Ocean warming has greater and more consistent negative effects than ocean acidification on the growth and health of subtropical macroalgae

Abstract

Macroalgae are the major habitat-forming organisms in many coastal temperate and subtropical marine systems. Although climate change has been identified as a major threat to the persistence of macroalgal beds, the combined effects of ocean warming and ocean acidification on algal performance are poorly understood. Here we investigate the effects of increased temperature and acidification on the growth, calcification and nutritional content of 6 common subtropical macroalgae; Sargassum linearifolium, Ulva sp., Amphiroa anceps, Corallina officinalis, Delisea pulchra and Laurencia decussata. Algae were reared in a factorial cross of 3 temperatures (23°C [ambient], 26°C and 28°C) and 3 pH levels (8.1 [ambient], 7.8 and 7.6) for 2 wk. The highest (28°C) temperature decreased the growth of all 6 macroalgal species, irrespective of the pH levels. In contrast, the effect of decreased pH on growth was variable. The growth of Ulva sp. and C. officinalis increased, L. decussata decreased, while the remaining 3 species were unaffected. Interestingly, the differential responses of macroalgae to ocean acidification were unrelated to whether or not a species was a calcifying alga, or their carbon-uptake mechanism-2 processes that are predicted to be sensitive to decreased pH. The growth of the calcifying algae (C. officinalis and A. anceps) was not affected by reduced pH but calcification of these 2 algae was reduced when exposed to a combination of reduced pH and elevated temperature. The 3 species capable of uptake of bicarbonate, S. linearifolium, L. decussata and Ulva sp., displayed positive, negative and neutral changes in growth, respectively, in response to reduced pH. The C:N ratio for 5 of the 6 species was unaffected by either pH or temperature. The consistent and predictable negative effects of temperature on the growth and calcification of subtropical macroalgae suggests that this stressor poses a greater threat to the persistence of subtropical macroalgal populations than ocean acidification under ongoing and future climate change.

Subsurface Ocean Warming Hotspots and Potential Impacts on Marine Species: The Southwest South Atlantic Ocean Case Study

“…Brazilian seagrass communities are being affected by eutrophication, increased storm frequency, and sediment shifts associated with climate change (Short et al, 2006). Increased temperatures negatively affect growth and calcification of subtropical macroalgae, posing a great threat to macroalgal populations (Koch et al, 2013;Graba-Landry et al, 2018). But compelling evidence suggests that jellyfish abundances fluctuate with climatic cycles (Condon et al, 2013), with the majority of the temperate species studied increasing their abundance in warm temperatures due to increased asexual reproduction (Purcell, 2005;Purcell et al, 2007).…”

Impact of ocean acidification on the metabolome of the brown macroalgae Lobophora rosacea from New Caledonia

“…(Diaz-Pulido et al, 2011;Gordillo et al, 2016;Xu et al, 2017), but their responses also depend on other factors such as developmental stages or carbon uptake mechanisms (e.g. passive CO 2 uptake without carbon-concentrating mechanism (CCM), or with CCM combined to high or low affinity for Dissolved Inorganic Carbon (DIC)) (Britton et al, 2016;Cornwall et al, 2017;Graba-Landry et al, 2018). Moreover, as observed in C 3 -terrestrial plants, an increase in CO 2 would likely affect the production of allelochemicals in macroalgae (e.g.…”

A multistressor model of carbon acquisition regulation for macroalgae in a changing climate

“…Prior studies have looked at the effects of temperature, light, or inorganic carbon concentration on photosynthetic rates at different pH values, but not all in combination (Beer and Eshel 1983;Beer et al 1990;Drechsler and Beer 1991;Henley 1992;Xu and Gao 2012;Rautenberger et al 2015;Gao et al 2016;Young and Gobler 2016;Ober and Thornber 2017;Graba-Landry et al 2018;Legrand et al 2018). Here, we synthesize these data to model primary production simultaneously over the ranges of 5 C to 30 C, sub-saturating (50 μmol photons m −2 s −1 ) and saturating (400 μmol photons m −2 s −1 ) photon flux densities, and 180 to 1600 μatm pCO 2 (pH range 7.5 to 8.3) to compare their relative magnitudes of influence.…”

“…On the left side of Eq. (1), values for net photosynthesis [ C i ( P net )] at a given temperature, light intensity and p CO 2 come from established relationships among these parameters reported in papers by Beer and Eshel (1983), Beer et al (1990), Drechsler and Beer (1991), Henley et al (1992), Xu and Gao (2012), Olischläger et al (2013), Rautenberger et al (2015), Gao et al (2016), Graba‐Landry et al (2018) ( see model parameterization below). The expression on the right side of the equation shows the three DIC uptake mechanisms that, summed together, must account for the observed photosynthetic rate at a specified combination of environmental parameters.…”

“…Interestingly, growth may be enhanced under OA even when photosynthesis is not (Xu and Gao 2012; Kroeker et al 2013; Olischläger et al 2013). Temperature appears to have stronger effects on photosynthesis and growth than does OA, but direct comparisons of the two and synergistic interactions between them are only beginning to be understood (Johnson and Carpenter 2012; Koch et al 2013; Olischläger et al 2013; Sarker et al 2013; Graba‐Landry et al 2018). The effects of OA on macroalgae appear to be small compared to those of co‐occurring environmental variables such as nutrient loading and light intensity, in addition to temperature (Kübler and Raven 1994, 1995; Xu and Gao 2012; Rautenberger et al 2015; Kang and Chung 2017; Reidenbach et al 2017; Gao et al 2018; Graba‐Landry et al 2018, but see Young and Gobler (2016) and Xu et al (2017) for exceptions).…”