| Rotifera, as a Phylum of primary freshwater Metazoa with small body size, isdistributed widely in natural water bodies. Rotifers have great advantages in thestudies on the relationship between aquatic organisms and environment, and betweencommunity structure and level of lake eutrophication. Up to now, the view of relativeimportance of the roles of water temperature, N and P concentrations, and the effectsof ‘bottom-up’ and ‘top-down’ in regulating the spatio-temporal dynamics of thecommunity structure and food guilds of rotifers has been debated. In order toinvestigate their relative importance in controlling rotifer community structure andeach food guild in subtropical shallow lakes, the rotifers in two subtropical lakes,Lake Jiuliantang and Lake Tingtang located in Wuhu city, Anhui province, werecollected once weekly from July2011to June2012. The relationships between theindex of community structure such as species diversity and eveness index and thedensity of each food guild in each lake, and the concentrations of N and P, as well asthe densities of potential competitors and predators of rotifers were analyzed,respectively. The main results were presented as following:1. A total of48rotifer species belonging to15families and21genera in LakeJiuliantang, and55rotifer species belonging to15families and24genera in LakeTingtang were identified, of which Synchaeta, Brachionus and Trichocerca accountedfor the most proportion of the rotifer species numbers in both lakes. The dominantspecies in density contained7species and4species in Lake Jiuliantang and LakeTingtang, respectively. Carlson trophic state index of Lake Jiuliantang and LakeTingtang was60.77and62.21, respectively, and both lakes could be characterized asslightly eutrophic. In all the environmental factors, only the annual averageconcentrations of TN and NO3-, and the annual average densities of the rotiferAsplanchna, the copepoda and its nauplius were significantly different between thetwo lakes (P<0.05).In Lake Jiuliantang, the densities of copepoda and its naupliuswere higher in July, August, early September, November2011and April2012than inthe other months (P<0.05). In Lake Tingtang, the densities of Asplanchna were higherin July, August, September, November2011and May2012than in the other months(P<0.05). The analysis of Pearson moment correlation showed the P concentration was negatively correlated with both the species diversity index and evenness index ofrotifer community in Lake Jiuliantang (P<0.05), whilst the N concentration waspositively correlated with the species diversity index of rotifer community in LakeTingtang (P<0.05). In addition, the mass ratio of TN:TP showed positive relationswith species diversity index in both lakes (P<0.05). All these findings suggested thatthe parameter of TN:TP (mass ratio) could be more suitable than single factor of N orP for reflecting the effects of N and P on the species diversity dynamics of the rotifercommunity structure. Canonical correspondence analysis (CCA) indicated that bothlakes exhibited a high degree similarity in rotifer communities and could be clusteredas ‘type I and II’ when the densities of potential predators of rotifers, such ascopepoda and its nauplius, and Asplanchna, were respectively high. The other rotifercommunities in both lakes were assembled together as ‘type III’. The spatio-temporaldynamics of rotifer community structure depended mainly on the effect of ‘top-down’when the density of potential predators of rotifers were high, and the effect of‘bottom-up’ were the most important factor in regulating the rotifer communitystructure when few potential predators of rotifers occurred in both slightly eutrophiclakes.2. Among all the major dominant rotifer species, Polyarthra trigla wasconsidered as the grasping species in both lakes. Both Brachionus angularis andAnuraeopsis fissa were recognized as the filer-feeding species, and Trichocercapusilla and Trichocerca rousseleti were regarded as suckers in Lake Jiuliantang.While in Lake Tingtang, Brachionus diversicornis, A. fissa and Filinia longiseta wereassembled together as filer-feeding species. Pearson correlation suggested that thedensity and the egg ratio of each rotifer guild in both lakes were not negativelycorrelated with the densities of potential competitors and predators of rotifers. In LakeJiuliantang, water temperature was positively associated with the density offiler-feeding species (including total density, and the densities of A. fissa and B.angularis), the density of grasping species (P. trigla) and the density of sucker species(T. pusilla). That positive correlations mentioned above also showed between watertemperature and both the density of filer-feeding species (including total density, B.diversicornis, A. fissa and F. longiseta and the density of grasping species (P. trigla).In both lakes, the total density of filer-feeding species was positively correlated withthe concentration of both chlorophyll-a (Chl-a) and Chl-a <25μm (i.e. thechlorophyll-a in the water filtered through a25μm net), respectively. Only in LakeTingtang with a higher concentration of N, the densities of total filer-feeding speciesand the filer-feeders of F. longiseta, and the grasping species of P. trigla were negatively associated with the concentrations of TN and NO3-, respectively. In bothlakes, the egg ratios of grasping species of P. trigla showed a reverse relation withwater temperature and the concentration of chlorophyll-a, while that correlation wasonly presented between water temperature and the egg ratios of filer-feeders of B.diversicornis and F. longiseta. All the findings indicated that water temperature andthe food resources might be the important factors controlling the density dynamics offiler-feeding and grasping rotifers in both lakes. The concentration of N had a greatereffect on the density dynamics of filer-feeding and grasping rotifers in Lake Tingtangwith a higher concentration of N than that in Lake Jiuliantang. |
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