Detection of Ecological Thresholds and Selection of Indicator Taxa for Epibenthic Communities Exposed to Multiple Pressures

Laurie Isabel,David Beauchesne,Chris Mckindsey,Philippe Archambault

doi:10.3389/fmars.2021.720710

Laurie Isabel, David Beauchesne + Show 2 more

Open Access

https://doi.org/10.3389/fmars.2021.720710

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Abstract

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.

Highlights

Marine ecosystems are changing faster than ever, causing profound changes to communities of living organisms (Walther et al, 2002; Myers and Worm, 2003; Worm et al, 2006)
This study explores the spatial variation of EGSL epibenthic communities, identifies thresholds of community composition, and further quantifies the impact of oxygen to select indicator species
Salinity, oxygen, and positive temperature anomalies were the main predictors of community composition and distribution

Summary

Introduction

Marine ecosystems are changing faster than ever, causing profound changes to communities of living organisms (Walther et al, 2002; Myers and Worm, 2003; Worm et al, 2006). Increasing types and intensities of human activities over the last century have been identified as the main cause for these rapid changes (Halpern et al, 2015; Jouffray et al, 2020). Anthropocene-related climate changes are occurring and interacting with other long-term trends (Hoegh-Guldberg and Bruno, 2010). Together, these pressures dominate the human footprint on marine ecosystems, with the potential for significant overlap between pressures (Halpern et al, 2008, 2015). The number and types of pressures have increased tremendously in recent decades, little is known about which are having the greatest impacts on communities and how they interact over space and time (Halpern et al, 2015)

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