厄尔尼诺对柔鱼亚科近缘种茎柔鱼与鸢乌贼营养生态位的影响

Impact of El Niňo event on trophic niches of closely related Ommastrephinae species,Dosidicus gigas and Sthenoteuthis oualaniensis

为了解环境异常变化对大洋性柔鱼类动物的潜在影响及其适应机制,以同域分布的柔鱼亚科近缘种茎柔鱼(Dosidicus gigas)与鸢乌贼(Sthenoteuthis oualaniensis)为研究对象,利用稳定同位素技术分析两者的营养生态位,结合海表面温度和叶绿素浓度,探究正常气候和厄尔尼诺时期的环境变动对营养生态位的潜在影响及其种间差异。结果显示,茎柔鱼和鸢乌贼的δ13C值存在显著差异,说明二者食物来源存在差异。尽管本研究中茎柔鱼个体较大,但其δ15N值显著低于鸢乌贼,表明后者营养级较高。正常气候时期两个物种的营养生态位存在重叠,而在厄尔尼诺时期缩小且分离,说明厄尔尼诺现象可对二者的摄食和洄游产生差异化影响。研究结果可为理解大洋性头足类动物摄食策略对环境变动的适应机制及其营养生态位动态格局提供有益参考。

There are interspecific differences in the effects of environmental changes on marine organisms.In order to adapt to variability in environmental conditions,sympatric closely related species always form different feeding strategies.Such differences in diet should maximize the utilization of available resources and increase adaptation to changing environmental conditions.In this study,we focus on two closely related Ommastrephinae species,Dosidicus gigas and Sthenoteuthis oualaniensis.These commercially important mesopelagic cephalopods are highly abundant and endemic in waters of the equatorial eastern Pacific and play a key role in marine ecosystem.To investigate the potential impact of El Niňo event on these two squid species,we evaluated the trophic niche variations and overlap of D.gigas and S.oualaniensis from 2017 to 2019,during normal and El Niňo periods by using stable isotope analysis.Combined with sea surface temperature and chlorophyll-a concentration,we assessed the potential impact of environmental changes on trophic niches.Results showed significant variations in δ13C values of muscle tissues between these two species,indicating a difference in dietary sources.Although D.gigas had larger mantle length in this study,significantly lowerδ15N values were observed in D.gigas muscle tissues than that of S.oualaniensis,suggesting that S.oualaniensis had a higher trophic position.This phenomenon may be possibly due to D.gigas’s predation of smaller and/or less nutritious foods to reduce the interspecific competition.The trophic niches were overlapped during normal climatic periods,while they were separated and shrinked during the El Niňo period,indicating that El Niňo event might influence the feeding and migration behavior of both species,which was related to the increased sea surface temperature and the reduced primary productivity.In summary,this study provides a better understanding of temporal variation in the trophic ecology of sympatric D.gigas and S.oualaniensis from the equatorial eastern Pacific.Although further research is required,our results highlighted interspecific adaptation mechanisms in trophic patterns of closely related Ommastrephinae species to environmental changes.Dietary flexibility allows D.gigas and S.oualaniensis to occupy different trophic niches across changing oceanographic environments,suggesting the interspecific sensitivity and resilience to environmental impacts.These results emphasize the importance of intraspecific variation in trophic ecology of Ommastrephinae species before addressing policy and fishery management.