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Living coccolithophores(LC) are important in marine ecology,biogeochemistry,and especially the carbon cycle.Our chief aim in investigating the geographic distribution of LCs has been to provide data to help understand their roles.We investigated LCs in the East China Sea(ECS) from 7 October to 5 November 2010.Seawater samples from CTD arrays were filtered through 25 mm cellulose mixed-ester membrane filters on board as soon as possible,and dried.Then a piece of the membrane was cut out and,using neutral balsam,mounted beneath a cover glass.The samples were observed with a polarizing microscope at 1000× magnification.Twenty-six taxa were identified at different depths from 108 samples in ECS,the dominant species being Emiliana huxleyi,Gephyrocapsa oceanica,Helicosphaera carteri and Algirosphaera robusta.The abundance of coccoliths and cells ranged from 0—76 cells/mL and 0—4500 coccoliths/mL,the average being 18 cells/mL,613 coccoliths/mL,respectively.The distributed pattern of LCs and coccoliths in surface and bottom layers were patchy.The outer areas of the sea basin had more species but showed less abundance than the inner area.The highest abundance was found at a station supporting a diatom bloom.We further observed the distribution of: total coccoliths;total cells;coccoliths and cells of E.huxleyi and G.oceanica;and compared these distributions among PN sections(PNs,starts from the Changjiang River estuary(121.5°E,31.5°N) to the south-east corner of Ryukyu(128.23°E,27.45°N)),Coastal Current sections(CCs) and the Kuroshio Current sections(KCs).PNs supoorted the highest abundance except for the cells of E.huxleyi.The distributions of coccoliths and cells between CCs and KCs(except in the bottom-most layer) showed slightly higher abundances in deep than in surface water.At the KC stations,however,coccolithophorids thrived between 25m and 80m.Our observations suggest that water-column mixing,sediment resuspension and nitrate concentration affect the distribution patterns of both species numbers and individual species. more...

Totally 284 phytoplankton water samples were collected in a multidisciplinary investigation in East China Sea(24°00′—32°00′N,120°00′—128°00′E) from December 23th 2009 to January 5th 2010.Phytoplankton species composition and assemblage structure were studied by Utermhl method.A total of 171 taxa which belong to 67 genera of 4 phyla were identified.The phytoplankton community was mainly composed of Bacillariophyta and Dinophyta,and there were also a few species belonging to Cyanophyta and Chrysophyta.Most of the ecotypes of phytoplankton were temperate coastal species,and dominant species were Paralia sulcata,Thalassionema nitzschioides,Pseudo-nitzschia delicatissima,Thalassiosira angulata and Thalassiosira subtilis etc.Cell abundance ranged from 0.356×103 to 142.578×103cells/L with an average of 14.137×103cells/L,of which Bacillariophyta was the major group ranging from 0.356×103 to 142.578×103cells/L with an average of 13.023×103cells/L,followed by Dinophyta,ranging from 0.356×103 to 11.378×103cells/L with an average of 1.177×103cells/L.Horizontally,the surface distribution of cell abundance in survey area was mainly dominated by Bacillariophyta and the high value appeared in the sea northeast of Changjiang estuary.Dinophyta mostly concentrated in the southern and southeast part of the survey area where Kuroshio water flowed by.Vertically,the maximum of cell abundance was found in subsurface water,and along with the increase of the depth cell abundance firstly increased then decreased.According to the Pearson correlation analysis,the distribution of phytoplankton cell abundance was positively correlated with phosphate and silicata,negatively correlated with temperature,and nitrate′s effect on cell abundance wasn′t obvious. more...

In consideration of the close relationship of the clearance rate to the growth and development of filter-feeding mollusks,the joint effects of temperature(18—34℃),salinity(20—40) and pH(6.5—9.5) on the clearance rate(CR) of the juveniles of Pinctada martensii was studied using the Box-Behnken experimental design and response surface method under laboratory conditions,aimed at quantifying the relationship between the clearance rate and the above three factors,and obtaining the optimal factor combination through statistical optimization approach.The results showed that the liner effect of temperature,the interaction effects between temperature and pH,and between salinity and pH,the quadratic effects of temperature,salinity and pH on the clearance rate of juveniles of P.martensii were highly significant(P0.01).The liner effects of salinity and pH,the interaction effect between temperature and salinity were not significant(P0.05).The clearance rate model was derived,with the R2 being 0.9950.The Predictive R2 for the model reached 0.9284,showing that it could be employed to forecast the CR of the juveniles of P.martensii.The optimization results of the response surface showed that the optimal factor combination was 26.95℃/29.69/8.09,at which the maximum clearance rate,1.4894×10-3L/h,was arrived,with the desirability of 0.9886. more...

Benthic macroinvertebrate Index of Biological Integrity(B-IBI) was developed of relationships among habitat variables,water quality variables and benthic macroinvertebrate data from 340 sampling sites in the Huntai River for assessment of stream health and standardized reference and impaired sites selection.In this study,9 reference sites and 6 impaired sites were selected to construct the B-IBI index.Five major benthic macroinvertebrate metric parameters(i.e.taxonomic composition,relative abundance,pollution tolerance characteristics,dominant groups,and functional feeding groups) were assessed by applying the B-IBI.The results showed that the Huntai River is highly degraded and loss of biological integrity in which 24.8% of sampling sites were in "excellent" and "good" conditions,27.8% of sampling sites were in "normal" conditions,and 47.4% of sampling sites were in "poor" or "very poor" conditions.The box-plot distributions of B-IBI were highly clustered within the references sites,impaired sites and test sites indicated that the assessment was reliable.Moreover,the resulting B-IBI was highly correlated with the data set of macroinverterbates across 70 sampling sites in the Taizi River in May 2009,with 58% of the total sampling sites graded in the same stream health categories and 40.6% of total sampling sites with one grade difference in stream health.This correlation was employed to check the accuracy of the assessment result between standardized sites selection and "expert option" reference sites selection and showed strong consistency between two methods.The regression between the B-IBI and habitat assessment was significant in linear regression(R2=0.25,P0.01).And the regressions between the B-IBI and conductivity(Cond.),permanganate index(CODMn) and ammonia(NH3-N) were also significant in curved regressions(R2=0.23—0.34,P0.01).According to the regressions,the inflexion values of three water quality variables were around 1,000 μs/cm(Cond.),5.0mg/L(CODMn) and 1.0mg/L(NH3-N),respectively.The B-IBI decrease sharply when these water quality variables are lower than the inflexion value and decrease minimally when the concentration is higher than the inflexion value.The CODMn and NH3-N would have significant effect on the stream health and macroinvertebrates communities when the concentration is higher than the III grade of Chinese surface water standards.The sensitivity of the B-IBI and its component metrics to environmental stressors supports the use of this index for monitoring ecological conditions in streams in the Huntai River. more...

Fire disturbance is one of the key processes affecting forest succession in boreal forest ecosystems.Variations in disturbance characteristics have an important effect on ecosystem properties and processes.Due to the diversity of topography,fuel heterogeneity and micro-climatic conditions during a fire,the intensity of fires is quite variable,producing landscapes in different mosaic patterns.Although the resulting heterogeneity of fire characteristics(e.g.,burn severity) has been widely recognized as an important driver of boreal forest regeneration,its effects on early post-fire tree recruitment has not been thoroughly studied in boreal forests of the Great Xing′an Mountains.Early post-fire tree recruitment can reflect future forest structures and succession pathways.A clear understanding of the controls and mechanisms of post-fire tree recruitment is therefore necessary for us to predict future forest dynamics,devise reasonable forest management practices,and properly maintain natural landscape structures. In addition to fire characteristics,environmental conditions and pre-fire vegetation can also have important effects on post-fire tree recruitment.Environmental conditions such as elevation,slope,aspect,soil can affect post-fire seed germination.Pre-fire vegetation can affect seed banks and the distribution of post-fire seed sources.Post-fire tree recruitment in boreal forest ecosystems,as a whole,is influenced by multiple factors,including elevation,slope,aspect,soil depth,pre-fire forest type,pre-fire stand age,burn severity,and burned patch size.The objective of this study is to discover which factors are the most important controls on post-fire conifer and broadleaf tree recruitment and to predict what succession pathways will take place. We selected Huzhong and Xinlin Forestry Bureaus as study area to carry out field survey.The forest type of the study area is typical in Great Xing′an Mountains with major tree species being white birch(Betula platyghylla) and Dahuirian larch(Larix gmelini).Post-fire forest succession in this study area can be divided into two pathways,which are self-replacement(i.e.,the composition of immediately re-established post-fire tree species is the same as pre-fire canopy dominated ones,and continues as canopy dominant) and relay succession(i.e.,different tree species successively assume post-fire canopy dominance,which is firstly dominated with early-successional tree species and gradually by late successional ones).This study analyzed relative influences of various controls(environmental conditions,pre-fire vegetation,and fire disturbance characteristics) on post-fire tree recruitment and their marginal effects using a boosted regression tree method and data collected from 55 recently burned sites.Our results showed that 1) elevation was the most important factor for conifer tree recruitment;2) slope was the most important factor for broadleaf tree recruitment;3) time-since-last-fire was the most important control of the post-fire conifer seedling proportion,and forest type was the second;4) Post-fire conifer seedling proportion was higher in plots with conifer forest as pre-fire forest type than that with mixed or broadleaf forest;5) conifer tree regeneration after intermediate-severity fires was better than that after low-and high-severity fires.Our study suggested that self-replacement often occurred in the sites with single-species forest as the pre-fire forest type;while relay succession often occurred in the sites with mixed forest. more...

A metapopulation describes a system of many small and extinction-prone fragmented local populations that are connected via migration.Spatial synchrony of oscillating populations has been observed in many ecological systems,and identifying its causes has attracted the interest of ecologists.Theory has shown that spatially autocorrelated environmental noise,dispersal,and trophic interactions are capable of producing spatial synchrony.Synchrony of a metapopulation has been shown to be detrimental to its persistence because all local populations may go extinct simultaneously. Allee effects at the local population level and Allee-like effects at the metapopulation level are important topics in ecology and conservation.Allee effects result in the existence of a threshold density below which the population goes extinct.At low density,fecundity may decrease while mortality may increase because of a range of factors including difficulties in finding mates,social dysfunction and inbreeding depression.These demographic changes lead to negative population growth rates and ultimately extinction.Many studies have demonstrated the potential importance of Allee effects for the dynamics of small populations,range expansion,community composition and biological invasion.It is widely accepted that Allee effects may increase the extinction risk of low density populations.However,insufficient attention has been paid to the relationship between metapopulation synchrony and Allee effects within local populations.By incorporating detailed information on dispersal strategy in a heterogeneous landscape,we were able to address the following questions:(1) how do Allee effects affect the synchrony of metapopulations?(2) Does the impact of the Allee effect depend on the dispersal strategy? In this paper,we begin by assuming that local populations experience Allee effects and construct a coupled map lattice model of connected local populations,i.e.a metapopulation model.A stability criterion for synchrony involving the Lyapunov number of the local population system,the frequency of dispersal and the network configuration matrix was obtained by Earn et al.We extend these ideas to the situation of a metapopulation comprising local populations subject to Allee effects.Using analysis and simulations,the results suggest that when the intensity of the Allee effect on local populations is strong,the metapopulation goes extinct;(2) when the intensity of the Allee effect on local populations is relatively weak,the local populations fluctuate in synchrony.In this latter case,the metapopulation persists,but the synchronous fluctuations of the local populations cause it to be more susceptible to environmental and demographic stochasticity,which increases metapopulation extinction risk;(3) the connectivity of the network has an important effect on metapopulation synchrony,and fragmented habitat is beneficial for metapopulation survival.Global migration combined with Allee effects increases the possibility of synchronous oscillation,and therefore enhances extinction risk of the metapopulation.As a result,when local populations are subject to Allee effects,the metapopulation quickly goes extinct or has a relatively high extinction risk.Allee effects have a deleterious effect on metapopulation persistence.These results may play an important role in understanding the mechanism underlying population synchrony as well as in developing conservation management plans and controlling the abundance of pest species. more...