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

Area of Science:

• Marine Biology
• Ecology
• Benthic Ecology

Background:

• Rhodoliths are unattached calcareous nodules formed by coralline red algae.
• Dead rhodoliths can persist on the seafloor, potentially influencing benthic communities.
• The habitat function of dead rhodoliths for macroinvertebrates is not well understood.

Purpose of the Study:

• To determine if dead rhodoliths differ from living rhodoliths in their habitat function for macroinvertebrates.
• To assess the structural legacy of rhodoliths in supporting benthic communities.

Main Methods:

• A 35-day recolonization experiment was conducted.
• Treatments included living rhodoliths, experimentally killed rhodoliths, and unmanipulated living rhodoliths (controls).
• Macroinvertebrate taxa, density, richness, and diversity were recorded across treatments.

Main Results:

• 122 macroinvertebrate taxa were recorded across all treatments.
• Overall macroinvertebrate density, richness, and diversity did not significantly differ between living and dead rhodoliths.
• Macroinvertebrate assemblages on living and dead rhodoliths were statistically indistinguishable and differed only slightly from controls.

Conclusions:

• The calcareous structure of rhodoliths provides a lasting habitat function, supporting macroinvertebrate communities even after algal death.
• Dead rhodoliths are ecologically significant and rhodolith beds should not be considered 'dead systems' when non-living nodules dominate.
• The long-term persistence of rhodoliths highlights their contribution to habitat complexity and biodiversity, but also their vulnerability to human activities.