Are artificial wetlands good alternatives to natural wetlands for waterbirds? – A case study on Chongming Island, China

Loss of natural wetlands is a global phenomenon that has been a serious threat to the wildlife. A common practice is to construct artificial wetlands to compensate for the loss of natural wetlands. To test whether artificial wetlands as habitats for waterbirds are good alternatives to natural wetlands, we compared species richness, abundance, and seasonal dynamics of waterbird communities of natural (here tidelands) and artificial wetlands (here aquacultural ponds) on Chongming Island, China. Our results indicate that habitat preference of waterbirds showed seasonal difference: most of the shorebirds were found on tidelands in spring, whereas most of the natatorial birds were recorded in aquacultural ponds in winter. Waterbirds preferred the tidelands rather than aquacultural ponds in both spring and autumn, whereas they showed no preference for either the tidelands or the ponds in summer and winter. It is concluded that natural wetlands are better habitats for waterbirds than artificial wetlands on Chongming Island, while the artificial ones are also suitable habitats for waterbirds in winter. The waterbirds might use artificial wetlands only when natural wetlands are unavailable or of poor quality. An over-emphasis that artificial wetlands are suitable habitats for waterbirds might encourage land managers to convert natural wetlands into the artificial ones, resulting in considerable loss of bird diversity. Therefore, for the purpose of bird conservation, it would be a better practice to conserve natural wetlands rather than to construct artificial ones after destruction of natural wetlands.     

Seasonal Changes in Zooplankton and Macro-fauna Populations of the East Calcutta Wetland Fish Ponds

The current study was to explore the seasonal variation in the zooplankton and aquatic macroinvertebrate population in India’s oldest and largest sewage fed fish ponds of East Kolkata Wetlands and whether they show different trends from the natural ponds. Zooplankton diversity was significantly higher in fish ponds whereas macroinvertebrate diversity was higher in natural ponds. Zooplanktons showed significant seasonal variation in the natural ponds but did not show any variation throughout the year in sewage fed fisheries. Among zooplankton species Brachionus spp., Keratella tropica which are pollution (eutrophy) indicator were found in greater abundance in EKW fisheries than natural ponds. Chironomid larvae which thrive and flourish in highly organically polluted or eutrophicated waters were dominant in EKW. The regular input of sewage provides a certain high level of nutrient to the fisheries which help to maintain greater and consistent population density and diversity of zooplanktons forming a strong base for the food webs in the EKW ponds.     

刺参池塘底质微生物群落功能多样性的季节变化

利用BIOLOG技术和冗余分析(Redundancy analysis,RDA)方法对刺参(Apostichopus japonicus)养殖池塘底质环境(底泥、附着基)微生物群落功能多样性的季节变化及其与环境因子的关系进行了研究。结果表明:(1)刺参池塘底泥和附着基微生物对碳源总量和单类碳源的利用均具有显著的季节变化,总体表现为春、夏、秋季节高于冬季,其中,底泥微生物利用比例较高的碳源类型为聚合物、糖类、羧酸和氨基酸,附着基微生物利用比例较高的碳源类型为聚合物、糖类、氨基酸和胺。(2)主成分分析表明,刺参池塘底泥和附着基微生物碳代谢方式均具有显著的季节变化。底泥中,与主成分显著相关的碳源有18种,其中与主成分1显著相关的主要是糖类、羧酸和氨基酸,与主成分2显著相关的主要是聚合物和糖类;附着基中,与主成分显著相关的碳源有22种,其中与主成分1显著相关的主要是聚合物、糖类、羧酸和氨基酸,与主成分2显著相关的是羧酸。(3)刺参池塘底泥和附着基微生物多样性指数Shannon、McIntosh、Simpson和S-E均匀度均存在显著的季节变化,但不同指数之间的变化有较大差异。(4)RDA分析表明,TP、NO3-N和PO4-P是影响底泥微生物功能多样性季节变化的主要因素,SOM、NO3-N和TN是影响附着基微生物功能多样性季节变化的主要因素。结论认为,刺参池塘底泥和附着基微生物功能多样性具有显著的不同的季节变化,这些变化与环境因子具有很好的相关性。     

Environment-dependent admixture dynamics in a tiger salamander hybrid zone

After an estimated five million years of independent evolution, the barred tiger salamander (Ambystoma tigrinum mavortium) was introduced by bait dealers into the native range of the California tiger salamander (A. californiense). Hybridization and backcrossing have been occurring in central California for 50-60 years, or an estimated 15-30 generations. We studied genetic and ecological factors influencing admixture of these two divergent gene pools by analyzing frequencies of hybrid genotypes in three kinds of breeding habitats: natural vernal pools, ephemeral man-made cattle ponds, and perennial man-made ponds. Perennial ponds tended to have higher frequencies of nonnative alleles than either type of seasonal pond, even in cases where perennial and seasonal ponds are within a few hundred meters. Thus, the hybrid zone has a mosaic structure that depends on pond hydrology or ecology. The presence of some broadly acting constraints on admixture is suggested by linkage disequilibria between physically unlinked molecular markers within ponds. In addition, we found several marker-specific deviations from Hardy-Weinberg equilibrium. One marker showed a consistent deficit of heterozygotes across pond types. Another showed heterozygote deficits only in vernal pools. A third was more likely to have heterozygote excess in ephemeral cattle ponds. These patterns indicate that admixture is influenced by complex genotype-by-environment interactions.     

A report on the artificial fertilization of the smallmouth yellowfish, Barbus holubi (Steindachner, 1894)

Artificial fertilization was successfully applied in the culture of Barbus holubi . By this method the fertilization potential was raised considerably and the mortality rate under normal conditions during the incubation period was less than 5 %. The handling and transferring of larvae to fertilized rearing ponds was simplified and an estimation of the seasonal production could be made without waiting for the fish to attain the fingerling stage. Normal breeding activities were not disturbed by frequent handling and natural breeding took place in ponds where the fish were kept.     

Measurements of some Groups of Microbial Populations with Special Reference to Denitrification in Water and Sediments of Fish Farming Ponds under Mono- and Polyculture Systems

The spatial and seasonal distribution of some groups of bacteria as well as the rates of denitrification (natural and potential) have been investigated in water and sediments of four fish farming ponds under monoculture, traditional and polyculture systems in India. Marked differences in the monthly means of bacteria were found to exist in these fish ponds depending upon their trophic statuses. The seasonal changes of bacteria are discussed in relation to the variation of environmental factors.     

Juvenile Chinook salmon (<Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis>) growth in off-channel and main-channel habitats on the Sacramento River,CA using otolith increment widths

Few studies have quantified juvenile salmon growth among different habitats or evaluated the mechanisms controlling salmon growth and survival. We used otolith microstructure to compare daily relative growth rates among main-channel riverine areas, off-channel ponds, and non-natal seasonal tributaries of the Sacramento River, CA. We compared prey availability, prey preference, and stomach fullness between these sites. We observed larger average otolith growth increments, higher prey densities, and warmer water temperatures in both off-channel ponds and non-natal seasonal tributaries compared to the main-channel areas in both 2001 and 2002. Our findings suggest that warmer temperatures and abundant prey in off-channel habitats during Central Valley Chinook salmon rearing periods may lead to higher growth rates, which in turn may improve juvenile survival. Our results suggest that off-channel habitats may be critical habitats to include in conservation and management plans for juvenile salmon.     

On the Possibilities of Averaging the Seasonal Pattern in Kjeldahl Nitrogen in a Group of Water Bodies

It is shown that the seasonal change of Kjeldahl nitrogen in several ponds and several years shows an average seasonal change which is statistically significant on a month-to-month basis although not apparent at first sight. The relative deviation of Kjeldahl nitrogen values in individual months and individual ponds from seasonal averages of individual ponds is closer to lognormal than to normal distribution. The seasonal curve based on average values of relative deviations in individual months and ponds from the seasonal averages of individual ponds shows the lowest variation of average monthly values and is therefore most adequate to a comparison of the seasonal pattern of two or more groups of water bodies.     

Food habits, feeding behaviour and impact of triploid bighead carp, Hypophthalmichthys nobilis, in experimental ponds

Food of sterile triploid bighead carp, Hypophthalmichthys nobilis , was examined in ponds receiving water from a hypereutrophic take in Florida. No distinctive seasonal changes in food composition were found. The fish fed selectively on Botryococcus braunii Kuetzing, a large nuisance algal species, which constituted 61% of the volume and 50% of the dry weight of the food. Zooplankton was highly selected, but constituted only 3% of the food volume because of the low zooplankton density in the ponds. The remaining proportion of food consisted mainly of blue-green algae. Final fish biomass was low, ranging from 60 to 97 kg ha⁻¹ in individual ponds. Low biomass was due to slow fish growth and high fish mortality. Despite low biomass, the fish lowered the ratio of blue-green/green algae in the ponds and tended to lower phyto- and zooplankton abundance.     

Alternative life histories in the water strider Gerris lacustris: time constraint on wing morph and voltinism

The wing dimorphic water strider Gerris lacustris L. (Heteroptera: Gerridae) switches to a bivoltine life cycle under favorable climatic conditions. The switch in voltinism is accompanied by a reduction of wing development in the directly reproducing midsummer generation, while the diapausing generation has a high fraction of long‐winged individuals. We investigated whether the thermal energy (degree‐days) available in natural habitats constrains the combination of developmental pathway and wing morph. Offspring of G. lacustris were reared under quasi‐natural conditions at two temperature regimes to determine the thermal constant k required to complete adult development in either wing morph. The thermal constant for egg‐to‐adult development of the short‐winged morph was about 20% lower than of the long‐winged morph. Based on the results from the outdoor laboratory experiment, we calculated the total degree‐days necessary to complete the possible combinations of wing morph pattern and voltinism. Comparison of these estimates with the thermal energy actually available during the reproductive season of 2004 for various natural habitats (sun‐exposed field ponds and shaded forest ponds) suggests that voltinism as well as wing morph pattern is strongly limited by the number of degree‐days available in these habitats. On forest ponds, only univoltine life cycles were possible, whereas on field ponds temperature allowed bivoltine life cycles. However, only the eggs laid at the very beginning of the season had the potential to accumulate enough degree‐days to complete a bivoltine life cycle with both generations long‐winged. We conclude that thermal energy is the main environmental constraint limiting voltinism of populations in the two habitat types. Furthermore, the available thermal energy also seems to influence the determination of the seasonal wing pattern in G. lacustris.     

Effects of crowding and availability of food on growth rate of fry in the European and Chinese races of the common carp

Fry of the European and Chinese races of the common carp and interracial crossbred fry were grown together in a series of ponds for 28 days after hatching. The degree of crowding and the amount of available natural food were intentionally varied in these experimental ponds. This resulted in a large variation in mean growth between ponds, ranging from 0·1 to 5·2 g per fish during the 28 days growth period. Under conditions of very slow growth, resulting from severe crowding and lack of natural food, fry of the Chinese carp grew several times faster than European carp. At lower densities and when natural food was more abundant, resulting in a faster rate of growth, this difference between the two races disappeared. Crossbred fry between the Chinese and European carp grew faster than either of their parents under all conditions tested.     

Spatial variation in abiotic and biotic factors in a floodplain determine anuran body size and growth rate at metamorphosis

Body size at metamorphosis is a critical trait in the life history of amphibians. Despite the wide-spread use of amphibians as experimental model organisms, there is a limited understanding of how multiple abiotic and biotic factors affect the variation in metamorphic traits under natural conditions. The aim of our study was to quantify the effects of abiotic and biotic factors on spatial variation in the body size of tadpoles and size at metamorphosis of the European common toad (Bufo b. spinosus). Our study population was distributed over the riverbed (active tract) and the fringing riparian forest of a natural floodplain. The riverbed had warm ponds with variable hydroperiod and few predators, whereas the forest had ponds with the opposite characteristics. Spatial variation in body size at metamorphosis was governed by the interactive effects of abiotic and biotic factors. The particular form of the interaction between water temperature and intraspecific tadpole density suggests that abiotic factors laid the foundation for biotic factors: intraspecific density decreased growth only at high temperature. Predation and intraspecific density jointly reduced metamorphic size. Interspecific density had a negligible affect on body size at metamorphosis, suggesting weak inter-anuran interactions in the larval stage. Population density at metamorphosis was about one to two orders of magnitudes higher in the riverbed ponds than in the forest ponds, mainly because of lower tadpole mortality. Based on our results, we conclude that ponds in the riverbed appear to play a pivotal role for the population because tadpole growth and survival is best in this habitat.     

Estimates of Microbial Populations Involved in the N Cycle and their Activity in Water and Sediments of Fish Farming Ponds under Mono and Polyculture Systems in India

The population sizes of ammonifying, protein mineralizing, nitrogen fixing and nitrifying bacteria, and the rates of ammonification and nitrification (natural and potential) were measured in water and sediments of four fish ponds being used for traditional, mono- and polyculture systems of fish farming. Spatial differences in the microbial density in these ponds were related to the fish culturing practices adopted. The seasonal variation of ammonifying bacteria was found to be positively correlated with the NH₄-N level in the water. The natural and potential capacity to generate both nitrite and nitrate in these water bodies was strongly correlated with the concentrations of the different forms of inorganic nitrogen present. The rates of NO₂-N and NO₃-N formation occurring in these fish ponds were directly proportional to the amount of dissolved oxygen and pH of the environment, respectively.     

Hypoxia induces surfacing behaviour in brown-striped frog (Limnodynastes peronii) larvae

In their natural habitat, brown-striped frog (Limnodynastes peronii) larvae periodically swim rapidly from the bottom of their ponds to the water surface and then immediately dive to the bottom again. This behaviour is presumably related to air-breathing. We examined the behavioural and metabolic responses to aquatic hypoxia in L. pernoii larvae. Gas filled lungs were found in all free-swimming larval stages of L. peronii, but air-breathing occurred infrequently in normoxic water. The frequency of air-breathing at 30°C increased rapidly in hypoxic water when oxygen partial pressure (P_o2) fell below 10 kPa. Only a slight increase was observed at similar oxygen partial pressures at 20°C. The critical oxygen tension at 30°C was about 7kPa, below which, aquatic breathing larvae become metabolic oxygen conformers. In natural habitats where surfacing behaviour was observed, temperatures during summer months frequently exceed 25°C and some ponds become extremely hypoxic (po₂ < 3.0 kPa); therefore air-breathing appears to be the only way in which these larvae can maintain a fully aerobic metabolism.     

The effect of biomanipulation of the zooplankton on the growth, feeding and survival of pikeperch (Stizostedion lucioperca) in nursing ponds

The following treatments were evaluated for use in rearing pikeperch larvae (Stizostedion lucioperca L.) in nursing ponds: treatment with Dipterex (Bayer); concurrent stocking with common carp (Cyprinus carpio L.); short flooding periods and prefeeding fish larvae. Treatment with Dipterex (active ingredient trichloorfon, i.e. 00-dimethyl-2,2,2, trichlorohydroxyethyl phosphonate) gave zooplankton populations dominated by rotatoria and nauplii at the onset of exogenous feeding and dominated by copepods later on. Cladocerans dominated the plankton in untreated ponds but were never prominent in treated ones. Stomach analysis revealed a fast changing feeding preference in pikeperch from nauplii and copepodites towards cladocerans and chironomids. The excellent food conditions for first feeding pikeperch larvae in Dipterex treated ponds resulted in a significant higher number of harvested fingerlings. In spite of the more favourable food conditions in untreated ponds during the second half of the culture period, a significant growth difference was not found. Concurrent carp stocking did not affect significantly the survival and growth of the pikeperch, although it decreased the accessability of chironomids for pikeperch. Short flooding periods and prefeeding pikeperch larvae failed as useful management strategies for pikeperch nursing. Pikeperch fingerlings cultured in ponds are larger than those found in natural populations at the same time, giving them a high chance to become piscivorous and to increase the year class strength when stocked in natural waters.     

GENETIC VARIATION FOR LARVAL ANURAN (SCAPHIOPUS COUCHII) DEVELOPMENT TIME IN AN UNCERTAIN ENVIRONMENT

Couch's spadefoot toads (Scaphiopus couchii) breed in ponds of uncertain duration. In natural ponds, larvae exhibit considerable variation in growth, size at metamorphosis, and development time. Phenotypic differences in development time may dramatically affect survivorship in these ponds. A quantitative-genetic analysis of larval traits was undertaken to determine the potential evolutionary relevance of phenotypic variation observed in the field. Additive genetic variance was detected for development time, but not for any other trait. Some variation in early growth was attributed to maternal effects; maternal effects, however, were not apparent for size at metamorphosis or development time. Nonadditive genetic effects were not statistically significant for any trait, but the nonsignificance of these effects must be interpreted cautiously, as the sample of females was relatively small and the mating design used is not very effective for detecting interactions. Genetic variation in development time in this population is most likely maintained by variability in the direction of selection as a consequence of variation in pond duration.     

Interspecific competition between larvae is not an important strncturing force in mixed communities of Rana and Bufo on an English sand-dune system

We investigated the roles of competition and predation in the structuring of mixed anuran communities ( Rana temporaria and Bufo bufo ) in an English sand-dune system. Rana temporaria breeds earlier in spring than B. bufo. but the latter species was numerically superior in all ponds at the study site. We measured survival and growth rates of larvae in three duplicate sets of natural ponds. In one set we removed B. bufo spawn, leaving only R. temporaria^: in a second sel we removed R. temporaria spawn, leaving only B. bufo: and in a third set we left boih together. The third set also contained substantial numbers of predatory fish ( Perea fluviatilis and Gasterosteus aeuleatus ). Rana temporaria survival was lower than that of B, bufo in all ponds, on average by sixfold. Rana temporaria fared better on its own than in the mixed-species ponds, but lower survival in the latter ponds was probably due to fish predation rather than to Inierspecific competition. By eonlrast, B. bufo survival was sevenfold higher in mixed-species compared with single-species ponds, probably because they are distasteful to fish and thus benefited indirectly from fish-predation of invertebrates, Protothieca rieharsi. a mediator of interference competition between anuran larvae under laboratory conditions, was present in some of the dune ponds but was not correlated with larval growth inhibition. Taken together the evidence implicated predation of larvae and intraspecific competition, rather than interspecific competition, as the dominant structuring forces in this community.     

Seasonal Patterns of Abundance: Do Zooplankton in Small Ponds do the Same Thing Every Spring–Summer?

Small ponds ( ≤ 2 ha) are often a common landscape feature, but their ecology has been less well studied than that of lakes. Studies of some lakes and reservoirs show among-year repeatability in the seasonal abundance of different zooplankton (i.e., succession). For small ponds the seasonal dynamics of zooplankton community structure are relatively unstudied, as are any mechanisms underlying these dynamics. We took a community-level approach to studying the spring–summer abundance of zooplankton in two small Ohio ponds. In particular we wanted to know if repeatable patterns exist for zooplankton community structure in these ponds. We surveyed the spring–summer zooplankton communities in the ponds from 2001 to 2003 and used community-level ordination techniques (i.e., non-metric multidimensional scaling, NMDS) to characterize the assemblages. For both ponds the seasonal pattern of total zooplankton abundance differed significantly among years. We found that the proportional abundance of taxa across the season also varied among years. Elements of the zooplankton community, as described by the NMDS dimensions, showed among-year variation in the spring–summer trajectories that developed. Some of the variation in these zooplankton communities was associated with seasonal changes in water temperature. This among-year variation in the seasonal pattern of zooplankton community structure suggests that community dynamics in these small ponds may not be very repeatable. These complex dynamics of zooplankton thus challenges us to improve our characterization of zooplankton communities in small ponds such that we can better understand the factors that drive the patterns we observe.     

Emergence of the damselfly Pyrrhosoma nymphula (Sulzer) (Zygoptera: Coenagrionidae) from two adjacent ponds in northern England

Emergence of the damselfly Pyrrhosoma nymphula was followed closely at two similar and adjacent ponds in northern England. Males emerged earlier than females at both ponds (significantly so at one). The sex ratio was significantly male biased at both ponds. Size of emerging adults declined through the emergence period at both ponds. Adults emerging from one pond did so significantly earlier and were significantly larger than those from the other pond. The density of larvae was approximately twice as high in the pond from which larvae emerged early; this pond was also slightly deeper and usually achieved higher maximum daily water temperatures. These findings are discussed in the light of the conventional view of seasonal regulation in a spring-emerging damselfly.     

The diets and parasites of larval and 0+ juvenile twaite shad in the lower reaches and estuaries of the rivers Wye,Usk and Towy,UK

Aquatic predators and habitat permanence can jointly affect benthic invertebrate biomass and community composition. In 2006 I sampled fish and invertebrates in ten ponds embedded in a seasonal wetland before and after a natural drought. Drought reduced fish biomass and density leaving some ponds in a fishless condition when rains returned in July. In July, large aquatic insects and crayfish colonized and reproduced in the ponds, but did not colonize all of the ponds equally. Using measurements of fish abundance and other environmental parameters of the ponds, I conducted linear regression analyses to explore potential drivers of variable invertebrate biomass in July. Fish biomass had a negative effect on invertebrate biomass and it explained more of the variation in total invertebrate biomass and total non-shrimp biomass than fish abundance (number of fish caught). Dissolved oxygen and pond depth were both correlated with fish biomass, but were poorer predictors of invertebrate biomass. Ponds with few or no fish had 20× greater total biomass and 200× more non-shrimp biomass than ponds with high fish biomass. Shrimp dominated the invertebrate composition, and were only found in the two deepest ponds with the highest fish biomass; predatory insects and crayfish dominated the other eight ponds. When taxa were analyzed separately, fish biomass explained a large portion of the variation for predatory insects (Coleoptera, Hemiptera, and Odonata) and crayfish (Procambarus alleni), but dissolved oxygen was the best predictor of larval stratiomyid (order Diptera) biomass. These results are generally consistent with studies demonstrating negative effects of fish on large predatory invertebrates, but also suggest that more severe local droughts can seasonally enhance insect and crayfish populations by generating fishless or nearly fishless conditions. Handling editor: J. Trexler