Seaweed are ecologically important organisms playing a central structural and functional role in coastal ecosystems (providing habitat, mating and nursery grounds, food and refuge for several marine organisms). Additionally, their commercial potential has been rising since seaweed are directly or indirectly used by humans in many countries. This work aimed to evaluate the temporal and spatial variation of target species biomass and the composition of seaweed assemblages at an exposed rocky shore, in Northern Portugal. The targeted species were: Codium spp., Chondrus crispus, Mastocarpus stellatus, Osmundea pinnatifida and Chondracanthus acicularis. Two sampling sites were defined and in each one 18 haphazard placed quadrats (50 × 50 cm) were sampled: 9 in the low-shore and 9 in the mid-shore. Sampling was conducted periodically from April 2017 to January 2018, in six sampling occasions. Significant temporal variation was detected in the mean biomass values of Codium spp. and O. pinnatifida, at low-shore, where high abundance of these species in typically cold months could be related to the atypical warmer year 2017 in Portugal. C. acicularis revealed a significant spatial variation at both shore levels, which could be explained by different water channels orientations at the two sampling sites. The multivariate analysis showed that the effect of sampling occasion on the seaweed assemblage structure depended on site and revealed that some species, such as Ulva spp., apparently play an important role in seaweed assemblages of Belinho-Mar intertidal and highlights its ecological importance for these community. This study provides a baseline data for future work in similar areas, allowed the development of effective management plans as basis for seaweed exploitation guidelines.

海藻是生态上重要的生物，在沿海生态系统中发挥着重要的结构和功能作用（为几种海洋生物提供栖息地、交配和育苗场、食物和避难所）。此外，由于海藻在许多国家被人类直接或间接使用，其商业潜力一直在上升。这项工作旨在评估葡萄牙北部暴露的岩石海岸上目标物种生物量的时间和空间变化以及海藻组合的组成。目标物种是：Codium spp.、Chondrus creamus、Mastocarpus stellatus、Osmundea pinnatifida和Chondracanthus acicularis. 定义了两个采样点，每一个采样点有 18 个随意放置的样方（50 × 50 厘米）：9 个在低岸，9 个在中岸。抽样于 2017 年 4 月至 2018 年 1 月定期进行，分六次抽样。在Codium spp的平均生物量值中检测到显着的时间变化。和O. pinnatifida ，在低海岸，在通常寒冷的月份，这些物种的高丰度可能与葡萄牙 2017 年的非典型温暖年有关。C. acicularis揭示了两个海岸水平的显着空间变化，这可以通过两个采样点的不同水道方向来解释。多变量分析表明，采样时机对海藻组合结构的影响取决于地点，并揭示了一些物种，如石莼属，显然在 Belinho-Mar 潮间带的海藻组合中起重要作用，并突出了其对这些海藻组合的生态重要性社区。这项研究为类似领域的未来工作提供了基线数据，允许制定有效的管理计划作为海藻开发指南的基础。