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

Abstract

Rhodoliths - unattached calcareous nodules formed by coralline red algae - can persist on the seafloor long afteralgal death, creating structural legacies that shape benthic communities. To test whether dead rhodoliths differfrom living ones in their habitat function for macroinvertebrates, we conducted a 35-day recolonizationexperiment using living rhodoliths cleared of macroinvertebrates (“living” treatment), rhodoliths experimentallykilled and cleared by boiling (“dead” treatment), and unmanipulated living rhodoliths as controls. Acrosstreatments, 122 macroinvertebrate taxa were recorded. Overall density, richness, and diversity did not differsignificantly 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 habitatfunction, sustaining macroinvertebrate communities even after algal death. Recognition of the ecological role ofdead rhodoliths emphasizes that rhodolith beds should not be considered “dead systems,” even when dominatedby non-living nodules. Their likely centennial - to millennial - scale persistence highlights their long-term contributionsto habitat complexity and biodiversity support, while also underscoring their vulnerability todestructive human activities such as trawling and seabed mining.