Seasonal change in the structure of fig-wasp community and its implication for conservation

Figs (Moraceae) and their pollinating wasps (Agaonidae) constitute a famous reciprocal mutualism in which figs provide some female flowers for the development of fig wasp offspring while the fig wasps pollinate Fig flowers. However, figs also host many no

Structure of the phytoplankton community and its relationship to water quality in Donghu Lake, Wuhan, China

The phytoplankton community structure, in terms of species composition, total standing crop, and abundance of the dominant algal species, at four stations in Donghu Lake, Wuhan, China, was investigated monthly from January 1994 to December 1996. A total of 260 taxa was observed, of which Chlorophyta (106 taxa) contributed the highest portion of the total number of taxa, followed by Bacillariophyta (82 taxa) and Cyanophyta (32 taxa). The total standing crop measured by means of chlorophyll a content, cell density, and cell biovolume, as well as the abundance of the dominant species, declined in the order of Station I to Station IV. Seasonal changes of the standing crop varied greatly among the four stations. Although the cell density at the four stations showed a single peak within a year, the peak density varied from July to November, dependent on the sampling year and the station. For chlorophyll a content and cell biovolume, multiple peaks were observed at Stations I and II, but a single peak was found at Stations III and IV. The phytoplankton community structure indicated that the trophic status was the highest at Station I (most eutrophic), followed by Station II; Stations III and IV were the least trophic areas. The long-term changes in phytoplankton community structure further suggested that changes in phytoplankton community structure were correlated with water quality, and eutrophication of Donghu Lake had been aggravated since the 1950s.

Changes in the structure of a zooplankton community during a Ceratium (dinoflagellate) bloom in a eutrophic fishless pond

The community structure of zooplankton was studied in a eutrophic, fishless Japanese pond. The ecosystem was dominated by a dinoflagellate, Ceratium hirundinella, two filter-feeding cladocerans, Daphnia rosea and Ceriodaphnia reticulata, and an invertebrate predator, the dipteran Chaoborus flavicans. The midsummer zooplankton community showed a large change in species composition (the Daphnia population crashed) when a heavy Ceratium bloom occurred. It is shown that (i) the rapid density decline of D.rosea in mid-May was mainly caused by a shortage of edible phytoplankton, which was facilitated by the rapid increase in C.hirundinella abundance; (ii) the low density of D.rosea in June-July was considered to be mainly caused by the blooming of Ceratium hirundinella (which may inhibit the feeding process of D.rosea), while predation by C.flavicans larvae, the changing temperature, the interspecific competition and the scarcity of edible algae were not judged to be important; (iii) the high summer biomass of the planktonic C.flavicans larvae was maintained by the bloom of C.hirundinella, because >90% of the crop contents of C.flavicans larvae were C.hirundinella during this period. The present study indicates that the large-sized cells or colonies of phytoplankton are not only inedible by most cladocerans, but the selective effect of the blooming of these algae can also influence the composition and dominance of the zooplankton community, especially for the filter-feeding Cladocera, in a similar way as the selective predation by planktivorous fish. The large-sized phytoplankton can also be an important alternative food for ominivorous invertebrate predators such as Chaoborus larvae, and thus may affect the interactions between these predators and their zooplanktonic prey. In this way, such phytoplankton may play a very important role in regulating the dynamics of the aquatic food web, and become a driving force in shaping the community structure of zooplankton.

Soil microbial community analysis using terminal restriction fragment length polymorphisms

Terminal restriction fragment length polymorphism (T-RFLP) analysis is a polymerase chain reaction (PCR)-fingerprinting method that is commonly used for comparative microbial community analysis. The method can be used to analyze communities of bacteria, archaea, fungi, other phylogenetic groups or subgroups, as well as functional genes. The method is rapid, highly reproducible, and often yields a higher number of operational taxonomic units than other, commonly used PCR-fingerprinting methods. Sizing of terminal restriction fragments (T-RFs) can now be done using capillary sequencing technology allowing samples contained in 96- or 384-well plates to be sized in an overnight run. Many multivariate statistical approaches have been used to interpret and compare T-RFLP fingerprints derived from different communities. Detrended correspondence analysis and the additive main effects with multiplicative interaction model are particularly useful for revealing trends in T-RFLP data. Due to biases inherent in the method, linking the size of T-RFs derived from complex communities to existing sequence databases to infer their taxonomic position is not very robust. This approach has been used successfully, however, to identify and follow the dynamics of members within very simple or model communities. The T-RFLP approach has been used successfully to analyze the composition of microbial communities in soil, water, marine, and lacustrine sediments, biofilms, feces, in and on plant tissues, and in the digestive tracts of insects and mammals. The T-RFLP method is a user-friendly molecular approach to microbial community analysis that is adding significant information to studies of microbial populations in many environments.

Macrozoobenthic community of Poyang Lake, the largest freshwater lake of China, in the Yangtze floodplain

Poyang Lake (Poyang Hu) is located at the junction of the middle and lower reaches of the Yangtze (Changjiang) River, covering an area of 3283 km(2). As one of the few lakes that are still freely connected with the river, it plays an important role in the maintenance of the unique biota of the Yangtze floodplain ecosystem. To promote the conservation of Poyang Lake, an investigation of the macrobenthos in the lake itself and adjoining Yangtze mainstream was conducted in 1997-1999. Altogether 58 benthic taxa, including, 22 annelids, 8 mollusks, 26 arthropods, and 2 miscellaneous animals, were identified from quantitative samples. The benthic fauna shows a high diversity and a marine affinity. The standing crops of benthos in the lake were much higher than those in the river, being 659 individuals/m(2) and 187.3g/m(2) (wet mass) in the main lake, and 549 individuals/m(2) and 116.6 g/m(2) in the lake outlet, but only 129 individuals/m(2) and 0.4g/m(2) in the river. The dominant roup in the lake was Mollusca, comprising 63.4% of the total in density and 99.5% in biomass. An analysis of the functional feeding structure indicated that collector-filterers and scrapers were predominant in the lake, up to 42.2% and 24.7% in density and 70.2% and 29.2% in biomass, respectively, while shredders and collector-gatherers were relatively common in the river. The present study was restricted to the northern outlet and the northeast part of Poyang Lake. A scrutiny is required for the remaining areas.

Gastropods on submersed macrophytes in Yangtze lakes: Community characteristics and empirical modelling

Epiphytic gastropods in Yangtze lakes have suffered from large-scale declines of submersed macrophytes during past decades. To better understand what controls gastropod community, monthly investigations were carried out in four Yangtze lakes during December, 2001-March, 2003. Composed of 23 species belonging to Pulmonata and Prosobranchia, the community is characterized by the constitution of small individuals. The average density and biomass were 417 +/- 160 ind/m(2) and 18.05 +/- 7.43 g/m(2), with maxima a-round August. Submersed macrophyte biomass is shown to be the key factor affecting species number, density, and biomass of gastropods. Accordingly, a series of annual and seasonal models yielding high predictive powers were generated. Preference analyses demonstrated that pulmonates and prosobranchs with different respiratory organs prefer different macrophyte functional groups.

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.

Impact of eutrophication on biodiversity of the macrozoobenthos community in a Chinese shallow lake

Comparative studies on community structure and biodiversity of macrozoobenthos were carried out in three lake areas with different states of eutrophication (mesotrophic, eutrophic and hypereutrophic) in a shallow subtropic lake (Lake Donghu) in the middle basin of the Yangtze River of China. Thirty-three taxa (including six Mollusca, five Oligochaeta, 15 Chironomidae and seven other zoobenthos) were found during February 1998 to April 1999. The results show that the more eutrophic the lake water, the lower the macrozoobenthos species diversity (measured as species number, diversity index, and K-dominant curves). Abundance of the oligochaete Limnodrilus hoffmeisteri was positively correlated with the degree of eutrophication, which was due mainly to its ability to tolerate low dissolved oxygen. The chironomid Tanypus chinensis also thrived in the hypereutrophic environment; however, it was less endurable to eutrophication than L. hoffmeisteri.

Long-term changes of Copepoda community (1957-1996) in a subtropical Chinese lake stocked densely with planktivorous filter-feeding silver and bighead carp

In contrast to the relatively well documented impact of particulate-feeding fish on zooplankton communities, little attention has been devoted to the impact of filter-feeding fish. Filter-feeding silver and bighead carp are the most intensively cultured fish species in Asia and comprise much of the production of Chinese aquaculture. However, little information is known about the impact of either fish on the zooplankton community. Long-term changes in the Copepoda community (1957-1996) were studied at two sampling stations of a subtropical Chinese lake (Lake Donghu) dominated by silver and bighead carp. For both calanoids and cyclopoids, the littoral station (I) was much more resource profitable than the pelagic station (II). There has been a tremendous increase in the annual fish catch over the past 30 years due to the increased stocking with fingerlings of the two carp species. There was a notably higher fish density at Station I than at Station II. Cyclopoid abundance was notably higher at Station I than at Station II during the 1950s to the 1980s, while the reverse became true in the 1990s. This is probably because when fish abundance increased to an extremely high level, the impact of fish predation on the cyclopoids became more important than that of food resources at the littoral station. At both stations, cyclopoid abundance was relatively low in spite of the presence of abundant prey. Similarly, calanoid density did not differ significantly between the two stations in the 1950s and 1960s, but was significantly lower at Station I than at Station II during the 1980s and 1990s. Such changes are attributed to the gradient of fish predation between the stations and an increasing predation pressure by the fish. The increased fish predation also correlated with a shift in summer-dominant calanoids from larger species to smaller ones. In conclusion, the predaceous cyclopoids are affected by fish predation to a much lesser extent than the herbivorous calanoids, and therefore increased predation by filter-feeding fish results in a definite increase in the cyclopoid/calanoid ratio. Predation by filter-feeding fish has been a driving force in shaping the copepod community structure of Lake Donghu during the past decades.

Particle-attached and free-living bacterial communities in a contrasting marine environment: Victoria Harbor, Hong Kong

Diversity of particle-attached and free-living marine bacteria in Victoria Harbor, Hong Kong, and its adjacent coastal and estuarial environments was investigated using DNA fingerprinting and clone library analysis. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes showed that bacterial communities in three stations of Victoria Harbor were similar, but differed from those in adjacent coastal and estuarine stations. Particle-attached and free-living bacterial community composition differed in the Victoria Harbor area. DNA sequencing of 28 bands from DGGE gel showed Alphaproteobacteria was the most abundant group, followed by the Bacteroidetes, and other Proteobacteria. Bacterial species richness (number of DGGE bands) differed among stations and populations (particle-attached and free-living; bottom and surface). BIOENV analysis indicated that the concentrations of suspended solids were the major contributing parameter for the spatial variation of total bacterial community structure. Samples from representative stations were selected for clone library (548 clones) construction and their phylogenetic distributions were similar to those of sequences from DGGE. Approximately 80% of clones were affiliated to Proteobacteria, Bacteroidetes and Cyanobacteria. The possible influences of dynamic pollution and hydrological conditions in the Victoria Harbor area on the particle-attached and free-living bacterial community structures were discussed.

Particle-attached and free-living bacterial communities in a contrasting marine environment: Victoria Harbor, Hong Kong

Diversity of particle-attached and free-living marine bacteria in Victoria Harbor, Hong Kong, and its adjacent coastal and estuarial environments was investigated using DNA fingerprinting and clone library analysis. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes showed that bacterial communities in three stations of Victoria Harbor were similar, but differed from those in adjacent coastal and estuarine stations. Particle-attached and free-living bacterial community composition differed in the Victoria Harbor area. DNA sequencing of 28 bands from DGGE gel showed Alphaproteobacteria was the most abundant group, followed by the Bacteroidetes, and other Proteobacteria. Bacterial species richness (number of DGGE bands) differed among stations and populations (particle-attached and free-living; bottom and surface). BIOENV analysis indicated that the concentrations of suspended solids were the major contributing parameter for the spatial variation of total bacterial community structure. Samples from representative stations were selected for clone library (548 clones) construction and their phylogenetic distributions were similar to those of sequences from DGGE. Approximately 80% of clones were affiliated to Proteobacteria, Bacteroidetes and Cyanobacteria. The possible influences of dynamic pollution and hydrological conditions in the Victoria Harbor area on the particle-attached and free-living bacterial community structures were discussed.

Effects of increased pCO(2) and temperature on the North Atlantic spring bloom. I. The phytoplankton community and biogeochemical response

The North Atlantic spring bloom is one of the largest annual biological events in the ocean, and is characterized by dominance transitions from siliceous (diatoms) to calcareous (coccolithophores) algal groups. To study the effects of future global change on these phytoplankton and the biogeochemical cycles they mediate, a shipboard continuous culture experiment (Ecostat) was conducted in June 2005 during this transition period. Four treatments were examined: (1) 12 degrees C and 390 ppm CO2 (ambient control), (2) 12 degrees C and 690 ppm CO2 (high pCO(2)) (3) 16 degrees C and 390 ppm CO2 (high temperature), and (4) 16 degrees C and 690 ppm CO2 ('greenhouse'). Nutrient availability in all treatments was designed to reproduce the low silicate conditions typical of this late stage of the bloom. Both elevated pCO(2) and temperature resulted in changes in phytoplankton community structure. Increased temperature promoted whole community photosynthesis and particulate organic carbon (POC) production rates per unit chlorophyll a. Despite much higher coccolithophore abundance in the greenhouse treatment, particulate inorganic carbon production (calcification) was significantly decreased by the combination of increased pCO(2) and temperature. Our experiments suggest that future trends during the bloom could include greatly reduced export of calcium carbonate relative to POC, thus providing a potential negative feedback to atmospheric CO2 concentration. Other trends with potential climate feedback effects include decreased community biogenic silica to POC ratios at higher temperature. These shipboard experiments suggest the need to examine whether future pCO2 and temperature increases on longer decadal timescales will similarly alter the biological and biogeochemical dynamics of the North Atlantic spring bloom.

The environment effect on fish assemblage structure in waters adjacent to the Changjiang (Yangtze) River estuary (1998-2001)

We collected fish abundance data in the Changjiang (Yangtze River) estuary and adjacent waters in November 1998, May 1999, November 2000, and May 2001. Using the data, we evaluated the characteristics of the fish assemblages at each site and investigated the effect of several environmental factors. We used a multivariate analysis, including community ordination methods such as detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA), and two-way indicator species analysis (TWINSPAN). We analyzed the biological community structure and environmental factors to determine their spatial distributions, temporal dynamics, and seasonal variations. Among the fish species, five exceeded 5% of the total abundance: Harpodon nehereus (42.82%), Benthosema pterotum (13.85%), Setipinna taty (11.64%), Thryssa kammalensis (9.17%) and Apogonichthys lineatus (6.49%). These were separated into four ecological assemblages: hypsithermal-saline, hypsithermal-brackish, hypothermal-brackish, and hypothermal-saline. We evaluated the degree of influence of environmental factors on the fish community. Our analyses suggested that environmental factors including water depth, salinity, turbidity, transparency, nutrient, and suspended matter formed a synthetic spatial gradient between the coastal and pelagic areas. Ecological and environmental factors changed temporally from 1998 to 2001, and drove the fish community succession. The environmental factors driving the fish community structure included bottom temperature, water depth, bottom and surface pH, surface total phosphorous, and bottom dissolved oxygen. This investigation was completed before completion of the Three Gorges Dam; therefore the results of this study provide an important foundation for evaluating the influence of the human activities.

Evolution of nutrient structure and phytoplankton composition in the Jiaozhou Bay ecosystem

The inventories of nutrients in the surface water and large phytoplankton( > 69 pm) were analyzed from the data set of JERS ecological database about a typical coastal waters, the Jiaozhou Bay, China, from 1960s for N, P and from 1980s; for Si. By examining long-term changes of nutrient concentration, calculating stoichiometric balance, and comparing diatom composition, Si limitation of diatom production was found to be more possible. The possibility of Si limitation was from 37% in 1980s to 50% in 1990s. Jiaozhou Bay ecosystem is becoming serious eutrophication, with notable increase of NO2-N, NO3-N and NH4-N from 0.1417 mumol/L, 0.5414 mumol/L, 1.7222 mumol/L in 1960s to 0.9551 mumol/L, 3.001 mumol/L, 8.0359 mumol/L in late 1990s respectively and prominent decrease of Si from 4.2614 mumol/L in 1980s to 1.5861 mumol/L in late 1990s; the nutrient structure is controlled by nitrogen; the main limiting nutrient is probably silicon; because of the Si limitation the phytoplankton community structure has changed drastically.

Restructuring of a zooplankton community by perturbation from a wind-forced coastal jet

The impact of transient wind events on an established zooplankton community was observed during a, field survey in a, coastal region off northern Norway in May 2002. A transient wind event induced a coastal jet/filament intrusion of warm, saline water into our survey area where a semi-permanent eddy was present. There was an abrupt change in zooplankton community structure within 4-7 days of the wind event, with a change in the size structure, an increase in lower size classes less than 1 mm in equivalent spherical diameter (ESD) and a decrease in larger size classes greater than 1.5 mm in ESD. The slope of zooplankton biovolume spectra changed from -0.6 to -0.8, consistent with the size shifting towards smaller size classes. This study shows that even well established zooplankton communities are susceptible to restructuring during transient wind events, and in particular when wind forcing induces horizontal currents or filaments.