Abundance of living coccolithophores in the northern Arabian Sea (Table 2)

The present study was conducted to provide information about living coccolithophores from the northern Arabian Sea as potential proxies in palaeoceanographic studies. In all, 71 plankton samples from 16 stations collected in September 1993 were analysed for their contents of living coccolithophores. Absolute abundances range from less than 400 coccospheres per litre in surface waters to 35 000 spheres per litre at intermediate water depths. From 49 identified taxa, nine species contribute significant cell numbers of more than 2000 coccospheres per litre and comprise more than 10% of the communities in at least one sample. Important species are (in approximate order of cell abundances): Gephyrocapsa oceanica, Florisphaera profunda, Oolithotus antillarum, Calciosolenia murrayi, Umbellosphaera irregularis, Emiliania huxleyi, Umbellosphaera tenuis, Calciopappus rigidus, and Algirosphaera robusta. At most profiles, a vertical succession of coccolithophore species was found. Calciosolenia murrayi and C. rigidus were restricted to surface waters, whereas high numbers of F. profunda and A. robusta occurred at depths below 40 m. The coccolithophore communities reflected the local oceanographic situation and seemed to be more dependent on mixed layer depth and nutrient availability than on temperature and salinity changes. Additionally, synecologic competition with diatoms in part controlled the species composition and generally reduced the abundance of coccolithophores. Synecological and ecological tolerances of species were discussed with the help of cluster analysis.本研究旨在为阿拉伯海北部的现生颗石藻（coccolithophores）提供基础数据，使其可作为古海洋学（palaeoceanography）研究中的潜在替代性指标（proxies）。本次研究对1993年9月采集自16个站位的71份浮游生物（plankton）样品进行分析，以检测其中现生颗石藻的组成与丰度。样品中颗石藻的绝对丰度范围为：表层水体中每升不足400颗颗石球（coccospheres），至中层水深处的每升35000颗颗石球。在已鉴定的49个分类群（taxa）中，有9个物种的每升颗石球丰度超过2000颗，且在至少一份样品中占群落总丰度的10%以上。按丰度大致排序的优势物种如下：大洋桥石藻（Gephyrocapsa oceanica）、深海光球藻（Florisphaera profunda）、安的列斯卵石藻（Oolithotus antillarum）、默里钙管藻（Calciosolenia murrayi）、不规则伞球藻（Umbellosphaera irregularis）、赫氏艾密里藻（Emiliania huxleyi）、细弱伞球藻（Umbellosphaera tenuis）、坚硬钙盘藻（Calciopappus rigidus）及强壮阿尔及尔球藻（Algirosphaera robusta）。在多数采样剖面中，均可观测到颗石藻物种的垂直分布演替规律。默里钙管藻与坚硬钙盘藻仅分布于表层水体；而大量的深海光球藻与强壮阿尔及尔球藻则集中出现于40米以深的水层。颗石藻群落结构可反映当地的海洋环境特征，其分布更多受控于混合层深度与营养盐可获得性，而非温度与盐度的变化。此外，与硅藻（diatoms）的群落间竞争在一定程度上调控了物种组成，并普遍降低了颗石藻的总丰度。本研究通过聚类分析（cluster analysis）探讨了各物种的群落生态与生态耐受特性。