Bo-Ping Han

Comparing biological classifications of freshwater phytoplankton: a case study from South China

The use of ecological classification systems is becoming more and more widely used when studying phytoplankton. Grouping phytoplankton species into ecologically coherent groups allow to reduce redundancy and in this way, to handle a minor number of biological variables when investigating the ecological status of aquatic ecosystems. Three ecological classifications are mostly used when freshwater phytoplankton is studied: functional groups or coda, morpho-functional groups (MFGs) and morphology-based functional groups (MBFGs). In this study, these three ecological classifications were comparatively used along with two taxonomic classifications based on species and genera to analyse phytoplankton response to environmental variability in three sub-tropical Chinese reservoirs. Canonical correspondence analysis was performed to compare the five mentioned biological classifications. When ecological classifications were used, the percentage of variance explained in the biological groups–environmental variables was higher than that explained by the taxonomic classifications. Coda and MFGs showed a very high degree of overlapping, but since coda are associated to very detailed environmental templates, this method was more helpful in explaining phytoplankton variability in relation to environmental factors.

Assessing ways to combat eutrophication in a Chinese drinking water reservoir using SWAT

Across China, nutrient losses associated with agricultural production and domestic sewage have triggered eutrophication, and local managers are challenged to comply with drinking water quality requirements. Evidently, the improvement of water quality should be targeted holistically and encompass both point sources and surface activities within the watershed of a reservoir. We expanded the ordinary Soil Water Assessment Tool - (SWAT) with a widely used empirical equation to estimate total phosphorus (TP) concentrations in lakes and reservoirs. Subsequently, we examined the effects of changes in land and livestock management and sewage treatment on nutrient export and derived consequences for water quality in the Chinese subtropical Kaiping (Dashahe) drinking water reservoir (supplying 0.4 million people). The critical load of TP was estimated to 13.5 tonnes yr � 1 in order to comply with the minimum drinking waterrequirements,whichcorrespondsto87%ofthesimulatedloadtothereservoiratpresent.Boththeimplementationof buffer zones along rivers and removal of sewage discharges showed marked improvement in reservoir water quality. Future research should focus on both hydrological model performance and nutrient transport pathways, which are challenged by a complex artificially altered water infrastructure in the form of ditches, channels and ponds in monsoon- influenced subtropical watersheds. Additional keywords: agriculture, reservoir water quality, sewage, subtropical watershed.

Carnivory and active hunting by the planktonic testate amoeba Difflugia tuberspinifera

Difflugia tuberspinifera, a testate amoeba found in the open water plankton of Liuxi He and other south Chinese reservoirs during summer, is one of six or more species that occasionally live a pelagic life. Here, we suggest that its incentive to leave the bottom might be the abundance of food in the water column rather than temperature. This Difflugia (and perhaps the other pelagic species as well) is indeed an actively hunting carnivore that catches small rotifers and other prey in the same size range. In Liuxi He, it readily feeds on Collotheca cf. mutabilis, which it catches and consumes with remarkable agility: it first inspects the jelly tube that protects the prey, then moves to the bottom of it, perforates the jelly near the prey’s foot, and finally ingests the rotifer foot-first.

Floating-leaved macrophyte (Trapa quadrispinosa Roxb) beds have significant effects on sediment resuspension in Lake Taihu, China

Trapa quadrispinosa Roxb is a common floating-leaved macrophyte in China. In this study, the effects of Trapa on sediment resuspension in Lake Taihu, a large, shallow, eutrophic lake in eastern China, were investigated using sediment traps. The study was conducted at stations with and without Trapa beds from 7 September to 18 October, 2003. Results showed that sediment resuspension rates at the station without Trapa were significantly higher than those at the station with Trapa. During the study period (41 days), 10,970 g dw m−2 of surface sediment was resuspended within the Trapa beds and 29,903 g dw m−2 in the pelagic zone. These equate to phosphorus fluxes of 7.4 g m−2 to the water column at the station with Trapa and 16.1 g m−2 at the station without Trapa. Floating- leaved macrophytes, such as Trapa, may be important in sediment resuspension and internal phosphorus loading in shallow lakes.

Does stocking of filter-feeding fish for production have a cascading effect on zooplankton and ecological state? A study of fourteen (sub)tropical Chinese reservoirs with contrasting nutrient concentrations

Stocking of filter-feeding fish is a common tool used in Chinese reservoirs to increase fish production because of low natural recruitment. Whether such stocking has important negative effects on zooplankton with cascading effects on phytoplankton is debated. We compared the zooplankton communities in fourteen reservoirs with different nutrient concentrations and fish densities. Both chlorophyll a (Chla) and fish catch were positively related with total phosphorus (TP), whereas zooplankton biomass did not show a similar relationship with TP. Zooplankton seemed to be influenced by fish as high fish catches coincided with a low proportion of calanoids of the total copepod biomass, a high proportion of rotifers of the total zooplankton biomass, a low zooplankton:phytoplankton biomass ratio, and the absence of Daphnia irrespective of TP concentration. Both zooplankton biomass and most of the zooplankton:phytoplankton biomass ratios were among the lowest reported in the literature for the nutrient range studied. Furthermore, the Chla:TP ratio was higher than what is typically observed in temperate lakes. We conclude that top-down control of zooplankton is of key importance in reservoirs in South China where frequent stocking of filter-feeding fish seems to contribute to poor water quality in the form of higher algal biomass and reduced clarity.

Pelagic flatworm predation on daphniids in a subtropical reservoir: different effects on Daphnia galeata and on Ceriodaphnia quadrangula

Following a reduction in fish populations in 2004–2005, a new, single annual pulse of pelagic flatworms was observed in early summer during 2006–2009 in Liuxihe, a freshwater reservoir in South China. As soon as these worms appear, Daphnia galeata retreats into dormancy, one month earlier (July) in the presence of flatworms than previously observed (August) with fish, while the population of the related Ceriodaphnia quadrangula tends to increase. We show, through in situ lake sampling, in large enclosures and by laboratory observations, that Ceriodaphnia, although perhaps competitively inferior in its ability to acquire algal food, has a higher tolerance to flatworm toxins. As a result, Ceriodaphnia manages to coexist with and proliferate in the presence of the flatworm. Observations in the laboratory suggest that flatworm population autoregulates by being sensitive to their own toxins and that Ceriodaphnia, even if prey to the worms, likely incurs more benefit than cost from their presence.

Why is Diaphanosoma (Crustacea: Ctenopoda) so common in the tropics? Influence of temperature and food on the population parameters of Diaphanosoma dubium, and a hypothesis on the nature of tropical cladocerans

Diaphanosoma dubium Manuilova from (sub)tropical South China, cultured in the laboratory at 23–29°C, did not show a shortening of its lifespan at increasing temperatures, although its postembryonic development shortened, while individual clutch sizes became bigger. The optimum temperature for the population performance of this species (measured as lifetime fecundity or intrinsic rate of increase) therefore lies above 29°C. Limited literature data suggest that in tropics-adapted species, the shortening of the lifespan with temperature, which follows a quadratic function, reverses at higher temperatures. Thus, the most general descriptor of the complete temperature-lifespan relationship might be a parabola. D. dubium did not show shorter lifespans when offered more food either, and again shared this characteristic with few other tropical cladocerans (and probably copepods as well) studied by other authors. Both properties combined might be typical of tropical species and offer them an advantage (a long, prolific life in warm water rich in algae) over temperate species (like Daphnia) that, if occurring in the tropics at all, live above their temperature optimum there.

Pyrrhosoma and its relatives: a phylogenetic study (Odonata: Zygoptera)

The placement and relationships of the red-and-black zygopteran Pyrrhosoma, currently considered to be part of the Teinobasinae, has long been uncertain. DNA fragments (COI and ITS) reveal that Pyrrhosoma s.s. is restricted to the West Palaearctic, with two morphologically distinct name-bearing clades (nymphula, elisabethae), and with a morphologically indistinct third clade in the Middle Atlas, Morocco, that might be close to the common ancestor of all three. Chromagrion, the closest relative of Pyrrhosoma, is found in North America, not in South Asia. Two isolated Chinese taxa (tinctipenne and latiloba) are morphologically similar to Pyrrhosoma, but their molecular distance is so large that a new genus, Huosoma, is required to accommodate them. Past climate change is suggested as the driver of the biogeography and evolution of this group of zygopterans. The origin of the Moroccan isolate and of elisabethae might predate the glaciations, and be of Pliocene age. The much wider disjunction between the American and South Asian groups and the western group suggests an older, perhaps Miocene age.

Annotated Checklist of Chinese Cladocera (Crustacea: Branchiopoda). Part I. Haplopoda, Ctenopoda, Onychopoda and Anomopoda (families Daphniidae, Moinidae, Bosminidae, Ilyocryptidae)

Approximately 199 cladoceran species, 5 marine and 194 freshwater and continental saltwater species, live in China. Of these, 89 species are discussed in this paper. They belong to the 4 cladoceran orders, 10 families and 23 genera. There are 2 species in Leptodoridae; 6 species in 4 genera and 3 families in order Onychopoda; 18 species in 7 genera and 2 families in order Ctenopoda; and 63 species in 11 genera and 4 families in non-Radopoda Anomopoda. Five species might be endemic of China and three of Asia. Many records are suspect at the species level, and numerous taxonomic problems remain to be settled.

A review of typhloplanid flatworm ecology, with emphasis on pelagic species

Abstract The study of microturbellaria is not popular, and hence, the taxonomy and ecology of these animals are poorly known. In temperate zone ponds and lakes, the number of species may be up to 50+ per water body. The Typhloplanidae, the subject of this review, live in the littoral–benthic zone, but pelagic occurrences have been accumulating since the first case was reported in 1952. Four species are currently known to be occasionally pelagic; all live in warm–temperate or tropical lakes. Typically, one species per lake is found, but in one lake in Brazil, 2 species co-occur. One of these feeds on the other and on zooplankton, with a preference for Cladocera. Flatworms seem to trade the littoral zone for the pelagic if predation pressure in the littoral exceeds that in the open water, and if the pelagic offers better food. Most Typhloplanidae feed on arthropods, often with a preference for cladocerans, and show parallels with the cladocerans and rotifers in that 2 types of eggs (subitaneous and resting) are produced. In some flatworms, however, resting egg formation does not require amphimixis. There is also great variation between species in both the number of clutches and their composition, and within species, latitudinal differences may be important. At the cold extreme, species produce only one clutch of resting eggs; at the tropical extreme, species produce many subitaneous clutches, although resting eggs continue to be produced as well. The factors driving the life cycles of the pelagic species are discussed and include familiar variables such as temperature (circulation patterns), food, and predation. Flatworms also produce mucus and toxins that add complexity to their ecology; toxins are used for catching prey, and possibly for defense against predators (but not fish). If they become too abundant for their food supply, flatworms also seem to switch to resting egg production or block reproduction.