Warmer more acidic conditions cause decreased productivity and calcification in subtropical coral reef sediment‐dwelling calcifiers

Abstract

The effects of elevated CO 2 and temperature on photosynthesis and calcification in the calcifying algae Halimeda macroloba and Halimeda cylindracea and the symbiont-bearing benthic foraminifera Marginopora vertebralis were investigated through exposure to a combination of four temperatures (28uC, 30uC, 32uC, and 34uC) and four CO 2 levels (39, 61, 101, and 203 Pa; pH 8.1, 7.9, 7.7, and 7.4, respectively). Elevated CO 2 caused a profound decline in photosynthetic efficiency (F V : F M ), calcification, and growth in all species. After five weeks at 34uC under all CO 2 levels, all species died. Chlorophyll (Chl) a and b concentration in Halimeda spp. significantly decreased in 203 Pa, 32uC and 34uC treatments, but Chl a and Chl c 2 concentration in M. vertebralis was not affected by temperature alone, with significant declines in the 61, 101, and 203 Pa treatments at 28uC. Significant decreases in F V : F M in all species were found after 5 weeks of exposure to elevated CO 2 (203 Pa in all temperature treatments) and temperature (32uC and 34uC in all pH treatments). The rate of oxygen production declined at 61, 101, and 203 Pa in all temperature treatments for all species. The elevated CO 2 and temperature treatments greatly reduced calcification (growth and crystal size) in M. vertebralis and, to a lesser extent, in Halimeda spp. These findings indicate that 32uC and 101 Pa CO 2 , are the upper limits for survival of these species on Heron Island reef, and we conclude that these species will be highly vulnerable to the predicted future climate change scenarios of elevated temperature and ocean acidification.

Calcareous green alga H alimeda tolerates ocean acidification conditions at tropical carbon dioxide seeps

“…also arrived at varying conclusions, with some suggesting that growth and calcification of several Halimeda spp. may be impacted under future CO 2 conditions (Price et al 2011;Ries et al 2009;Sinutok et al 2011), while others suggest that several others are unlikely to be impacted by OA alone (Comeau et al 2013;Hofmann et al 2014;N. Vogel et al pers.…”

“…were absent at mean X ar 2.5 (HallSpencer et al 2008). Laboratory experiments revealed mixed responses of OA on Halimeda spp., with some species being negatively impacted, while others are not (Hofmann et al 2014;Koch et al 2013;Price et al 2011;Ries et al 2009;Sinutok et al 2011;N. Vogel et al pers.…”

Ocean Acidification Alters the Photosynthetic Responses of a Coccolithophorid to Fluctuating Ultraviolet and Visible Radiation

“…Ocean acidification generally decreases calcification by coccolithophores (Riebesell et al, 2000;Zondervan et al, 2002;Delille et al, 2005;Beaufort et al, 2011) and other calcifying algae (Gao and Zheng, 2010;Sinutok et al, 2011), with responses differing across species or different environmental conditions (Langer et al, 2006(Langer et al, , 2009Iglesias-Rodriguez et al, 2008;Doney et al, 2009;Shi et al, 2009). Algal calcification, in turn, influences the impacts of solar ultraviolet radiation (UVR; 280-400 nm) on the algae's photophysiology Gao and Zheng, 2010;Guan and Gao, 2010).…”

A novel mechanism for host-mediated photoprotection in endosymbiotic foraminifera

“…The dynamic nature of the regulation of endosymbiont location by the host suggests that it is closely coupled with the intensity of the incoming irradiance and the time of exposure. Furthermore, the ability for M. vertebralis to move its symbionts within its test may explain its propensity to attach to opaque surfaces (Sinutok et al, 2011;Sinutok et al, 2013), thereby eliminating light input from the attached side and thus optimise the efficacy of shading and photoprotection during the retraction of the symbionts.…”

“…It has also been shown that the coral host can contribute to light protection via accumulation of fluorescent proteins that absorb light in the harmful wavelengths (Salih et al, 2000;Dove et al, 2008), or more directly via contraction or expansion of tissue, which modulates the light field around the symbionts within specific tissue layers (Brown et al, 2002;Dimond et al, 2012;Wangpraseurt et al, 2014). Similar to corals, M. vertebralis is often found in shallow, well-lit waters of the sandy reef sediment (Sinutok et al, 2011) and, therefore, must balance incoming energy with photoprotection. Unlike corals, however, M. vertebralis are motile and as such can achieve photoprotection through relocation to more shaded habitats.…”