanographic heterogeneity structures the composition of the zooplankton assemblages. The low-salinity and cold Black Sea water coming from the Dardanelles Strait is modified by mixing with the underlying warm and saline Aegean water. These hydrological features result in a pronounced thermohaline front in the northern Aegean Sea throughout the year. In both seasons, zooplankton was collected using both 45 and 200 µm mesh plankton nets. A high abundance of zooplankton was observed in the surface layer at the stations closest to the Dardanelles Strait on the stratified side of the front. The zooplankton distribution and community structure in the northern Aegean Sea were strongly influenced by the hydrological features. The frontal structure acts as a boundary for the zooplankton community. The surface layer at the stratified stations had the lowest copepod diversity, from where it increased with depth and horizontally as the stratification weakened outside of the front. The total abundance of zooplankton collected with the 200 µm net was between two and 20 times lower than samples taken with the 45 µm net. The most pronounced differences were observed for the adults and copepodids of the small genera Oithona, Oncaea and Microsetella. Thus, to manage and understand the transfer of primary production up the food chain in the Aegean Sea, the smaller fraction of copepods should be taken into account in future investigations.     

Zooplankton composition of ten reservoirs in southern Brazil

The zooplankton of ten reservoirs of Sao Paulo State was analyzed as part of a larger project, Typology of Reservoirs of São Paulo State.Twenty-four genera of Rotifera, six species of Copepoda and at least nine species of Cladocera were found in samples collected on four occasions in 1979. In general, Rotifera dominated in most reservoirs, although fluctuations occurred during the year.The reservoirs were arranged in four groups, according to zooplankton density, whose range was 10 to 500 i 1^–1.The average composition of Crustacea, in number of species at any one time is comparable to those of other water bodies, being a little higher than that of Colorado lakes.The number of species of limnetic Cladocera in Brazil is between those of Holarctic Region and Tropical Asia. Ceriodaphnia cornuta and Bosminopsis deitersi, and a few species of Daphnia are typical of Brazilian zooplankton. Thermocyclops crassus is common in the southern reservoirs but T. minutus seems to be more widely distributed in Brazil. Calanoida occurred in relatively few reservoirs in São Paulo and usually one species at one time. Brachionus and Keratella were more abundant closer to the Equator then to the Tropics, where other genera seem to be more abundant.The range in size of the planktonic Crustacea is relatively small when compared to temperate lakes, being similar to that of other tropical lakes.     

Zooplankton variability related to environmental changes in a eutrophic coastal lagoon in the Po Delta

Zooplankton variability in a lagoon of the Po Delta, the Sacca di Goro, was studied in relation to changes in its hydrodynamic and hydrological features. From 1987 to 1992 the lagoon was affected each summer by severe anoxia due to the decomposition of dense and widespread beds of Ulva rigida. In August 1992 a canal was opened through the sand bank closing off the lagoon from the sea in order to improve the water circulation. This hydraulic intervention led to significant environmental changes in the lagoon: during the two subsequent years the summer dystrophic crises were brief and less severe, due to a sharp decrease in the Ulva cover. At the same time a clear increase in phytoplankton biomass values was observed. Following the opening of the channel, the most remarkable change in zooplankton was a significant density increase of calanoids, particularly of Acartia tonsa.     

Zooplankton abundance in the River Danube, Austria: the significance of inshore retention

1. Zooplankton density was examined in a free-flowing section of the River Danube, Austria. Spatial and temporal patterns were used to identify mechanisms regulating zooplankton dynamics. 2. Zooplankton abundance differed significantly between sampling sites. These differences were the result of variations in water residence time within the habitats. Inshore habitats with low flushing rates act as storage zones for zooplankton. 3. The hydrological conditions govern the number and size of storage zones. In the study area, the highest availability of storage zones was observed at medium water level. 4. Total zooplankton numbers, total rotifer numbers and the densities of the most abundant rotifer taxa were significantly positively related to the availability of adjacent storage zones. 5. The present authors propose that inshore retention capacity, and the hydrological processes and mechanisms controlling the extent of inshore retention may be of major significance in regulated rivers with high water velocities, preventing substantial zooplankton growth in the main channel.     

Dispersal-limited zooplankton distribution and community composition in new ponds

Twelve new experimental ponds were constructed identically, filled simultaneously, had similar physical and chemical properties, and were maintained with minimal manipulation. Colonizing zooplankton communities were sampled bi-weekly for one year. Rotifers dominated zooplankton communities in densities, biomass, and species number (47 of 61 observed species were rotifers). Only 14 species were observed in all 12 ponds; 9 were rotifers. Twenty-nine species (26 rotifers) were recorded in <-6 ponds. Species with high vagility exhibited greater viability. Ponds differed in zooplankton community composition throughout the year, due to differences in both vagility and viability among colonizing species.