Seasonal and interannual variations in coccolithophore abundance off Terceira Island, Azores (Central North Atlantic)

• Published in: Continental Shelf Research
• Main Authors: Narciso, Áurea, Gallo, Francesca, Valente, André, Cachão, Mário, Cros, Lluïsa, Azevedo, Eduardo B., Ramos, Joana Barcelos
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2016
• Subjects: Living coccolithophores; Seasonality; Phytoplankton ecology; Azores archipelago (Portugal); Faculdade de Ciências da Vida; North Atlantic
• Online Access: http://hdl.handle.net/10400.13/3840; https://doi.org/10.1016/j.csr.2016.01.019

In order to characterize the natural coccolithophore community occurring offshore Azores and to de-termine their annual and interannual patterns, monthly samples were collected, from September 2010 toDecember 2014, in the photic zone off Terceira Island.The present study revealed a clear seasonal distribution and a considerable interannual variability of theliving coccolithophore community. The highest coccolithophore abundances were observed during spring andwinter months, especially due to the smaller speciesEmiliania huxleyiandGephyrocapsa ericsonii. In fact, thehighest biomass period was registered during April 2011, associated with enhanced abundance of the over-calcified morphotype ofE. huxleyi,whichwaspossiblyinfluenced by subpolar waters and subsequent up-welling conditions. The highest abundances ofGephyrocapsa muelleraewere recorded during June 2011 and2014, indicating that this species characterizes the transition between the period of maximum productivity andthe subsequent smoother environmental conditions, thefirst and the later stages of the phytoplankton suc-cession described by Margalef, respectively. During summer to early fall, a gradual decrease of the overallcoccolithophore abundance was observed, while the species richness (Margalef diversity index) increased. Asubtropical coccolithophoreassemblage mainly composed byUmbellosphaera tenuis,Syracosphaeraspp.,Dis-cosphaera tubifera,Rhabdosphaera clavigeraandCoronosphaera mediterraneaindicated the presence of surfacewarmer waters accompanied by reduced mixing and low nutrients concentration. During late fall to winter, thecoccolithophore abundance increased again with a concomitant reduction in species diversity. This is poten-tially linked to low sea surface temperatures, moderate nutrients concentration and surface mixed layerdeepening. During 2011, colder and productive waters led to an increase in the total coccolithophore abun-dances. On contrary, during 2012, characterized by milder environmental conditions, an increase in the di-versity of ...