岛礁水域海藻场食物网基准生物的选择

Investigation on food web's isotopic baseline in typical reef ecosystem-seaweed bed

岛礁海域海藻场是近岸浅海重要的湿地生境之一,其所在水域的食物网往往较开阔水域复杂,而利用稳定同位素方法来揭示其独特的物质传递和能量流动规律是当前国内外研究的趋势。在利用该技术之前,往往需选择恰当的基准生物以更准确地阐释海藻场食物网各阶层的营养关系。为此,于2014年春季(5月)和秋季(10月)在浙江省枸杞岛海藻场选取4种大型底栖动物优势种[蝾螺(Turbo petholatus)、角蝾螺(Turbo cornutus)、条纹隔贻贝(Septifer virgatus)和带偏顶蛤(Modiolus comptus)]为实验对象,利用多元方差分析检验其δ^(13)C和δ^(15)N值的种内(间)时空差异,并分析造成该差异的原因,评估其作为基准生物的可行性。结果显示,4种底栖动物的δ^(13)C和δ^(15)N值受其食性和栖息地环境的影响,呈现不同程度的时空差异,发现带偏顶蛤和角蝾螺的δ^(13)C和δ^(15)N值相对更为稳定,因此可分别作为浮游和底层营养关系的基准生物。本文结果可为我国在东海岛礁水域开展相关研究提供基础数据和重要参考。

Kelp bed is a typical rocky inshore ecosystem whose trophic structure is much more complicated than the offshore habitats. Pelagic food chain and benthic food chain exist simultaneously, with phytoplankton and macrophytes as their primary production. Recently, more and more stable isotope analysis has been employed to investigate inter and intraspecific relationships between species in the kelp ecosystems. The accurate identification on isotopic baseline species of the food web is of importance in estimating the trophic positions of consumers and evaluating the trophic structure of kelp ecosystem. Aquatic biota samples were collected off the Gouqi Island rocky kelp bed in Jan. and Oct. 2014. Based on the survey results of benthic species in 2012, we chose four primary consumer species with large abundance and wide distribution. Two snail species （ Turbo petholatus, Turbo cornutus ） and two mussel species （ Septifer virgatus and Modiolus comptus） were collected in kelp ecosystem, the foot tissues of snail and mussels were used for the stable isotope analysis, respectively. δ13C and δ15N of all species from seaweed field between sampling sites （seasons） were explored to select the isotopic baseline species by multivariate analysis of variance （MANOVA）. In this study, snails and mussels exhibited significantly different stable carbon but similar stable nitrogen signatures, suggesting that they had similar trophic position but selectively ingested and assimilated different suspended particulate mixture from littoral and pelagic food chain, respectively. The results showed that δ13C and δ15N of macro-benthos were affected both by their diets and habitat environment. Compared with T. petholatus, we found that T. cornutus reflected the isotopic signature of the base of the littoral food web. The variation scales in δ13C and δ15N of different mussels species were different. In this sense, using a more stable long-lived primary consumer mussel species with large abundance to present the pelagic baseline species could facilitate estimating the trophic position of higher trophic level consumers. Our results can provide basic data and important references for the research on other waters of islands in the East China Sea.