CONICET | Buscador de Institutos y Recursos Humanos

Organisms boring into intertidal consolidated sediments generate bioerosion. It isgenerally unknown, however, whether they can significantly contribute to coastlineretraction. In this paper we describe endolithic communities, and estimate bioerosionand physical erosion rates at three Southwestern Atlantic intertidal sites (37, 38, and42°S; Argentina). In the Northernmost site, we have also analyzed spatial variation inspecies richness and abundance as a function of height within the tidal slope,orientation of the rock surface in relation to breaking waves (i.e. facing or not), and rockhardness. The number of species and the combined abundance of individuals from thedifferent species were larger at the low intertidal level but did not differ between surfaceorientations. The density of chemically-boring organisms increased with increasingrock hardness and calcium carbonate content. In contrast, no correlation was foundbetween rock hardness and the abundance of organisms that bore by mechanicalmeans. Endolithic community composition and bioerosion rates differed among thethree sites, the latter being higher at the site with the softer substrate. Bioerosionestimates were two orders of magnitude lower than physical erosion estimates at eachsite. The bivalve Lithophaga patagonica was the species that contributed the most tobioerosion at all these locations. While results suggest that bioerosion contributes littleto overall coastal erosion at the three study sites, boring organisms might still facilitatephysical erosion by weakening the rock either via chemical or mechanical means.Besides, their apparently inconsequential direct action as bioeroders can have positiveconsequences for biodiversity via increased habitat complexity.

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