CO2 effects on taxonomic composition and nutrient utilization in an Equatorial Pacific phytoplankton assemblage

Abstract

We report the results of a field incubation experiment demonstrating a substantial shift in the taxonomic composition of Equatorial Pacific phytoplankton assemblages exposed to CO 2 levels of 150 and 750 ppm (dissolved CO 2~3 to 25 µM). By the end of the experiment, the phytoplankton community in all samples was dominated by diatoms and Phaeocystis sp. However, the relative abundance of these phytoplankton taxa differed significantly between CO 2 treatments. Taxonomic pigment analysis and direct microscopic examination of samples revealed that the abundance of diatoms decreased by ~50% at low CO 2 relative to high CO 2 , while the abundance of Phaeocystis increased by ~60% at low CO 2 . This CO 2 -dependent shift was associated with a significant change in nutrient utilization, with higher ratios of nitrate:silicate (N:Si) and nitrate:phosphate (N:P) consumption by phytoplankton in the low CO 2 treatment. Despite the significant changes in taxonomic composition and nutrient consumption ratios, total biomass and primary productivity did not differ significantly between the CO 2 treatments. Our results suggest that CO 2 concentrations could potentially influence competition among marine phytoplankton taxa and affect oceanic nutrient cycling.

Effects of elevated CO<sub>2</sub> and temperature on phytoplankton community biomass, species composition and photosynthesis during an experimentally induced autumn bloom in the western English Channel

“…Elevated pCO 2 may therefore lead to lowered energetic costs of carbon assimilation in some species and a redistribution of the cellular energy budget to other processes (Tortell et al, 2002). In this study, under elevated pCO 2 where the dominant group was nanophytoplankton, the most abundant species was the haptophyte Phaeocystis spp.…”

Increased carbon dioxide availability alters phytoplankton stoichiometry and affects carbon cycling and growth of a marine planktonic herbivore

“…Higher availability of carbon and the subsequent changes in seawater nutrient composition, caused by the relatively lower availability of mineral nutrients compared to C, may also cause shifts in competitive interactions between algae (e.g. Kuffner et al 2007;Rost et al 2003;Swanson and Fox 2007;Tortell et al 2002), thus changing the community composition of primary producers, possibly leading to the loss of species or the replacement of some species with others. Taken together, these changes may alter the flow of energy and matter through the food web and modify the functioning of communities.…”

Effects of elevated CO2 on phytoplankton community biomass and species composition during a spring Phaeocystis spp. bloom in the western English Channel

“…A number of other studies have shown that the growth rates of specific diatoms can increase by 5% to 33% following 20 generations acclimated at elevated pCO 2 between 750 and 1000 matm (Phaeodactylum tricornutum, Thalassiosira pseudonana, T. guillardi, T. weissflogii, T. punctigera and Cocinodiscus wailesii) (Wu et al, 2014(Wu et al, , 2010 and that the highest growth occurred in diatoms > 40 mm in diameter (T. punctigera and C. wailesii). Similarly in some natural phytoplankton communities exposed to elevated pCO 2 (750 ppmv) diatoms and prymnesiophytes become dominant, making up 60% and 30% of the total biomass (Tortell et al, 2002). Tortell et al (2008) also observed in Ross Sea phytoplankton, a shift in dominance from Phaeocystis antarctica (contributing > 90% community biomass) to large chain-forming diatoms (Chaetoceros spp.)…”

“…Endo et al, 2013;Eggers et al, 2013;Feng et al, 2009;Hare et al, 2007;Schulz et al, 2008;Tortell et al, 2002). Since a wide variety of processes are affected, high variability in responses has been reported within and across taxa.…”