Subtidal unstable bottoms are sensitive to the environmental disturbances that determine the structure of macroalgal communities. Here, three variables (substrate size, depth and site) are tested together to explore their effect on the community structure on cobble and gravel bottoms. Diversity metrics (richness per sample, richness per area, diversity (H '), total cover), cover of life forms (hypnophyceae, ephemerophyceae, phanerophyceae, hemiphanerophyceae, chamaephyceae) and cover of the predominant species (Harveylithon samoënse, Jania pedunculata var. adhaerens, Lobophora spp., Canistrocarpus cervicornis, Halopteris scoparia) are used as descriptors of communities. Descriptors response was modeled using multiple regression analyses, in which each descriptor was considered separately as the dependent variable, while substrate size, depth and site was used as independent variables. Results show the substrate size was the most important variable with depth only being important for some perennial species although there was often site-site variability in these patterns. Richness per sample of macroalgal communities increased with substrate size; however, the highest values of richness per area and total cover increased towards the smallest substrates. Substrate size also positively influenced the cover of the perennial life forms hemiphanerophyceae and phanerophyceae, but do not on the cover of chamaephyceae. The perennial crustose Harveylithon samoënse showed a significant relationship with all variables increasing its cover towards small substrates in shallow, while the perennial erect Lobophora spp. are more abundant on large substrates at greater depths. Together these results showed that the substrate size was consistently the most important factor for algal diversity in unstable-bottom habitats.

潮下不稳定底部对决定大型藻类群落结构的环境干扰很敏感。在这里，三个变量（基质尺寸、深度和位置）一起测试，以探索它们对鹅卵石和砾石底部群落结构的影响。多样性度量（每个样品的丰富性，每单位面积的丰富度，多样性（H“），总盖），生命形式（hypnophyceae，ephemerophyceae，phanerophyceae，hemiphanerophyceae，chamaephyceae）和盖的主要种类的（盖Harveylithonsamoënse，Jania长柄变种adhaerens , Lobophora spp., Canistrocarpus cervicornis , Halopteris scoparia) 用作社区的描述符。使用多元回归分析对描述符响应进行建模，其中每个描述符被单独视为因变量，而底物尺寸、深度和位置被用作自变量。结果表明，基质大小是最重要的变量，深度仅对某些多年生物种很重要，尽管这些模式中通常存在场地变化。每个大型藻类群落样本的丰富度随着基质尺寸的增加而增加；然而，单位面积和总覆盖度的最高值向最小的基质增加。基质大小也对多年生生命形式半毛藻科和显藻科的覆盖率产生积极影响，但对茶藻科的覆盖率没有影响。多年生地壳Harveylithon samoënse显示出与所有变量的显着关系，增加其对浅层小基质的覆盖，而多年生直立Lobophora spp。在更深的大基板上更丰富。这些结果共同表明，基质大小始终是不稳定底部栖息地藻类多样性的最重要因素。