Zooplankton dynamics in the upstream part of Stratos reservoir (Greece)

The investigation of the zooplankton community in the upstream part of Stratos reservoir during a 24 months survey (September 2004–August 2006) revealed 26 invertebrate species (14 rotifers, 6 cladocerans, 5 copepods and one mollusk larva). The mean abundance of the total zooplankton was higher in the first sampling period (2004–2005) and ranged between 8.81 and 47.74 ind. L⁻¹, than the second period (2005–2006) when fluctuated between 1.91 and 43.09 ind. L⁻¹. The seasonal variation was strongly influenced by the presence of rotifers, which accounting on average for 68.4% in total. Among them Keratella cochlearis and the order Bdelloidea were numerically the most important, while Macrocyclops albidus prevailed among the copepods and Bosmina longirostris among the cladocerans. Dreissena polymorpha was the only mollusk found in the zooplankton community. Rotifers, copepods and cladocerans showed a seasonal succession with the former preceding in the abundance having their first maximum in spring, while copepods and cladocerans followed, having peaks of abundance in early summer and in autumn, respectively. No seasonal succession among the cladoceran species was observed. The intense water flow in the upstream part of the reservoir, as well as temperature, conductivity, DO, pH, phosphates and silicates, were significant parameters controlling abiotic and biotic elements of the ecosystem and consequently influencing the seasonal variation and the dynamics of the zooplankton community.     

A comparison between predation effects on zooplankton communities by Neomysis and Chaoborus

Community level effects of predation by two invertebrate predators, the opossum shrimp (Neomysis intermedia), and the larva of the phantom midge (Chaoborus flavicans) were studied and compared. N. intermedia appeared abundantly in the shallow eutrophic Lake Kasumigaura and had a significant impact on the zooplankton community. The predation pressure by Neomysis was highest on cladocerans, followed by rotifers, and finally copepods. At high densities (maximum nearly 20 000 individuals m^–2), Neomysis excluded almost all cladocerans, rotifers and copepods from the lake.Zooplankton communities were established in experimental ponds, into which C. flavicans was introduced. The predator's density was around 1 individual l^–1, and was probably controled by cannibalism. Although Chaoborus larvae feed on various zooplankton species, their predation impact on zooplankton populations was markedly selective. They eliminated medium- and small-sized cladocerans and calanoid copepods from the ponds, but rotifers increased.Although the feeding selectivities of Neomysis and Chaoborus individuals were similar, the predation effects on zooplankton communities by the two predators were different.     

Creating conditions for changes in prey community structure by Chaoborus spp. in a lake in Sweden

In Lake G»rdsjön (Southwest Sweden), liming as an experimental improvement of living conditions for pelagic algae, resulted in a significant increase of algal biomass and a reduction of mean cell size. The algal development was beneficial for small sized filter feeding zooplankton, particularly rotifers, which showed a significant increase. The increase in abundance of small sized zooplankton created better food conditions for the smaller instars, and thus a much better overall survival of Chaoborus larvae. The resulting, 6–7 times larger population of Chaoborus larvae significantly changed the structure of the crustacean zooplankton community. Bosmina coregoni, the fastest swimmer of the crustacean species suffered most and was strongly reduced by the increased predation from Chaoborus. The share of cladocerans decreased, while copepods increased in importance.     

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.     

Feeding habits of sand smelt (Atherina boyeri, Risso 1810) in Trichonis Lake (Western Greece)

The feeding habits of sand smelt (Atherina boyeri, Risso, 1810) from Trichonis Lake (Western Greece) were investigated. Stomach contents were analyzed from 240 specimens with total lengths ranging from 35 to 112 mm. Samples were taken at monthly intervals (January–December 1997). Of the total number of stomachs examined, 53 were empty (22.1%). However, values varied greatly with season (maximum in January: 50%; minimum in August: 7.6%). Prey analyses of stomach contents identified 15 important items (%Rn > 0.05) belonging to six major groups: crustacean (copepods, cladocera), mollusca (bivalve: larvae), insects (larvae), cestode worms and finfish (fry and eggs). Dominant prey were larvae of the bivalve Dreissena polymorpha (%Rn = 33.8), the copepods Eudiadomus drieschi (%Rn = 26.4) and the cladocera Diaphanosoma brachyurum (%Rn = 24.2). The importance of cladocera and copepods decreased with increasing size of the sand smelt, while the importance of bivalve larvae, fish eggs and finfish fry increased with increasing sand smelt size. Seasonal changes in diet composition and prey abundance in sand smelt stomachs were recorded as coinciding with the seasonal composition and abundance of the zooplankton community in the surface layers of Trichonis Lake. Bivalve larvae were the dominant prey of A. boyeri during January to May, while copepods and cladocera dominated from June to December.     

Seasonal variability of secondary production of cladocerans and rotifers,and their trophic role in Lake Tana,Ethiopia, a large,turbid, tropical highland lake

Daily and annual production rates of eight cladoceran and two rotifer species, and their seasonal variation and trophic role in the large, turbid, tropical Lake Tana, Ethiopia, were assessed in 2003–2005. Laboratory cultures were used to infer cladoceran development times, and secondary production was estimated using the growth increment summation and recruitment methods. Production for both taxa was highest in October–November, after the rainy season, and lowest in January–April during the dry season. Cladocerans and rotifers comprised 24% of the metazoan zooplankton biomass of 45.1 mg DW m^?3, but comprised 53% of its production. Daily production for cladocerans and rotifers, respectively, was 1.23 and 0.94 mg DW m^?3 d^?1, and annual production was 447.9 and 353.5 mg DW m^?3 y^?1. Energy transfer efficiency from producers to zooplankton was 1.3% and 4.4% from zooplankton to planktivores. Herbivores consumed 3.4% of primary production and planktivores 36% of zooplankton production. High biomass turnover rates of cladocerans and rotifers sustain planktivores and, after a month's delay, decomposed Microcystis provides their main food source during the pre- and post-rainy months in Lake Tana.     

鄱阳湖丰水期水位波动对浮游动物群落演替的影响

为了解鄱阳湖夏季丰水期水位剧烈波动过程中浮游动物的群落演替特征,2012年夏季鄱阳湖水位剧烈波动期间,于6月24日、7月7日和8月27日当水位下降且接近17.6 m时,在江西鄱阳湖国家级自然保护区内的1个浅水碟形湖泊设置4个采样点进行采样调查。共发现浮游动物65种,其中轮虫52种,枝角类7种,桡足类6种,多为营浮游生活的广温性和嗜温性种类。单因子方差分析(one-way ANOVA)显示3个月之间浮游动物的密度和生物量均具有显著差异(P0.05),7月份浮游动物密度(1030.17±68.18个/L)显著高于6月份(325.16±41.60个/L)和8月份(203.79±24.91个/L);6月份浮游动物的生物量(0.56±0.04 mg/L)显著低于7月份(1.22±0.11 mg/L)和8月份(0.99±0.11 mg/L)。基于浮游动物多度的聚类分析和自组织映射神经网络图均揭示夏季3个月份的浮游动物可区分为明显的3个群落:6月群落、7月群落和8月群落。蒙特卡罗检验发现水温、电导率、浊度和溶氧与浮游动物群落结构变化显著相关(P0.05)。典型相关分析显示,6月份浮游动物群落与叶绿素a含量呈显著正相关关系,7月份浮游动物群落与水体温度呈显著正相关关系,8月份浮游动物群落与水深和电导率、浊度和溶氧呈显著正相关关系(P0.05)。在3个月均为优势物种的盖氏精囊轮虫与叶绿素a含量呈正相关关系(P0.05),与水温、pH、溶氧呈负相关(P0.05)。夏季水位波动过程中浮游动物的群落结构在时间上(月份之间)发生明显演替,呈现轮虫密度逐渐降低,枝角类和桡足类密度逐渐增加的变化规律。水位波动引起环境因子的改变,从而对浮游动物的群落演替产生了重要影响。     

Zooplankton community structure driven by vertebrate and invertebrate predators

Summary A zooplankton community was established in outdoor experimental ponds, into which a vertebrate predator (topmouth gudgeon: Pseudorasbora parva) and/or an invertebrate predator (phantom midge larva: Chaoborus flavicans) were introduced and their predation effects on the zooplankton community structure were evaluated. In the ponds which had Chaoborus but not fish, small- and medium-sized cladocerans and calanoid copepods were eliminated while rotifers became abundant. A large-sized cladoceran Daphnia longispina, whose juveniles had high helmets and long tailspines as anti-predator devices, escaped from Chaoborus predation and increased. In the ponds which had fish but not Chaoborus, the large-sized Daphnia was selectively predated by the fish while small-and medium-sized cladocerans and calanoid copepods predominated. In the ponds containing both Chaoborus and fish, the fish reduced the late instar larvae (III and IV) of Chaoborus but increased the early instar larvae (I and II). Small- and large-sized cladocerans were scarcely found. The former might have been eliminated by predation of the early instar larvae of Chaoborus, while the latter was probably predated by fish. Consequently, the medium-sized cladocerans, which may have succeeded in escaping from both types of predator, appeared abundantly. The results suggest that various combinations of vertebrate and invertebrate predators are able to drive various kinds of zooplankton community structure.     

Only the small survive: monitoring long-term changes in the zooplankton community of an Alpine lake after fish introduction

The zooplankton community of Alpine lake Seehornsee (1,779 m a.s.l.) was studied over a period of 13 years. In 1994, a typical high-altitude zooplankton community, consisting of two calanoid copepods (Mixodiaptomus laciniatus, Arctodiaptomus alpinus), one cladoceran (Daphnia rosea), and two rotifers (Keratella quadrata, Synchaeta pectinata) coexisted with infertile charr hybrids, which had been introduced in 1969 and again in 1974. When the aged fish were removed by intensive gill netting, they had fed predominantly on aquatic insects. After a fish-free period of 4 years, 2000 fertile juvenile Alpine charr (Salvelinus umbla) were stocked in 1998 and again in 1999. They preyed on benthic (chydorids, ostracods, cyclopoid copepods, chironomid larvae and pupae) and planktonic prey (diaptomid copepods, Daphnia). Between 2004 and 2006 charr successfully reproduced. Nine years after stocking of fertile charr, the two calanoids had virtually disappeared, and Daphnia rosea had notably declined in abundance. In concordance with the size efficiency hypothesis (Brooks and Dodson 1965), the newly appearing and smaller cladoceran Ceriodaphnia pulchella, together with the two resident, and two emerging species of rotifers (Polyarthra luminosa, Gastropus stylifer) dominated the zooplankton community.     

Zooplankton in Rainbow Bay, a Carolina bay pond: population dynamics in a temporary habitat

SUMMARY.

• 1 Rainbow Bay is a temporary freshwater pond in South Carolina, U.S.A., that typically fills in winter and dries in spring or summer. We studied population dynamics of zooplankton in 1984 and 1985 when it held water for 282 and 57 days, respectively. The zooplankton were diverse, including one species of calanoid copepod, nine or more cyclopoid copepods, nineteen or more cladocerans, and twelve or more rotifers. The community was initially dominated by the copepods Diaptomus stagnalis and Acanthocyclops vernalis or Diacyclops haueri, later by cyclopoids and cladocerans including Daphnia laevis and Simocephalus spp.
• 2 Laboratory experiments with sediments from the dry pond support the inference from field data that time of emergence from resting stages was a proximate cause of the initial succession of species. The experiments also showed that eggs of the calanoid copepod, Diaptomus stagnalis, were inhibited from hatching in early November, but became ready to hatch by late November. A similar inhibition was not observed for cladocerans or cyclopoid copepods.
• 3 Food limitation appeared to influence population dynamics following emergence. For the cladocerans Daphnia laevis and Simocephalus spp., great reductions in size-specific fecundity occurred 1 month (1985) or 3 months (1984) after the pond filled and were associated with disappearance of the rotifer Conochilus hippocrepis. The cladocerans produced ephippia when their fecundities declined. Reproduction of Diaptomus occurred before cladoceran fecundities decreased in 1984, but during their decline in 1985. Broods of Diaptomus were smaller in 1985.
• 4 The impact of invertebrate predators was probably greater than that of vertebrate predators, but neither was sufficient to prevent over-exploitation of food resources. Prey consumption rates by salamander larvae were estimated from diets and population densities of the larvae in 1984 (Taylor et al., 1988). Their impact on the zooplankton was low in February, increased in March and April as the larvae grew, and then

     

Effects of the blue-green alga Microcystis aeruginosa on zooplankton competitive relations

Summary Field distribution patterns and laboratory feeding experiments have suggested that blooms of colonial blue-green algae strongly inhibit relatively large-bodied daphnid cladocerans. We conducted laboratory experiments to test the hypothesis that blooms of the colonial blue-green alga Microcystis aeruginosa would shift competitive dominance away from large-bodied daphnid cladocerans toward smaller-bodied cladocerans, copepods, and rotifers. In laboratory competition experiments, increasing the proportion of M. aeruginosa in the algal food supply resulted in a shift from dominance by the relatively largebodied cladoceran Daphnia ambigua to dominace by the copepod Diaptomus reighardi. The small-bodied cladoceran Bosmina longirostris was always numerically heavily dominant over D. ambigua, but its estimated population biomasses were only slightly higher than those of D. ambigua. Daphnia ambigua consistently outcompeted the rotifer Brachionus calyciflorus. Our results demonstrate that blooms of M. aeruginosa can alter zooplankton competitive relations in laboratory experiments, favoring small-bodied cladocerans and copepods at the expense of large-bodied cladocerans. However, contrary to predictions, blooms of M. aeruginosa did not improve the competitive ability of rotifers.     

Recovery of zooplankton diversity in a restored Mediterranean temporary marsh in Doñana National Park (SW Spain)

Over 30 years after drainage for agriculture, a 2700 ha temporary marshland was recently restored in Doñana National Park. We describe the recovery of zooplankton communities (copepods, cladocerans and rotifers) in 47 new temporary ponds excavated as part of the restoration project during the first two hydroperiods (April 2006 and 2007), and compare them to those of eight reference sites in the surrounding marshland. Major changes in the species composition and abundance occurred in new ponds between years. While rotifers and cyclopoid copepods dominated in terms of number of individuals in 2006, calanoid copepods and cladocerans were the most abundant groups in 2007. Rotifer species richness was significantly lower in 2007, but there was an increase in Simpson and β-diversity in 2007 owing largely to a dramatic decline in the abundance of Hexarthra cf. fennica (rare in reference sites) from 93% of all rotifer individuals in new ponds in 2006 to only 32% in 2007. In contrast, species richness of copepods and cladocerans was significantly higher in new ponds in 2007, but there were no changes in Simpson diversity. β-Diversity of cladocerans was also significantly higher in 2007. In 2006, the species richness of cladocera and copepods was significantly lower in new ponds than in reference sites, but by 2007 there were no differences in richness or Simpson diversity. Overall, 7 copepod, 13 cladoceran and 26 rotifer taxa were recorded in new ponds, including 80% of taxa recorded in reference sites. These results indicate that zooplankton communities can be rapidly restored in Mediterranean temporary wetlands, at least when large source populations in the surrounding area reduce dispersal limitation. They also illustrate the importance of comparing different metrics of richness and diversity in studies of zooplankton restoration.     

Increasing dominance of small zooplankton with toxic cyanobacteria

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The predator-prey relationship of perch,Perca fluviatilis,larvae and zooplankton in two Scottish lochs

Synopsis Food consumption of perch larvae and the impact of this on zooplankton were examined in two adjacent shallow Scottish lochs. Maximum annual abundance of zooplankton occurred in mid-May at L. Kinord with minimum values in mid-June. Copepods were prominent in spring but were followed by a multi-species community of cladocerans and rotifers in summer. At L. Davan zooplankton biomass remained high through summer with cladocerans dominating andDaphnia longispina the most frequent species. Availability of food items was a principal factor governing feeding behaviour of larvae. Copepodite stages were initially the most common item in the diet in L. Kinord in 1976 and 1977 and rotifers the principal food in June 1977, reflecting the dominance of these items in the zooplankton. Cladocerans were dominant in the plankton community in L. Davan and constituted the greater part of food intake. Overlying this general pattern there was an increase in the size of food items taken by larvae with time and also a definite pattern of food selection for copepods, with initially selection for smaller copepodite stages and later for larger stages and adults. On most occasions larvae selected forCyclops strenuus abyssorum andPolphemus pediculus and selected againstDaphnia longispina. The reduction in the total zooplankton biomass attributed to perch larvae was minimal, with the exception of mid-June at L. Kinord in 1976. However, predation on particular species and copepodite stages was occasionally intense and may have impacted the zooplankton populations.     

Experimental analysis of the predation impact of the larvae of pond smelt (<Emphasis Type="Italic">Hypomesus transpacificus nipponensis</Emphasis>) on zooplankton populations established in mesocosms

The predation impact of the larvae of pond smelt Hypomesus transpacificus nipponensis on a zooplankton community was studied using mesocosms. The fish significantly depressed the abundances of copepod nauplii and rotifers, especially Hexarthra mira. The vulnerabilities of these prey might be determined by their swimming behavior and population density, suggesting that larval fish selectively prey on zooplankton that have a high encounter rate with the predator. The larvae did not have a negative effect on the densities of cladocerans, but fish predation altered the cladoceran community structure from the dominance of B. longirostris to that of B. fatalis. This result suggests that larval fish predation is an important factor that shifts the species composition of Bosmina in some lakes, the shift occurring in the season when fish larvae are abundant. Our results have shown that predation by the larval fish would control not only the abundance, but also the community structure of the small-sized zooplankton prey.     

The influence of bird colonies on the zooplankton in the Rybinsk Reservoir overgrown shallows

This article describes the peculiarities of the structural organization of zooplankton influenced by the waste products of the black-headed gull (Larus ridibundus Linnaeus) nesting colony in the protected overgrown shallow in Rybinsk Reservoir. The bird colony facilitates a modification of the zooplankton structure that is similar to the modifications of communities at early stages of eutrophication: the number of invertebrate species increases thanks to rotifers and cladocerans and the number and biomass of community increases due to cladocerans and copepods.     

Zooplankton Variability in 49 Shallow Tropical Reservoirs of Ivory Coast (West Africa)

Zooplankton samples were collected from 49 small reservoirs of northern Ivory Coast in April 1997. Thirty taxa were identified, including 20 rotifers, 3 copepods and 6 cladocerans. The number of taxa per lake ranged between 12 to 22 and decreased with the total abundance of zooplankton. Copepods dominated standing biomass. Coinertia analysis suggested the role of seston food abundance, oxygen depletion and turbidity for zooplankton abundance and community structure. Rotifers, and particularly Brachionus angularis, Polyarthra and Filinia, were more abundant than copepods in the most eutrophic, turbid and deoxygenated reservoirs. The role of oxygen as a determinant of community structure is probably linked to the specific tolerance of taxa, but turbidity role could not be evaluated with certainty in the absence of information on visual predators.     

Qualitative and quantitative structure,diversity and fluctuations in abundance of zooplankton in Lake Xolotlán (Managua)

The qualitative and quantitative structure of the zooplankton community was studied in 11 localities of Lake Xolotlan (Managua). Twelve rotifers, 4 cladoceran and 5 copepods species were identified. Community diversity (Shannon-Wienerindex) is low,viz. 0,83–2.20. At all times, copepods were the most abundant group. Rotifer densities were higher in zones influenced by rivers and organic pollution. Cladocerans were permanently present in low densities. Climatic events (rainfalls and dry periods) determined population fluctuations of the main zooplankton groups.     

Long-term Annual and Seasonal Changes of Meta- and Protozooplankton in Lake Müggelsee (Berlin): Effects of Eutrophication,Grazing Activities,and the Impact of Predation

Annual changes of rotifers, copepods, cladocerans, the ciliate Epistylis rotans, and larvae of Dreissena polymorpha were analysed for the period 1908–1990. Though food resources increased 6–10 fold in the course of eutrophication, only rotifers and Epistylis increased accordingly. Probably as a result of increased predation pressure crustaceans increased only twice. The seasonal pattern of metazoans and protozoans (flagellates, sarcodines, ciliates) were analysed for 12 and 3 years, resp. During winter and spring, large heterotrophic flagellates and ciliates dominated the zooplankton and were responsible for a pronounced - formerly underestimated - grazing pressure on phytoplankton. In early summer, metazoan filter-feeders were often able to cause a significant reduction of phyto- and protozooplankton. However, during some years, phytoplankton declined in the absence of a pronounced grazing pressure. Field data and experiments revealed that predators were able to regulate the density of cladocerans in early summer (mainly cyclopoids) and summer (mainly Leptodora, smelt and fish juveniles).     

Food and food selection of cisco (Coregonus albula L.) in a dysoligotrophic lake

With minor exceptions, cisco (C. albula) in Lake Suomunjärvi fed on cladocerans and copepods. The food habits were different among two size classes of fish. The composition of cisco diet changed at different depths and times of the day, but the distribution of zooplankton was usually very similar in each period irrespective of the depth or diel period. Daphnia, Bosmina, Cyclops scutifer and Heterocope appendiculata were the main diet of cisco. Calculations of fish electivity indices showed that cisco selected usually large species of cladocerans and copepods and a small cladoceran, Bosmina coregoni. Body-size selection was clear for Daphnia and Bosmina.