Diversity of turf-forming <i>Gelidium</i> species growing on subtidal crustose coralline algae in the East Sea of Korea with a description of <i>G. cristatum</i> sp. nov.

Abstract Crustose coralline algae (CCA) beds are lower-diversity ecosystems compared to typical algal beds. However, we found many turf-forming algae growing on CCA beds in the East Sea of Korea during an ecological survey. We investigated species diversity using molecular markers, focusing on the most commonly found algal genus, Gelidium . Phylogenetic analyses of rbc L sequences revealed six Gelidium species, including three undescribed species from collections of CCA. In addition, mitochondrial cox 1 and plastid psa A sequences were analyzed to confirm their phylogenetic positions. Of these, we describe one as a new species; Gelidium cristatum sp. nov. is distinguished by its small size and erect branches arising radially from the dorsal surface of the prostrate axes in the same position the brush-like haptera grow from the ventral surface, and tetrasporangial sori and cystocarps borne on determinate erect axes. We speculate that Gelidium may possess higher species diversity than previously assumed. However, data on turf-forming species on CCA beds are lacking. Therefore, continuous investigation and observations are necessary.