We measured stable carbon and nitrogen isotopes and calculated trophic level and trophic niche of Trichiurus japonicus, with samples collected from the Beibu Gulf from 2008 to 2009 and 2018. The differences between two periods were compared and analyzed to explore the changes of its ecological adaptation. The results showed that value of δ13C varied substantially between the two periods. The narrowed range and the smaller mean value of δ13C in 2018 suggested that their food source changed from upper-middle to lower-middle waters. The values of δ15N were stable, and the range and mean values of trophic level (3.38-3.43) did not change significantly, which indicated a stable trophic level of T. japonicas in the past decade. The correlation between δ13C and preanal length was not significant, but a positive correlation between δ15N and preanal length. In terms of trophic niche, the indicators had decreased in different degrees in 2018 with 1.1%-32.1%. The value of total area and standard ellipse area decreased from 20.20 and 4.68 to 14.20 and 3.18, respectively, indicating that the niches of T. japonicas in the Beibu Gulf had varied obviously and that their ability to use resources and adapt to the environment had declined. It was speculated that in the past decade, the mean trophic level of T. japonicas in the Beibu Gulf had not changed significantly. Due to the change of food sources, however, the diversity of trophic sources had decreased, and the trophic niche had become smaller.
基于2008—2009年和2018年对北部湾日本带鱼的采样,通过测定碳氮稳定同位素,计算其营养级、营养生态位等指标,对比分析10年前后日本带鱼营养生态位的差异,探究其生态适应能力的变动。结果表明: 2个时期北部湾日本带鱼碳稳定同位素(δ13C)值差异明显,2018年δ13C值范围变窄,平均值变小,推测日本带鱼食物来源由偏中上层向偏中下层水域转变;氮稳定同位素(δ15N)值的范围和平均值基本保持不变,营养级范围和平均值(3.38和3.43)变化不明显,说明近10年来北部湾日本带鱼在生态系统中的营养层次比较稳定。日本带鱼δ13C值与肛长相关性不显著,δ15N则为极显著正相关性。在营养生态位方面,2018年的生态位指标均出现不同程度的下降,下降幅度的范围为1.1%~32.1%;生态位总面积和核心生态位面积分别由20.20和4.68缩小至14.20和3.18,说明北部湾日本带鱼的营养生态位发生了显著变化,对资源利用能力和环境适应能力下降。推测,10年来北部湾日本带鱼的营养级变化不明显,但由于食物来源发生变化,营养来源多样性下降,营养生态位变小。.
Keywords: Beibu Gulf; Trichiurus japonicas; stable isotope; trophic level; trophic niche.