Rocky intertidal community structure in oceanic islands: scales of spatial variability

Abstract

There is a clear bias in the literature on island ecology towards terrestrial rather than
marine systems, which have remained comparatively poorly studied. Marine populations are typically
open, and local production may have little impact on local recruitment, such that long-distance
dispersal is an important determinant of population ecology. Since oceanic islands form discrete
patches of habitat surrounded by a structurally different environment, we tested the general hypothesis
that processes operating at the scale of islands have a greater influence on these populations
than the processes operating at smaller, intra-island scales. A hierarchical design examined the patterns
of abundance and distribution of conspicuous taxa at 3 tidal heights at a range of spatial scales,
ranging from a few meters to hundreds of kilometres apart in the rocky intertidal of the Azores. Both
uni- and multivariate analyses showed that at the largest scale (islands), significant variation was
detected in the lower and mid-shore communities, but not on the upper shore. Along the vertical
gradient of immersion there was a trend for increasing small-scale patchiness towards the top of the
shore. The potential role of local environmental stress gradients and broad-scale oceanographic
patterns of recruitment in structuring these assemblages is discussed. This study corroborates the
suitability of the analytical tools used here to examine patterns of distribution over a range of spatial
scales and its applicability in the field of island marine ecology.

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