Daphnia dominance and zooplankton community structure in fishless ponds

Predation by fish has commonly been viewed as a primary driverof spatial and seasonal variation in Daphnia dominance and thesize structure of zooplankton communities. Yet, previous researchsuggests that large Daphnia do not always dominate in the absenceof predation. As alternatives to the planktivory model, numerousmechanisms have been put forth, including the effect of resourcecompetition and its interaction with resource quantity and qualityand abiotic factors (e.g. temperature). Here results are presentedof a field survey of 18 fishless, permanent ponds in southwestMichigan in which spatiotemporal variation in Daphnia pulexabundance and several potential determinants of this variationare explored. Results revealed a large amount of variation inD. pulex incidence and relative biomass, with some ponds exhibitingseasonal losses, some having few or no Daphnia, and some beingdominated by D. pulex for the entire sample period. Redundancyanalysis of zooplankton composition and pond environmental variables(biotic and abiotic) showed no relationship between D. pulexbiomass and measures of Chaoborus abundance, algal resourceproduction, or algal resource quality (including seston C:N:P).Instead, pH and temperature (both of which covaried) showedthe strongest relationship with D. pulex biomass.     

Dispersal-limited zooplankton distribution and community composition in new ponds

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

Crustacean zooplankton community structure in temporary and permanent grassland ponds

Lentic community structure varies across a size gradient of ponds and lakes with physical factors, such as pond drying, and biotic factors, such as fish predation, determining the species assemblage. We studied the effects of pond drying and fish absence on crustacean zooplankton across a gradient of pond sizes in a Texas grassland. We determined the species compositions and size distributions of crustacean zooplankton in 20 temporary and 18 permanent ponds in April after March rains had refilled the ponds. The surface areas of temporary and permanent ponds ranged from <0.01 to 0.21 ha and 0.04 to 13.8 ha, respectively, and temporary ponds were significantly smaller, on average, than permanent ponds. Fish were absent from all temporary ponds and present in all permanent ponds. We detected a difference in the zooplankton species assemblages of the temporary and permanent ponds. Out of 14 total zooplankton taxa that occurred in eight or more ponds, seven taxa were significantly more prevalent in temporary ponds and four taxa were significantly more prevalent in permanent ponds. The sizes of zooplankton in the temporary fishless ponds were greater than those in the permanent ponds with fish present. We concluded that pond size mediated susceptibility to pond drying, and pond drying determined the presence and absence of fish and their secondary trophic-level effect on zooplankton community structure. Handling editor: Steven Declerck     

滤食杂食性鱼类放养对浮游动物群落结构的影响

滤食杂食性鱼类是我国南方水体中常见鱼类,本文调查了放养滤食杂食性鱼类后浮游动物的丰度和种类组成的变化,以探讨其对浮游动物群落的影响.结果显示,滤食杂食性鱼类放养之后,枝角类模糊秀体溞(Diaphanosoma dubium)、微型裸腹溞(Moina micrura)和桡足类蒙古温剑水蚤(Thermocyclops mongolicus)、南方近镖水蚤(Tropodiaptomus australis)等丰度迅速下降,而轮虫丰度在鱼类放养一周后迅速增加,且保持较高的密度;轮虫优势种也发生了变化,调查前两周主要以臂尾轮虫(Brachionus)为主,两周后以暗小异尾轮虫(Trichocereidae pusilla)、广布多肢轮虫(Polyarthra trigla)和裂痕龟纹轮虫(Anuraeopsisfissa)等个体更小的种类为主.本研究说明,滤食杂食性鱼类能够显著影响浮游动物群落结构,个体较大的种类受到的影响较大,最后导致浮游动物群落的小型化.     

Recurrent response patterns of a zooplankton community to whole-lake fish manipulation

1. In a series of whole-lake manipulations conducted from 1984 to 1991, planktivorous fishes were alternately removed and restocked in a small mesotrophic lake, resulting in dramatic changes in the zooplankton community. 2. Response patterns in the zooplankton community, which include species and size structure, and within-year community variability, were examined. Variation in the zooplankton community in unmanipulated years was much lower than that in manipulated years, regardless of direction of the manipulation (i.e. decreasing or increasing planktivory). 3. The succession of zooplankton species abundance was repeated in the second removal of planktivorous fishes. The community shifted from small-bodied cladocerans, copepods and rotifers, through an intermediate state with high abundance of Holopedium, to an assemblage dominated by large-bodied daphnids.     

Alterations in zooplankton community structure after selenium-induced replacement of a fish community: a natural whole-lake experiment

Most of the fish species in Belews Lake, a cooling reservoir in the Piedmont area of North Carolina (USA), were eliminated in 1976–77 because of selenium poisoning. Zooplankton samples collected in 1974–75, prior to the fish kill, when the lake's fauna included a regionally-typical assemblage of piscivores and planktivores at a density of 14000 ha^–1, were compared to those collected in 1984–86, when the piscine community was dominated by three planktivorous fish (Notropis lutrensis, Pimephales promelas and Gambusia affinis) at a density of 28000 ha^–1. Zooplankton diversity was similar in 1984–86 compared to that in 1974–75. However, densities of the predominant cladocerans (Bosmina longirostris, Pseudosida bidentata, Ceriodaphnia pulchella, Holopedium amazonicum, Daphnia parvula, D. ambigua) and copepods (Diacyclops thomasi, Mesocyclops edax, Tropocyclops prasinus, Skistodiaptomus pallidus, S. reighardi) declined, though the magnitude of the reduction was greatest for the cladocerans and S. reighardi. Densities of copepod nauplii and rotifers also decreased markedly. No colonizations or extinctions of crustacean species occurred between 1975 and 1986. Thus, while crustacean species richness (n = 18 species) remained the same, the relative proportions of individual species changed dramatically, most notably among the Cladocera. The observed changes in crustacean species densities and dominance are attributed to the replacement of the regionally-typical fish fauna by one consisting primarily of planktivores.     

Relationship between nutrient concentration,phytoplankton density,and zooplankton density in nutrient enriched experimental ponds

The effects of different levels of nutrient input on the plankton community was investigated in a two-year controlled fertilization study of eight experimental ponds. There were four treatments, each replicated: a control, to which no fertilizer was added, and three levels of nutrient addition. Limnological parameters including phytoplankton and zooplankton densities were measured frequently during both summers and less frequently during the rest of the year. Inorganic nitrogen and phosphorus concentrations in the treated ponds increased. Phytoplankton and zooplankton density increased with treatment level but was variable. There was a limited relationship between the average chlorophyll a concentration per summer and the average cladoceran dry weight per summer. Above chlorophyll a concentrations greater than 60–70 mg/m³ other factors such as a pH zooplankton mortality effect, prevailed.     

Impacts of fish predation on an Ohio River zooplankton community

Compared to lentic systems, much less is known about the factorsthat structure zooplankton communities in large river environments.In this study, we used an in situ mesocosm system, the potamocorrals,to assess the impact of larval fish on the zooplankton communityin the Ohio River (USA). The responses of zooplankton to increasingbiomasses of fish were taxon-dependent. The population growthrates of the most common zooplankton, Diacyclops thomasi, variedinversely with fish biomass, while other crustacean zooplanktonshowed no significant responses to the fish treatment. The reversepattern was seen for the rotifer Polyarthra sp. whose populationgrowth rates increased with increasing fish biomass. This isthe first in situ evaluation of fish predation on zooplanktonin a large river system and demonstrates that predation as wellas physical factors may influence riverine zooplankton densitiesand community structure.     

Influence of Chaoborus density on the effects of an insecticide on zooplankton communities in ponds

Zooplankton communities with a high or low density of Chaoborus larvae were established in outdoor concrete ponds, to which a carbamate insecticide, carbaryl, was applied at 0.1 or 0.5 mg l⁻¹. The lower concentration of the chemical was harmful only to Cladocera. The higher concentration damaged Chaoborus, Copepoda, and some rotifer species, as well as Cladocera. In the ponds with a low density of Chaoborus, chemical application altered the cladoceran community from dominance by Daphnia to that by Bosmina and Moina. In the ponds with a high density of Chaoborus, Chaoborus excluded cladocerans from the zooplankton community presumably by predation, and supported the dominance of rotifers. Cladocera did not recover after application of the chemical, even when Chaoborus was eliminated by the higher concentration of chemical. The relatively rapid recovery of Chaoborus seemed to interrupt the recovery of Cladocera.     

Biomass and production estimates of a fish community in a small South African estuary

The fish community of the small (17·5 ha) intermittently open East Kleinemonde estuary was sampled between 1994 and 1997 to estimate population size, standing stock, growth and productivity. The estuarine-spawning species were numerically more abundant ( n c . 750 000) but due to their small size contributed only 11·7% to the total biomass. The total annual productivity of all fishes in the estuary ( n c . 890 000), with a standing stock of 28·44 g m ⁻², was calculated at 55·89 g m⁻² year⁻¹. The small sparid Rhabdosargus holubi with a production estimate of 41·35 g m⁻² year⁻¹ accounted for <74% of the total fish production in this estuary.     

Acoustical estimates of fish and zooplankton distribution in the Piaseczno reservoir, Southern Poland

Hydroacoustical surveys in the Piaseczno reservoir were performed in May and September 2002 using a Biosonics 101 dual beam echo sounder. They have revealed very scarce fish populations in pelagic waters with twice-higher abundance in autumn (530 fish ha⁻¹) as compared with spring (280 fish ha⁻¹). Small and very small fish (below 10 cm length) dominated. Apart from fish, Chaoborus larvae were producing acoustical echoes of the TS similar or slightly weaker than that of small fish. Invertebrates formed a thin layer, less than 2 m thick at the border of an anoxic zone, and were changing their depth position between 6 and 16 m, both diurnally and seasonally.     

The loss of submerged plants with eutrophication II. Relationships between fish and zooplankton in a set of experimental ponds, and conclusions

SUMMARY. 1. In 1982 and 1983 sets of experimental ponds were left with their submerged plant communities intact (plant ponds) or were cleared manually of them (cleared ponds). The ponds were all fertilized with ammonium nitrate and with variable amounts of phosphate. In 1982 fish were removed from the ponds. Zooplankton communities were dominated by large Cladocera with Daphnia prominent in the cleared ponds and Simocephalus in the plant ponds. There was no detectable effect of differential phosphorus additions on zooplankton communities or populations.
2. In 1983 zooplanktivorous fish (mainly roach) were stocked in the ponds. In the plant ponds the fish did not survive, probably through severe deoxygenation and the zooplankton community again included large-bodied Simocephalus. Fish survival was variable in the cleared ponds. Where fish stocks were absent or low (0.5–1 g m⁻²) a Daphnia- dominated community persisted; at intermediate fish stocks (18.1 g m⁻²) Eudiaptomus gracilis was predominant and where fish stock was high (22.8–29.1 g m⁻²) Bosmina longirostris , and cyclopoid copepods dominated the communities. Mean biomass of the zooplankton community declined with increase in fish stock to between 5.1 and 18.1 g m⁻² then increased.
3. On the basis of results from the experimental ponds and elsewhere, a new hypothesis is put forward to account for the switch from aquatic plant to phytoplankton dominance in eutrophicated shallow lakes. It envisages dominance by either group to be possible as alternative states over a wide range of high nutrient loadings. It suggests that each state is buffered against increased loading by mechanisms involving plant and algal physiology and zooplankton grazer populations. The nature of the buffers and the reasons by which one state may be switched to the other are, discussed.     

Assembly of zooplankton communities in newly created ponds

1. The creation or severe disturbance of habitat patches is generally followed by a phase of community (re)assembly. After such an event, the trajectory of community assembly in habitat patches may be highly variable because of stochasticity during the dispersal and colonization process. Conversely, assembly patterns may also be deterministic if communities are shaped by prevalent environmental conditions in the habitat patches (species sorting), or by systematic differences in the dispersal capacities of species. 2. In this study, we investigated the pattern of community assembly of zooplankton species in 25 newly created ponds at 13 different sites in Flanders (Belgium). Over a period of three consecutive years, we assessed at what rate and with what frequency species of the regional species pool colonized the newly created ponds. We also studied the development of community structure over time and tested whether the dynamics were consistent across different ponds at the different locations. In addition, we characterized the dynamics of metacommunity features, such as alpha, beta and gamma diversity in clusters of ponds. 3. Even within the first year after their creation, the new ponds were rapidly colonized by a small subset of species from the regional species pool (Daphnia obtusa, Chydorus sphaericus and Simocephalus vetulus). These species dominated the cladoceran assemblages during the subsequent years. Other species in the regional species pools were only sporadically able to colonize ponds. 4. During the entire study period, we observed no significant shifts in species lists or in the occurrences of species among years. The low incidence of the majority of species may be the result of dispersal limitation or the failure of immigrants to establish due to priority effects exerted by the first colonizers. There was, nevertheless, a consistent change in the relative abundance of species, which was most probably mediated by differences in the hatching time among species influencing species composition in the first year. 5. In contrast to expectations, we observed no increase in average alpha diversity (local species richness) and gamma diversity (total richness of entire pond clusters) during the course of the study period. Beta diversity was relatively low from the beginning and remained constant throughout the study period. These deterministic patterns can mainly be attributed to the dominance of the three first colonizing species and the low success rate of other species in colonizing the ponds.     

Structural and grazing responses of zooplankton community to biomanipulation of some Dutch water bodies

Structure and grazing activities of crustacean zooplankton were compared in five lakes undergoing manipulation with several unmanipulated eutrophic (shallow) and mesotrophic (deep) lakes in The Netherlands. The biomanipulated lakes had lesser number of species and their abundance, both of rotifers and crustaceans, and had much larger mean animal size (3–11 μg C ind.⁻¹) than in the unmanipulated eutrophic lakes (0.65 μG C ind.⁻¹). WhereasD. hyalina (=D. galeata) andD. cucullata generally co-occurred in the unmanipulated lakes, in the manipulated lakes bothD. hyalina and other large-bodied daphnids,D. magna,D. pulex (=D. pulicaria), were the important grazers. In the biomanipulated lakes an increase in the individual crustacean size and of zooplankton mass were reflected in a decrease in seston concentration, higher Secchi-disc depth and a marked decrease in the share in phytoplankton biovolume of cyanobacteria. Biomass relationship between seston (150 μm) and zooplankton indicated a Monod type relationship, with an initial part of the curve in which the zooplankton responds linearly to the seston increase up to aboutca. 2 mg C l⁻¹, followed by a saturation of zooplankton mass (0.39 mg C l⁻¹) at 3–4 mg C l⁻¹ seston, and an inhibitory effect on zooplankton mass at seston levels>4 mg C l⁻¹. This latter is related to predominance in the seston of cyanobacteria. In the biomanipulated lakes, the zooplankton grazing rates often exceeded 100% d⁻¹, during the spring, and food levels generally dropped to <0.5 mg C l⁻¹. The computed specific clearance rate (SCR) of zooplankton of 1.9 l mg⁻¹ Zoop C is well within the range of SCR values (1.7–2.2 l mg⁻¹ Zoop C) from deep and mesotrophic waters, but about an order of magnitude higher than in the eutrophic lakes, with the food levels 10-fold higher. For 25% d⁻¹ clearance of lake seston between 35 and 60 ind. l⁻¹ are needed in the biomanipulated lakes against 1200–1300 ind. l⁻¹ in eutrophic lakes. Similarly, about 10 to 15 times more crustacean grazers are required to eliminate the daily primary production in the eutrophic lakes than in the biomanipulated lakes. These numbers are inversely related to the differences in animal size. The corresponding biomass values of zooplankton needed to clear the daily primary production in the eutrophic waters were 0.1–0.2 mg C l⁻¹ in the biomanipulated lakes, but about 0.45 mg C l⁻¹ in the unmanipulated eutrophic waters. Only if the water was kept persistently clear by zooplankton was there a balanced seston budget between the inputvia primary production and elimination by zooplankton. Mostly, however, the input exceeded the assimilatory removal by zooplankton, such that the estimated seston loss could be attributed to sedimentation and mineralization.     

Sampling related individuals within ponds biases estimates of population structure in a pond‐breeding amphibian

Effective conservation and management of pond‐breeding amphibians depends on the accurate estimation of population structure, demographic parameters, and the influence of landscape features on breeding‐site connectivity. Population‐level studies of pond‐breeding amphibians typically sample larval life stages because they are easily captured and can be sampled nondestructively. These studies often identify high levels of relatedness between individuals from the same pond, which can be exacerbated by sampling the larval stage. Yet, the effect of these related individuals on population genetic studies using genomic data is not yet fully understood. Here, we assess the effect of within‐pond relatedness on population and landscape genetic analyses by focusing on the barred tiger salamanders (Ambystoma mavortium) from the Nebraska Sandhills. Utilizing genome‐wide SNPs generated using a double‐digest RADseq approach, we conducted standard population and landscape genetic analyses using datasets with and without siblings. We found that reduced sample sizes influenced parameter estimates more than the inclusion of siblings, but that within‐pond relatedness led to the inference of spurious population structure when analyses depended on allele frequencies. Our landscape genetic analyses also supported different models across datasets depending on the spatial resolution analyzed. We recommend that future studies not only test for relatedness among larval samples but also remove siblings before conducting population or landscape genetic analyses. We also recommend alternative sampling strategies to reduce sampling siblings before sequencing takes place. Biases introduced by unknowingly including siblings can have significant implications for population and landscape genetic analyses, and in turn, for species conservation strategies and outcomes.     

The restoration of fish ponds in agricultural landscapes

Fish ponds in central and eastern Europe are artificial lakes of less than 1 ha to several 100 ha in size. Some of them were created around 900 years ago. These fish ponds form an important part of the hydrological system in the landscape; they also serve as water purification systems and sediment traps, provide habitat for many plant and animal species, as well as being used for recreation purposes—but above all, they are dedicated to fish production. The original oligo- or mesotrophic character of these fish ponds has been altered to one of eutrophic or even hypertrophic conditions due to the nature of the intensive management for high fish production, as well as agriculture practices within the catchment area. It can also be due to other uses of fish ponds, such as wastewater recipients. A thick layer of black anaerobic sediment invariably develops and serves as an uncontrolled internal source of nutrients. In order to stop the development of water blooms and restore the lake to reasonable healthy conditions, both the external and internal loading has to be reduced. An example of such a fish pond restoration within the Czech Republic is described. The phosphorus budget of the Vajgar fish pond (40 ha, S Bohemia) was evaluated and the dry matter, organic matter, nutrients, heavy metals and other metals content were estimated in the vertical profile of the fish pond's sediment. A precision suction dredger was designed, constructed, and used for the selective removal of 330 000 m³ black sediment from the Vajgar fish pond. The sediment was pumped to settling ponds at a distance of 2.5 km. Later, the suction dredger was used for sediment removal from other fish ponds. In one case, 40 000 m³ of eutrophic sediment was directly applied on an agriculture field. In another case, sediment containing oil products was decontaminated by using a biocatalyst and bacterial culture. Sediment removal from Vajgar fish pond resulted in a temporary negative phosphorus budget (lower concentrations in the outflow than the inflow). The temporary absence of cyanobacteria (Microcystis sp.) blooms was the result of the removal of the black sediment layer. The improvement of water quality after sediment removal was, however, temporary. A more holistic approach, aimed at the reduction of matter losses from the fish pond's catchment area, is therefore being adopted. The principles of such an holistic approach are described.     

The influence of flatworm predation on zooplankton inhabiting small ponds

Experiments were performed in 1977 to determine which large zooplankton in a series of high altitude ponds can be consumed by the predatory flatworm Mesostoma ehrenbergii. This predator consumes Daphnia at a high rate and the fairy shrimp Branchinecta at a low rate, but does not consume Diaptomus. Experiments were performed in 1978 and 1979 to determined the rate of predation on Daphnia in 30 liter tubs and to determine if predation rate is correlated with surface to volume ratio of experimental containers. There is a clear correlation between surface to volume ratio and predation rate. Determinations of Mesostoma and Daphnia densities were made in a series of eight high altitude ponds, and pond surface to volume ratios were determined. Examination of these parameters lends credence to the argument that Mesostoma predation affects Daphnia dynamics in some circumstances. The results suggest that benthic invertebrate predators may affect zooplankton dynamics, especially in shallow ponds.     

Spatial organization and population density of the fish community of the litter banks within a central Amazonian blackwater stream

Results of a study of the fish community of the leaf litter banks in the lower reaches of the Taruma-Mirim, a small central Amazonian stream is presented. The Taruma-Mirim is an acidic, blackwater, forest stream which flows through igapo forest and enters the Rio Negro close to Manaus. The commonly held view that these blackwaters hold an impoverished ichthyofauna is challenged. The studied litter banks hold about 20 species of fish, all of which were found to live within distinct subregions of the habitat. Average fish density was about 100 individuals m⁻². Absolute population sizes were found to be remarkably small; within a 200 m² area the most abundant species had a population size of about 10⁴ and the least abundant <10² individuals. It is argued that high species richness linked to specialized habitat requirements and small population size indicates considerable population stability. The factors leading to the evolution of such species richness are discussed.     

Response of littoral invertebrates to reduction of fish density: simultaneous experiments in ponds with different fish assemblages

1. We experimentally reduced densities of predatory fish in replicated 2 m² areas of the littoral zone in two ponds to test whether density and biomass of invertebrates would respond to release from fish predation. The ponds are of similar size and in close proximity, but support different fish assemblages: bluegills ( Lepomis macrochirus Rafinesque) and largemouth bass ( Micropterus salmoides (Lacepede)) in one pond, and bluespotted sunfish ( Enneacanthus gloriosus (Holbrook)) and chain pickerel ( Esox niger Lesueur) in the other. Fish densities were reduced to less than 15% of ambient levels in both experiments.
2. In the bluegill–bass pond, density and biomass of most invertebrate taxa and size classes were unaffected by the fish manipulation. Total invertebrate densities did not differ significantly between fish treatments, but total invertebrate biomass was significantly greater where fish density was reduced, averaging 30% higher over the course of the study. Likewise, manipulation of fish in the bluespotted sunfish–pickerel pond had few significant effects on individual taxa and size classes. There were no significant effects on total invertebrate abundance in the bluespotted sunfish–pickerel pond.
3. Our results provide direct experimental evidence consistent with the collective evidence from previous work, suggesting that the impact of fish predation on density and biomass of invertebrate prey in littoral habitats is variable, but generally weak. Invertebrates that coexist successfully with fish in littoral systems probably are adept at taking advantage of refugia offered by the structurally complex physical environment.     

Response of littoral invertebrates to reduction of fish density: simultaneous experiments in ponds with different fish assemblages

1. We experimentally reduced densities of predatory fish in replicated 2 m² areas of the littoral zone in two ponds to test whether density and biomass of invertebrates would respond to release from fish predation. The ponds are of similar size and in close proximity, but support different fish assemblages: bluegills ( Lepomis macrochirus Rafinesque) and largemouth bass ( Micropterus salmoides (Lacepede)) in one pond, and bluespotted sunfish ( Enneacanthus gloriosus (Holbrook)) and chain pickerel ( Esox niger Lesueur) in the other. Fish densities were reduced to less than 15% of ambient levels in both experiments.
2. In the bluegill–bass pond, density and biomass of most invertebrate taxa and size classes were unaffected by the fish manipulation. Total invertebrate densities did not differ significantly between fish treatments, but total invertebrate biomass was significantly greater where fish density was reduced, averaging 30% higher over the course of the study. Likewise, manipulation of fish in the bluespotted sunfish–pickerel pond had few significant effects on individual taxa and size classes. There were no significant effects on total invertebrate abundance in the bluespotted sunfish–pickerel pond.
3. Our results provide direct experimental evidence consistent with the collective evidence from previous work, suggesting that the impact of fish predation on density and biomass of invertebrate prey in littoral habitats is variable, but generally weak. Invertebrates that coexist successfully with fish in littoral systems probably are adept at taking advantage of refugia offered by the structurally complex physical environment.