Distribution Characteristics And The Effect Of Nursery Restoration Of Acanthopagrus Latus In Wanshan Islands

The Wanshan Islands waters are important traditional fishing grounds in China,and Acanthopagrus latus is an important economic species in the waters.With the rapid social and economic development in the Pearl River Delta region,the aggravation of human activities has led to the degradation of fishery habitats,the damage to spawning grounds,feeding grounds,wintering grounds,and migration channels,and the continued decline of fishery resources.The A.latus is one of the important proliferation and release species in the Wanshan Islands and adjacent waters.To find out the current situation of the fishery resources community structure in the Wanshan Islands,and to describe the feeding habits and habitat preferences of A.latus can provide information for the scientific conservation of fishery resources.Based on the survey data of trammel net and bottom trawls carried out in the waters of Wanshan Islands in spring（March-April）and autumn（September-October）in 2021,this paper analyzes the species composition,quantity distribution,community structure,seasonal differences and their correlations with environmental factors as well as the distribution characteristics of A.latus in the Wanshan Islands waters.The dietary composition of A.latus at each growth stage in different habitats was studied by using the observation method of stomach contents,eukaryotic biodiversity sequencing method and stable isotope method.It was preliminarily revealed that the mangrove habitat of Wanshan Islands was an important feeding place for A.latus.The main findings are as follows:（1）In the spring and autumn of 2021,334 species of fishery organisms were found in the waters of Wanshan Islands,belonging to 17 orders,91 families and 195 genera.The main dominant species in the community are 9 species,and A.latus is the common species in this water area（100≤IRI<1000）.The results of correlation study showed that temperature,salinity and nutrient concentration(PO₄^3--P、Si O₄^3--Si、NO₂^--N)were the main environmental factors affecting the fishery resource structure of Wanshan Islands.A.latus was mainly distributed in the waters of the north and south of Guishan Island and the northwest of Dong’ao Island,and the quantity and biomass in autumn were higher than those in spring.The average individual mass and body length of A.latus in the northwestern waters of Guishan Island were the largest,and the average body length in the southern waters of Dong’ao Island was the smallest.The average individual mass and body length in spring were larger than those in autumn.（2）Almost all of the individual body lengths in the Wanshan Islands waters were greater than 170 mm,and the dominant body length group was 180-200 mm,accounting for24.3%;the dominant body weight range was 150-250 g,accounting for 28.6%.Through gonad observation and analysis,the gonads in the spring samples were more mature and females were in the majority,while the sex ratio in autumn was close to 1:1.According to the analysis of stomach contents,A.latus was mainly crab,shrimp,shellfish and fish,and the feeding intensity in spring was much higher than that in autumn.Sequencing analysis of eukaryotic biodiversity showed that juvenile fish ingested plants more intensively than adults.The food composition includes 10 phyla,of which Chordata and Streptophyta are the dominant phyla.Contains 25 genera,Brachidontes,Centropages and Hordeum have the highest relative abundance.Contains 52 species,the most important animal and plant food components are Xenophthalmus pinnotheroides and Hordeum jubatum.The main food components of A.latus in the reef area of Wanshan Islands are shrimps,crabs,algae,copepods and sea anemones.（3）Based on the stable isotope method,the study on the dietary characteristics of A.latus in the mangrove habitat in the waters of Qi’ao Island showed that the mangrove environmental conditions were more suitable for the development of most fish eggs and larvae.Carbon and nitrogen stable isotope analysis showed that the food sources of A.latus were different in contrasting reef areas and mangrove areas.The main food groups in mangrove habitats are crabs,shrimps,and fish in descending order of importance.The contribution rate was followed by Pseudogobius javanicus,Collichthys lucidus,and Charybdis hongkongensis.The main food groups in the reef habitat are fish,crabs,echinoderms etc,in descending order of importance.Contribution rates were followed by Pennahia anea,Mugil cephalus and Microcanthus strigatus.All in all,the temporal and spatial changes of the fishery resource community structure in the Wanshan Islands are closely related to environmental factors such as temperature,salinity and nutrient concentration(PO₄^3--P、Si O₄^3--Si、NO₂^--N).The feeding habits of A.latus will change with the growth process,the juveniles are partial to herbivorous,and the adults are typical omnivorous fish.The mangrove habitat of Qi’ao Island in the northern Wanshan Islands can provide enough food for juvenile A.latus.