Spatial and Temporal Variability of Zooplankton in a Great Plains Reservoir (original) (raw)
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Daphnia lumholtzi, an Exotic Zooplankton, Invading a Nebraska Reservoir
2002
, D. lumholtzi was found in all fifteen stations at an average density of 2.17 ± 3.10 1. 1 with a site maximum density of 11.43 1. 1 • Length measurements of D. lumholtzi ranged from 0.80 mm to 5.66 mm with a mean length of2.38 ± 1.107 mm. During sampling, the abundance of D. lumholtzi increased relative to the native Daphnia retrocurva from less than 1 % to greater than 45% of all zooplankton collected. Our finding represents the first account in a Nebraska water system of D. lumholtzi, a native of Africa, Asia, and Australia, and shows a northern expansion in the Great Plains of this exotic species.
Ecological consequences of intraspecific variation in lake Daphnia
Freshwater Biology, 2010
1. Although populations harbour considerable diversity, most ecological studies still assume they are homogeneous. However, mounting evidence suggests that intraspecific diversity is not only common, but also important for interactions with community members. Here, intraspecific variation in Daphnia dentifera in haemoglobin content is shown to be a marker of hypolimnion use.2. Hypolimnion use differed substantially within and among D. dentifera populations. Daphnia dentifera with haemoglobin resided primarily in the hypolimnion, while D. dentifera lacking haemoglobin migrated vertically. These ‘deep’ and ‘migratory’D. dentifera had different seasonal phenologies and dynamics.3. Deep and migratory D. dentifera had qualitatively different relationships with an important competitor, Daphnia pulicaria. Deep D. dentifera density was negatively correlated with D. pulicaria density, whereas migratory density was not correlated with D. pulicaria density.4. Given that D. pulicaria tends to reside in the hypolimnion, this negative correlation probably reflects competition between D. pulicaria and the deep D. dentifera. This pattern would have been missed if only the relationship between the overall lake populations of D. dentifera and D. pulicaria had been studied.5. Abundances of deep D. dentifera and D. pulicaria were both correlated with the size of the hypolimnetic refuge from fish predation, but in opposite directions. Lakes with large refuges generally had high D. pulicaria and low deep D. dentifera densities.
Freshwater Biology, 2008
1. Strong vertical gradients in light, water temperature, oxygen, algal concentration and predator encounters during summer in stratified lakes may influence patterns of depth selection in crustacean zooplankton, especially Daphnia species. 2. To test how crustacean depth selection varies among lakes along a gradient of catchment disturbance by recent residential development and land use change, we calculated the weighted mean depth distribution of the biomass of crustaceans by day and night in eight nutrient-poor boreal lakes. 3. Generally, the greatest biomass of crustaceans was located at the metalimnion or at the lower boundary of the euphotic zone during thermal stratification in July. The crustacean zooplankton avoided warm surface layers and tended to stay in colder deep waters by both day and night. They also remained at greater depths in lakes with a more extensive euphotic zone. 4. There was some evidence of upward nocturnal migrations of large Daphnia and copepods in some lakes, and one case of downward migration in a lake inhabited by chaoborid larvae. 5. Multivariate regression trees (MRT) were used to cluster crustaceans and Daphnia species in homogeneous groups based on lake natural and disturbance factors. For crustaceans, the depth of the euphotic zone, the sampling depth (epilimnion, metalimnion and hypolimnion), time (day or night) of sampling and the biomass of chlorophyll a were the main driving factors. For Daphnia species, the drainage area, the sampling depth, the cleared land surface area within the catchment and the concentration of total dissolved phosphorus were the main factors.
Aquatic Ecology, 2007
The abundance, composition and dynamics of zooplankton were followed in two reservoirs of the River Douro catchment. The Serra Serrada Reservoir is subject to marked fluctuations in water levels. The highest values of total phosphorus, soluble reactive phosphorus, nitrate, water colour and chlorophyll a were found during the minimum level phase. Rotifera was dominant except in late summer and autumn when the cladoceran Ceriodaphnia quadrangula or the copepod Tropocyclops prasinus replaced them as the dominant zooplankton. Among the rotifers the most common taxa were Keratella cochlearis, Conochilus sp. and Asplanchna priodonta. Maximum rotifer density was about 80,000 ind m−3 in 2000, 200,000 ind m−3 in 2001 and 100,000 ind m−3 in 2002. Among the crustacean zooplankton C. quadrangula achieved densities of up to 45,000 ind m−3 and T. prasinus, up to 80,000 ind m−3. Canonical correspondence analysis revealed a strong contribution of the variation in the stored water volume, temperature, total phosphorus, chlorophyll, nitrates, and water transparency to the observed, significant association between zooplankton assemblage and environmental variables. In the Azibo Reservoir, fluctuations in water level are smaller. Only total phosphorus, cholorophyll and conductivity varied seasonally. Cladocera and Copepoda were dominant during the whole study period. The most abundant taxa were Ceriodaphnia pulchella, Daphnia longispina, Diaphanosoma brachyurum, Bosmina longirostris and Copidodiaptomus numidicus. Cladocera achieved densities of up to 25,000 ind m−3 and Copepoda up to 15,000 ind m−3. Rotifera in general reached densities of up to 6,000 ind m−3. On the basis of canonical correspondence analysis only temperature and conductivity were significantly associated with zooplankton assemblage.
2012
We assessed if the qualitative and quantitative aspects of plankton composition in reservoirs of the middle Missouri River were influenced by hydrologic variability. Phytoplankton and zooplankton communities in six reservoirs of this highly regulated system were sampled between 2004 and 2011 during historic drought, subsequent recovery, and a 100-year flood event. The reservoir system encompasses a broad latitudinal gradient of decreasing depth, decreasing water residence time and increasing trophic state. Phytoplankton communities of the upper three reservoirs were co-dominated by planktonic and meroplanktonic diatoms during the drought, recovery, and flood periods, but the proportion of more silicified meroplanktonic diatoms increased in the lower three reservoirs as water residence time decreased. Peak phytoplankton biovolume usually occurred during spring/early summer and was associated with increased hydrologic inflows and outflows. Zooplankton biomass of the reservoir system was dominated by Daphnia spp., but all zooplankton groups decreased as inflows and outflows accelerated during the recovery and flood periods. Rotifer abundances were higher under turbulent conditions associated with dam operations. Canonical correlation analyses suggested that temperature, water residence time, station depth, and water clarity explained more variance in the structures of phytoplankton and zooplankton communities than bioavailable nutrient parameters.
Hydrobiologia, 2007
Spatial and temporal variation in phytoplankton community structure within a large floodcontrol reservoir (Sardis Reservoir, MS, USA) was investigated in relation to variation in physicochemical properties, location within the reservoir, hydraulic residence time (HRT), nutrient concentrations, temperature, and light conditions over a 14-month period. During periods of short HRT, phytoplankton communities throughout the reservoir were homogeneous in biomass, composition, and production. With a gradual increase in HRT from spring to summer, spatially heterogeneous phytoplankton communities developed along the longitudinal axis of the reservoir. During this period of longer HRT, diatoms and chlorophytes were a larger proportion of total phytoplankton biomass at shallow and more turbid locations near the head of the reservoir, whereas cyanobacteria were a larger proportion of the community at deeper and less turbid locations closer to the outflow. Seasonal succession of the phytoplankton community was represented by high abundance of diatoms in spring, increasing biomass of cyanobacteria through summer, and a secondary bloom of diatoms in fall. Species of Cyclotella, Asterionella, Nitzschia, and Ankistrodesmus were among the first colonizers in the early growing season, closely followed by Aulacoseira, whereas species of Staurastrum and Tetraedron appeared later in the spring. Species of Synedra, Crucigenia, Selenastrum, Scenedesmus, and Merismopedia occurred throughout the sampling period. As the diatoms started to decrease during mid-spring, cryptophytes increased, prior to dominance of species of Pseudanabaena in summer. Reservoir management of HRT, in combination with spatial variation in reservoir morphology and seasonal variation in temperature and riverine nutrient inputs, creates seasonally variable yet distinct spatial patterns in phytoplankton community biomass, composition, and production.
Limnology and Oceanography, 1990
The ability of planktivorous fish to regulate the population dynamics of Daphnia gale&a in Lake Mendota, Wisconsin, was examined during spring and summer 1987. Low rates of consumption by yellow perch (Percaflavescens) and cisco (Coregonus artedii) allowed populations of D. galeata to expand rapidly during spring, resulting in a distinct clear-water period that lasted from mid-May until early June. A subsequent decline in D. guleatu abundance resulted from low food availability brought about by its exploitation of algal resources. Once populations of D. guleuta were reduced, predation by perch and cisco was sufficient to keep populations of D. g,lleata at low densities during July and August in spite of more abundant algal food resources, Extreme seasonal variation in the degree to which planktivorous fish can regulate daphnid population dynamics may have allowed daphnids to persist in Lake Mendota during the past century in the presence of abundant zooplanktivores.
2007
1. Structural complexity may stabilise predator-prey interactions and affect the outcome of trophic cascades by providing prey refuges. In deep lakes, vulnerable zooplankton move vertically to avoid fish predation. In contrast, submerged plants often provide a diel refuge against fish predation for large-bodied zooplankton in shallow temperate lakes, with consequences for the whole ecosystem. 2. To test the extent to which macrophytes serve as refuges for zooplankton in temperate and subtropical lakes, we introduced artificial plant beds into the littoral area of five pairs of shallow lakes in Uruguay (30°-35°S) and Denmark (55°-57°N). We used plants of different architecture (submerged and free-floating) along a gradient of turbidity over which the lakes were paired. 3. We found remarkable differences in the structure (taxon-richness at the genus level, composition and density) of the zooplankton communities in the littoral area between climate zones. Richer communities of larger-bodied taxa (frequently including Daphnia spp.) occurred in the temperate lakes, whereas small-bodied taxa characterised the subtropical lakes. More genera and a higher density of benthic/plant-associated cladocerans also occurred in the temperate lakes. The density of all crustaceans, except calanoid copepods, was significantly higher in the temperate lakes (c. 5.5-fold higher). 4. Fish and shrimps (genus Palaemonetes) seemed to exert a stronger predation pressure on zooplankton in the plant beds in the subtropical lakes, while the pelagic invertebrate Chaoborus sp. was slightly more abundant than in the temperate lakes. In contrast, plantassociated predatory macroinvertebrates were eight times more abundant in the temperate than in the subtropical lakes. 5. The artificial submerged plants hosted significantly more cladocerans than the freefloating plants, which were particularly avoided in the subtropical lakes. Patterns indicating diel horizontal migration were frequently observed for both overall zooplankton density and individual taxa in the temperate, but not the subtropical, lakes. In contrast, patterns of diel vertical migration prevailed for both the overall zooplankton and for most individual taxa in the subtropics, irrespective of water turbidity. 1009 6. Higher fish predation probably shapes the general structure and dynamics of cladoceran communities in the subtropical lakes. Our results support the hypothesis that horizontal migration is less prevalent in the subtropics than in temperate lakes, and that no predatoravoidance behaviour effectively counteracts predation pressure in the subtropics. Positive effects of aquatic plants on water transparency, via their acting as a refuge for zooplankton, may be generally weak or rare in warm lakes.