The reef-building coralSiderastrea sidereaexhibits parabolic responses to ocean acidification and warming

Abstract

Anthropogenic increases in atmospheric CO2 over this century are predicted to cause global average surface ocean pH to decline by 0.1–0.3 pH units and sea surface temperature to increase by 1–4°C. We conducted controlled laboratory experiments to investigate the impacts of CO2-induced ocean acidification (pCO2 = 324, 477, 604, 2553 µatm) and warming (25, 28, 32°C) on the calcification rate of the zooxanthellate scleractinian coral Siderastrea siderea, a widespread, abundant and keystone reef-builder in the Caribbean Sea. We show that both acidification and warming cause a parabolic response in the calcification rate within this coral species. Moderate increases in pCO2 and warming, relative to near-present-day values, enhanced coral calcification, with calcification rates declining under the highest pCO2 and thermal conditions. Equivalent responses to acidification and warming were exhibited by colonies across reef zones and the parabolic nature of the corals' response to these stressors was evident across all three of the experiment's 30-day observational intervals. Furthermore, the warming projected by the Intergovernmental Panel on Climate Change for the end of the twenty-first century caused a fivefold decrease in the rate of coral calcification, while the acidification projected for the same interval had no statistically significant impact on the calcification rate—suggesting that ocean warming poses a more immediate threat than acidification for this important coral species.

Impact of diurnal temperature fluctuations on larval settlement and growth of the reef coral <i>Pocillopora damicornis</i>

“…The relationship between skeletal growth in corals and temperature is nonlinear and characterized by a parabola with an optimum and threshold, beyond which the stimulatory impact of temperature will be reversed (Wírum et al, 2007;Buddemeier et al, 2008;Inoue et al, 2012;Castillo et al, 2014). Although the optimal temperature for calcification by P. damicornis recruits remains unknown, it is possible that the recruits exposed to the fluctuating 31 • C treatment calcified at a slower rate when the temperature was below 31 • C compared to those in the constant 31 • C treatment.…”

Effects of seawater pCO2 and temperature on calcification and productivity in the coral genus Porites spp.: an exploration of potential interaction mechanisms

“…Anthony et al 2008;Castillo et al 2014). Many combined seawater pCO 2 /temperature studies raise temperature above the coral thermal stress threshold (Castillo et al 2014;Bahr et al 2016). These studies mimic the effects of stressful, short-term increases in seawater temperature but do not simulate the impact of more subtle, long-term temperature change (Hoegh-Guldberg et al 2007).…”

“…Coral responses can be modified by variations in other environmental parameters, e.g. light and nutrient availability (Chan and Connolly 2013;Chauvin et al 2011), by study duration (Huang et al 2014;Castillo et al 2014) or by nonlinear relationships between seawater pCO 2 /temperature and calcification (e.g. Anthony et al 2008;Castillo et al 2014).…”

“…light and nutrient availability (Chan and Connolly 2013;Chauvin et al 2011), by study duration (Huang et al 2014;Castillo et al 2014) or by nonlinear relationships between seawater pCO 2 /temperature and calcification (e.g. Anthony et al 2008;Castillo et al 2014). Many combined seawater pCO 2 /temperature studies raise temperature above the coral thermal stress threshold (Castillo et al 2014;Bahr et al 2016).…”

Baseline Levels of <i>Siderastrea siderea</i> Bleaching under Normal Environmental Conditions in Little Cayman

“…Siderastrea siderea, commonly known as the massive starlet coral, is an abundant reef building coral in both shallow and deep Caribbean waters and is resilient when exposed to several non-ideal conditions [5]. Although S. siderea has been shown to have a stable relationship with its symbionts [6], it is one of the first species to bleach, making it a useful early indicator of disturbance events [7].…”