DNA metabarcoding analysis of macroalgal seed banks on shell surface of the limpet Niveotectura pallida

In macroalgal restoration on urchin barren coasts, understanding the variability in microscopic stages of canopy-forming macroalgae such as kelps and fucoids is critical to reduce restoration effort (i.e. sea urchin removal). In the present study, we used epilithic macroalgae present on the limpet Niveotectura pallida to determine the macroalgal seed bank along a depth gradient of habitats (surf, turf, barren and sandy zones). We collected a total of 46 limpets in two seasons (summer: August and winter: December) and from four zones at Sashiga-hama on the north-east coast of northern Honshu, Japan. The attached organisms on the limpet shells were brushed off and identified using a plastid-encoded rbcL gene and high throughput sequencing (HTS) based DNA metabarcoding. The original data set consisted of 432 macroalgal and 224 microalgal operational taxonomic units (OTUs). For macroalgae, 37, 190 and 205 OTUs were assigned to Ulvophyceae, Phaeophyceae and Rhodophyta, respectively. For canopy-forming macroalgal OTUs, Agaraceae, Alariaceae, Lessoniaceae, Laminariaceae and Sargassaceae were detected. In summer, the OTU was significantly richest in the sandy zone (77.0 ± 15.2 OTUs), but the difference among zones was less conspicuous in winter, ranging from 52.8 ± 16.4 to 64.3 ± 13.2 OTUs. The Shannon–Wiener diversity index showed similar patterns. The laminarialean and sargassacean OTUs were significantly the richest in the sandy zone during summer (p < 0.001). In light of these results, macroalgal restoration (i.e. through sea urchin removal) should be initiated in summer and the sandy zone should be preferentially targeted.