基于碳、氮稳定同位素技术的大亚湾紫海胆食性分析

摘要

为掌握大亚湾紫海胆(Heliocidaris crassispina)的食性特征,应用碳、氮稳定同位素技术对2015年8月所采集紫海胆样本的稳定同位素特征、营养级和食性特征进行了初步研究.结果表明,大亚湾紫海胆平均 δ13C值为?(13.35±1.21)‰,平均 δ15N值为(9.14±0.38)‰,平均营养级为2.11±0.14.不同壳径紫海胆之间的碳、氮稳定同位素比值无显著性差异(P>0.05).大亚湾海域紫海胆生活环境周围生物δ13C值分布范围为?20.76‰~?9.93‰,δ15N值分布范围为?0.16‰~14.99‰,营养级范围为1.34~3.77.大亚湾主要生物种类可划分为悬浮物、初级生产者和初级消费者、次级消费者、顶级消费者4个营养组群,其中紫海胆属于次级消费者.8月份调查海域珊瑚稀少,大型海藻密度低且死亡降解形成颗粒有机物(Particulate Organic Matter,POM),陆源POM随降雨大量流入大亚湾,导致紫海胆在8月份摄食偏向碎屑食物链,主要食物来源为POM,平均贡献率为67.3%;其余摄食种类为沉积物(Sediment Organic Matter,SOM)、裂叶马尾藻(Scagassum siliquastrum)、底栖硅藻、浮游动物及浮游植物,平均贡献率分别为9.7%、9.3%、6.7%、3.7%及3.3%.大亚湾紫海胆摄食种类与其栖息地底栖生物存在重叠,具有一定的食物竞争关系.研究表明,分析紫海胆食性特征对了解其所在生态系统中营养级水平具有重要意义.%Purple sea urchin Heliocidaris crassispina is an important benthic species in the western Pacific Ocean. In recent years, environmental disruption and over-exploitation have damaged the resources of this species. Stable isotope analysis has become a powerful tool for studying the feeding habits of marine animals, and this method can overcome some of the limitations associated with traditional stomach contents analysis. Carbon (δ13C) and nitrogen (δ15N) were used as tools to evaluate the stable isotopic characteristics, trophic levels, shell diameter, and feeding habits ofH. crassispina, from Daya Bay on the south coast of Guangdong Province, using data collected in August 2015. In the present study, the trophic levels ofH. crassispina and other benthic species in Daya Bay were based onδ15N. Averageδ13C ofH. crassispina was?(13.35±1.21)‰, averageδ15N was (9.14±0.38)‰, and the trophic levels ranged from 2.09 to 2.13 (mean 2.11); no significant correlation was found between the different shell diameters of theH. crassispina sampled and the recorded values ofδ13C andδ15N (P>0.05). Averageδ13C values of the potential food sources were between?(9.93±1.59)‰ and?(20.76±1.42)‰, and their averageδ15N values were between (?0.16±1.34)‰ and 14.99‰; the trophic levels ranged from 1.34 to 3.77. Cluster analysis showed that the food web among major species of Daya Bay could be classified into four trophic groups: sus-pended organic matter, primary producers and primary consumers, secondary consumers, and top predators. There were two main channels in the overall food chain: one was the grazing food chain, and the other was the detritus food chain.H. crassispina have a tendency to feed on detritus in August, when corals are scarce, macroalgae den-sity is low, and the terrigenous materials present as particulate organic matter (POM) into Daya Bay follow a pe-riod of heavy rains. The main food resources ofH. crassispinawere: POM, sediment organic matter (SOM), the brown macroalgaeSargassum siliquastrum, bacillariophyceae (diatoms), zooplankton and phytoplankton Among these, POM was the most important food item forH. crassispina, accounting for 67.3% of its food consumption; the other food categories accounted for 9.7%, 9.3%, 6.7%, 3.7% and 3.3% of its food composition, respectively. Considerable competition exists betweenH. crassispina and the benthos, which suggests urgent efforts are needed to improve this ecological environment as well as to increase the seaweed biomass. Variations in the trophic levels were related to differences in the isotope baseline, and temporal and spatial variations. There was no significant correlation between shell diameter ofH. crassispina and its feeding habits, perhaps because its food source is relatively singular. Thus, it is evident that feeding habits play an important role in population resource recovery and ecological niches of the system.