A Common Terminology to Unify Research and Conservation of Coralline Algae and the Habitats They Create

Linguistic uncertainty is a prime source of uncertainty pervading ecology and conservation. Coralline algae are a widespread and diverse group of calcifying red macroalgae that underpin coastal ecosystem function and service provision. Recent increasing interest in coralline algae in the scientific literature has revealed a diverse but confusing terminology at organism to habitat scales. Coralline algal research and conservation are international and multidisciplinary, so there are geographic and disciplinary imbalances in research and conservation efforts. To reach consensus and reduce uncertainty, we propose a unified terminology. We review trends in cultural and scientific use of coralline algal terms and propose a system based on six morphologies: (1) attached, (2) free-living geniculate, (3) encrusting and free-living nongeniculate coralline algae, the latter either being (4) nucleated or (5) non-nucleated thalli or (6) fragments. We take inspiration from other coastal systems that have achieved consensus through umbrella terms, such as ‘coral’ and ‘kelp’, to accelerate global progress in coralline algal research and conservation. We characterise 14 coralline algae–dominated habitat global types, falling within seven functional groups, four biomes and four realms: (1) freshwater coralline streams; (2) coralline tide pools; (3) intertidal coralline rims and (4) turf; (5) coralline sea caves; (6) coral–algal reefs; (7) algal ridges; (8) coralligenous reefs; subtidal (9) carbonate crusts, (10) coralline barrens and (11) turf; and (12) articulith, (13) maerl and (14) rhodolith beds, which fall into the coralline algal bed functional group. We hope this unified terminology promotes data comparison, enables cross-boundary and cross-sector sharing of best practices, develops capacity for meta-analyses and improves conservation strategies.