Coccolithophores are an ecologically and biogeochemically important group of calcifying marine plankton, contributing globally to both the organic carbon pump and the carbonate counter pump. Understanding their distribution in today's ecosystems is crucial for both paleoenvironmental reconstruction and for predicting their fate under climate change and environmental pollution. Traditionally regarded as open ocean dwellers, more recent studies have highlighted their importance in coastal systems.

Here we describe the coccolithophore community in the Catalan Sea (Northwestern Mediterranean), off the Ebro River Delta, based on an oceanographic survey conducted in autumn 2019. We identify three environmentally distinct regimes: mixed (mostly shallow), transition (upper photic layers offshore), and stratified deep waters (below 75 m). Total coccolithophore density is driven by E. huxleyi and peaks in the mixed zone where nutrient concentrations are low, but nitrite concentrations are high. We propose that peak cell densities are partly explained by a switch from nitrate to nitrite usage similarly to diatoms behavior. Species diversity peaks in deeper offshore waters due to vertical stratification. Helicosphaera carteri and Algirosphaera robusta benefit from Emiliania huxleyi decrease both in coastal and offshore environment.

颗石藻是生态和生物地球化学上重要的钙化海洋浮游生物群，在全球范围内对有机碳泵和碳酸盐反泵做出贡献。了解它们在当今生态系统中的分布对于古环境重建以及预测它们在气候变化和环境污染下的命运至关重要。传统上被视为公海居民，最近的研究强调了它们在沿海系统中的重要性。

在此，我们根据 2019 年秋季进行的海洋学调查，描述了埃布罗河三角洲附近加泰罗尼亚海（地中海西北地区）的颗石藻群落。我们确定了三种不同的环境状况：混合型（大部分是浅层）、过渡型（近海上部光层） ）和分层深水（75 m 以下）。总颗石藻密度由赫胥氏埃球菌驱动，并在营养物浓度较低但亚硝酸盐浓度较高的混合区达到峰值。我们认为，峰值细胞密度的部分解释是由硝酸盐使用转变为亚硝酸盐使用，类似于硅藻的行为。由于垂直分层，近海较深水域的物种多样性达到顶峰。Helicosphaera carteri和Algirosphaera robsta受益于沿海和近海环境中Emiliania huxleyi 的减少。