摘要:为了探寻海草床浮游-底栖营养传递耦合特征，于2017年7月对黄河口近海海草床碳源和消费者功能群进行样品采集和碳氮稳定同位素（δ¹³C和δ¹⁵N）测定，计算了消费者功能群的营养级，利用基于贝叶斯的稳定同位素混合模型定量化消费者功能群的食源组成，计算了消费者功能群的浮游、底栖营养贡献比例。结果表明：黄河口近海海草床的碳源和消费者功能群的δ¹³C和δ¹⁵N值均呈现显著性差异（P<0.05），浮游碳源的δ¹³C值显著低于底栖碳源，消费者功能群的营养级范围为1.49-4.20。浮游动物和腹足类分别由浮游和底栖营养传递途径提供能量来源，其余消费者功能群共同依赖于这两种营养传递路径。消费者功能群随着浮游营养贡献比例的增加，其δ¹³C值逐渐降低。反之，随着底栖营养贡献比例的增加，其δ¹³C值逐渐增加。这与浮游碳源和底栖碳源的δ¹³C值的分化现象一致。对该海草床营养传递特征的系统性定量化解析有助于了解海草床的能量传递模式，为海草床的生态保护和修复提供系统性视角。



Abstract:Seagrass ecosystems form the foundation of one of the most important coastal wetlands, whereas their habitat quality is declining due to the climate change and multiple anthropogenic pressures. Understanding the pelagic-benthic coupling in energy flows is essential to the protection and restoration of seagrass beds. Stable isotope analysis (mostly δ¹³C and δ¹⁵N) constitutes a radical improvement to analyze diets, which is now widely used to trace the pathways of energy flows and determine the contributions of different diet sources to the ingestion of consumers. In this paper, we conducted the field sampling of the carbon sources and consumer trophic groups of the seagrass bed in the Yellow River estuary wetland in July 2017. In total, we divided all organisms into 15 trophic groups, comprising detritus (suspended particular matter), phytoplankton, epilithic algal matrix, seagrass, Spartina alterniflora, zooplankton, gastropods, bivalves, crabs, polychaetes, shrimps, Planiliza haematocheila, Cynoglossus semilaevis, Synechogobius hasta, and Lateolabrax japonicus. We then detected the stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) of all trophic groups. The trophic positions of consumer trophic groups were estimated based on the δ¹⁵N values. We obtained the potential diet sources for each consumer trophic group based on the published diet data using gut content analysis or isotope signatures in other seagrass beds or closing to our study area. We ran the Bayesian mixing isotope model (SIAR package in R) each time for each consumer trophic group to quantify its diet composition, and then calculated its pelagic and benthic contributions. The results showed that the δ¹³C and δ¹⁵N values of carbon sources and consumer trophic groups in the seagrass bed all showed significant differences (P<0.05). The δ¹³C value of pelagic carbon source (phytoplankton) was significantly lower than that of benthic carbon sources (-22.26‰ and -12.34‰, respectively). The trophic positions of consumer trophic groups ranged from 1.49 (zooplankton) to 4.20 (Lateolabrax japonicus). Zooplankton relied on pelagic pathway and gastropods relied on the benthic pathway, whereas other consumer trophic groups relied both on the two pathways. Moreover, we found that the δ¹³C values of consumer trophic groups decreased significantly with the increasing pelagic contribution, otherwise increased significantly with the increasing benthic contribution (Adj R²=0.49, P=0.015), which is consistent with the distinction of δ¹³C values between pelagic and benthic carbon sources. The quantitative analysis of the seagrass bed in terms of trophic structure and its pelagic-benthic coupling can help us to gain insight on the trophic transferring characteristics and thereby provide a more systematic perspective on the ecological protection and restoration of seagrass beds.





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