基于稳定同位素技术的光背团水虱食性分析

为了探究光背团水虱的食性特征，本研究利用碳、氮稳定同位素技术于2015年冬季和2016年夏季对广西北海廉州湾红树林中光背团水虱及其食物来源的碳、氮稳定同位素比值（δ13C值和δ15N值）进行分析。结果显示，冬季和夏季光背团水虱的δ13C值大小范围为-22.85‰~-21.87‰，平均值为（-22.46±0.35）‰；δ15N值大小范围为11.02‰~12.85‰，平均值为（11.88±0.56）‰；光背团水虱的δ13C值、δ15N值变化范围较小，表明其食物来源较为简单。单因素方差分析结果显示，冬季与夏季光背团水虱的平均δ13C值差异不显著（P>0.05），而夏季的δ15N值普遍高于冬季δ15N值，差异显著（P<0.05）；不同生长阶段的光背团水虱δ13C值、δ15N值会随着体长的增长而增大，差异显著（P<0.05），表明光背团水虱在生长的过程中可能发生了食性转变。光背团水虱的δ13C值与浮游生物的δ13C值相近，而与红树植物δ13C值差距较远，说明光背团水虱主要以浮游生物为食物来源。基于R语言稳定同位素混合模型（SIAR）计算结果显示，冬季和夏季各粒径级别浮游生物对不同生长阶段的光背团水虱的贡献率趋势基本一致，表现为1.2~25 μm粒级的浮游生物对光背团水虱平均贡献率最高，其次为25~50 μm粒级，粒径大于100 μm的浮游生物对体长小于5.5 mm的光背团水虱贡献率较低，对体长大于5.5 mm的光背团水虱的贡献率随着体长增大而相应增大，说明不同生长阶段的光背团水虱食性有差异。对光背团水虱食性分析的结果可为深入研究团水虱爆发的原因及危害红树林的作用机理提供基础资料。

Feeding habits of Sphaeroma retrolaeve based on stable isotope analysis

In order to explore the feeding characteristics of Sphaeroma retrolaeve, we analyzed the carbon and nitrogen isotopic ratios (δ13C values, δ15N values) of S. retrolaeve and its food sources which were collected from the mangrove of Lianzhou Bay, Beihai, Guangxi, in the winter of 2015 and summer of 2016, based on the stable carbon and nitrogen isotope analysis. The results showed that the average δ13C and δ15N values of S. retrolaeve were (-22.46±0.35) ‰ and (11.88±0.56)‰, in a range of -22.85‰ to -21.87‰ and 11.02‰ to 12.85‰, respectively. The range of δ13C value and the δ15N value of S. retrolaeve was small, which indicated that the food sources of S. retrolaeve were relatively simple. The results of one-way ANOVA showed that the δ13C values of S. retrolaeve were insignificantly different between winter and summer (P>0.05), while the δ15N values in summer were generally higher than those in winter, and the difference was significant (P<0.05); δ13C and δ15N values of S. retrolaeve of different growth stages significantly correlated with body size (P<0.05), which indicated that its feeding habits shift during its growth process. The δ13C values of S. retrolaeve were similar to the δ13C values of the plankton, which were far different from the δ13C values of the mangrove plants, indicating that the main food sources of S. retrolaeve was plankton. The results of SIAR mixing model analysis showed that contribution rates of plankton to different growth stages of S.retrolaeve were basically the same in winter and summer. The plankton with the fraction of 1.2-25 μm had the highest contribution to S. retrolaeve, and followed by the fraction of 25-50 μm, the fraction more than 100 μm had a lower contribution to S. retrolaeve with body length less than 5.5 mm, while the proportion of contribution would increase with increasing body length, which showed that there were something differences in the feeding habits for S. retrolaeve at different growth stages. The results of the feeding habits of S. retrolaeve could provide basic information for further studying the causes of Sphaeroma outbreak and the mechanism of damage to mangroves.