Marine habitat formers such as seaweeds and corals are lynchpins of coastal ecosystems, but their functional diversity and how it varies with scale and context remains poorly studied. Here, we investigate the functional diversity of seaweed assemblages across the rocky intertidal stress gradient at large (zones) and small (quadrat) scales. We quantified complementary metrics of emergent group richness, functional richness (functional space occupied) and functional dispersion (trait complementarity of dominant species). With increasing shore height, under species loss and turnover, responses of functional diversity were scale- and metric-dependent. At the large scale, functional richness contracted while—notwithstanding a decline in redundancy—emergent group richness and functional dispersion were both invariant. At the small scale, all measures declined, with the strongest responses evident for functional and emergent group richness. Comparisons of observed versus expected values based on null models revealed that functional richness and dispersion were greater than expected in the low shore but converged with expected values higher on the shore. These results show that functional diversity of assemblages of marine habitat formers can be especially responsive to environmental stress gradients at small scales and for richness measures. Furthermore, niche-based processes at the small—neighbourhood—scale can favour co-occurrence of functionally distinctive species under low, but not high, stress, magnifying differences in functional diversity across environmental gradients. As assemblages of marine habitat formers face accelerating environmental change, further studies examining multiple aspects of functional diversity are needed to elucidate patterns, processes, and ecosystem consequences of community (dis-)assembly across diverse groups.

海藻和珊瑚等海洋栖息地的形成者是沿海生态系统的关键所在，但其功能多样性以及其随规模和环境的变化方式仍然很少研究。在这里，我们研究了在大（区域）和小（四边形）尺度上跨潮间带岩石应力梯度的海藻组合的功能多样性。我们量化了新兴群体丰富度，功能丰富度（功能空间占用）和功能分散（优势物种的特征互补）的互补度量。随着海岸高度的增加，在物种丧失和周转的情况下，功能多样性的响应与规模和度量有关。尽管冗余度有所下降，但在大规模情况下，功能丰富性下降了，而应急组的丰富性和功能分散性却是不变的。在小范围内 所有指标均下降，对功能性和突发性群体富裕度的响应最明显。基于零模型的观测值与预期值的比较显示，功能丰富性和分散性在低岸地区大于预期，但在岸上则与较高预期值收敛。这些结果表明，海洋生境形成者集合体的功能多样性可以在小规模和富裕措施下对环境应力梯度产生特别的响应。此外，在小范围内以小生境为基础的过程可能有利于在低但不是高压力下共同存在功能独特的物种，从而扩大了整个环境梯度下功能多样性的差异。随着各种海洋栖息地形成者面临加速的环境变化，