| The purple-back flying squid,Sthenoteuthis oualaniensis,is an important economic cephalopod resources widely distributed in the warm waters of the Indian Ocean and the Pacific Ocean,and is also the important resources of cephalopod fishery in the South China Sea.This important potential economic fishery has inadequately exploited.S.oualaniensis plays an important role in the marine ecosystem,which can connect the energy flow in the food chain in ecosystem.S.oualaniensis is an oceanic cephalopod with short life cycle,and its life history is easily affected by the changes of marine environmental factors and marine ecosystem.Therefore,full understanding of the relationship between fishery ecology of S.oualaniensis and climatic and marine environmental changes in the South China Sea will help enhance the understanding of resources,and provide a basis for scientific conservation and rational development of the resources.In this study,based on the ecological information of beaks,we analyzed the age and growth of S.oualaniensis in the South China Sea under different climate events during 2018-2020,and analyzed the key life history stage and migration routes of S.oualaniensis and their response mechanism to different climate events.The results of these study are as following:（1）The mechanism of body growth patterns in response to different climatic events in individuals of S oualaniensis in the South China Sea.In this study,growth characteristics of S.oualaniensis in the South China Sea were analyzed based on samples collected from August to November in 2018（El Nino period）,2019（normal period）and 2020（La Nina period）,to explore the differences in growth of S.oualaniensis under different climatic events and the response mechanism to changes in marine environment.The results indicated that there were significant differences in mantle length and body weight between different genders under different climatic events.The mantle length,body mass,the mantle length and the age at first maturity were the lowest in 2018,the highest in 2019,and the median in 2020.The results of mantle length-body weight growth models showed that samples in 2018 and 2019 showed positive tendency,while samples in 2020 showed negative tendency.Gradient forest model results showed that the growth rate of adults in 2018 had a strong threshold response to the depth of the mixed layer,the temperature of the 100-meter layer and the sea surface chlorophyll concentration;growth rate in 2019 strong threshold response to the sea surface salinity,sea surface chlorophyll concentration and temperature of the 50-meter layer;growth rate in 2020 strong threshold response to the sea surface chlorophyll concentration,temperature of the 50-meter layer and sea surface height.The results showed that the body size and first maturity characteristics of S.oualaniensis had a lag effect under different climatic events,which was mainly responded to sea water temperature changes experienced in the early life history stage.And adult growth rate and fatness were mainly responded to changes of temperature and food abundance in subadult-adult stage.（2）The mechanism of morphological growth patterns of beaks in response to different climatic events in individuals of S oualaniensis in the South China Sea.In this study,morphological growth patterns of beak of S.oualaniensis in the South China Sea were analyzed by geometric morphometric methods based on samples collected from August to November in 2018（El Nino period）,2019（normal period）and 2020（La Nina period）,to explore macroscopically the differences in morphological growth patterns of S.oualaniensis under different climatic events and the response mechanism to changes in marine environment.The centroid size can be as an indicator of external morphology of beak after standardization.The results indicated that effects of climatic events on the external morphology of beaks were mainly reflected in the upper beak tip,hood,lateral wall and wing.There were significant differences in the centroid size and pigmentation stages in beak.In 2018,beaks had the highest pigmentation stages and the largest centroid size,while it was intermediate in 2019 and it was the smallest in 2020.Multiple regression analysis showed that the growth patterns were positive allometry in 2018 and 2020.During El Nino period,the external morphology of beaks is suitable for catching fish,with good tearing ability and flexibility.During La Nina,the external morphology of beaks is suitable for hunting crustaceans,with good crushing and piercing ability.The results showed that the changes of external morphological and pigmentation stages of upper beak of S.oualaniensis were mainly responded to climatic events and seawater temperature in later life period.（3）The mechanism of growth patterns of later history stage in response to different climatic events in individuals of S oualaniensis in the South China Sea.In this study,daily increment of beak of S.oualaniensis in the South China Sea were analyzed based on samples collected from August to November in 2018（El Nino period）,2019（normal period）and 2020（La Nina period）,to explore microscopically the differences in late life period of S.oualaniensis under different climatic events and the response mechanism to changes in marine environment.The results showed that there were significant differences in the age distribution of S.oualaniensis and daily increment width of beak microstructure under climatic events.The dominant age in 2018 was the smallest,the largest in 2019,and the second in 2020.The groups belonged to the spring/summer hatching group.The daily increment width was the smallest in 2018,the middle in 2019,and the largest in 2019.With individual growth,the daily increment width of beak in later life period of S.oualaniensis gradually decreased.However,the daily increment width increased gradually with the increase of seawater temperature,showing a stable positive correlation.The results showed that the growth of beaks accelerated gradually with seawater warming and slowed down gradually with individual growth.The growth rate of beaks in El Nino period was slower than that in La Nina period.Sea water temperature was closely related to daily increment width of beak.The results showed that the growth patterns of beak microstructures in later life history stages of S.oualaniensis were mainly in response to changes of ocean temperature under different climatic events.（4）The mechanism of migrating routes in response to different climatic events in individuals of S oualaniensis in the South China Sea.In this study,trace elements of beak of S.oualaniensis in the South China Sea were analyzed based on samples collected from August to November in 2018（El Nino period）,2019（normal period）and 2020（La Nina period）,to explore differences of migration routes of S.oualaniensis under different climatic events and the response mechanism to changes in marine environment.The results showed that the migration routes of different genders were basically the same.There was no significant gender difference in concentration and species of element.There are some differences in ranking order of elemental concentrations under different climatic events,which may be related to the differences of marine environmental factors in different climatic events.The analysis showed that the relationship between Temp50 and Na/Ca,Mn/Ca,Zn/Ca and Sr/Ca could be used as an indicator to predict the potential migration routes.During La Nina,the potential spawning grounds of S.oualaniensis moved northward in search of lower water temperatures and abundant food.During El Nino,the potential spawning ground of S.oualaniensis moved southward in search of higher water temperature.Both of them migrated northward with counterclockwise circulation current driven by summer monsoon after hatching activity,and drifted to the Xisha Islands waters for feeding activity.The changes of potential spawning ground and feeding ground of S.oualaniensis under different climatic events were mainly in response to sea temperature changes。... |
PDF Full Text Request