Abstract
The biodiversity of hard-bottom substrata comprises species growing on exposed rock and in hidden microhabitats, such as cracks and crevices. This study examines the succession of epibenthic organisms colonizing an artificial substratum with one surface exposed and one surface hidden on a vertical wall off northern Chile. On each sampling date species coverage of three replicate panels on both surfaces was assessed. The hidden surface was dominated in terms of coverage by the bryozoans Membranipora isabelleana and Lagenicella variabilis , while algae were absent. In contrast, the exposed surface was dominated by encrusting red corallines and the red alga Rhodymenia corallina . At the end of the experimental period both surfaces were dominated by colonial suspension feeders, but showed a different community structure and successional pattern. On the exposed surface, competitive exclusion was identified as an important aspect of succession, whereas on the hidden surface this pattern was not observed. These findings have implications for overall biodiversity, because pioneer species that are not able to survive long periods on exposed surfaces become restricted to hidden surfaces, from where they spread laterally. Thus, hidden microhabitats provide refuges for certain species, and may play an important role in the overall succession on rock faces. We conclude that examination of hidden microhabitats is necessary in order to fully understand succession in hard-bottom habitats.
Highlights
Natural shallow subtidal rocky habitats are structured heterogeneously
This study examines the succession of epibenthic organisms colonizing an artificial substratum with one surface exposed and one surface hidden on a vertical wall off northern Chile
The hidden surface was dominated in terms of coverage by the bryozoans Membranipora isabelleana and Lagenicella variabilis, while algae were absent
Summary
Natural shallow subtidal rocky habitats are structured heterogeneously. Variable slope, topography, orientation, angle and the characteristics of the substratum have major consequences for the small-scale variability of abiotic and biotic factors (i.e. light intensity, currents, sediment and detritus accumulation, and barriers to predators), and thereby influence the establishment of epibenthic organisms (Witman and Dayton, 2001; Miller and Etter, 2008). Hidden microhabitats occur beneath or within biogenic substrata, including kelp canopies (Melville and Connell, 2001; Villegas et al, 2008) and foliose corals (Jackson, 1977; Richter et al, 2001) These hidden microhabitats can be important for the survival of poorly competitive epibenthic species. Hidden microhabitats may alleviate competition, both from species that dominate in more exposed habitats (Irving and Connell, 2002; Miller and Etter, 2008) and between congeners (Navarrete et al, 2008) Such habitats may serve as refuges from harmful abiotic conditions such as strong currents or solar radiation Species that first settle on inner (hidden) rock surfaces, from which they later spread onto exposed surfaces, form an important component of the community
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