| Zusammenfassung: | ABSTRACT: Two distinct morphotypes of the coccolithophoreEmiliania huxleyiwere observed as part of the phytoplankton succession offshore of Namibia, where coastal upwelling created strong gradients in sea surface temperature (SST), salinity, and nutrient conditions. The sampled surface waters hosted a characteristic succession of phytoplankton communities: diatoms bloomed in newly upwelled waters above the shelf, whereas dense coccolithophore communities dominated byE. huxleyiwere found farther offshore, in progressively aging upwelled waters. A substantially calcifiedE. huxleyimorphotype (labeled Type A*) dominated plankton assemblages at stations influenced by upwelling, that immediately succeeded coastal diatom blooms. This morphotype caused a chlorophyll and 19’-hexanoyloxyfucoxanthin (19’-HF) maximum with >1 × 10⁶ cells l−1, straddling a pycnocline at 17 m depth where thein situN:P ratio was ≈13. Farther offshore, within <20 nautical miles distance, populations of Type A* drastically declined, and a more delicate morphotype with thin distal shield elements and open central area (Type B/C) was found. This morphotype was most abundant (~0.2 × 10⁶ cells l−1) in high-phosphate, nitrogen-depleted surface waters (N:P ≈ 8), where it co-existed with other coccolithophores, most notablySyracosphaeraspp. Extensive surface blooms of coccolithophores observed by satellites in the same region in the past were identified by microscopy as being produced byE. huxleyiandS. pulchra. However, blooms ofE. huxleyiat greater depths in the euphotic zone, such as those observed in this study, will go undetected by satellites and thus underestimate coccolithophore biomass and calcification within upwelling regions.
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