The tropical western Pacific, one of the most oligotrophic seas on Earth, has a large number of seamounts. In this sea, we hypothesize that although the presence of shallow seamounts can enhance phytoplankton biomass, they do not alter the phytoplankton community composition. The concentration and distribution of size-fractionated chlorophyll a (Chl a) on the C4 Seamount were measured, and the phytoplankton community was analyzed based on photosynthetic pigments. The results showed that the deep chlorophyll maximum (DCM) was located between 100 and 150 m and that picophytoplankton such as prochlorophytes and cyanobacteria (mainly Synechococcus) were the dominant groups, contributing approximately 85% of the Chl a. The integrated Chl a concentration above the seamount was significantly higher than that off the seamount, and most communities were enhanced near the peak. The physical, chemical, and biological coupling processes of the C4 Seamount support the classic hypothesis of the seamount effect. However, the relative contributions of different phytoplankton groups to Chl a were not significantly different between stations above and off the seamount, and the analysis of similarities among results also indicated that the community composition on the C4 Seamount did not differ significantly from that off the seamount. In addition, size-fractionated Chl a data from two nearby shallow seamounts also supported our hypothesis. More studies on the ecology of seamounts in the tropical western Pacific are required to further confirm and refine these results.

热带西太平洋是地球上最富营养的海洋之一，拥有大量的海山。在这个海洋中，我们假设尽管浅海山的存在可以增强浮游植物的生物量，但它们不会改变浮游植物的群落组成。测量了C4海山上大小分级的叶绿素a（Chl a）的浓度和分布，并基于光合色素分析了浮游植物群落。结果表明，深层叶绿素最大值（DCM）位于100至150 m之间，浮游植物，如原绿藻类和蓝细菌（主要为Synechococcus）是主要的类群，约占Chla的85％。集成的Chl海山上方的浓度显着高于海山以外的浓度，并且大多数社区在山顶附近得到了增强。C4海山的物理，化学和生物耦合过程支持海山效应的经典假设。但是，不同的浮游植物基团与叶绿素的相对贡献一个不站上方和关闭海山之间显著不同，并且结果中的相似的分析还表明，在C4海山社区组合物不显著从关闭海山不同。此外，大小分级叶绿素一来自附近两个浅海山的数据也支持了我们的假设。需要进一步研究热带西太平洋海山生态，以进一步证实和完善这些结果。