A comparison of zooplankton assemblages in Nansi Lake and Hongze Lake,potential influences of the East Route of the South-to-North Water Transfer Project,China

Nansi Lake and Hongze Lake are both water storage lakes along the East Route of the South-to-North Water Transfer project(ESNT).Frequent changes in hydrologic properties are responsible factors for controlling the zooplankton community assemblages in both lakes,so we studied the possible influence of water transfer and environmental factors on zooplankton community structure and abundance.Zooplankton assemblages were investigated seasonally for one year in both lakes;a total of 133 and 122 zooplankton taxa were identified in Nansi Lake and Hongze Lake,respectively.The most dominant rotifer species were littoral,e.g.,Keratella tecta,Keratella valga and Lecane lunaris in Nansi Lake and Brachionus angularis,Brachionus forficula and Polyarthra vulgaris in Hongze Lake.Comparatively,Nansi Lake had a higher Shannon-Wiener diversity index value(5.13),while Hongze Lake had a higher species richness index(4.21).The average number of zooplankton across seasons in Nansi Lake(protozoa:774±63 ind./L,rotifers:4817±212 ind./L,cladocerans:896±14 ind./L,copepod:435±42 ind./L)was comparatively lower than Hongze Lake(protozoa:1238±63 ind./L,rotifers:6576±112 ind./L,cladocerans:1013±20 ind./L,copepod:534±25 ind./L).Canonical correspondence analysis identified differing environmental gradients that were most responsible for influencing zooplankton communities in the two lakes(Hongze Lake:NH4-N,total nitrogen,transparency and pH;Nansi:pH,temperature and total phosphorus).Frequent changes related to water transfer in lakes favoured the diversity of rotifers and protozoa communities.Zooplankton habitat preference,changes in community structure and opportunistic peaks and extinction of certain taxa were also observed in the study lakes.

Water transfer determines the regional spread dynamics of non-native fish species

Interbasin water transfer projects(IBWT's)have emerged as dispersal corridors for aquatic species.However,little is known about how water transfer affects regional spread dynamics,or shapes the genetic diversity patterns of non-native populations.Shimofuri Goby Tridentiger bifasciatus is a globally introduced fish species with many wellestablished populations in IBWT's.Here,we used nuclear microsatellites to assess the genetic diversity and population structure of the Shimofuri Goby in its native and introduced sites belonging to two IBWT's in China.Our objectives were to(1)reveal the genetic diversity patterns of the Shimofuri Goby during regional spread,and(2)identify its mode of spreading in water transfer systems.We observed(1)a high level of genetic diversity in non-native populations without evidence of bottleneck effects,(2)that non-native populations with a longer water transfer times had a higher private allele richness,and(3)that non-native populations showed a highly mixed genetic structure,low level of genetic differentiation,and no significant relationship between geographical and genetic distances.Our results indicate that the genetic patterns of diversity of non-native populations are mainly shaped by a linear cascade spread processes due to long-distance movement of larvae,and are probably related to propagule pressure caused by the construction of water transfer.To manage the non-native populations of T.bifasciatus,preventive actions and physical removal should be implemented in IBWT's.

Fish diversity reduction and assemblage structure homogenization in lakes:A case study on unselective fishing in China

Unselective fishing involves activities that target the entire assemblage rather than specific fish species,size classes,or trophic levels.This common fishing approach has been in practice for decades in inland waters in China but its implications for biodiversity remain unclear.We addressed this issue by studying fish assemblages in freshwater lakes(five fishing lakes,one reference lake,and a total of 51 sampling sites)between pre-and postfishing time-periods in Eastern China during 2017–2019.The effects of lake,fishing period,and their interactions on fish abundance,biomass,and diversity indices were assessed.Multivariate analysis was conducted to test for differences in fish assemblages among lakes and between fishing periods.After the implementation of fishing activities,significant reductions in fish species richness,abundance,biomass,and all three life-history strategies(opportunistic,equilibrium,and periodic)were observed in fishing lakes,whereas opposite trends were observed in the reference lake.Compositional similarity of fish assemblages among fishing lakes increased over the threeyear monitoring period.Our results suggest that unselective fishing reduces fish diversity and homogenizes fish assemblage structure in lakes.These findings have important implications for protecting both biodiversity and fisheries in inland waters in China and are applicable to other countries or regions that rely on fish as a major food source.