The Study On Foraging Ecology Of Jumbo Squid(Dosidicus Gigas)in Equatorial Waters Of The Central Eastern Pacific Based On The Stable Isotopic Information In The Eye Lenses

Dosidicus gigas is one of the largest and most abundant species in the Ommatostrephes and one of the most important cephalopod resources in the world.As a pelagic cephalopod,the D.gigas plays an important role in the marine ecosystem of the Eastern Pacific Ocean.It is not only a greedy predator,but also a valuable source of prey.Although scholars at home and abroad have studied the feeding ecology of D.gigas to a certain extent,the research on the feeding ecology of D.gigas in the equatorial waters of the East Pacific is not systematic and comprehensive.As one of the hard tissues of the D.gigas,eye lenses have the advantages of large size,easy extraction,and corrosion resistance.Compared with existing research materials,continuous segments of eye lenses can better fit the life cycle of individuals,and further increase the resolution of individual feeding ecological information represented by the values of carbon and nitrogen of lenses fragments.The samples of D.gigas collected by Chinese jigging vessels in the equatorial waters of the eastern Pacific Ocean from 2017 to 2019 were used as research objects.According to the tissue turnover rate of soft tissues?ovary?and hard tissues?eye crystals?,combined with carbon and nitrogen isotope ratios to reveal the differences in feeding ecology and mother-offspring relationship between mother and offspring.Through the determination of carbon and nitrogen isotope ratios in successive segments of eye lenses,the use of Bayesian standard ellipse method and otolith age inversion to explore the feeding changes of different individuals.Samples of D.gigas in normal,El Ni?o and La Ni?a were collected,the carbon and nitrogen isotope ratios of the eye lenses were measured in three climate years.The general additive model,Bayesian standard ellipse method and other research methods were used to explore the response mechanism of the D.gigas feeding ecology in the equatorial waters of eastern Pacific to climate change.The findings are as follows:?1?Cross-generation trophic ecology of Dosidicus gigas revealed from isotopic signatures in eye lenses.In this research,the relationships and differences between?¹³C and?¹⁵N between the lens core,the lens periphery,and the ovarian tissue were analyzed in combining with the isotope fractionation rates of soft tissue?ovary?and hard tissue?lens core,lens peripheral?.Results showed that the?¹³C and?¹⁵N values for three tissues increased in the sequence lens core,lens periphery and ovary.However,paired sample t-test shows that there was no significant difference between?¹³C and?¹⁵N in lens core and lens periphery?P>0.05?,indicating that the insignificant difference between lens core and lens periphery may be caused by a change of?¹³C baseline in the equatorial waters of the central eastern Pacific.There were significant differences in?¹³C and?¹⁵N values between the lens periphery and ovary?P<0.05?,indicating different tissue turnover rates in the lens periphery and ovary.In addition,there was a significant difference in the?¹³C values between the lens core and ovary?P<0.05?,but there was no significant difference in?¹⁵N value?P>0.05?.The degree of fitting of the probability density distribution curves of?¹³C and?¹⁵N,and the SEAc between mother and offspring,indicate that the degree of mother-offspring relationship was lower and the mother and offspring of D.gigas in equatorial waters of the central eastern Pacific may live near the equator but spawn in different locations.?2?Study on the changes of feeding among individuals of D.gigas.In this research,28 samples of D.gigas from the equatorial waters of the Eastern Pacific Ocean were collected,and the corresponding eye lenses were removed.The eye lenses were stripped into continuous fragments and subjected to stable isotope determination.The results show that the largest changes in?¹³C and?¹⁵N values of the individual samples were2.1‰and 4.78‰,and the smallest changes were 0.27‰and 0.3‰,respectively.The maximum SEAc among individuals is 1.2‰²,and the minimum is 0.03‰².On the whole,the feeding level of D.gigas increases with the growth of individuals.In addition,the change of individual SEAc is small,which also reflects the phenomenon that the isotopic baselines of the equatorial waters of the eastern Pacific is low and the change is not obvious from side.GAM model results show that the average ln(?¹³C)value in eye lens has significant correlation with Lat and LD?R²=0.746?,the deviation interpretation rate is 85.3%,and the ln(?¹⁵N)value has a significant correlation with Lon,Lat,and LD?R²=0.760?,the deviation interpretation rate is 90%.According to analysis,space-time location and individual growth are potential factors that affect the values of?¹³C and?¹⁵N in tissues of D.gigas.?3?Study on the feeding changes individuals in different developmental stages of D.gigas.In this research,28 specimens of D.gigas from the equatorial waters of the Eastern Pacific Ocean were randomly selected.According to the method of dividing the D.gigas group,the samples of D.gigas in this study are divided into medium and small groups,the corresponding eye lens were stripped into continuous fragments,and the?¹³C and?¹⁵N values were measured.The results show that the SEAc between the medium and small groups are 2.82‰² and 4.23‰²,respectively,and the overlap area is1.40‰²,which is a moderate overlap,indicating that medium and small groups have similar trophic levels.However,SEAc results of individual developmental stages in different populations shows that the medium-sized group?3.19‰²,4.89‰²,3.95‰²,5.02‰²?had larger nutrient niche areas than the small group?2.29‰²,2.32‰²,3.38‰²,2.06‰²?in the embryo,paralarvae,juvenile and adult stages,indicating that the medium group is slightly higher than the small group.In addition,the isotopic overlap in the paralarvae and juvenile stages of the small group is 0.38,indicating that the small group had greatly changed in feeding species and habitats,the isotopic overlap in juvenile and adult stage is highly overlapped?0.76?,which indicates that small group in juvenile stage basically do not change their feeding targets and habitats substantially.The isotopic overlap between embryo and paralarvae stage is 0.59,which indicates that there is a slight change in the feeding species and habitat.The isotopic overlap between paralarvae and juvenile stage is 0.79 while the isotopic overlap between juvenile and adult stage is 0.76,indicating that juvenile and adult stage have similar trophic levels.In summary,the medium and small groups have basically stabilized specific food species and habitats during the juvenile stage.?4?Response of the feeding ecology of D.gigas to climate change.By collecting the samples of D.gigas from normal years?June-July 2017?,La Ni?a?December2017-February 2018?and El Ni?o?December 2018-January 2019?.The?¹³C and?¹⁵N values of different fragments of the eye lens in different climate years were measured.The effects of different climatic events on the feeding ecology of D.gigas were compared in order to explore the response mechanism of the foraging ecology of D.gigas to climate change.The results show that,in normal years,the?¹³C values has a significant positive correlation with the increase in LD?R²=0.190,P<0.05?,and the?¹⁵N values has no significant change with the increase in LD?R²=0.093,P>0.05?.At the year of La Ni?a,the values of?¹³C and?¹⁵N have a significant positive correlation with the increase of lens diameter?R²=0.467,P<0.01,R²=0.177,P<0.05?;the?¹³C value of El Ni?o has a significant positive correlation with the increase of LD?R²=0.511,P<0.01?,?¹⁵N values has no significant change with the increase of LD?R²=0.088,P>0.05?.The results of SEAc show that the SEAc?3.4‰²?in normal years was greater than the El Ni?o years?SEAc=0.86‰²?and La Ni?a years?SEAc=0.44‰²?.GAM model results show that the values of ln(?¹³C)in lens periphery has a positive correlation with Lon,SST and DSB,and the values of ln(?¹⁵N)has a positive correlation with Lon and SST.The results of the study indicate that,whether in normal or climatic years,the feeding level of D.gigas increases with the growth of individuals.Moreover,the occurrence of climatic events will shorten the range of waters inhabited by D.gigas,resulting in changes in?¹³C and?¹⁵N values in individual tissues.In addition,combined with GAM model analysis,we found that Lat and Lon,SST and DSB are also potential factors that affect the?¹³C and?¹⁵N values in individual tissues.