Rhodoliths is a general term used to designate non-geniculate coralline red algae (Rhodophyta) that live unattached (Riosmena-Rodríguez, 2017). The term is used here to encompass (i) branched free-living coralline algae devoid of an evident nucleus, but also (ii) nucleated nodules where the biogenic calcium carbonate deposit around the core represents >50%, as well as (iii) “coated grains” where the core is larger than the algal carbonate component.

In 2022 and 2023, the CoastalWarming research team at CIBIO, in Portugal, surveyed the intertidal biodiversity of rocky shores along the North Atlantic coast, from Scotland to Morocco. The sampling protocol encompassed two approaches to identify and estimate the abundance of the main macrospecies typifying each shore: (i) quadrat sampling and (ii) SACFOR scaling. Some specimens were collected to confirm identifications with a magnifying lens.