Abstract Halodule wrightii meadows in Southern Brazil have been regressing in an unsheltered area of the subtropical Paranaguá Bay, near their southern limit in the SW Atlantic, since 2006. To identify early indicators of regression events, we assessed variations in plant and macrobenthic structure in two local meadows under unsheltered and protected conditions. Differences between sites increased after an epiphytic overgrowth of the alga Hincksia mitchelliae at the unsheltered site. Seagrass growth was suppressed and the numbers of burrowing and opportunistic benthic species increased with the increase of algal biomass. In the protected meadow, seagrass biomass and number of leaves changed seasonally, but macrobenthic abundance and species richness remained stable. Ecosystem changes were evident when the unsheltered meadow was already collapsing. The number of leaves per shoot, the horizontal internode length, the abundance and structure of the macrofaunal associations, and the host-epiphyte surface interactions, were the first variables to reflect the early stages of seagrass regression. Our results suggest that the persistence of H. wrightii meadows at their southern distribution limit in the SW Atlantic will be affected by local hydrodynamics and their ability to compete with ephemeral macroalgal species under stress conditions.

中文翻译：

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大西洋西南部 Halodule wrightii 草甸及其南部分布界限附近的相关动物群的时间变化

摘要 自 2006 年以来，巴西南部的 Halodule wrightii 草甸一直在靠近西南大西洋南部边界的亚热带巴拉那瓜湾的一个未受庇护地区退化。为了确定退化事件的早期指标，我们评估了两种植物和大型底栖动物结构的变化。在不受庇护和受保护条件下的当地草地。在无遮蔽地点的海藻 Hincksia mitchelliae 附生过度生长后，地点之间的差异增加。随着藻类生物量的增加，海草生长受到抑制，穴居和机会性底栖物种的数量增加。在保护草甸，海草生物量和叶片数量随季节变化，但大型底栖动物丰度和物种丰富度保持稳定。当无人庇护的草地已经坍塌时，生态系统的变化就很明显了。每枝叶的数量、水平节间长度、大型动物群的丰度和结构以及寄主-附生植物表面相互作用，是反映海草退化早期阶段的第一个变量。我们的研究结果表明，H. wrightii 草甸在西南大西洋南部分布范围内的持久性将受到当地流体动力学及其在压力条件下与临时大型藻类物种竞争的能力的影响。