基于多组织稳定同位素比值的热带大西洋4种鲨鱼营养生态位分化

Trophic niche partitioning of four pelagic shark species in the tropical Atlantic based on multi-tissue stable isotopes ratios

不同代谢速率组织间的碳、氮稳定同位素比值(δ^(13)C和δ^(15)N)可以反映生物不同时间尺度的摄食信息,对探讨物种间摄食、栖息地利用和营养生态位的变化具有重要的指示作用。本研究以在大西洋热带海域兼捕的大青鲨、长鳍鲭鲨、拟锥齿鲨和尖吻鲭鲨为对象,通过测定其肌肉、肝脏和血液的δ^(13)C和δ^(15)N值,探讨4种鲨鱼营养生态位分化。结果表明:与长鳍鲭鲨相比,尖吻鲭鲨、拟锥齿鲨和大青鲨的δ^(15)N值相似且相对较高;大青鲨与其他鲨鱼存在摄食隔离,表现出独特的营养生态位;尖吻鲭鲨营养生态位宽幅最大,摄食食物种类和(或)栖息环境类型更多样化,其与拟锥齿鲨的营养生态位重叠度最高,说明两种鲨鱼具有潜在的资源竞争关系。尖吻鲭鲨、拟锥齿鲨和大青鲨组织间的δ^(13)C、δ^(15)N差值与其叉长均无显著相关关系,说明3种鲨鱼近期内无明显摄食变化;而长鳍鲭鲨的肝脏、血液和肌肉组织的δ^(15)N差值与叉长显著相关,说明长鳍鲭鲨在短期内存在摄食变化。肝脏和血液的δ^(13)C、δ^(15)N值的相似性反映了两种组织整合摄食时间周期相近,其较高的代谢速率可以反映相对短时间周期的摄食信息。

Stable carbon and nitrogen isotope ratios(δ^(13)C andδ^(15)N,respectively)of multiple tissues with different turnover rates can provide trophic information at different timescales,and thus play an important role in tracing the changes of feeding,habitat utilization and trophic niche of consumers.Theδ^(13)C andδ^(15)N contents of muscle,liver and blood of blue sharks(Prionace glauca),longfin mako sharks(Isurus paucus),crocodile sharks(Pseudocarcharias kamoharai)and shortfin mako sharks(I.oxyrinchus)from tropical Atlantic were measured,and the trophic niche was evalua-ted.The results showed that I.oxyrinchus,P.kamoharai,and P.glauca had similarδ^(15)N values,higher than that of I.paucus.Feeding segregation was found between P.glauca and other species,showing unique trophic niche.The largest trophic niche width was observed in I.oxyrinchus,indicating the high diversity of prey and(or)feeding habitats.High trophic niche overlap was found in P.kamoharai and I.oxyrinchus,implying their potential competition for resources.There was no correlation between the differences among tissues in theδ^(13)C orδ^(15)N values and the body size of I.oxyrinchus,P.kamoharai and P.glauca,indicating no recent diet shifts for those species.I.paucus showed significant correlation betweenδ^(15)N differences in liver,blood and muscle with the shark fork length,indicating its short-term diet shift.The similarity ofδ^(13)C andδ^(15)N values and the higher metabolic rates of liver and blood were found in all four shark species,implying the similar incorporation rates of both tissues,which were considered as the short-term indicator of diet.