The rolling stones' legacy: Rhodoliths retain their habitat function after algal death

Rhodoliths - unattached calcareous nodules formed by coralline red algae - can persist on the seafloor long after algal death, creating structural legacies that shape benthic communities. To test whether dead rhodoliths differ from living ones in their habitat function for macroinvertebrates, we conducted a 35-day recolonization experiment using living rhodoliths cleared of macroinvertebrates ("living" treatment), rhodoliths experimentally killed and cleared by boiling ("dead" treatment), and unmanipulated living rhodoliths as controls. Across treatments, 122 macroinvertebrate taxa were recorded. Overall density, richness, and diversity did not differ significantly among treatments. Assemblages in living and dead rhodoliths were statistically indistinguishable, while both differed slightly from controls, although such differences accounted for less than 9 % of total variation. Taxon-specific contrasts contributed little to dissimilarities, with no single species explaining more than 3 % of variation. These findings indicate that the calcareous structure of rhodoliths provides a lasting habitat function, sustaining macroinvertebrate communities even after algal death. Recognition of the ecological role of dead rhodoliths emphasizes that rhodolith beds should not be considered "dead systems," even when dominated by non-living nodules. Their likely centennial - to millennial - scale persistence highlights their long-term contributions to habitat complexity and biodiversity support, while also underscoring their vulnerability to destructive human activities such as trawling and seabed mining.