New insights on the dominance of cryptophytes in Antarctic coastal waters: A case study in Gerlache Strait

Abstract

Changes in phytoplankton composition from large diatoms to small cryptophytes and their implications to the food web have been previously associated with rapid warming of surface waters in the western Antarctic Peninsula (WAP).However, ecological and physiological attributes that favor dominance of these flagellates in the region have not been fully explored. The overall aim of this work was to characterize the phytoplankton pigments and assemblages in relation to environmental conditions during three successive summer cruises (2013, 2014 and 2015) in the Gerlache Strait − a coastal area in the northern WAP. Data on phytoplankton (through HPLC/CHEMTAX pigment analysis) and associated physical (water column structure) and chemical (macronutrients) parameters were determined. Cryptophytes were conspicuously found in shallow mixed layers, under stratified conditions, as the main contributors to total phytoplankton biomass. Their greatest contributions were associated with warmer surface waters at the northwestern sector of the strait. Other phytoplankton groups (Phaeocystis antarctica in 2013 and small diatoms in both 2014 and 2015) were also important components. Photoprotective carotenoids (mainly alloxanthin), with an important role in preventing photodamage caused by excess light, were closely linked with the dominance of cryptophytes at surface layers. The results of this study suggest that the prevalence of cryptophytes in WAP coastal waters can be, to a great extent, due to a particular ability of those small flagellates to successfully grow in highly illuminated conditions in shallow upper mixed layers and strong water column stratification.

Recurrent seascape units identify key ecological processes along the western Antarctic Peninsula

“…Diatoms are known to form plentiful blooms early in the season (Goldman et al, 2015;Schofield et al, 2017) and in offshore regions (Whitehouse, Priddle, & Woodward, 1995). We observed considerable drawdown of nitrate + nitrite relative to silicate in the highest January chlorophyll concentrations associated with SU 5 however, suggesting that these nearshore blooms ( Figure S3) likely reflect mixed or flagellate-dominated blooms, consistent with previous studies (Borges Mendes et al, 2017;Goldman et al, 2015;Schofield et al, 2017). It is important to recognize that these January accumulations of biomass do not necessarily represent the peak in the annual cycle of primary production (Goldman et al, 2015).…”

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

“…The production of fucoxanthin is an important mechanism for diatom assemblages to increase light harvesting in the tip of Antarctic Peninsula as addressed by Mendes et al . [] and similarly observed in surface Argentinean waters [ Lutz et al ., ]. In fact, the production of photosynthetic pigments is feasible in nonlimiting nutrient conditions.…”

“…Note that the samples were taken during middle/late summer, thus, they do not represent average growth conditions, which can only be described when similar analyses and comparisons are performed in other periods for the studied area. Similar proportions of photoprotective pigments to those for lower latitudes suggest that algal communities around the Antarctic Peninsula are not light limited in summer [see also Mendes et al ., ]. In fact, during our surveys, the ratios of Z eu to Z MLD were generally higher than 1, which implies that phytoplankton cells within Z MLD probably did not experience light limitation while they mixed vertically through the mixed layer.…”

“…A detailed description of the phytoplankton composition observed in GS is found in Mendes et al . []. In BS, the proportion of diatoms was low to moderate in 2013 (13–58% in L < 37% ), but contributed substantially to the phytoplankton biomass in all regions in 2014 (0–81% in L > 37% ).…”

Antarctic phytoplankton community composition and size structure: importance of ice type and temperature as regulatory factors

“…Decreased ice cover has been associated with a reduction in photosynthetic efficiency (Schofield et al 2018) and several studies have described a reduction in overall phytoplankton biomass and a shift from large phytoplankton (diatoms) to smaller flagellated species. These shifts have been associated with reduced salinities, higher temperatures and stronger vertical stratification (Moline and Prezelin 1996;Moline et al 2004;Montes-Hugo et al 2009;Venables et al 2013;Mendes et al 2017;Rozema et al 2017c). However, the physicochemical drivers behind community shifts towards flagellated phytoplankton remain unclear, likely due to the diversity among flagellated phytoplankton spanning different taxonomic groups and cell sizes, and each may interact differently with the physicochemical environment.…”