DOI: 10.5061/dryad.8gtht76rx
title: Long-term coastal macrobenthic Community Trajectory Analysis reveals habitat-dependent stability patterns

description: Long-term monitoring programs are fundamental to detecting changes in
 ecosystem health and understanding ecological processes. In the current
 context of increasing anthropogenic threats on marine ecosystems,
 understanding the dynamics and response of communities becomes essential.
 We used data collected over 14 years in the REBENT benthic coastal
 invertebrates monitoring program, at a regional scale in the North-East
 Atlantic, covering a total of 26 sites and 979 taxa. Four distinct
 habitats were studied: two biogenic habitats associated with foundation
 species in the intertidal and subtidal zones and two bare sedimentary
 habitats in the same respective tidal zones. We used Community Trajectory
 Analysis, a statistical approach that allows for quantitative measures and
 comparisons of temporal trajectories of ecosystems. We compared observed
 community trajectories to trajectories simulated under a non-directional
 null model in order to better understand the dynamics of the communities,
 their potential drivers, and the role of the studied habitats in these
 dynamics. Despite strong differences in the community compositions between
 sites and habitats, the communities followed non-directional dynamics
 during the 14 years monitored, which suggested stability at the regional
 scale. However, the shape, size, and direction of the trajectories of
 benthic communities were more similar within than among habitats, also
 suggesting the influence of the nature of the habitat on community
 dynamics. Results showed a higher variability in community composition in
 the first years of the monitoring in the intertidal bare habitat and
 confirmed the role of biogenic habitats in maintaining temporal stability.
 They also highlighted the need to apprehend the role of transient and rare
 species and the scale of observation in temporal beta diversity analyses.
 Finally, our study confirmed the usefulness of Community Trajectory
 Analysis to link observed trajectory patterns to fundamental ecological
 processes.
description: Benthic communities have been monitored yearly since 2003 along
 the coast of Brittany (France) within the REBENT program
 (http://www.rebent.org). We focused on four habitats and their associated
 endofaunal communities: intertidal seagrass beds (only Zostera marina beds
 are monitored within the REBENT), intertidal sandy beaches, subtidal maerl
 beds and subtidal soft sediments (respectively referred to as intertidal
 biogenic habitat (IBIO), intertidal bare habitat (IBAR), subtidal biogenic
 habitat (SBIO) and subtidal bare habitat (SBAR) in the
 manuscript). At each site, three faunal samples were
 taken at each of three fixed sampling points distributed 200 m apart (0.03
 m<sup>2</sup> cores in the intertidal and 0.1
 m<sup>2</sup> Smith-McIntyre grabs in the subtidal), except
 for Pierre Noire (8) where up to 10 grabs were taken at the sampling
 site. Sampling was performed between the end of
 February and the beginning of May before recruitment of most species
 occurs in the region. In the laboratory, specimens were sorted, counted
 and identified to the lowest possible taxonomic level (usually species).
 Since the acquisition and identification of specimens were not carried out
 by the same people over the years of the monitoring program, we proceeded
 to a taxonomic homogenization: each recorded taxon was scrutinized by
 experts in benthic taxonomy and their names were checked thanks to the
 World Register of Marine Species (WoRMS Editorial Board 2021) to ensure a
 consistent taxonomic resolution. In order to minimize the prevalence – and
 potential effect – of missing data as much as possible, we only selected
 sites with complete time series and with at least 3 core or grab samples
 in any particular year. Samples were pooled to estimate abundances at the
 site level. In the end, this led to a selection of 26 sites monitored from
 2005 to 2018 while keeping a spatial resolution covering the coasts of
 Brittany and encompassing most of the environmental settings found in this
 region. Of these 26 sites, 5 were in IBAR, 7 in IBIO, 8 in SBAR and 6 in
 SBIO . We conducted the analyses at the habitat level or within the same
 tidal level because it may not be relevant to run analyses including two
 different tidal levels since sampling gears differ between intertidal and
 subtidal sites. More details can be found in the
 article.
description: All analyses were conducted with the R programming language
 version 4.1.2. (R Core Team, 2021. R: A language and environment for
 statistical computing. R Foundation for Statistical Computing, Vienna,
 Austria. https://www.R-project.org/).