Analysis Of Changes In Fish Eggs And Larvae Community Structure And Spawning Ground Size In Xiangshan Bay

The bay provides climate,nutrition and sites for the survival of fish eggs and larvae.By understanding the trends in the community structure of fish eggs and larvae,we can understand the distribution characteristics of fish eggs and larvae in the sea within a certain spatial and temporal range,and the differences in the spatial and temporal distribution of fish eggs and larvae reflect the relationship between their own nutritional characteristics,reproductive and ecological habits and environmental conditions,so that we can predict the possible environmental problems in the future The spatial and temporal distribution of eggs and juveniles reflects the relationship between their nutritional characteristics,reproductive and ecological habits and environmental conditions,and thus predicts possible environmental problems in future development.In this study,we investigated the fish eggs and larvae in Xiangshan Bay for four seasons from 2021 to2022.The spatial distribution of species composition,resource density,dominant and important species,spatial ecological position and overlap of major larvae,community structure,species diversity characteristics and their relationship with environmental factors were also investigated.The geographically weighted regression(GWR)model was used to predict the effects of temperature increase on the distribution of fish spawning grounds in Xiangshan Bay in 2050 and 2100.The main research methods and conclusions are as follows.(1)A total of 40 species of fish eggs and larvae,belonging to 11 orders and 20families,were collected in four voyages from spring,summer,autumn and winter from2021 to 2022,and the fish composition as a whole showed a predominance of Perciformes and Herring.One species of sedentary species in winter,three species of sedentary species in spring,seven species of offshore species,two species of migratory species,seven species of sedentary species in summer,seven species of offshore species,and one species of rocky reef species,from the perspective of ecological types,the composition of fish eggs and larvae community in Xiangshan Bay is dominated by sedentary species and offshore species;one species of warm-temperate fish in winter,five species of warm-water fish in spring,seven species of warm-temperate fish,six species of warm-water fish in summer,and a total of nine species of warm-temperate fish,from the perspective of temperature-appropriate From the viewpoint of temperature-appropriate types,the sea area of Xiangshan Bay is influenced by the warm current of Taiwan,and the eggs and young fish are all warm and warm fish,and the number of warm species is smaller than the number of warm species.In winter,there was one species of demersal fish,six species of pelagic fish and six species of demersal fish in spring,four species of pelagic fish and11 species of demersal fish in summer.In autumn,no eggs and juveniles were collected.No eggs were collected in winter,and the average density of juvenile fish was 0.20ind./100 m~3.The average density of eggs in spring was 180.15 ind./100 m~3 and the average density of juvenile fish was 17.23 ind./100 m~3,and the average density of eggs in summer was 16.93 ind./100 m~3 and the average density of juvenile fish was 4.85ind./100 m~3.The species,number and average density of eggs and juveniles were higher in spring and summer than in other seasons,indicating that spring and summer are the main time for fish breeding in Xiangshan Bay.In February 2022(winter),the dominant species of juvenile fish were Mugilidae sp..In April 2022(spring),the dominant species of eggs were Eggs sp.1 and Engraulis japonicus,and the important species were Eggs sp.2,Konosirus punctatus,Ilisha elongata and Liza haematocheila.The dominant species of juvenile fish were Engraulis japonicus and Liza haematocheila,and the important species were Lateolabrax maculatus and Takifugu sp.In August 2022(summer),the dominant species of fish eggs were Cynoglossidae sp.and the important species were Sciaenidae sp.and Stolephorus sp.The dominant species of larvae were Stolephorus sp.and the important species were Omobranchus spp.and Ilisha elongata,respectively.The dominant and important species of fish eggs and larvae in Xiangshan Bay varied among seasons.The dominant and important species showed a predominance of small fishes such as anchovy and herring at the family classification level.This indicates that the traditional dominant species in the fish community in Xiangshan Port waters are gradually replaced by smaller,lower trophic level and lower economic value bait fish.There are differences in the width of the ecological niches of the major larvae in Xiangshan Bay,and competition exists among a few larvae in Xiangshan Bay waters.Cluster analysis of29 stations in spring and summer were 4 and 6 clusters,respectively.The main characteristic species and divergent species in spring were Engraulis japonicus,Ilisha elongata,Sciaenidae sp.,Eggs sp.1,Planiliza haematocheilus,Eggs sp.1 and Konosirus punctatus.The main characteristic species and divergent species in summer were Stolephorus sp.、Omobranchus spp.、Ilisha elongata、Cynoglossidae sp.、Sciaenidae sp.and Harpadon nehereus.The characteristic and divergent species in both seasons are mostly dominant and important,and most of the characteristic species within the group are also divergent between the groups.This is mainly due to the spatial variation in the number of species.The diversity indices(H’)in spring and summer were 1.546 and 0.951,respectively,indicating that the biodiversity in this area was low and seriously affected by external anthropogenic activities.(2)Winter temperature has a strong influence on the density of juvenile fish.Spring RDA ordination plots explained a total of 84.83%of the variation in egg and juvenile composition of fish.Temperature,chlorophyll a and water depth had greater effects on egg density in spring.Salinity and nitrite had a greater effect on juvenile fish density.The summer RDA ordination plot explained 46.21%of the variation in egg and juvenile fish composition.Temperature and dissolved oxygen had a greater effect on egg density,and transparency and p H had a greater effect on the density of juvenile fish.The correlation coefficients between the predicted spring and summer GWR model fish spawning density and the original fish spawning density were 0.744 and 0.741,respectively.It shows that the model is highly reliable and can be used to predict the distribution of major fish spawning grounds in Xiangshan Bay in the future.under the future increase in sea surface temperature,the area of spring fish spawning grounds in Xiangshan Bay increased by116.00%and 113.00%in 2050 and 2100,respectively.The location of the main spawning grounds is concentrated in the area from the top of the bay to the middle of the bay.The area of summer fish spawning grounds shrinks to 87.50%in both 2050 and 2100.The location of the main spawning grounds is concentrated in the section from the middle of the bay to the bay.As a whole,there is a trend of decreasing fish spawning ground area and fish egg density in Xiangshan Bay from 2050 to 2100.