Cryptophytes: An emerging algal group in the rapidly changing Antarctic Peninsula marine environments.

The western Antarctic Peninsula (WAP) is a climatically sensitive region where foundational changes at the basis of the food web have been recorded; cryptophytes are gradually outgrowing diatoms together with a decreased size spectrum of the phytoplankton community. Based on a 11-year (2008-2018) in-situ dataset, we demonstrate a strong coupling between biomass accumulation of cryptophytes, summer upper ocean stability, and the mixed layer depth. Our results shed light on the environmental conditions favoring the cryptophyte success in coastal regions of the WAP, especially during situations of shallower mixed layers associated with lower diatom biomass, which evidences a clear competition or niche segregation between diatoms and cryptophytes. We also unravel the cryptophyte photo-physiological niche by exploring its capacity to thrive under high light stress normally found in confined stratified upper layers. Such conditions are becoming more frequent in the Antarctic coastal waters and will likely have significant future implications at various levels of the marine food web. The competitive advantage of cryptophytes in environments with significant light level fluctuations was supported by laboratory experiments that revealed a high flexibility of cryptophytes to grow in different light conditions driven by a fast photo-regulating response. All tested physiological parameters support the hypothesis that cryptophytes are highly flexible regarding their growing light conditions and extremely efficient in rapidly photo-regulating changes to environmental light levels. This plasticity would give them a competitive advantage in exploiting an ecological niche where light levels fluctuate quickly. These findings provide new insights on niche separation between diatoms and cryptophytes, which is vital for a thorough understanding of the WAP marine ecosystem.

Dinoflagelados (Peridiniales, Prorocentrales) do microplâncton na plataforma continental e talude do extremo sul do Brasil (inverno 2005, verão 2007) / Microplankton dinoflagellates (Peridiniales, Prorocentrales) at the continental shelf and slope in Southern Brasil (winter 2005, summer 2007)

Este estudo teve por objetivo identificar as morfo-espécies de dinoflagelados do microplâncton (>20 μm) das Ordens Peridiniales e Prorocentrales ao largo do Cabo de Santa Marta Grande, CSMG (SC, 28º 40' S) e Albardão-Chuí, AC (RS, 34º 40' S) durante dois cruzeiros oceanográficos: inverno de 2005 e verão de 2007. Amostras de plâncton foram coletadas através de arrastos verticais com rede de plâncton (20 μm), preservadas com formalina 4 por cento e analisadas ao microscópio invertido equipado com câmara digital. Quando necessário, a identificação de espécies de Peridiniales foi efetuada através do número e morfologia das placas da teca realçadas com Calco Flúor Branco MR2; espécies de Prorocentrales foram identificadas com base em seu tamanho, forma, presença de processos apicais, padrão dos poros e marcas na faixa intercalar. Foram identificadas 25 espécies, das quais Protoperidinium (11), Prorocentrum (6), Corythodinium (3), Podolampas (2), Oxytoxum (2) e Heterocapsa (1). Espécies de Prorocentrum apresentaram ampla distribuição na plataforma continental do extremo sul do Brasil, enquanto as espécies de Peridiniales foram observadas principalmente na região do Albardão-Chuí durante o inverno, sob a influência da Pluma do Río de la Plata. Oxytoxum milneri foi pela primeira vez registrada na região sul do País, e Protoperidinium cassum var. cassum, P. curtipes e Heterocapsa triquetra foram registradas pela primeira vez no Brasil.

This study aimed at identifying morpho-species of microplankton dinoflagellates (> 20 μm) of the order Peridiniales and Prorocentrales off Santa Marta Grande Cape, CSMG (SC, 28º 40' S) and Albardão-Chui, AC (RS, 34º 40' S) during oceanographic cruises conducted in winter 2005 and summer 2007. Plankton samples were obtained by vertical net (mesh size 20 μm) hauls preserved with formaldehyde 4 percent and analyzed using the inverted microscope equipped with a digital camera. The identification of Peridiniales species was based on the number and morphology of thecal plates enhanced with Calco Fluor White MR2 whenever necessary and the identification of Prorocentrales was based on cell size, shape, presence of apical processes, pore pattern and marks at the intercalary band. We identified 25 species, including Protoperidinium (11), Prorocentrum (6), Corythodinium (3), Podolampas (2), Oxytoxum (2) and Heterocapsa (1). Prorocentrum species were widely distributed on the continental shelf of southern Brazil, while Peridiniales species were mainly found off Albardão-Chui during winter, especially under the influence of the plume of La Plata River. Oxytoxum milneri was the first time recorded in southern Brazil, while Protoperidinium cassum var. cassum, P. curtipes and Heterocapsa triquetra, were first registered in Brazil.