Effects of ocean acidification on growth and physiology of Ulva lactuca (Chlorophyta) in a rockpool‐scenario

Abstract

Rising atmospheric CO2-concentrations will have severe consequences for a variety of biological processes. We investigated the responses of the green alga Ulva lactuca (Linnaeus) to rising CO2-concentrations in a rockpool scenario. U. lactuca was cultured under aeration with air containing either preindustrial pCO2 (280 matm) or the pCO2 predicted by the end of the 21st century (700 matm) for 31 days. We addressed the following question: Will elevated CO2-concentrations affect photosynthesis (net photosynthesis, maximum relative electron transport rate (rETR(max)), maximum quantum yield (Fv/Fm), pigment composition) and growth of U. lactuca in rockpools with limited water exchange? Two phases of the experiment were distinguished: In the initial phase (day 1-4) the Seawater Carbonate System (SWCS) of the culture medium could be adjusted to the selected atmospheric pCO2 condition by continuous aeration with target pCO2 values. In the second phase (day 4-31) the SWCS was largely determined by the metabolism of the growing U. lactuca biomass. In the initial phase, Fv/Fm and rETR(max) were only slightly elevated at high CO2-concentrations, whereas growth was significantly enhanced. After 31 days the Chl a content of the thalli was significantly lower under future conditions and the photosynthesis of thalli grown under preindustrial conditions was not dependent on external carbonic anhydrase. Biomass increased significantly at high CO2-concentrations. At low CO2-concentrations most adult thalli disintegrated between day 14 and 21, whereas at high CO2-concentrations most thalli remained integer until day 31. Thallus disintegration at low CO2-concentrations was mirrored by a drastic decline in seawater dissolved inorganic carbon and HCO3 -. Accordingly, the SWCS differed significantly between the treatments. Our results indicated a slight enhancement of photosynthetic performance and significantly elevated growth of U. lactuca at future CO2-concentrations. The accelerated thallus disintegration at high CO2-concentrations under conditions of limited water exchange indicates additional CO2 effects on the life cycle of U. lactuca when living in rockpools.

The short-term effects of elevated CO2 and ammonium concentrations on physiological responses in Gracilariopsis lemaneiformis (Rhodophyta)

“…However, the role of CO 2 is debatable with some studies showing that F v /F m is not affected by elevated CO 2 levels (Hofmann et al 2012;Olischläger et al 2013;Kram et al 2016) and others indicating that chlorophyll fluorescence increases under high CO 2 concentrations . We found here that the photosynthetic efficiency of G. lemaneiformis was more strongly affected by greater NH 4 + concentrations than by higher CO 2 levels.…”

Effects of NaCl and Na2CO3 stresses on photosynthetic ability of Chlamydomonas reinhardtii

“…However, this was not found in algal cells stressed by Na 2 CO 3 , due to the high pH and Na + toxic effects. High pH can reduce algal photosynthetic ability and pigment content, because the dissolved CO 2 in water is limited (Axelsson et al 1999;Olischläger et al 2013). Meanwhile, the depletion of dissolved CO 2 stimulates ROS formation (Sültemeyer et al 1993).…”

“…In algae, lower dose of NaHCO 3 can promote the photosynthesis as HCO − 3 is the carbon source (Bhatti & Colman 2011;Huege et al 2011), but higher dose of NaHCO 3 and Na 2 CO 3 is harmful due to the high pH and Na + toxic effects. It has been reported that high pH reduces algal photosynthetic ability and pigment content, because it limits dissolved CO 2 -concentration in water (Axelsson et al 1999;Olischläger et al 2013). The depletion of dissolved Effects of NaCl and Na2CO3 stresses 1315 CO 2 can stimulate ROS formation, increase antioxidant enzyme activity (Sültemeyer et al 1993) and even induce PCD (Vardi et al 1999).…”

The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve

“…Contrary to the negative effects of increased CO2 on calcifying organisms, previous studies have shown that some photosynthetic organisms, such as seagrasses (Koch et al, 2013;Palacios and Zimmerman, 2007), phytoplankton (Fu et al, 2012;Hattenrath-Lehmann et al, 2015), and macroalgae (Olischläger et al, 2013;Young and Gobler, 2016) may benefit from a high CO2 environment. Such photosynthetic autotrophs may also have the capacity to buffer carbonate chemistry, 15 potentially alleviating the harmful effects of excessive CO2 on calcifying organisms.…”

“…While future increases in CO2 may promote the growth of fast-growing, macroalgae such as Ulva (Björk et al, 1993;Olischläger et al, 2013;Gobler, 2016, 2017) and could, in turn, could provide chemical resilience for calcifying organisms in acidified environments (Anthony et al, 2013;Wahl et al, 2017), such interactions have yet to be fully explored.…”