Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss The efect of a transient frontal zone on the spatial distribution of extant coccolithophores around the Madeira archipelago (Northeast Atlantic) Áurea Narciso a,b,∗ , Rui Caldeira c,d , Jesus Reis c , Mona Hoppenrath e , Mário Cachão d , Manfred Kaufmann a,b,f a CIIMAR-Madeira, Caminho da Penteada, 9020-105, Funchal, Madeira, Portugal b CIIMAR, University of Porto, Av. General Norton de Matos s/n, 4450-208, Matosinhos, Portugal c Oceanic Observatory of Madeira (OOM), Edifício Madeira Tecnopolo, Piso 0, 9020-105, Funchal, Madeira, Portugal d Dom Luiz Institute, Faculty of Sciences, University of Lisbon, 1749-016, Lisboa, Portugal e Senckenberg am Meer, German Centre for Marine Biodiversity Research (DZMB), D-26382, Wilhelmshaven, Germany f University of Madeira, Faculty of Life Sciences, Marine Biology Station of Funchal, 9000-107, Funchal, Portugal ARTICLE INFO Keywords: Phytoplankton Biodiversity Ecology Islands Subtropical northeast Atlantic ABSTRACT In order to characterize the coccolithophore community around the Madeira archipelago and to understand the efect of a transient frontal zone on its distribution, 149 seawater samples from the frst 150 m were collected in 37 stations, during the research cruise POS466 of RV Poseidon. The present study revealed the occurrence of two biogeographic domains, NE and SW, during the late winter of 2014, with distinct physical-chemical and cal- careous nannoplankton characteristics. The NE sector was characterized by higher coccolithophore cell densities (mean of 56 × 10 3 cell L −1 ) and a slightly lower diversity (Margalef diversity index of 1.80) when compared with the SW sector (mean of 47 × 10 3 cell L −1 ; Md index of 1.86). The more productive sector, NE, was asso- ciated with colder, less saline and higher nutrient content water masses, linked to the injection of a westerly fow with origin in the Azores frontal system. Total cell densities ranged between 12 × 10 3 and 112 × 10 3 cell L −1 , being Emiliana huxleyi the dominant species followed by small Gephyrocapsa. The most common and subordinate taxa, in order of decreasing abundance, were: Gephyrocapsa oceanica, Michaelsarsia spp., Syracosphaera spp., Umbilicosphaera spp. and Algirosphaera robusta. Relationships between environmental conditions and spatial and vertical variability in coccosphere abundance, associated E. huxleyi and small Gephyrocapsa with the more productive water mass conditions, linked to the thermohaline transient front. G. oceanica distribution indicated its preference for warmer and less turbulent coastal waters, when compared to E. huxleyi and small Gephyrocapsa. Michaelsarsia spp. and A. robusta revealed preference for the northwest coast of Madeira, associated with mesotrophic con- ditions of the water column. Syracosphaera spp. and Umbilicosphaera spp. were well distributed throughout the archipelago and along the sampled depths, from the coast to open ocean conditions, as well as from lower to higher productive zones, displaying afnities for the meso to oligotrophic conditions, typical of these subtropical waters. The broad depth range of several taxa and the nonexistence of the coccolithophore vertical succession were the result of homogeneous and generalized well-mixed surface layer during the present survey. 1. Introduction Phytoplankton biomass in the oceans constitutes about 1–2% of the total primary producers on earth (Falkowski, 1994). Despite its low biomass, these organisms contribute with approximately 46% per annum of the global primary production and carbon fxation (Falkowski et al., 1998; Field et al., 1998). They also play an important role in the oxygen cycle, releasing in the atmosphere about 40–50% of the global oxygen (Anderson, 2005). Due to its crucial involvement in climate regulation and biogeochemical cycles, marine phytoplankton has been increasingly targeted in global change studies. Coccolithophores are pelagic unicellular algae, which represent about 10% of the global phytoplankton biomass (Tyrrell and Young, 2009). Members of the Haptophyte class Prymnesiophyceae Hibberd, they are characterized by the ability to produce calcite platelets, at least by one of its life cycle stages. These structures, referred as coccoliths, surround the living cell https://doi.org/10.1016/j.ecss.2019.04.014 Received 5 December 2018; Received in revised form 22 March 2019; Accepted 10 April 2019 ∗ Corresponding author. CIIMAR-Madeira, Caminho da Penteada, 9020-105, Funchal, Madeira, Portugal. E-mail address: aurea.narciso@ciimarmadeira.org (Á. Narciso). Estuarine, Coastal and Shelf Science 223 (2019) 25–38 Available online 20 April 2019 0272-7714/ © 2019 Elsevier Ltd. All rights reserved. T