Large-bodied Cladocerans Research Articles

Feeding Ecology of Lake Whitefish in Lake Huron

We determined diet composition, feeding strategy, prey size, and effects of prey type on food weight and energy in stomachs for lake whitefish Coregonus clupeaformis in Lake Huron during 2002–04. Age-0 lake whitefish (73–149 mm TL) ate mainly large-bodied cladoceran zooplankton in the summer (July–mid September). Medium lake whitefish (≤ 350 mm TL excluding age-0) generally ate softbodied macroinvertebrates, especially Chironomidae larvae and pupae, in the spring (mid May-June). Zooplankton, if eaten, were generally most important in the summer. Molluscs were generally a minor part of medium lake whitefish diets. Large lake whitefish (> 350 mm) mainly ate molluscs, particularly quagga mussels ( Dreissena bugensis), despite geographic differences in mussel abundance. Large-bodied crustaceans ( Diporeia spp., Mysis relicta, Isopoda) were a minor part of large lake whitefish diets. Lake whitefish demonstrated a flexible feeding strategy, with individual specialization on some prey and generalized feeding on others. The size of benthic prey ( Diporeia spp., Chironomidae, and Dreissena spp.) eaten increased with fish size and influenced the energetic value of prey for medium and large lake whitefish. The type of prey eaten affected the food and energy intake differently for each size class of lake whitefish. Age-0 lake whitefish that ate mainly zooplankton had more food and energy in stomachs than fish eating shelled prey or other macroinvertebrates. On the other hand, food weight in stomachs did not differ across prey groups for medium fish, but energy in stomachs was lowest for fish that ate shelled prey. For large lake whitefish, there was no difference in food weight or energy in stomachs for different prey groups.

Impact of three-spined stickleback Gasterosteus aculeatus on zooplankton and chl a in shallow, eutrophic, brackish lakes

The 3-spined stickleback Gasterosteus aculeatus often dominates fish communities in eu- trophic, brackish, north-temperate lakes where it is thought to contribute significantly to the low zoo- plankton biomass and low grazing pressure on phytoplankton. To elucidate its effect on zooplankton community structure and phytoplankton biomass (chl a), we conducted a 5.5 mo enclosure experiment with sticklebacks at different densities in high nutrient concentrations and a salinity of 2 psu. Increas- ing fish density (0 to 10.2 sticklebacks m -2 ) led to substantial changes in the zooplankton community structure, an increase in phytoplankton chl a, and a reduction in water clarity. At densities below 4 to 6 sticklebacks m -2 , large-bodied cladocerans dominated the zooplankton biomass, the zoo- plankton:phytoplankton biomass ratio was high (>1), and chl a was accordingly low (<20 µg l -1 ). At higher stickleback densities, large cladocerans disappeared and the abundance of small cladocerans was low. Instead, cyclopoid copepods and rotifers dominated, the zooplankton:phytoplankton biomass ratio was well below 0.5, and chl a exceeded 200 µg l -1 in late summer. The fish density level for a shift from a clear to a turbid state is low compared to the densities observed in several eutrophic, brackish lagoons. We conclude that fish have a strong impact on water clarity in shallow, eutrophic, brackish lakes with low salinity, which may explain the usually low zooplankton:phytoplankton biomass ratio and the turbid state of such aquatic environments. However, our results also indicate that once the density level declines to below 4 to 6 sticklebacks m -2 , a shift to a clear state is likely to occur.

Cascading trophic interactions in the littoral zone: an enclosure experiment in shallow Lake Stigsholm, Denmark

The importance of grazer versus resource control has been extensively studied in the pelagic zone of lakes. In contrast, comparatively little is known about trophic interactions within the littoral zone. We conducted an experiment in the littoral zone of a eutrophic shallow lake using six 20 m 2 polyethylene enclosures, which 2.5 month prior to the experiments were mounted above the water surface on a stainless steel ring to allow development of natural pelagic, benthic and epiphytic communities. Half of the enclosures were kept free of plants by harvesting. In late July, the sheets were released from a distance of 5 m and trapped the present biotic community. Fish were removed and the experiment ran for 6 days. Major differences in trophic structure and dynamics were found amongst the treatments, which we attribute to differences in fish density and predation risk prior to the experiment. In the plant-free controls (M-), the zooplankton were dominated by rotifers and cyclopoid copepods, while large-bodied cladocerans dominated in the enclosures with plants (M+). In both sets of enclosures, diel variations in abundance of large-bodied zooplankton were found, with higher densities at night, whereas no significant differences were found amongst small-bodied species (rotifers, nauplii), ciliates, heterotrophic nanoflagellates and bacterioplankton. Phytoplankton dominated the living suspended particulate carbon pool in the plant-free enclosures (69 %), while zooplankton dominated in the enclosures with plants (85 %). Zooplankton (>140 μm) community clearance rates of phytoplankton and bacterioplankton were low (<54 ml/l/d) in M- and high (2200-3000 ml/l/d) in M+. Grazing exceeded phytoplankton production (3.7-fold) in M+, but only amounted to 6 % of the phytoplankton production in M-. For bacterioplankton, zooplankton grazing was equivalent to production in M+, but amounted to < 3 % of production in M-. Our results combined with earlier studies indicate that the zooplankton in plant-rich littoral zones do not alone feed on particles produced in the water, but also exploit alternative sources such as periphyton or benthic food sources or particles entering from outside the plant beds. Thus, zooplankton in such environments may continuously maintain high densities even with low abundance of phytoplankton and bacterioplankton, and are thereby able to maintain high grazing pressure on these pelagic food sources. We hypothesize that the strong cascading effects of zooplankton on chlorophyll-a and microorganisms in the littoral zone at natural fish densities are restricted to eutrophic lakes with high plant densities.

Experimental study of trophic cascade effect of silver carp (Hypophthalmichthys molitrixon) in a subtropical lake, Lake Donghu: on plankton community and underlying mechanisms of changes of crustacean community

An enclosure experiment was carried out to test trophic cascade effect of filter-feeding fish on the ecosystem: growth of crustacean zooplankton, and possible mechanism of changes of crustacean community structure. Four fish biomass levels were set as follows: 0, 116, 176 and 316 g m-2, and lake water (containing ca. 190 g m-2 of filter-feeding fishes) was comparatively monitored. Nutrient levels were high in all treatments during the experiment. Lowest algal biomass were measured in fishless treatment. Algal biomass decreased during days 21–56 as a function of fish biomass in treatments of low (LF), medium (MF) and high (HF) fish biomass. Crustaceans biomass decreased with increasing fish biomass. Small-bodied cladocerans, Moina micrura, Diaphanosoma brachyurum and Scapholeberis kingii survived when fish biomass was high whilst, large-bodied cladocerans Daphnia spp. and the cyclopoids Theromcyclops taihokuensis, T. brevifuratus, Mescyclops notius and Cyclops vicinus were abundant only in NF enclosures. Evasive calanoid Sinodiaptomus sarsi was significantly enhanced in LF, but decreased significantly with further increase of fish biomass. Demographic data indicated that M. micrura was well developed in all treatments. Our study indicates that algal biomass might be controlled by silver carp biomass in eutrophic environment. Changes of crustacean community are probably affected by the age of the first generation of species. Species with short generation time were dominant and species with long generation time survived less with high fish biomass. Evasive calanoids hardly developed in treatments with high fish biomass because of the (bottle neck) effect of nauplii. Species abundance were positively related to fish predation avoidance. Other than direct predation, zooplankton might also be suppressed by filter-feeding fish via competition.

Fish predation pressure on and interactions between cladocerans: Observations using enclosures in three temperate lakes (Germany) and one tropical lake (Ethiopia)

Observations were made on the response of cladocerans to fish predation and the interactions among cladocerans using enclosure experiments in three temperate lakes (Germany) and one tropical lake (Ethiopia). In all lakes large-sized cladocerans were removed by fish until small-sized ones and rotifers remained. In apparently all cases the cladocerans of small-bodied species assumed their largest sizes in no-fish enclosures. In fish-enclosures, the small-bodied cladocerans assumed high biomasses due to elevated food resources in the absence of competition from large-bodied cladocerans. It was also observed that in the absence of fish predation, the dominating large-sized species had an excluding effect on other small-bodied cladocerans. In all cases variations between lakes were observed in the behavior of cladocerans even when fishes were absent.

Pelagic C:N:P Stoichiometry in a Eutrophied Lake: Responses to a Whole-Lake Food-Web Manipulation

Changes in the ecological stoichiometry of C, N, and P in the pelagic zone are reported from a whole-lake manipulation of the food web of Lake 227, an experimentally eutrophied lake at the Experimental Lakes Area, Canada. Addition of northern pike eliminated populations of planktivorous minnows by the third year (1995) after pike introduction, and in the fourth year after pike addition (1996), a massive increase in the abundance of the large-bodied cladoceran Daphnia pulicaria occurred. Accompanying this increase in Daphnia abundance, zooplankton community N:P declined, seston concentration and C:P ratio decreased, and dissolved N and P pools increased. During peak abundance, zooplankton biomass comprised a significant proportion of total epilimnetic phosphorus (greater than 30%). During the period of increased Daphnia abundance, concentrations of dissolved inorganic nitrogen (TIN) increased more strongly than dissolved phosphorus (TDP), and thus TIN:TDP ratios were elevated. Sedimentation data indicated that increased grazing led to greatly reduced residence times of C, N, and especially P in the water column during 1996. Finally, previously dominant N-fixing cyanobacteria were absent during 1996. Our results show that strong effects of food-web structure can occur in eutrophic lakes and that stoichiometric mechanisms play a potentially important role in generating these effects.

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.

Initial Findings Regarding Changes in Phyto- and Zooplankton Composition and Abundance Following the Temporary Drawdown and Refilling of a Shallow, Hypertrophic South African Coastal Lake

ABSTRACT Marked changes in phyto- and zooplankton assemblage and abundance were observed in a regulated, shallow, hypertrophic lake following temporary drawdown and refilling. Despite significant increases in the ambient concentrations of nitrogen and phosphorus, levels of chlorophyll-a fell from a mean of 260 νg·L−1 before drawdown and refilling to 70 μg·L−1 thereafter. The concentration of chlorophyll-a fell to 3 μg·L−1 during aspring clearwater phase previously unobserved in Zeekoevlei, but observed in other, adjacent shallow lakes. This clearwater phase was characterized by an increase in mean water transparency from 0.3 to 0.75 m. A marked swing towards an algal assemblage comprised of chlorophyte species occurred during aseasonal period historically-dominated by cyanophytes. Levels of pH and dissolved oxygen declined with the reduced phytoplankton activity in the lake. The zooplankton assemblage was dominated by large-bodied cladocerans, this in contrast to dominance by cyclopoid copepods. It is hypothesized that reduced grazing pressure on the zooplankton, brought about by loss offish from the lake, and in combination with other, as yet unidentified forcing functions, contributed to the observed changes. It is suggested that the implementation of the temporary drawdown and refilling of the lake served to reinitiate seasonal biotic characteristics which would have been common in this and other shallow seasonal waters prior to the introduction of water level regulation. It is further suggested that this procedure should be repeated on an annual basis in order to further entrench beneficial effects and improvements in water quality, and without loss of recreational amenity value.

Effects of interference and exploitative competition from large-bodied cladocerans on rotifer community structure

Effects of interference and exploitative competition from large-bodied cladocerans on rotifer community structure

Biomanipulation of Lake 221 in the Experimental Lakes Area (ELA): Effects on Phytoplankton and Nutrients

Lake 221 was dominated by omnivorous perch (Perca flavescens); the addition of northern pike (Esox lucius) resulted in trophic changes that eventually affected the phytoplankton community. Two years following the introduction of pike, perch were greatly reduced. Subsequently, Chaoborus abundance increased, rotifer and cladoceran abundance and biomass decreased, and the large-bodied cladoceran Daphnia catawba increased. The phytoplankton community shifted from chlorophyte to cyanophyte codominance with dinoflagellates. Phytoplankton biomass and phosphorus (P) increased because of nutrient recycling and excretion by pike and zooplankton. In years three and four, algal biomass and the ratio of suspended to dissolved P decreased because a larger portion of dissolved P was bound in an increased bacterial population. Phytoplankton cell size and production decreased, but the production:biomass ratio increased. In year five, chrysophytes dominated as phytoplankton biomass and production increased and bacterial abundance declined. Phytoplankton responses were primarily an indirect result of the introduction of piscivorous fish, which altered internal nutrient recycling.

Low fish predation pressure in London reservoirs: II. Consequences to zooplankton community structure

The 1992 survey of zooplankton structure in fourteen London supply reservoirs showed the overall dominance of large-bodied zooplankton, mainly species of Daphnia. These reservoirs can be considered as ‘anti-fish’ by virtue of their steeply sloping concrete or brick sides. The average biomass of large Daphnia spp (retained on a 710 µm sieve) in the total zooplankton biomass was higher than 20% for twelve out of fourteen reservoirs. The cladoceran-copepod ratio was inversely correlated with both dominance of large-bodied Daphnia magna and cladoceran body-size structure. Parallelly, there were tendency of more efficient utilization of lowered algal crops in reservoirs dominated by large-bodied Daphnia spp.

Top-down control of phytoplankton in a shallow hypertrophic lake: Little Mere (England)

Top-down control of phytoplankton by zooplankton is possible through reductions in density of zooplanktivorous fish. Little Mere is a shallow lake where the effects of sewage effluent caused such a reduction. This allowed the large-bodied cladoceran, Daphnia magna Straus, to develop huge populations, preventing potentially large algal crops from developing.

Influence of Water Chemistry on Size Structure of Zooplankton Assemblages

A stratified-random selection of all lakes in the northeastern United States was sampled for zooplankton composition, and physical and chemical characteristics during midsummer 1986. In all, 146 lakes were sampled from five geographic subregions and three categories of water alkalinity. There was no significant variation in total zooplankton abundance among regions or alkalinity categories; however, the body-size structure of assemblages was dependent on both alkalinity and geographic subregion. The largest change in size structure occurred at alkalinity levels &gt; 150 μeq∙L−1and pH &gt; 7.0, and appeared less related to change in pH than to variation in water hardness. This shift of size structure was caused by a loss of large-bodied zooplankton and an increase in small rotifers with decreasing water hardness. Exploratory analysis revealed that lake stratification also explained significant variation in zooplankton size structure, but was largely independent of the effects of water chemistry. We hypothesize that the association of large zooplankton with hard water is casual; large-bodied cladocerans may require high calcium levels.

Applicability of planktonic biomanipulation for managing eutrophication in the subtropics

Although large-bodied cladocerans such asDaphnia can reduce algal biomass significantly in temperate lakes if freed from fish predation, the applicability of such biomanipulation techniques for eutrophication management in the subtropics and tropics has been examined only recently. Subtropical cladoceran assemblages differ from those of temperate lakes by their low species richness, early summer gameogenesis, and greatly reduced body size. Eutrophic Florida lakes are dominated by pump-filter feeding fish rather than by size selective planktivores as a temperate lakes. Cladocerans in Florida lakes can increase in abundance significantly if freed from fish but fail to have an impact on algal biomass or composition. The greatest potential for using biomanipulation to manage phytoplankton-dominated lakes in the subtropics and tropics lies with phytophagous fish. Future research should concentrate on defining the role of individual fish taxa on phytoplankton composition and community structure, nutrient cycling, and planktonic productivity before embarking on whole lake manipulation projects.

富栄養湖におけるラン藻と動物プランクトンの相互関係

Studies on interrelations between blue-green algae and zooplankton are reviewed, and the interrelations in eutrophic lakes are discussed. Laboratory experiments have shown that several blue-green algae are toxic to zooplankton and reduce the feeding, assimilation, survival and growth rates of various zooplankters. The algal toxicity differs among algal species and among algal strains. Blue-green algae are considered to be nutritionally inadequate to zooplankton, even if they are non-toxic. In nature, however, the deleterious effects of blue-green algae are recognized only on large bodied cladocerans. In lakes where blue-green algae are blooming, the zooplankton community is usually dominated by small-bodied cladocerans, rotifers and copepods. They seem to have different mechanisms to coexist with the algal blooms ; i.e., inability to consume filamentous or large colonial blue-green algae (small-bodied cladoccerans), resistance to toxic chemicals of the algae (rotifers), avoidance of consumption of the algae by chemosensory feeding (cope-pods). Zooplankters probably promote the dominance of filamentous or colonial blue-green algae by grazing on small edible algae which compete with blue-green algae for nutrients and by releasing nutrients obtained from these algae for use by the blue-green algae. In eutrophic lakes, bloom forming blue-green algae are considered to be hardly ingested by zooplankton. The organic matters produced by the algae are probably utilized by zooplankton through bacteria which had grown in the process of the decomposition of the algae. Thus, the main path way of the organic matters from phytoplankton to zooplankton is detritus food-chain in these lakes.

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

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.

Predation-driven dynamics of zooplankton and phytoplankton communities in a whole-lake experiment

1. Species compositions of zooplankton and phytoplankton were followed in Tuesday Lake before and after experimental manipulation of its fish populations (addition of piscivorous largemouth bass, removal of planktivorous minnows). Plankton dynamics were compared to those of adjacent, unmanipulated Paul Lake, where piscivorous fish have been dominant historically. 2. Indices of similarity for the zooplankton communities in the two lakes in 1984 prior to the manipulation were low; however, following the manipulation in spring, 1985, similarity of the zooplankton in the two lakes rose considerably and remained high throughout 1986. This was the result of an increase in Tuesday Lake of previously rare large-bodied cladocerans (Daphnia pulex, Holopedium gibberum) which were the dominants in Paul Lake, and the disappearance in Tuesday Lake of the dominant small-bodied copepod Tropocyclops prasinus, a minor component of the Paul Lake zooplankton. These observations are consistent with prior observations of the effects of size-selective predation on zooplankton communities. 3. Phytoplankton communities also responded strongly to the manipulation, with similarity indices for the two lakes rising from low levels in 1984 to high levels of similarity in 1985 and 1986, reflecting the decrease of formerly dominant Tuesday Lake taxa which were unimportant in Paul Lake and the appearance or increase in Tuesday Lake of several taxa characteristic of the Paul Lake phytoplankton assemblage. these results clearly show that food web structure can have pronounced effects on community composition at all levels of the food web, and that, just as zooplankton communities are structured by sizeselective predation, phytoplankton communities are structured by herbivory. These observations may provide some insight into factors governing the complex distributions of phytoplankton species among various lakes.

Impact of Fenvalerate on Enclosed Freshwater Planktonic Communities and on in situ Rates of Filtration of Zooplankton

The treatment of large-volume (~ 125 m3) in situ lake enclosures with fenvalerate at realistic field levels of agricultural contamination by drift or overspray (0.4–4.0 g fenvalerate∙ha−1) resulted in the disruption of the structure and function of the planktonic communities. The toxic effects ranged from short-term changes in the feeding behaviour of several species of zooplankton (Daphnia spp. and Ceriodaphnia lacustris) at 0.05 μg fenvalerate∙L−1 to a drastic reduction in the densities of most of the major groups of zooplankton at 0.1 μg fenvalerate∙L−1 for periods of up to 3 wk following treatment. In addition, indirect effects of toxicity were observed, e.g. populations of rotifers and phytoplankton increased in enclosures after the removal of the large-bodied cladocerans. This is thought to be the result of a reduction in competition and grazing, respectively. The emulsifying agents used in the emulsifiable concentrate formulation of fenvalerate were not found to be toxic to zooplankton at concentrations expected after agricultural use. The half-life of fenvalerate in an enclosure treated with a nominal concentration of 0.1 μg∙L−1 was estimated to be4.1 d by first-order reaction kinetics.

The influence of whole lake aeration on the limnology of a hypereutrophic lake in central Florida

To determine the influence of a multiple inversion aeration system upon the limnology of a small sinkhole lake, we monitored physical-chemical and biological parameters for 15 months prior to starting aeration and for 24 months thereafter. Aeration eliminated thermal stratification and dissolved oxygen concentrations of bottom waters increased significantly. Secchi disk transparency increased during aeration while turbidity, pH, alkalinity, total nitrogen, hydrogen sulfide and iron concentrations decreased significantly. Primary production and mean chlorophyll a did not change significantly during aeration but total phytoplankton cell volume decreased 2-fold. This decrease was caused by a marked reduction in blue-green algae which appears to be attributable to rapid mixing of the lake and to decreases in the pH. Cell volumes of green algae remained constant but numbers of taxa increased 70%. Densities of crustacean zooplankton were reduced markedly by aeration while densities of rotifers increased significantly during the first year but then returned to preaeration levels during the second year. Large-bodied cladocerans were replaced by small-bodied forms during aeration, and copepod populations became dominated by nauplii (97%). Densities of benthic macroinvertebrates declined 2-fold during aeration due to to a marked reduction (10-fold) in the Chaoborus population which correlated strongly with decreases in crustacean zooplankton abundance. The total number of taxa collected on individual sample dates increased throughout the two year aeration period (from 12 to 25) and chironomids became the predominant group (70%).

Toxic and inhibitory effects of the blue-green alga Microcystis aeruginosa on herbivorous zooplankton

Blooms of blue-green algae are often associated with declines in populations of large-bodied cladocerans and increased importance of small cladocerans, copepods, and rotifers. We conducted toxicity and herbivory experiments, using a wide range of herbivore taxa, to test the hypothesis that the blue-green alga Microcystis aeruginosa most strongly inhibits large cladocerans. For a variety of herbivore taxa, M. aeruginosa was toxic or non-nutritious, and inhibited feeding on co-occurring nutritious food. The rotifer Brachionus calyciflorus was unique in several respects: it was unaffected by M. aeruginosa toxins, it showed some ability to grow and reproduce on a diet of M. aeruginosa , and it maintained high feeding rates on co-occurring nutritious food in the presence of bloom densities of M. aeruginosa . There was a strong relation between the toxicity of M. aeruginosa and its inhibitory effect on herbivore feeding rates. Copepods strongly avoided consuming M. aeruginosa , but all cladocerans and rotifers tested filtered unicellular M. aeruginosa at rates similar to or higher than nutritious Chlamydomonas reinhardi . Our results indicate that there are a variety of mechanisms whereby herbivorous zooplankton can coexist with blooms of M. aeruginosa , including resistance to toxic chemicals ( B. calyciflorus ), and avoidance of consumption of M. aeruginosa by chemosensory means (copepods), or by the inability to consume large colonies (some small cladocerans).