In the brackish Baltic Sea, shedding of adventitious branches is central to asexual recruitment of new thalli in the brown algae Fucus vesiculosus and F. radicans. To test which factors influence the formation of adventitious branches in brackish and in more marine conditions, we sampled 29 Fucus sites in the Baltic Sea (salinity 3–11) and 18 sites from the Danish straits, Kattegat, Skagerrak, and the North Sea (salinity 15–35). Separately for each area, we used structural equation modelling to determine which of eight predictor factors (phosphate, nitrate, chlorophyll-a (as a proxy for turbidity), temperature, salinity, oxygen, grazing pressure, and thallus area) best explained observed numbers of adventitious branches. In more marine waters, high yearly average values of phosphate, salinity and turbidity had positive effects on the formation of adventitious branches. In brackish-waters, however, high numbers of adventitious branches were found in areas with low yearly average values of temperature, salinity and oxygen. Grazing intensity had no significant effect in either of the two study areas, contrasting findings from studies in other areas. In areas with both sexually and asexually reproducing Fucus individuals, clones had on average more adventitious branches than unique genotypes, although there was strong variation among clonal lineages. This study is the first to investigate multiple potential drivers of formation of adventitious branches in natural populations of Fucus. Our results suggest that several different factors synergistically and antagonistically affect the growth of adventitious branches in a complex way, and that the same factor (salinity) can have opposing effects in different areas.

中文翻译：

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影响海藻Fusus vesiculosus和F. radicans不定枝形成的因素

在咸淡的波罗的海，不定枝的脱落是无性招募新藻类在褐藻褐藻Fucus vesiculosus和F. radicans中的关键。为了测试哪些因素会影响咸淡及更多海洋环境中不定枝的形成，我们在波罗的海（盐度3-11）中采样了29个Fucus站点，并从丹麦海峡，Kattegat，Skagerrak和北海采样了18个Fucus站点（盐度15-35）。对于每个区域，我们分别使用结构方程模型来确定八个预测因子（磷酸盐，硝酸盐，叶绿素-a（作为浊度的替代指标），温度，盐度，氧气，放牧压力和河床面积中的哪一个）能最好地解释观测值不定分支机构。在更多的海水中，磷酸盐的年平均值很高，盐度和浊度对不定枝的形成有积极影响。然而，在微咸水中，在温度，盐度和氧气的年均平均值较低的地区发现了大量不定枝。放牧强度在两个研究领域均无显着影响，这与其他领域的研究结果形成鲜明对比。在有性生殖和无性生殖双胞胎个体的地区，尽管克隆世系之间存在很大的差异，但克隆平均具有比独特基因型更多的不定枝。这项研究是第一个调查富花属自然种群中不定枝形成的多种潜在驱动因素。我们的结果表明，几种不同的因素以复杂的方式协同和拮抗地影响不定枝的生长，