The Juvenile Larval Community Diversity Of Spatial-Temporal Characteristic And Influence Factors In Anqing Section Of Changjiang

Anqing section of the lower reaches of the Yangtze river flows through anqing city,anhui province,from susong county to zongyang county,with a total length of 243km.The river section has many branches and sandbars,numerous small and medium-sized lakes along the river,wide river,gentle water flow,and rich organic matter and nutrient salts in the water.The ideal hydrological environment and abundant bait organisms in anqing river section breed a good habitat for fish.Historical data show that there are as many as 80 species of fish in anqing river section,including 50 species of economic fish.In recent years,with the rapid economic development,anqing river section,as an important comprehensive water transport hub and an important chemical city connecting the Yangtze river delta city,has gradually intensified human disturbance factors such as commercial shipping,industrial wastewater and overfishing,resulting in a sharp decline in fishery resources and an unoptimistic fishery ecological environment.In order to fully understand the status quo of fishery resources in anqing river section,this paper studied the clustering structure characteristics of fish larvae and juvenile fish,and carried out the investigation and monitoring of larvae and juvenile fish and related environmental factors from April to August for three consecutive years from 2016 to 2018.Through similarity degree,relative importance index,diversity characteristic value,multivariate analysis and redundancy analysis,this paper explores the species composition characteristics of larval and juvenile fish in anqing section,the influence of spatial and temporal changes of larval and juvenile fish abundance and environmental factors on the abundance change.The main research results are as follows:1.In the anqing section,from 2016 to 2018,there were a total of 49 species of fish,belonging to 7 orders and 11 families,of which cyprinidae fish species and catch tails accounted for the largest proportion.In 2016 and 2018,there were 49 species and 43species respectively.The catch tails were 92 473 and 1021371,respectively.Compared with historical data,the number of species decreased and the biomass of larvae and juveniles increased.At the same time,the 28-day data analysis in 2017 shows that the smaller frequency of larval and juvenile fish surveys will lead to great errors in species composition,biodiversity and resources.Therefore,it is necessary to cover the reproductive cycle of most fish for daily collection.In terms of spatial and temporal changes,the number of species was relatively abundant from may to July,and there was no significant change in space.In terms of ecological types and spawning types,the number of species and catch tails of the fish that produced drifting eggs and that of the fish that settled in the lake accounted for the largest proportion.There are 10 species,7 species and8 species in the dominant species in 2016-2018,among which there are 5 species,Hemiculter bleekeri,Hemiculter leucisculus,Pseudolaubuca engraulis,Pseudobrama simoni,Rhinogobius giurinus,respectively;common species There are 7 species in2016-2018,among which there are 3 species of common species,namely Xenocypris davidi,Culter alburnus,Hyporhamphus intermedius;Hemiculter bleekeri and Hemiculter leucisculus have always been the first and second in the dominant species.The Hemiculter bleekeri proportion of the years among the years was 44.53%,49.16%and 63.60%.In terms of the biodiversity level of the community structure of juvenile and juvenile fish,the shannann-wiener（H’）index,Margalef richness index(D_MG)and Pielou evenness index（E）in 2016 were the largest,which were 2.03,3.87 and 0.57 respectively,indicating that the biodiversity level in this year was the highest,and the Simpson dominance index（C）in2018 was the largest between years.The highest levels of diversity were seen in the last two months of June;Spatially,the shannann-wiener（H’）index,the Margalef richness index(D_MG)and the Pielou evenness index（E）on the south bank were the largest in each year,which were 2.05,3.49 and 0.62,respectively,indicating the highest level of biodiversity on the south bank.The Simpson dominance index（C）on the north bank was the largest in 2016 and 2018,which were 0.26 and 0.44.Cluster and MDS analysis was carried out on the monthly time period of 2016-2018.The results show that both 2016 and2018 are divided into two groups,which are the main contributing species that cause the difference between the two clusters,Pseudolaubuca engraulis,Xenocypris argentea in 2016,Pseudolaubuca engraulis,Xenocypris argentea and Coilia nasus in 2018 mainly due to the breeding strategy of some species and lay their eggs in a different way.2.In 2016,the average abundance amplitude was 37.48-1608.44ind./100m³,with an average value of 407.56±353.25ind./100m³.In 2017,the average abundance amplitude was 15.30-3742.12ind./100m³,with an average value of 830.58j±925.49ind./100m³.The average abundance amplitude in 2018 was 5.59-4920.63ind./100m³,and the average value was 853.14±801.11ind./100m³.The peak value appeared on June 6,and the lowest value was on April 27.The variation characteristics of abundance in space show that the peak of abundance in the south bank is 2963.37ind./100m³,2793.85ind./100m³ and 1558.91ind./100m,showing a decreasing trend year by year.The peak of the north shore abundance was 2770.22ind./100m³,9347.54ind./100m³ and14057.37ind./100m³,showing a sharp upward trend year by year.The middle river has been at a low level relative to the two sides.The high vegetation coverage on the north bank and the connection of the estuary of Anhui province have promoted the fish reproduction.3.The water flow and water level trends in 2016-2018 are consistent,and the water flow ranges from 34700-70700m³/s,28100-70200m³/s and 20400-49900m³/s,respectively.The peak value is 2018 compared to the previous two years.Lower;water temperature range is 18-30°C,19.03-26.17°C and 21-30.37°C,showing a steady rise;transparency in 2016 and 2018 range of 16-41.33cm,12.67-70cm,and water There was a significant negative correlation between flow rate and water level（P<0.05）;the other environmental factors had no obvious change rules.Redundancy analysis（RDA）showed that water flow,water level,water temperature,transparency,turbidity,dissolved oxygen high potassium acid index and pH,and seven hydrological environmental factors were all related to abundance changes of larvae and juveniles.Among them,water flow,water level,water temperature and transparency are the main environmental factors.For example,the drifting egg fish such as Coilia nasus,Parabramis pekinensis,Pseudolaubuca engraulis are positively correlated with water flow and water level;the water temperature is below 27°C.When the temperature rises,it can promote the increase of the abundance of most fish,such as“four major chinese carps”,Parabramis pekinensis and Coilia nasus;the effect of transparency on the abundance of juveniles is mostly indirect.Generally speaking,the increase in transparency will increase the Juvenile fish avoidance ability.