Carlos Rafael Borges Mendes

Shifts in the dominance between diatoms and cryptophytes during three late summers in the Bransfield Strait (Antarctic Peninsula)

Recent global warming reduces surface water salinity around the Antarctic Peninsula as a result of the glacial meltwater runoff, which increases the occurrence and abundance of certain phytoplankton groups, such as cryptophytes. The dominance of this particular group over diatoms affects grazers, such as Antarctic krill, which preferentially feed on diatoms. Using three late summer data sets from the Bransfield Strait (2008–2010), we observed variations in the dominant phytoplankton groups determined by HPLC/CHEMTAX pigment analysis and confirmed by microscopy. Results indicate that the dominance of diatoms, particularly in 2008 and 2009, was associated with a deeper upper mixed layer (UML), higher salinity and warmer sea surface temperature. In contrast, cryptophytes, which were dominant in 2010, were associated with a shallower UML, lower salinity and colder sea surface temperatures. The low diatom biomass observed in the summer of 2010 was associated with high nutrient concentration, particularly silicate, and low chlorophyll a (summer monthly average calculated from satellite images). The interannual variability here observed suggests a delayed seasonal succession cycle of phytoplankton in the summer of 2010 associated with a cold summer and a late ice retreat process in the region. This successional delay resulted in a notable decrease of primary producers’ biomass, which is likely to have impacted regional food web interactions. This study demonstrates the susceptibility of the Antarctic phytoplankton community structure to air temperature, which directly influences the timing of ice melting and consequently the magnitude of primary production and succession pattern of phytoplankton groups.

Phytoplankton community during a coccolithophorid bloom in the Patagonian Shelf: microscopic and high-performance liquid chromatography pigment analyses

We describe the phytoplankton community and biomass during a summer coccolithophorid bloom sampled over the Patagonian shelf (48.5°S–50.5°S). Those phytoplankton species can contribute to the flux of calcium carbonate out of surface waters. Results from both microscope and high-performance liquid chromatography (HPLC) analysis are shown to complement information on the phytoplankton community. From CHEMTAX analysis of HPLC data, the most important organisms and groups identified were the coccolithophorid Emiliania huxleyi , the haptophyte Phaeocystis antarctica , dinoflagellates, diatoms, cryptophytes, prasinophytes and cyanobacteria. Phytoplankton microscope counts were converted into phytoplankton group-specific biovolume estimates. Although some microscope-identified taxa could not be determined by CHEMTAX, e.g. the autotrophic ciliate Myrionecta rubra , cluster analyses from both techniques showed similar results for the main groups. Both Emiliania huxleyi cell concentration and biomass, and the pigment 19′-hexanoyloxyfucoxanthin were the most important biological features during the sampling period. At surface, nitrate was moderately high (0.2–4.2 µM) in coccolithophorid-dominated samples, whereas phosphate ( E. huxleyi . Competition and probably differential grazing could also promote a coccolithophorid outgrowth over other photoautotrophs during the summer season in the Patagonian shelf.

Photobiology of the zoanthid Zoanthus sociatus in intertidal and subtidal habitats

Intertidal environments are boundaries between marine and terrestrial ecosystems that are subject to rapid fluctuations across tidal cycles. This study investigates, for the first time, the photobiology of symbiotic zoanthids inhabiting different tidal environments: subtidal, intertidal pools and intertidal areas exposed to air during low tide. More specifically, we assessed the photochemical efficiency, Symbiodinium density and photosynthetic pigments profile of Zoanthus sociatus during low tide. Photochemical efficiency was lower and cell density higher in air exposed zoanthids. The profile of photosynthetic pigments also varied significantly among tidal habitats, particularly photoprotective pigments such as dinoxanthin and diadinoxanthin. Differences were also observed for the pigment content per cell, but the proportion of particular pigments (peridinin/chlorophyll-a and diatoxanthin+diadinoxanthin/chlorophyll-a) remained stable. Results suggest that aerial exposure conditions induce reversible downregulation of photochemical processes but no photophysiological impairment or bleaching. These findings provide a baseline for future studies addressing the prevalence of these overlooked cnidarians in environmentally dynamic reef flats.

Pigment-based chemotaxonomy of phytoplankton in the Patos Lagoon estuary (Brazil) and adjacent coast

ABSTRACT The composition and distribution of phytoplankton assemblages were studied monthly at two sites in the Patos Lagoon estuary and at one site on the adjacent coast over three years (May 2012–April 2015). Samples were collected for microscopic examination and high-performance-liquid-chromatography pigment analysis. The pigment data were analysed using CHEMTAX software to estimate the contribution of different taxonomic groups to total chlorophyll a (Chl a). Phytoplankton assemblages were generally dominated by diatoms, which contributed, on average, 51% of the total Chl a, especially at the Cassino Beach surf zone, where Asterionellopsis guyunusae was the main species contributing to the high diatom-associated biomass. Cyanobacteria appeared as an important group at the lagoon’s mouth station, contributing, on average, 37% of the total Chl a. Cryptophytes, chlorophytes, prasinophytes and dinoflagellates were less important and contributed, on average, 13, 7, 5 and 3%, respectively, of the total phytoplankton biomass in the region. A good correlation was found between microscopy counts and CHEMTAX biomass estimates for most phytoplankton groups. The relationship, however, was poor for cyanobacteria and green algae, where the pigment-based approach estimated relatively higher biomasses. This discrepancy may be related to either the presence of plant/algae detritus in the samples (captured by the pigment method) and/or an underestimation by the microscopic method. Despite some differences, the pigment-based method successfully described the overall phytoplankton community pattern during the study period. Canonical Correspondence Analysis showed that temperature, salinity and dissolved inorganic nutrients are important driving forces of the observed variation in the phytoplankton community.

Phytoplankton light absorption and the package effect in relation to photosynthetic and photoprotective pigments in the northern tip of Antarctic Peninsula

This study investigates the variability in the spectral absorption of phytoplankton in Antarctic waters. A large in situ data set comprising phytoplankton pigments and hyperspectral absorption was measured in the northern tip of Antarctic Peninsula during 2013 and 2014 summers at several depths. A proxy of package effect was estimated from the phytoplankton absorption spectra, independently of chlorophyll a. Variations in the concentration of photosynthetic and photoprotective pigments were discernible by changes in this metric but not in the chlorophyll a specific absorption coefficient of phytoplankton. The fucoxanthin to chlorophyll a ratio correlated positively to package effect due to an increase in cell size of phytoplankton (diatoms) and increasing fucoxanthin content per cell to maximize light harvesting in depth. The package effect was found to covary inversely with photoprotective pigments relative to chlorophyll a, partially due to their contribution to enhance absorption in the blue part of the spectrum. Using a cluster analysis (k-means algorithm) on the phytoplankton absorption spectra, we illustrate the capacity to identify a regular increase in the degree of package effect. This approach can be useful to classify the phytoplankton assemblages in Antarctic waters according to different degrees of pigment packaging, each one related to a specific pigment composition. Our results demonstrate the potential for this classification at different temporal and spatial scales from ocean color satellite data. This should improve our understanding of deviations in global bio-optical algorithms when applied to the Southern Ocean.