基于稳定同位素技术的洈水水库鱼类群落营养结构

TROPHIC STRUCTURE OF FISH COMMUNITIES IN WEISHUI RESERVOIRBASED ON STABLE ISOTOPE TECHNIQUES

为调查山谷型水库的鱼类群落营养结构及其食物资源利用情况,基于碳(δ^(13)C)、氮(δ^(15)N)稳定同位素技术研究了湖北省洈水水库2020年夏季与秋季鱼类群落结构特征,并运用贝叶斯混合模型评价4种潜在碳源(颗粒有机物、陆生植物、周丛藻类和有机碎屑)对不同食性鱼类的贡献。结果表明:洈水水库鱼类群落的营养结构存在季节差异,鱼类群落的营养层次(NR)、基础食物来源(CR)、生态位总空间(TA)、群落的整体密度(NND)、聚集均匀程度(SDNND)和核心生态位空间(SEAc)等参数为夏季高于秋季,表明夏季食物源多样性高、营养冗余程度低、食物网结构更加复杂而稳定。洈水水库夏季和秋季鱼类均依赖外源性碳源,但两个季节的利用方式存在显著差异(P<0.05)。整体上,陆生植物在两个季节对洈水水库鱼类的碳源贡献最大,但夏季周丛藻类为次重要碳源,秋季有机碎屑为次重要碳源,颗粒有机物(POM)在两个季节均不重要。夏季和秋季对外源碳的依赖程度最高的鱼类均为黄尾鲴(碎屑食性鱼类),对外源碳的依赖程度最低的鱼类为鳙(滤食性鱼类)和团头鲂(植食性鱼类)。在夏季和秋季共有的9种鱼类中,肉食性鱼类(鳜、蒙古鲌)、杂食性鱼类(鲤、鲫)与碎屑食性鱼类(黄尾鲴)营养级变化显著。夏季鱼类营养级范围为2.5—3.5,平均3.01,而秋季鱼类营养级范围为2.9—3.8,平均3.32。基于稳定同位素技术分析不同食性鱼类的营养级发现,秋季鱼类的营养级普遍高于夏季(P<0.05)。研究揭示洈水水库鱼类夏季和秋季的碳源利用存在显著差别,鱼类的营养级秋季普遍高于夏季,这主要是由于洈水水库秋季的低水位不利于陆生植物进入水生食物网,鱼类食物资源竞争加剧、捕食作用加强所致。基于贝叶斯混合模型分析鱼类食物资源的利用情况表明:植食性鱼类和杂食性鱼类的鱼苗投放时间应选在早春(2—3月),碎屑食性鱼类鱼苗的投放时间在秋、冬季更加合适,这将为研究山谷型水库鱼类群落的营养结构及渔业结构调整方案提供科学依据。

To investigate the trophic structure of fish communities and utilization of fish food resources in valley-type reservoirs,the characteristics of fish community structure in the Weishui Reservoir(Hubei Province)were studied in summer and autumn 2020 based on stable carbon(δ13C)and nitrogen(δ15N)techniques.Moreover,the contributions of four potential carbon sources(particulate organic matter,terrestrial plants,epilithic algae,and organic detritus)to fish with different feeding habits were evaluated by a Bayesian stable isotope mixing model.The results showed that there were seasonal differences in the trophic structure of fish communities in the Weishui Reservoir.The Layman’s community-wide metrics showed that theδ15N range(NR),δ13C range(CR),total area(TA),mean nearest neighbor distance(MNND),standard deviation of nearest neighbor distance(SDNND)and standard ellipse area(SEA)of fish communities in summer were greater than those in autumn,suggesting a higher diversity of food sources,lower degree of trophic redundancy,and more complex and stable food web structure in summer.Fish relied on allochthonous carbon in summer and autumn,but significant differences between those in two seasons(P<0.05)were found.Overall,terrestrial plants made the greatest contribution to the carbon sources of fish in the Weishui Reservoir,however,epilithic algae and organic detritus were the secondary important carbon sources in summer and autumn,respectively.Particulate organic matter was unimportant for fish at two seasons.In summer and autumn,detritivorous fish Xenocypris davidi exhibited the highest reliance on allochthonous carbon,whereas filter-feeding fish(bighead carp)and herbivorous fish(blunt snout bream)showed the lowest reliance on allochthonous carbon.Trophic positions of fish ranged between 2.5—3.5(averaged 3.01)in summer,whereas between 2.9—3.8(averaged 3.32)in autumn.For the nine common species at two seasons,piscivorous fish(Siniperca chuatsi and Erythroculter mongolicus),omnivorous fish(Cyprinus carpio and Carassius auratus)and detritivorous fish(Xenocypris davidi)showed great variations in TPs.Based on the analysis of stable carbon and nitrogen isotopes for fish with different feeding habits,we found that TPs of fish in autumn were significantly higher than those in summer(P<0.05).Our study revealed a significant difference between the utilization of carbon sources by fish between summer and autumn,with TPs of fish in autumn was generally higher than that in summer.This is primarily ascribed to the low water levels of the Weishui Reservoir in autumn because low waterlevels do not allow the entry of terrestrial plants into aquatic food webs,thereby resulting in intensified competition of fish for food resources and predating.Analysis of the Bayesian stable isotope mixing models suggests that of herbivorous and omnivorous fries such as grass carp and blunt snout bream are recommended to release to the reservoir in early spring(February-March),while detritivorous fries are recommended for release in autumn and winter.