Many aquatic microbes form colonies, yet little is known about their abundance and fitness relative to single‐celled taxa. The formation of diatom chains, in particular, has implications for diatom growth, survival, and carbon transfer. Here, we utilize an autonomous underwater microscope, combined with traditional microscopy, to develop a novel, multiyear record of the abundance of single‐cell and colony‐forming diatoms at Scripps Pier, a coastal location in the Southern California Bight. The total abundance of diatoms was lower during the warmer and more stratified conditions from 2015 to early 2016, but increased in cooler and less stratified conditions in mid‐2016 to late 2017. Diatom blooms were dominated by chain‐forming taxa, whereas solitary diatoms prevailed during low‐biomass conditions. The abundance of dinoflagellates, some of which are important diatom predators, is highest when colonies (chains) are most abundant. These observations of the diatom assemblage are consistent with a trade‐off between resource acquisition and predator defenses. Solitary diatom cells dominated during conditions with weak nutrient supply because they have a greater diffusive catchment area per cell in comparison to cells living in colonies. In contrast, during bloom conditions when nutrient supply is high and predators are abundant, forming a colony may reduce predation losses to quickly growing microzooplankton predators, and afford chains a higher fitness despite the costs of sharing resources with neighboring cells. These results highlight the contrasting ecology of single‐cell and chain‐forming diatoms, and the need to differentiate them in monitoring campaigns and ecological models.

中文翻译：

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形成菌落的海洋硅藻种群变异的环境驱动因素

许多水生微生物形成菌落，但相对于单细胞类群它们的丰度和适应性知之甚少。硅藻链的形成尤其对硅藻的生长，存活和碳转移具有影响。在这里，我们利用自主水下显微镜与传统显微镜相结合，在南加利福尼亚湾沿岸的斯克里普斯码头（Scripps Pier）开发了长达数年的新颖的单细胞硅藻和硅藻形成记录。从2015年到2016年初，在温度较高且分层较多的条件下，硅藻的总丰度较低，但在2016年中至2017年底的温度较低且分层较少的条件下，硅藻的丰度有所增加。在低生物量条件下。丰富的鞭毛虫，其中一些是重要的硅藻掠食者，当菌落（链）最丰富时最高。这些对硅藻集合体的观察与资源获取与捕食者防御之间的权衡是一致的。在营养供应不足的情况下，孤立的硅藻细胞占主导地位，因为与居住在菌落中的细胞相比，它们每个细胞的扩散捕集面积更大。相反，在开花条件下，当养分供应量高且捕食者丰富时，形成菌落可以减少快速增长的微浮游动物捕食者的捕食损失，并为链提供更高的适应性，尽管需要与相邻细胞共享资源。这些结果凸显了单细胞硅藻和链形成硅藻的不同生态学，