Community Structure Of Ichthyoplankton In Spring And Autumn And Its Relationship With Environmental Factors In The South Of Zhejiang Province Coastal Waters

Based on the data of the fish eggs and larvae surveys of 4 voyages in the south of Zhejiang Province coastal waters.Using ecological types,relative importance index,species replacement rate,resource density,species diversity,cluster analysis and canonical correspondence analysis(CCA)and other methods.The community structure characteristics and species diversity status of fish eggs and larvae in South Zhejiang coastal areas were analyzed,and the correlation between the spatial distribution of fish eggs,fish larvae and environmental factors was also discussed.The related research results are as following:1.Species composition and dominant species:A total of 72 species of fish eggs and larvae were captured in 4 voyages in South Zhejiang coastal areas,belonging to 32 families and 9 orders.There were 28 species of fish eggs and 48 species of fish larvae were captured.The identified species are of the Osteichthyes,the ecological type is mainly based on the bottom,warm water and warm temperature species.In spring,the dominant species of fish eggs is Liza haematocheilus,the dominant species of fish larvae is Chaeturichthys stigmatias,and the dominant species of fish larvae is Harpodon nehereus in antumn.The main economic species found in the area:Pampus argenteus,Trichiurus lepturus,Larimichthys polyactis,Larimichthys croceus,Nibea albiflora,Decapterus maruadsi,Sparus macrocephalus and Engraulis japonicus,indicating that the coastal waters of southern Zhejiang Province are still one of the major economic species spawning grounds and feeding grounds in the East China Sea.2.Main species distribution and taxa: The spatial distribution of resource density showed that in the spring,the fish eggs and larvae are mainly distributed in the coastal bay and estuary.In autumn,the fish eggs and larvae were mostly distributed in the lateral deepwater.Cluster analysis showed that in 2017 and 2018,48 stations can be divided into 4groups,while autumn can be divided into 3 groups.According to the NMDS ranking test,the stress index are less than 0.2,indicating that the sorting effect has certain credibility.The characteristic species in the group and the divergent species between the groups are mainly bottom fish.In spring,they were mainly Liza haematocheilus,Chaeturichthys stigiamats and Amblyhaetucrichthys hexanema.In autumn,they were mainly Harpodon nehereus and Stolephorus sp..3.Seasonal change of species diversity and its relationship with environmental factors:The species diversity index showed that the species diversity in spring is greater than in autumn,which is related to the survey season and sea area.In spring,most fish migrate to the coastal waters for reproduction and habitation.In autumn,the water temperature decreases and fish migrate to deep water area.Environmental factor analysis showed that the spatial distribution of fish eggs and larvae is greatly affected by water depth,temperature and salinity.This study showed that fish eggs and larvae in spring and autumn in the coastal waters of southern Zhejiang are mainly the bottom,low-quality forage fishes.The large and high-nutrient fish are seldom,which shows the fish community structure suffering serious damage.Therefore,reasonable protection,effective restoration,scientific conservation and management are the focus of the future development of Zhejiang fishery and even the national fishery.