Interacting effects of habitat structure and seeding with oysters on the intertidal biodiversity of seawalls

greater on complex than flat tiles (Fig 2B, S2 Table). This difference was driven by the signifi- cantly higher number of live seeded S. glomerata in the crevices than the ridges of the complex tiles at Site 2, but not Site 1 (Fig 2B, S2 Table). The effects of adding habitat structure and seeding with oysters on the percentage cover of S. glomerata (which included both live and dead oysters and seeded as well as colonising indi- viduals) differed through time (Fig 3A, Table 1, S3 Table). At 1 and 6 months, the percentage cover of S. glomerata was greater on seeded than unseeded tiles, but was unaffected by habitat structure (Fig 3A, S3 Table). By 12 months, the percentage cover of oysters was greater on the seeded complex, unseeded complex and seeded flat tiles (each of which did not significantly differ) than unseeded flat tiles (Fig 3A, S3 Table). Similarly, within the complex tiles, whether seeding, microhabitat type, or an interaction between the two influenced the percentage cover of S. glomerata, varied through time (Fig 3B, Table 2, S3 Table). Initially, at 1 month, the percentage cover of S. glomerata was greater in seeded than unseeded microhabitats, irrespective of whether they were a crevice or ridge (Fig 3B, S3 Table). At 6 months, the percentage cover of S. glomerata was greater in the crevices that were seeded, than the ridges that were seeded, each of which had greater cover than the unseeded microhabitats (which did not significantly differ; Fig 3B, S3 Table). At 12 months, the percentage

cover of S. glomerata was significantly greater in the crevices than in the ridges, irrespective of seeding, with seeded ridges containing greater cover than unseeded ridges (Fig 3B, S3 Table). Fig 2. Effect of habitat structure (flat vs. complex tiles; a, b) and microhabitat identity (crevice vs. ridge, on complex tiles; c, d) on the mean (+/-SE) number of live seeded S. glomerata (transplants only) at each of two sites, 0, 1, 6 and 12 months following tile deployment, (n = 5). Tiles started with 52 oysters. https://doi.org/10.1371/journal.pone.0230807.g002 PLOS ONE Effects of microhabitats and seeding with oysters on intertidal biodiversity PLOS ONE | https://doi.org/10.1371/journal.pone.0230807 July 16, 2020 9 / 21