Seasonal Dynamics Of Zooplankton Research Articles

COMPOSITION OF ZOOPLANKTON ASSEMBLAGES ALONG THE ZAGYVA RIVER

The species composition, longitudinal distribution and seasonal dynamics of zooplankton were studied in the Zagyva River, Hungary. A total of 108 taxa was recorded from which 61 were new for the river. Rotatoria was the most abundant group, microcrustaceans were less important, only nauplii and copepodites were represented in similar individual numbers. Frequent species included Anuraeopsis fissa, Pompholyx spp., Keratella cochlearis, Brachionus angularis, Bdelloida sp., Bosmina longirostris. Dominance of cosmopolitan species was observed both in the river and its reservoir, and species characteristic of eutrophic waters were of major importance in the latter. There was a downstream decrease in zooplankton densities, which was explained by modified conditions. The relatively large number of individuals in autumn months, and the characteristic large number of individuals in the upper section contrasted general findings of potamoplankton dynamics. On the basis of the species abundance matrix, three river sections can be distinguished (upper, middle, lower section). Due to waste water discharges - received from the Tarjan Stream - we found extremely high number of individuals and the lowest diversity at the sampling site Nagybatony (148 rkm).

Seasonal zooplankton dynamics in Lake Michigan: Disentangling impacts of resource limitation, ecosystem engineering, and predation during a critical ecosystem transition

We examined seasonal dynamics of zooplankton at an offshore station in Lake Michigan from 1994 to 2003 and 2007 to 2008. This period saw variable weather, declines in planktivorous fish abundance, the introduction and expansion of dreissenid mussels, and a slow decline in total phosphorus concentrations. After the major expansion of mussels into deep water (2007–2008), chlorophyll in spring declined sharply, Secchi depth increased markedly in all seasons, and planktivorous fish biomass declined to record-low levels. Overlaying these dramatic ecosystem-level changes, the zooplankton community exhibited complex seasonal dynamics between 1994–2003 and 2007–2008. Phenology of the zooplankton maximum was affected by onset of thermal stratification, but there was no other discernable effect due to temperature. Interannual variability in zooplankton biomass during 1994 and 2003 was strongly driven by planktivorous fish abundance, particularly age-0 and age-1 alewives. In 2007–2008, there were large decreases in Diacyclops thomasi and Daphnia mendotae possibly caused by food limitation as well as increased predation and indirect negative effects from increases in Bythotrephes longimanus abundance and in foraging efficiency associated with increased light penetration. The Bythotrephes increase was likely driven in part by decreased predation from yearling and older alewife. While there was a major decrease in epilimnetic–metalimnetic herbivorous cladocerans in 2007–2008, there was an increase in large omnivorous and predacious calanoid copepods, especially those in the hypolimnion. Thus, changes to the zooplankton community are the result of cascading, synergistic interactions, including a shift from vertebrate to invertebrate planktivory and mussel ecosystem impacts on light climate and chlorophyll.

Seasonal zooplankton dynamics in main channel and backwater habitats of the Upper Mississippi River

This study used stratified random sampling to examine the spatial and temporal distribution of zooplankton communities in a large floodplain river (Mississippi River, USA). Potential mechanisms controlling zooplankton abundance and community structure were considered. Main channel and backwater habitats included in this study differed between a turbid upper pool reach where aquatic macrophytes were sparse and a lower pool reach which was considerably less turbid and had extensive aquatic macrophyte coverage. Samples were collected monthly during the summer over a 2-year period and multivariate analysis was used to examine the spatial and temporal distribution of zooplankton. Significant differences were found in zooplankton density and community composition among habitats and reaches within the pool. Rotifers were the dominant taxa and seasonality was pronounced, with peak densities often occurring in late-spring. Community structure varied by habitat and reach, which suggests that water quality, physical habitat characteristics, presence of aquatic macrophytes, and zooplankton sources can all influence the zooplankton communities of the Upper Mississippi River. Characterization of the zooplankton communities provides a basis for understanding changes in the river ecosystem and examination of zooplankton communities among habitats provides insight into the mechanisms affecting zooplankton dynamics.

Coupling of seasonal variations in the zooplankton community within the limnetic and littoral zones of a shallow pond

Seasonal dynamics of zooplankton were investigated in three different habitats of the shallow and temperate Kacležský pond (Czech Republic) during 2003–2004. The studied habitats included the limnetic zone and two littoral zones, each dominated by a different type of emergent macrophyte, reed grass (Glyceria maxima ) and common reed (Phragmites australis ). Species richness (calculated as number of taxa) was higher in both littoral zones than in the limnetic zone. The seasonal development of limnetic and littoral zooplankton communities differed. In contrast to the two littoral zones, close correlation with chlorophyll-a concentration was found for rotifers and cladocerans in the limnetic zone. Moreover, cladocerans inhabiting littoral areas (mainly Bosmina longirostris ) reached annual maxima during spring when chlorophyll-a concentrations were low.

Zooplankton seasonal dynamics in 2005–2007 at the eastern coast of southern Baikal, near the Pulp-and-Paper plant

The study investigated zooplankton seasonal dynamics in the pelagic and shelf zones at the eastern coast of Lake Baikal, near the Baikal Pulp-and-Paper Plant, in August and September of 2005, 2006, and 2007. It was shown that zooplankton development in the 0–50 mdepth over the study period followed a characteristic Baikal pattern despite increased industrial pressure on the study site.

Seasonal dynamics of zooplankton community in four Mediterranean reservoirs in humid area (Beni Mtir: north of Tunisia) and semi arid area (Lakhmes, Nabhana and Sidi Saâd: center of Tunisia)

The zooplankton community was studied in four Mediterranean reservoirs to assess the relative importance of environmental factors as determinants of zooplankton dynamic in the four seasons. The water temperature and hydrology variations affect the distribution of zooplankton. A positive correlation was established between the total zooplankton and the water temperature ( r=0.9, n=9, p<0.05). Fourteen zooplankton species were identified. Seasonal changes in the density (ANOVA, F=3.7, d.f=36, p<0.01) and the biomass of total zooplankton (ANOVA, F=4.4, d.f=36, p<0.001) were observed. Our results suggest that planktivorous fish may not modify the zooplankton dynamics in Beni Mtir reservoir (oligotrophic). On the contrary, in Sidi Saâd reservoir (mesotrophic), fish predation has major effects on seasonal zooplankton dynamics.

Two-way coupling versus one-way forcing of plankton and fish models to predict ecosystem changes in the Benguela

‘End-to-end’ models have been adopted in an attempt to capture more of the processes that influence the ecology of marine ecosystems and to make system wide predictions of the effects of fishing and climate change. Here, we develop an end-to-end model by coupling existing models that describe the dynamics of low (ROMS–N 2P 2Z 2D 2) and high trophic levels (OSMOSE). ROMS–N 2P 2Z 2D 2 is a biogeochemical model representing phytoplankton and zooplankton seasonal dynamics forced by hydrodynamics in the Benguela upwelling ecosystem. OSMOSE is an individual-based model representing the dynamics of several species of fish, linked through opportunistic and size-based trophic interactions. The models are coupled through a two-way size-based predation process. Plankton provides prey for fish, and the effects of predation by fish on the plankton are described by a plankton mortality term that is variable in space and time. Using the end-to-end model, we compare the effects of two-way coupling versus one-way forcing of the fish model with the plankton biomass field. The fish-induced mortality on plankton is temporally variable, in part explained by seasonal changes in fish biomass. Inclusion of two-way feedback affects the seasonal dynamics of plankton groups and usually reduces the amplitude of variation in abundance (top-down effect). Forcing and coupling lead to different predicted food web structures owing to changes in the dominant food chain which is supported by plankton (bottom-up effect). Our comparisons of one-way forcing and two-way coupling show how feedbacks may affect abundance, food web structure and food web function and emphasise the need to critically examine the consequences of different model architectures when seeking to predict the effects of fishing and climate change.

Seasonal dynamics of zooplankton in Lake Huetzalin, Xochimilco (Mexico City, Mexico)

We quantified the seasonal changes in the zooplankton abundances collected from the Huetzalin Lake (Mexico City, Mexico) for two years (February 2003–January 2004 and then March 2005–February 2006). Selected physicochemical variables (Secchi depth, temperature, pH, conductivity, dissolved oxygen, phosphorus, nitrogen, carbon and chlorophyll a concentration) were also measured at the time of zooplankton collection. The data on zooplankton abundances and the physicochemical variables were subjected to multiple correlation analysis and we also derived Shannon–Wiener species diversity index. Secchi depth ranged from 9 to 65 cm. Generally the lake was alkaline (pH 7–12). The conductivity ranged from 500–1000 mS cm −1, while the mean water temperature was 20.5 °C. Dissolved oxygen levels were generally >3 mg L −1 and were higher in the winter than warmer months. Nitrates (90–95 μg L −1) and phosphates (.2–.5 mg L −1) indicated that the water was eutrophic. Chlorophyll a levels ranged from 143 to 696 μg L −1 during the study period. The zooplankton community was dominated by rotifers (46 species), followed by cladocerans (9 species) and there were only two copepod species. The dominant rotifer species were Brachionus angularis, Brachionus calyciflorus, Brachionus havanaensis, Brachionus quadridentatus, Lecane bulla and Polyarthra vulgaris. Rare rotifer species in Lake Huetzalin were Lecane ohioensis, Dicranophorus forcipatus, Lecane pyriformis, Lindia torulosa, Pleurotrocha petromyzon and Brachionus durgae. Highest densities (occasional peaks of 400 ind L −1) of B. quadridentatus occurred between April and December, while B. havanaensis reached peak densities, during June to October. B. calyciflorus reached densities higher than 1240 ind L −1 during May–September. Cladoceran and copepod densities in Lake Huetzalin were much lower than that of the rotifers. This study confirmed the earlier findings that Xochimilco system of canals is dominated by rotifers and the crustacean zooplankton have much lower abundances possibly due to predation from fish.

The seasonal and interannual dynamics of zooplankton in Lake Teletskoye

Long-term data on the specific composition, seasonal abundance, and biomass dynamics of Lake Teletskoye zooplankton are given. The list of rotiferans and lower crustaceans includes 117 taxa of specific and subspecific rank. The dominating complex includes 10 species and remains unchanged during the whole period of investigations. The seasonal dynamics of zooplankton abundance and biomass in this deep and highly lotic oligotrophic waterbody is characterized by one peak of development noted in the second half of the summer. The rapid increase of Conochilus unicornis (Rousselet) rotifer abundance in conditions of high water level and low temperature is noted in the interannual aspect.

Seasonal dynamics of zooplankton in a shallow eutrophic, man-made hyposaline lake in Delhi (India): role of environmental factors

Old Fort Lake, a small (1.6 ha), shallow, and recreational water body in Delhi (India) was studied through monthly surveys in two consecutive years (January, 2000–December, 2001). Precipitation is the major source of water for this closed basin lake. In addition, ground water is used for replenishing the lake regularly. This alkaline, hyposaline hard water lake contains very high ionic concentration, especially of nitrates. Based on overall ionic composition, this lake can be categorized as chloride–sulfate alkaline waters with the anion sequence dominated by SO42− > Cl− > HCO3−, and the cations by Mg++ > Ca++. The overall seasonal variability in physicochemical profile was largely regulated by the annual cycle of evaporation and precipitation, whereas the ground water largely influences its water quality. The lake exhibited phytoplankton-dominated turbid state due to dominance of the blue green alga, Microcystis aeruginosa. The persistent cyanobacterial blooms and the elevated nutrient levels are indicative of the cultural eutrophication of the lake. This study focuses on the relative importance of eutrophic vis-a-vis hyposaline conditions in determining the structure and seasonal dynamics of zooplankton species assemblages. A total of 52 zooplankton species were recorded and rotifers dominated the community structure qualitatively as well as quantitatively. The genus Brachionus comprised a significant component of zooplankton community with B. plicatilis as the most dominant species. The other common taxa were B. quadridentatus, B. angularis, Lecane grandis, L. thalera, L. punctata, Mesocyclops sp., and Alona rectangula. Multivariate data analysis techniques, Canonical Correspondence Analysis (CCA) along with Monte Carlo Permutation Tests were used to determine the minimum number of environmental factors that could explain statistically significant (P < 0.05) proportions of variation in the species data. The significant variables selected by CCA were NH3–N followed by percent saturation of DO, COD, SS, BOD, NO2–N, rainfall, silicates, and PO4–P. The results indicate that the seasonal succession patterns of the zooplankton species were largely controlled by physicochemical factors related directly or indirectly to the process of eutrophication, whereas hyposaline conditions in the lake determined the characteristic species composition.

Zooplankton seasonal dynamics in a recently filled mine pit lake: the effect of non-indigenous Daphnia establishment

We examined the temporal and vertical dynamics of zooplankton in Weavers Lake, New Zealand, between October 2004 and October 2005, at a time when it was colonised by a non-indigenous Daphnia species. Zooplankton community composition changed during the study from one of rotifer dominance (e.g. Asplanchna, Polyarthra, Brachionus and Keratella species) to cladoceran (Daphniadentifera) dominance. Temporal changes in zooplankton community composition were strongly associated with a gradual increase in lake water clarity, and were attributable to the highly efficient filter feeding of D. dentifera. The corresponding reduction in rotifer densities may have resulted from the superior competitive abilities of the newly established Daphnia. As Daphnia were rare inhabitants of New Zealand lakes before 1990, the arrival and rapid spread of the non-indigenous D. dentifera has lead to widespread changes in both water clarity and zooplankton community composition. An apparent lack of mixing in the lake was facilitated by the lake’s extremely small surface area:depth ratio. However, we conclude that physical features of the lake had minimal influence on water clarity relative to the invasion of D. dentifera.

Seasonal dynamics of the crustacean zooplankton of a shallow eutrophic lake from the Mediterranean region

Little is known about the trophic interactions within shallow lakes from the Mediterranean region, although there is evidence of their distinctive features compared to northern temperate shallow lakes (particularly when considering their ichthyocenosis). To address this gap, we conducted a study on the seasonal dynamics of the zooplankton community in Lake Vela (Portugal), a turbid and eutrophic shallow lake, which exhibits marked dominance of alien fish species. Lake Vela was shown to be highly productive and turbid, except during a period of higher transparency, from January to April. The increase in transparency was attributable to a rise in water level, which reduced the amount of re-suspended particles. Transparency was additionally improved by a peak in Daphnia longispina densities (February and March), which transiently reduced chlorophyll concentrations to low levels (clear water phase). In the remainder of the year, the zooplanktonic assemblage was dominated by small-sized zooplankters (mainly Bosmina and cyclopoid copepods). Daphnia were virtually absent from August to December. Regression and multivariate analyses identified seston and fish predation as the main environmental gradients shaping the zooplanktonic assemblage. During the clear water phase, competition for resources also seemed to contribute to Daphnia dynamics. The observed pattern of seasonal dynamics of the zooplankton of Lake Vela was overall concordant with the PEG model, although the timing of certain events was different, most notably the peak of Daphnia dominance and the more prolonged influence of fish, relatively to northern temperate lakes. Our results suggest that both planktivory (by alien fish) and turbidity (seston) are issues that need to be addressed if adequate restoration programs are to be implemented.

Seasonal dynamics of zooplankton and grazing impact of microzooplankton on phytoplankton in Sanmen Bay, China

The species composition, biomass, abundance and species diversity of zooplankton were determined for samples collected from 12 stations in Sanmen Bay, China, in four cruises from August 2002 to May 2003. Growth of phytoplankton and grazing rates of microzooplankton were measured using the dilution technique. The spatial and temporal variation of zooplankton and its relationship with environmental factors were also analyzed. The results showed that a total of 89 species of zooplankton belonging to 67 genera and 16 groups of pelagic larvae were found in Sanmen Bay. The coastal low-saline species was the dominant ecotype in the study area, and the dominant species were Calanus sinicus, Labidocera euchaeta, Tortanus derjugini, Acartia pacifica, Pseudeuphausia sinica and Sagitta bedoti. Maximum biomass was recorded in August, followed by November and May, and the lowest biomass was recorded in February. Similarly, the highest abundance of zooplankton was observed in August, followed by May, November, and February. Grazing pressure of microzooplankton on phytoplankton in Sanmen Bay existed throughout the year, although the grazing rate of microzooplankton on phytoplankton varied with the season. Estimates for growth rate of phytoplankton ranged from 0.25 d −1 to 0.89 d −1, whereas grazing rate of microzooplankton ranged between 0.18 d −1 and 0.68 d −1 in different seasons. The growth rate of phytoplankton exceeded the grazing rate of microzooplankton in all the seasons. Grazing pressure of microzooplankton on phytoplankton ranged from 16.1% d −1 to 49.1% d −1, and the grazing pressure of microzooplankton on primary production of phytoplankton ranged from 58.3% d −1 to 83.6% d −1 in different seasons.

Linking oceanic food webs to coastal production and growth rates of Pacific salmon (Oncorhynchus spp.), using models on three scales

Abstract Three independent modeling methods—a nutrient-phytoplankton–zooplankton (NPZ) model (NEMURO), a food web model (Ecopath/Ecosim), and a bioenergetics model for pink salmon (Oncorhynchus gorbuscha)—were linked to examine the relationship between seasonal zooplankton dynamics and annual food web productive potential for Pacific salmon feeding and growing in the Alaskan subarctic gyre ecosystem. The linked approach shows the importance of seasonal and ontogenetic prey switching for zooplanktivorous pink salmon, and illustrates the critical role played by lipid-rich forage species, especially the gonatid squid Berryteuthis anonychus, in connecting zooplankton to upper trophic level production in the subarctic North Pacific. The results highlight the need to uncover natural mechanisms responsible for accelerated late winter and early spring growth of salmon, especially with respect to climate change and zooplankton bloom timing. Our results indicate that the best match between modeled and observed high-seas pink salmon growth requires the inclusion of two factors into bioenergetics models: (1) decreasing energetic foraging costs for salmon as zooplankton are concentrated by the spring shallowing of pelagic mixed-layer depth and (2) the ontogenetic switch of salmon diets from zooplankton to squid. Finally, we varied the timing and input levels of coastal salmon production to examine effects of density-dependent coastal processes on ocean feeding; coastal processes that place relatively minor limitations on salmon growth may delay the seasonal timing of ontogenetic diet shifts and thus have a magnified effect on overall salmon growth rates.

Trophic dynamics in a whole lake experiment: size‐structured interactions and recruitment variation

Horizontal and vertical heterogeneity as a result of size‐structured processes are important factors influencing indirect effects in food webs. In a whole‐lake experiment covering 5 years, we added the intermediate consumer roach (Rutilus rutilus) to two out of four lakes previously inhabited by the omnivorous top predator perch (Perca fluviatilis). We focused our study on the direct consumption effect of roach presence on zooplankton (and indirectly phytoplankton) versus the indirect effect of roach on zooplankton (and phytoplankton) mediated via effects on perch reproductive performance. The patterns in zooplankton and phytoplankton abundances were examined in relation to population density of roach and perch including young‐of‐the‐year (YOY) perch in the light of non‐equilibrium dynamics. The presence of roach resulted in changed seasonal dynamics of zooplankton with generally lower biomasses in May–June and higher biomasses in July–August in roach lakes compared to control lakes. Roach presence affected perch recruitment negatively and densities of YOY perch were on average higher in control lakes than in treatment lakes. In years when perch recruitment did not differ between lakes as a result of experimental addition of perch eggs, total zooplankton biomass was lower in treatment lakes than in control lakes. Phytoplankton biomass showed a tendency to increase in roach lakes compared to control lakes. Within treatment variation in response variables was related to differences in lake morphometry in treatment lakes. Analyses of the trophic dynamics of each lake separately showed strong cascading effects of both roach and YOY perch abundance on zooplankton and phytoplankton dynamics. Consideration of the long transients in the dynamics of top predators (fish) in aquatic systems that are related to their long life span involving ontogenetic niche shifts is essential for making relevant interpretations of experimental perturbations. This conclusion is further reinforced by the circumstance that the intrinsic dynamics of fish populations may in many cases involve high amplitude dynamics with long time lags.

Phytoplankton and zooplankton seasonal dynamics in a subtropical estuary: importance of cyanobacteria

A seasonal study of phytoplankton and zooplankton was conducted from 1999-2001 in Pensacola Bay, Florida, USA, to better understand pelagic food webs in sub-tropical estuaries. Monthly

The impact of regional‐scale changes in the weather on the long‐term dynamics of Eudiaptomus and Daphnia in Esthwaite Water, Cumbria

1. Year‐to‐year changes in the weather have a profound effect on the seasonal dynamics of zooplankton in lakes. Here, I analyse some zooplankton data from Esthwaite Water in Cumbria and demonstrate that much of the recorded inter‐annual variation can be related to regional‐scale changes in the weather. 2. The first data set analysed shows the effect of changes in the water temperature on the winter abundance of the calanoid copepod Eudiaptomus gracilis. The highest numbers of Eudiaptomus were recorded when the winters were mild and the lowest when the winters were cold. 3. Winter temperatures in northern and western Europe are now known to be influenced by the atmospheric feature known as the North Atlantic Oscillation (NAO). Positive values of the NAO are associated with mild winters and westerly winds and there was a significant positive correlation between the winter abundance of Eudiaptomus in Esthwaite Water and this empirical index of change. 4. The second data set analysed shows the effect of wind‐induced mixing on the summer abundance of Daphnia. The highest numbers of Daphnia were recorded in years when the early summer thermocline was deep and the lowest number in years when the thermocline was shallow. 5. One of the most important factors influencing the depth of the early summer thermocline in the English lakes is the position of the north‐wall of the Gulf Stream. Southerly movements of the Gulf Stream are typically associated with higher winds, whilst northerly movements are associated with stable conditions. In Esthwaite Water, a significant positive correlation was recorded between the abundance of Daphnia and the depth of the early summer thermocline and significant negative correlations between the same variables and the position of the Gulf Stream. 6. A detailed analysis of the seasonal variations recorded in one calm and one windy year suggest that the main factor responsible for these correlations was the entrainment of nutrients which then stimulated the growth of edible algae. Daphnia numbers were low in 1968 (a ‘north’ Gulf Stream year which was relatively calm) and high in 1972 (a ‘south’ Gulf Stream year with intense wind‐mixing).

Effect of body size and temperature on generation time in zooplankton

Effect of body size and temperature on generation time in zooplankton

The longitudinal distribution and community dynamics of zooplankton in a regulated large river: a case study of the Nakdong River (Korea)

The longitudinal distribution and seasonal dynamics of zooplankton were examined along a 200-km section of the middle to lower Nakdong River, Korea. Zooplankton was sampled twice a month from January 1995 to December 1997 at five sites in the main river channel. There was considerable longitudinal variation in total zooplankton abundance (ANOVA, p < 0.001). All major zooplankton groups (rotifers, cladocerans, copepodids and nauplii) increased significantly with distance downstream along the river. There also were statistically significant seasonal differences in zooplankton abundance at the sampling sites (ANOVA, p < 0.01). Zooplankton abundance was high in spring and fall and low in summer and winter. The seasonal pattern of rotifers was similar to that of total zooplankton. This reflected the fact that rotifers (Brachionus calyciflorus, B. rubens, Keratella cochlearis and Polyarthra spp.) strongly dominated the zooplankton community at all locations. Among the macrozooplankton, small-bodied cladocerans (e.g. Bosmina spp.) dominated; the abundance of large-bodied cladocerans (e.g. Daphnia) was negligible (0–5 ind. l−1). Among the environmental variables considered, partial residence time seemed to play the most important role in determining characteristics of the river zooplankton community.

Zooplankton seasonal dynamics in the neighbouring lakes Takvatn and Lombola (Northern Norway)

The zooplankton of two neighbouring lakes, situated in northern Norway (69° 07′ N), was studied during the ice-free season of 1994. Zooplankton structure and seasonal dynamics are compared, and the importance of biotic interactions and seasonality (temperature and photoperiod) as determinants of the observed patterns is evaluated in light of collected data and previous knowledge of the systems. The main events in zooplankton seasonal succession were restricted to the short period of stratification and were similar in the two lakes. Basin morphometry and biota are considered for explaining the marked between-lakes difference in community structure: Daphnia dominates in the shallow lake Lombola, where brown trout (Salmo trutta L.) is most represented; while rotifers and the copepods Eudiaptomus graciloides (Lilljeborg) and Cyclops scutifer Sars dominate in Takvatn, where Arctic charr (Salvelinus alpinus (L.)) has the hegemony of the pelagic.