The size, type and abundance of planktonic organisms influence the efficiency with which carbon is transferred through the lower trophic levels, ultimately affecting dynamics at the higher trophic levels of the marine food web. In temperate shelf sea, such as the waters south-west of the UK, the plankton growing season span from early spring to autumn. While the plankton spring bloom has been extensively studied, the end of the growing season in September-October has received less attention, despite its potential importance for autumn-spawning fish and their larval stage survival. In this study we investigated the variability of the structure and carbon content of the planktonic communities in the waters south-west of the UK in October 2013 and 2014, discussing potential implications of these changes to small pelagic fish and higher trophic levels. Microphytoplankton (20–200 µm) dominated the plankton community in terms of carbon in 2013, while nanophytoplankton (<20 µm) in 2014. Ciliates, Copepoda, Decapoda and Cnidaria represented the highest proportion of carbon in the zooplankton component in both years, although ciliates and Copepoda biomass was higher in 2014. Environmental conditions were linked to these changes and were significant in describing the carbon content of the plankton groups. In particular, silicate concentration appeared to be a key variable, affecting diatom/plankton dynamics at the end of the growing season. Other important environmental variables associated with the structure of plankton groups were salinity, sea surface temperature, chlorophyll-a, difference between sea surface temperature and bottom temperature, phosphate and nitrogen concentrations. Although the composition and carbon distribution of the plankton community were different in the two years, cluster and Random Forest analyses showed similarities in the clusters of stations identified, defining an area of higher plankton carbon along the south coast of Cornwall, and an area of lower carbon in the Bristol Channel in both years. Presence of suitable prey for planktivorous small pelagic fish (e.g. Paracalanus and Pseudocalanus), particularly in 2014, provided supporting evidence of the importance of this sea area as a foraging and nursery ground for sardines and other small pelagic fish, as well as for their predators.

浮游生物的大小、类型和丰度会影响碳通过较低营养级转移的效率，最终影响海洋食物网较高营养级的动态。在温带大陆架海域，如英国西南部海域，浮游生物生长季节从早春到秋季。虽然浮游生物春季开花已被广泛研究，但 9 月至 10 月生长季节的结束受到的关注较少，尽管它对秋季产卵鱼及其幼虫阶段的生存具有潜在的重要性。在这项研究中，我们调查了 2013 年 10 月和 2014 年 10 月和 2014 年英国西南部水域浮游群落结构和碳含量的变化，讨论了这些变化对小型中上层鱼类和更高营养水平的潜在影响。2013 年，微型浮游植物 (20–200 µm) 在浮游生物群落中占主导地位，而 2014 年纳米浮游植物 (<20 µm)。纤毛虫、桡足类、十足目和刺胞动物在浮游动物成分中的碳比例在这两年中最高，尽管纤毛虫和桡足类的生物量在 2014 年更高。环境条件与这些变化有关，并且在描述浮游生物群的碳含量方面具有重要意义。特别是，硅酸盐浓度似乎是一个关键变量，在生长季节结束时会影响硅藻/浮游生物的动态。与浮游生物群结构相关的其他重要环境变量是盐度、海面温度、叶绿素-a、海面温度和底部温度之间的差异、磷酸盐和氮浓度。尽管浮游生物群落的组成和碳分布在两年中有所不同，但集群和随机森林分析表明，确定的站点集群具有相似性，确定了康沃尔南海岸浮游生物碳含量较高的区域和较低的区域。这两年布里斯托尔海峡的碳排放量。存在适合浮游性小型中上层鱼类的猎物（例如Paracalanus和Pseudocalanus），特别是在 2014 年，提供了支持证据，证明该海域作为沙丁鱼和其他小型中上层鱼类及其捕食者的觅食和育苗场的重要性。