Table_1_Detection of Ecological Thresholds and Selection of Indicator Taxa for Epibenthic Communities Exposed to Multiple Pressures.DOCX

The estuary and the Gulf of St. Lawrence (EGSL), eastern Canada form a vast inland sea that is subjected to numerous anthropogenic pressures. Management tools are needed to detect and quantify their effect on benthic communities. The aims of this study are to analyze the spatial distribution of epibenthic communities in the EGSL and quantify the impact of important pressures on them to identify indicator taxa. Epibenthic communities were sampled at 1314 EGSL sites between 2011 and 2018 by bottom trawling. Cluster analyses revealed the presence of six distinct epibenthic communities that seem to be strongly influenced by oxygen concentration. Threshold analyses confirm that oxygen is an important predictor of epibenthic community composition and distribution. A major oxygen threshold is observed around 50–100 μmol O2 L–1, resulting in a shift of community type. At these concentrations and below, opportunistic taxa dominate the community while sensitive taxa are absent or present at very low abundance. Biomass of the latter only starts to increase when oxygen concentrations reach 150 μmol O2 L–1. The species Actinostola callosa, Actinauge cristata, Ctenodiscus crispatus, and Brisaster fragilis were identified as good indicators for detecting this impact threshold forepibenthic communities. This study provides threshold-based indicator species that help to establish and monitor the ecological state of epibenthic communities in a marine ecosystem exposed to multiple pressures.

加拿大东部的圣劳伦斯河口及海湾（Estuary and the Gulf of St. Lawrence，简称EGSL）为一片广袤的内陆海域，正面临诸多人为活动施加的压力，亟需配套管理工具以检测并量化这些压力对底栖生物群落（benthic communities）的影响。本研究旨在分析EGSL内表栖底栖生物群落（epibenthic communities）的空间分布特征，并量化主要压力因子对其产生的影响，从而确定指示分类群（indicator taxa）。2011年至2018年间，研究人员通过底拖网采样法，在EGSL的1314个采样站点采集了表栖底栖生物群落样本。聚类分析结果显示，该区域内存在6种截然不同的表栖底栖生物群落，且这些群落的分布似乎受溶解氧浓度的显著调控。阈值分析证实，溶解氧是影响表栖底栖生物群落组成与空间分布的重要预测因子。研究观测到一个关键溶解氧阈值区间为50–100 μmol O2 L–1，当溶解氧处于该区间及更低浓度时，群落类型会发生显著转变。在此浓度区间及以下，机会主义类群将占据群落主导地位，而敏感类群则完全消失或仅以极低丰度存在。仅当溶解氧浓度达到150 μmol O2 L–1时，敏感类群的生物量才会开始显著回升。研究确定Actinostola callosa、Actinauge cristata、Ctenodiscus crispatus及Brisaster fragilis这4个物种，可作为检测EGSL表栖底栖生物群落受干扰阈值的优良指示物种。本研究提供了基于阈值的指示物种体系，可为暴露于多重压力因子的海洋生态系统中表栖底栖生物群落的生态状态评估与长期监测提供科学支撑。