ORIGINAL PAPER A mesoscale study of phytoplankton assemblages around the South Shetland Islands (Antarctica) Cristina Garcı ´a-Mun ˜oz • Luis M. Lubia ´n • Carlos M. Garcı ´a • A ´ ngeles Marrero-Dı ´az • Pablo Sangra ` • Maria Vernet Received: 9 November 2012 / Revised: 8 April 2013 / Accepted: 25 April 2013 / Published online: 10 May 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract Phytoplankton assemblages around the South Shetland Islands (SSI) were closely related to mesoscale physical features, based on high spatial resolution sampling performed during the summer of 2010. Sampling was done in 8 transects with stations 9 km apart. Phytoplankton groups were described using flow cytometry, FlowCAM and HPLC/CHEMTAX pigment analysis. Nanophyto- plankton (2–20 lm) was predominant throughout the study area, which was dominated by small diatoms. They were distributed along the stratified waters of the SSI shelf and in the centre of the Bransfield Strait where an anticyclonic eddy was detected, established between two frontal struc- tures [Bransfield Front and Peninsula Front (PF)]. The highest concentrations correlated with mid-to-high temperatures (1.07 °C) and mid-salinities (34.03) corre- sponding with Transitional Bellinghausen Water stations. Haptophytes distribution co-varied with small diatoms but also appeared in those vertical mixed stations with Tran- sitional Zonal Water with Weddell Sea influence. A shift from smaller to larger diatoms was detected at the ice edge in the Antarctic Sound. Cryptophytes were restricted to stratified stations of the SSI shelf and those associated with the PF, while small prasinophytes were the only group occupying deeper and colder waters of the Drake Passage, beneath the Antarctic Surface Water, north of a narrow frontal region described here for the first time (Shetland Front). Phytoplankton assemblages around the SSI were strongly connected with the Bransfield Current System, supporting a clockwise circulation around the archipelago. The Bransfield Current System components are permanent structures during the austral summer suggesting that the distribution of phytoplankton, which responds to these structures, must also be a quasi-permanent feature. Keywords South Shetland Islands  Phytoplankton  Small diatoms  Mesoscale  Water masses  Fronts Introduction The composition of phytoplankton in coastal and frontal regions of Antarctic waters has previously been described as a nanoplankton-sized community (size range 2–20 lm, Equivalent Spherical Diameter (ESD)) (Hewes et al. 1985; Becquevort 1997; Ishikawa et al. 2002). This size range usually includes diatoms, flagellates and protozoa (Sme- tacek et al. 1990; Villafan ˜e et al. 1991; Ishikawa et al. 2002) with haptophytes and diatoms being the dominant groups (Marchant and Thomsen 1994; Arrigo and Electronic supplementary material The online version of this article (doi:10.1007/s00300-013-1333-5) contains supplementary material, which is available to authorized users. C. Garcı ´a-Mun ˜oz (&)  L. M. Lubia ´n Departamento de Ecologı ´a y Gestio ´n Costera, Instituto de Ciencias Marinas de Andalucı ´a (ICMAN-CSIC), 11510 Puerto Real, Ca ´diz, Spain e-mail: cristina.garcia@icman.csic.es C. M. Garcı ´a Departamento de Biologı ´a, Facultad de Ciencias del Mar y Ambientales, Universidad de Ca ´diz, 11510 Puerto Real, Ca ´diz, Spain A ´ . Marrero-Dı ´az  P. Sangra ` Departamento de Fı ´sica, Facultad de Ciencias del Mar, Universidad de Las Palmas de Gran Canaria, Campus de Tafira, 35017 Las Palmas de Gran Canaria, Spain M. Vernet Integrative Oceanographic Division, Scripps Institution of Oceanography, MC 0218, University of California San Diego, La Jolla, CA 92093-0218, USA 123 Polar Biol (2013) 36:1107–1123 DOI 10.1007/s00300-013-1333-5