Dual role of DOM in a scenario of global change on photosynthesis and structure of coastal phytoplankton from the South Atlantic Ocean

Impact of Increased Nutrients and Lowered pH on Photosynthesis and Growth of Three Marine Phytoplankton Communities From the Coastal South West Atlantic (Patagonia, Argentina)

“…A similar study in the Godavari River Estuary (India) on the other hand reported that not only lowered pH but also nutrient supply play key role in shaping the community structure during microcosms experiments (Biswas et al, 2011). The growth rates at PU determined during the mid-acclimation (Figure 6E) were similar to those reported by Durán-Romero et al (2017), while the growth rates for the long acclimation (Figure 6E) agrees with those reported by Villafañe et al (2018); in this latter study the Future condition had higher rates than the Present, as observed in our study. The differential responses observed among these studies are most likely related to the acclimation period that not only change community structure but also condition the physiology of cells.…”

“…This is a novel approach, as most field studies have generally considered the effects of global change variables on single photosynthesis targets. Our previous studies have determined that Future scenarios had differential impacts on oxygen dynamics and PSII photochemistry (Villafañe et al, 2018;Vizzo et al, 2021), and that acclimation over time changed the rETR vs. NCP relation (Villafañe et al, 2018).…”

“…The PU site is under the influence of riverine waters that carry a heavy load of anthropogenic nutrients (Helbling et al, 2010;Bermejo et al, 2018), which also results in high Chl a concentration at the plume of the river (Figure 1B). Several global change studies have been done on phytoplankton communities from this site, with variables such as lowered pH, nutrients, temperature, input of terrigenous materials and mixing (Helbling et al, 2015b;Bermejo et al, 2018;Villafañe et al, 2018;Bermejo et al, 2020). Contrary to the PU site, IE is located in the open waters, and is a highly productive area, being the main nursery location for the hake (Merlucius hubsii) (Álvarez-Colombo et al, 2011).…”

“…The differential responses observed among these studies are most likely related to the acclimation period that not only change community structure but also condition the physiology of cells. Villafañe et al (2018) addressed the dual role of DOM carried by the Chubut river, and determined that the photosynthesis of cells exposed to solar radiation with an input of DOM inside the microcosms (i.e., physico-chemical role, attenuation of solar radiation and chemical exposure) were less efficient compared to cells that received an extra input of DOM outside the microcosms (i.e., physical role, attenuation of solar radiation). In our study, using the same global change variables, NCP values at PU were positive throughout the day, with significant diurnal increases of ETR from morning to noon and continuous increases in P m B throughout a day, unlike in the other sites (Figure 5).…”

“…In this region, some studies have determined significant effects on different global change variables on the size structure, taxonomic composition and phytoplankton responses of natural communities [Villafañe et al (2021) and references therein]. Only few studies (Villafañe et al, 2015(Villafañe et al, , 2018Bermejo et al, 2020) assessed the effects of both increased nutrients and lowered pH, conditions that are already present in Patagonian coastal waters (Bermejo et al, 2018;Orselli et al, 2018), on phytoplankton communities, however, since these studies were conducted in an estuarine site with unique characteristics it made the extrapolation of these results to other ecosystems unfeasible. To get a broader range of responses, we selected three geographical sites with similar temperature and radiation conditions but different geomorphological characteristics, and thus with different water exchange frequencies, on the Patagonian coast.…”