Long-term coastal macrobenthic Community Trajectory Analysis reveals habitat-dependent stability patterns

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.