Small-scale variation in tropical tidepool fish assemblages.

Habitat heterogeneity is known to promote species diversity and other effects in communities by increasing structural complexity, access to food resources and to refuge spaces. However, the influence of environmental heterogeneity at small spatial scale settings is challenging to detect and to measure. In tropical intertidal rocky shores, the low tidal zones are sometimes encrusted by reef-building organisms forming complex biogenic flat reefs below rocky outcrops that appear at mid-to-upper intertidal level. Here, we investigated a tidepool community situated on an intertidal shore with marked variation in structure and texture within metres to test whether tidepool fauna would differ between biogenic and rocky reefs in regard to their composition, diversity and trophic structure. Our findings revealed that tidepool fish assemblages differed significantly between reef types. Trophic structure exhibited variations in resource use, food web hierarchy and trophic roles of species occurring in both biogenic and rocky tidepools. Our results imply that tropical intertidal reefs show pronounced taxonomic and trophic distinctiveness at small spatial scales.