Data from: Multi-scale drivers of community diversity and composition across tidal heights: an example on temperate seaweed communities

1. Despite recent advances in understanding community assembly processes,
appreciating how these processes vary across multiple spatial scales and
environmental gradients remains a crucial issue in ecology. 2. This study
aimed to disentangle the drivers of diversity and composition of seaweed
communities through a gradient of spatial scales based on a hierarchical
sampling design consisting of 19 sites distributed in four sectors along
the Brittany coastline. Using randomised community matrices and Moran’s
eigenvector maps (MEMs), we compared i) the relative importance of
deterministic and stochastic processes, ii) the environmental correlates
of community composition and iii) the scale of variation in community
composition for seaweed communities located at two different tidal
heights. 3. Processes shaping community patterns are expected to vary
along a gradient of tidal heights. Therefore, we specifically examined the
following hypotheses: the contribution of deterministic over stochastic
processes as well as the relative importance of environmental filtering
over biotic interactions should be enhanced for seaweed communities of the
infralittoral fringe compared to subtidal ones, whereas dispersal of
propagules in the water column should be more restricted resulting in
finer-scale variation in community composition for seaweed communities of
the infralittoral fringe compared to subtidal communities. 4. Seaweed
communities were largely shaped by deterministic processes, although the
relative importance of deterministic processes was greater for communities
of the infralittoral fringe than for subtidal communities. Sea surface
temperature and geophysical variables were correlates of community
composition at the two tidal heights; additionally, waves and current were
correlated with the composition of the communities of the infralittoral
fringe while kelp density was correlated with the composition of subtidal
communities. Variation in community composition was observed at a finer
scale for infralittoral fringe than for subtidal communities. Synthesis.
Our results suggest that the relative importance of deterministic and
stochastic processes in structuring seaweed communities varies across
tidal heights. Furthermore, the MEMs framework highlights that the nature
of environmental correlates and the spatial scale at which they were good
correlates of community composition also vary across tidal heights and may
therefore be useful to broaden our understanding of community assembly
across vertical gradients.