Many seaweed species are particularly important for passive marine dispersal, yet relatively little is known about their floating and stranding dynamics. Here, we studied these dynamics for two kelp species over four consecutive years at mid-latitudes (30°S). Floating kelps were found during all seasons, but Macrocystis pyrifera was always more abundant than Durvillaea incurvata. Highest floating biomasses were reached during summer and fall, whereas considerable stranded biomasses on nearby shores were only observed during summer. The proportion of fragments among the floating kelps was high throughout the entire study period and highest for M. pyrifera during summer. At the same time, blades of M. pyrifera that floated in nearshore waters in summer had a high blade index and thus were intact (i.e., not yet compromised by unfavorable environmental conditions). These results suggest that during summer, floating kelps become quickly resupplied from benthic sources, which compensates their frequent losses due to degradation and stranding. During fall, biomasses of floating kelps remain high because of reduced losses. Interestingly, increased wind speed was a good predictor for the biomass accumulations of the two kelp species, although the floating biomass of M. pyrifera was additionally influenced by oceanographic fronts. Our findings suggest that at mid-latitudes the dynamics of floating seaweed stocks are dependent on the availability of benthic source populations (continuous throughout the year) and export due to degradation (high in summer/fall) and stranding (high in summer).

中文翻译：

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受风的影响：中纬度漂浮和搁浅海藻的季节性动态

许多海藻物种对于被动海洋扩散特别重要，但对其漂浮和搁浅动态知之甚少。在这里，我们在中纬度 (30°S) 连续四年研究了两种海带物种的这些动态。一年四季都有漂浮的海带，但Macrocystis pyrifera 的数量总是比Durvillaea incurvata 多。夏季和秋季达到了最高的漂浮生物量，而附近海岸的大量搁浅生物量仅在夏季观察到。在整个研究期间，漂浮海带中的碎片比例很高，夏季最高的是M. pyrifera。同时，M. pyrifera 的叶片夏季漂浮在近岸水域的叶片指数很高，因此完好无损（即尚未受到不利环境条件的影响）。这些结果表明，在夏季，漂浮的海带从底栖来源迅速得到补充，弥补了由于退化和搁浅造成的频繁损失。在秋季，由于损失减少，漂浮海带的生物量仍然很高。有趣的是，增加的风速是两种海带物种生物量积累的良好预测指标，尽管M. pyrifera的漂浮生物量还受到海洋前沿的影响。我们的研究结果表明，在中纬度地区，漂浮海藻种群的动态取决于底栖来源种群的可用性（全年连续）和由于退化（夏季/秋季高）和搁浅（夏季高）导致的出口。