Variation in “bank of microscopic forms” in urchin barren coast: detection using DNA metabarcoding based on high-throughput sequencing

Abstract

Type of macroalgal beds that recovered from sea urchin barrens is determined by components of “bank of microscopic forms.” In the present study, we investigated the variation of the bank components, especially in the Phaeophyceae and Rhodophyta, on cobbles at four different vegetation and depths (1, 2, 5, and 7 m) of urchin barren grounds (UB1, UB2, UB5, and UB7), and alternative ecological phases (EB, ecklonian kelp bed and SC, soft coral bed). We collected 30 cobbles (3–7 cobbles per station) from the six stations and identified the attached algae by DNA metabarcoding based on high-throughput sequencing. In the rarefied data, 74 macroalgal operational taxonomic units (OTUs) were detected, of which 32 and 42 OTUs were assigned to Phaeophyceae and Rhodophyta, respectively. The OTU richness in urchin barrens increased with depth from UB1 (0.07 ± 0.03 OTUs cm−2 of cobble) to UB7 (0.21 ± 0.12 OTUs cm−2 of cobble), which was similar to the other ecological phases (EB and SC). The Shannon-Weiner diversity index in UB7 was also significantly highest and similar to EB and SC (p < 0.05). However, the ordination test (non-metric multidimensional scaling) assigned EB to different group apart from UB7 and SC, probably due to solely Phaeophyceae dominance in EB. Therefore, macroalgal richness and components of the bank could be determined by depth and ecological phases, respectively. Furthermore, OTU identified as Undaria pinnatifida was detected on a cobble collected UB7. Thus, in urchin barren coast, the richness in kelp gametophyte is probably also higher in deeper area.