Physiological and Biochemical Analyses Shed Light on the Response of Sargassum vulgare to Ocean Acidification at Different Time Scales

Abstract

Studies regarding macroalgal responses to ocean acidification (OA) are mostly limited to short-term experiments in controlled conditions, which hamper the possibility to scale up the observations to long-term effects in the natural environment. To gain a broader perspective, we utilized volcanic CO2 vents as a “natural laboratory” to study OA effects on Sargassum vulgare at different time scales. We measured photosynthetic rates, oxidative stress levels, antioxidant contents, antioxidant enzyme activities, and activities of oxidative metabolic enzymes in S. vulgare growing at a natural acidified site (pH 6.7) compared to samples from a site with current pH (pH 8.2), used as a control one. These variables were also tested in plants transplanted from the control to the acidified site and vice-versa. After short-term exposure, photosynthetic rates and energy metabolism were increased in S. vulgare together with oxidative damage. However, in natural populations under long-term conditions photosynthetic rates were similar, the activity of oxidative metabolic enzymes was maintained, and no sign of oxidative damages was observed. The differences in the response of the macroalga indicate that the natural population at the acidified site is adapted to live at the lowered pH. The results suggest that this macroalga can adopt biochemical and physiological strategies to grow in future acidified oceans.

Sediment Carbon Variations in the Venice Lagoon and Other Transitional Water Systems of the Northern Adriatic Sea

“…Indeed, the concentrations of Corg were strongly correlated to sediment fines percentage, whereas Cinorg was associated to sediment density and pH (Table 3). The positive correlation between Cinorg and pH (Table 3) may be explained by the reduction or disappearance of crustose coralline algae at low pH values (6.7 ≤ 8.0), and as a consequence, the loss of the sediment carbonate fraction, as previously described [45][46][47] for studies on volcanic marine CO 2 vents in the sea around Ischia Island. Likewise, researchers [48] found that pH had a strong correlation with Cinorg produced from the small microcalcareus macroalgae belonging to the epiphytic genera Pneophyllum, Hydrolithon, and Melobesia, which grow on the largest macroalgae and aquatic angiosperms of the Italian TWS.…”

Antioxidative Properties of Baltic Sea Keystone Macroalgae (Fucus vesiculosus, Phaeophyceae) under Ocean Warming and Acidification in a Seasonally Varying Environment

“…To our knowledge, there are only very few studies dealing with the effect of CO 2 -induced acidification of seawater on the antioxidative potential of micro- and macroalgae. Acidification increased the MDA content of a diatom ( Thalassiosira weissflogii ) and a brown seaweed species ( Sargassum vulgare) , indicating that membrane lipid peroxidation was enhanced [ 98 , 99 ]. Additionally, the induction of SOD in S. vulgare under acidified conditions points to its major role in preventing ·O 2 − overproduction.…”

“…Additionally, the induction of SOD in S. vulgare under acidified conditions points to its major role in preventing ·O 2 − overproduction. Kumar et al [ 99 ] found, for S. vulgare , a higher energy metabolism after exposure to low pH conditions at volcanic CO 2 vents. The study by Iñiguez et al [ 100 ] revealed on the molecular level that CO 2 enrichment induced only very few transcriptomic changes (e.g., induction of transcripts coding for RuBisCO rbcL ) in the brown seaweed Desmarestia anceps .…”

Molecular response of Sargassum vulgare to acidification at volcanic CO2 vents: Insights from proteomic and metabolite analyses

“…However, even those species with active CCMs may benefit from increased pCO 2 if they utilize directly CO 2 instead of HCO 3 − as a carbon source. Previous pH drift experiments have revealed that S. vulgare populations at acidified and control sites have active CCM (Kumar, AbdElgawad, et al, 2017). Our results are in line with a recent comparative proteomic study showing enrichment of proteins involved in photosynthesis in the natural population of the seagrass Cymodocea nodosa in the CO 2 vents at Vulcano Island (Piro et al, 2020).…”

“…Marine areas characterized by natural CO 2 vents represent useful “natural laboratories” to investigate the impact of OA on macroalgae in their natural habitat (Dahms et al, 2018; Kumar, AbdElgawad, et al, 2017; Kumar et al, 2018, 2020; Kumar, Castellano, et al, 2017). Off the Island of Ischia, along the Castello Aragonese, natural underwater vents of volcanic origins release gases, mainly CO 2 , causing seawater acidification (Hall‐Spencer et al, 2008) and offering a unique opportunity to investigate the long‐term effects of OA.…”