Sporophytic photosynthesis and gametophytic growth of the kelp Ecklonia stolonifera affected by ocean acidification and warming

Abstract

Juvenile sporophytes and gametophytes of Ecklonia stolonifera were incubated in combinations of three pCO 2 levels (360, 720 and 980 ppmv) and two temperatures (10 and 15°C for sporophytes; 15 and 20°C for gametophytes) to examine potential effects of climate change on photosynthesis and growth. Sporophytes had significantly higher maximum quantum yields (F v /F m ) and maximum relative electron transport rates (rETR max ) at 720 ppmv than 360 and 980 ppmv. Also, these parameters were significantly lower at higher temperature of 15°C than at 10°C. Growth of female gametophytes was maximal at 360 ppmv rather than enriched pCO 2 levels.Female gametophytes had significantly lower growth at higher temperature of 20°C than at 15°C. These results indicate effects of elevated pCO 2 varied between generations: stimulating sporophytic photosynthesis and inhibiting gametophytic growth.Ocean acidification and warming would constitute a grave threat to seedling cultivation of E. stolonifera caused by growth inhibition of gametophytes at high pCO 2 levels and temperatures. K E Y W O R D Sgametophytic growth, kelp aquaculture, ocean acidification, ocean warming, sporophytic photosynthesis

Effects of elevated pCO2 and nutrient enrichment on the growth, photosynthesis, and biochemical compositions of the brown alga Saccharina japonica (Laminariaceae, Phaeophyta)

“…Some results showed that OA negatively influenced the microscopic development of Macrocystis pyrifera and Undaria pinnatifida (Gaitán-Espitia et al, 2014; Xu et al, 2015; Gao et al, 2019a), which may be due to the inhibition of cell activities (Ragazzola et al, 2012). In contrast, kelp sporophytes exhibited positive physiological responses to OA (Schmid, Mills & Dring, 1996; Olischlaeger et al, 2012; Gao et al, 2019a; Gao et al, 2019b) due to stimulation of photosynthetic activities by increased inorganic carbon (Olischlaeger et al, 2012). Additionally, kelp species benefit from an increase in nutrient availability in seawater.…”

Effect of environmental history on the habitat-forming kelp Macrocystis pyrifera responses to ocean acidification and warming: a physiological and molecular approach

“…Saccharina latissima and Laminaria solidungula ) 88 . However, we do not discard the possibility that this effect might differ across different kelp life stages depending on their physiological requirements and inorganic carbon physiology 63 , 89 , 90 .…”

What does the future look like for kelp when facing multiple stressors?

“…Evidence suggests that climate warming can exacerbate the negative effects of acidification and pollutants. For instance, warming and acidification combine to inhibit gametophyte growth in Ecklonia stolonifera (Gao et al, 2019) and increase mortality of Macrocystis pyrifera zoospores (Gaitán-Espitia et al, 2014), while warming and copper pollution interact synergistically to decrease the size of Macrocystis pyrifera gametophytes (but do not affect Undaria pinnatifida gametophytes; Leal et al, 2018).…”

“…Evidence suggests that climate warming can exacerbate the negative effects of acidification and pollutants. For instance, warming and acidification combine to inhibit gametophyte growth in Ecklonia stolonifera (Gao et al, 2019 ) and increase mortality of Macrocystis pyrifera zoospores (Gaitán‐Espitia et al, 2014 ), while warming and copper pollution interact synergistically to decrease the size of Macrocystis pyrifera gametophytes (but do not affect Undaria pinnatifida gametophytes; Leal et al, 2018 ). Warming also exacerbates damage caused by elevated ultraviolet radiation on sporophyte formation causing reduced egg release in Saccharina latissima and Laminaria digitata (Müller et al, 2008 ) and decreases in the zoospore germination rate in Alaria marginata (Fredersdorf et al, 2009 ).…”