Coral Uptake of Inorganic Phosphorus and Nitrogen Negatively Affected by Simultaneous Changes in Temperature and pH

Abstract

The effects of ocean acidification and elevated seawater temperature on coral calcification and photosynthesis have been extensively investigated over the last two decades, whereas they are still unknown on nutrient uptake, despite their importance for coral energetics. We therefore studied the separate and combined impacts of increases in temperature and pCO2 on phosphate, ammonium, and nitrate uptake rates by the scleractinian coral S. pistillata. Three experiments were performed, during 10 days i) at three pHT conditions (8.1, 7.8, and 7.5) and normal temperature (26°C), ii) at three temperature conditions (26°, 29°C, and 33°C) and normal pHT (8.1), and iii) at three pHT conditions (8.1, 7.8, and 7.5) and elevated temperature (33°C). After 10 days of incubation, corals had not bleached, as protein, chlorophyll, and zooxanthellae contents were the same in all treatments. However, photosynthetic rates significantly decreased at 33°C, and were further reduced for the pHT 7.5. The photosynthetic efficiency of PSII was only decreased by elevated temperature. Nutrient uptake rates were not affected by a change in pH alone. Conversely, elevated temperature (33°C) alone induced an increase in phosphate uptake but a severe decrease in nitrate and ammonium uptake rates, even leading to a release of nitrogen into seawater. Combination of high temperature (33°C) and low pHT (7.5) resulted in a significant decrease in phosphate and nitrate uptake rates compared to control corals (26°C, pHT = 8.1). These results indicate that both inorganic nitrogen and phosphorus metabolism may be negatively affected by the cumulative effects of ocean warming and acidification.

Ocean acidification has no effect on thermal bleaching in the coral Seriatopora caliendrum

“…(F v /F m and DF/F m 0 ; Edmunds 2012), and increased concentration of chlorophyll a per algal cell in S. pistillata (e.g., photoacclimation; Crawley et al 2010), we found no effect of pCO 2 on photochemical efficiency and the content of chlorophyll a cm -2 or chlorophyll a cell -1 . However, our results are consistent with several other studies showing that pCO 2 as high as 227 Pa has no effect on photosynthesis in Acropora eurystoma (Schneider and Erez 2006) or S. pistillata (Godinot et al 2011). Further, high pCO 2 has no effect on F v /F m in S. pistillata (Godinot et al 2011), or chlorophyll content (a ?…”

“…However, our results are consistent with several other studies showing that pCO 2 as high as 227 Pa has no effect on photosynthesis in Acropora eurystoma (Schneider and Erez 2006) or S. pistillata (Godinot et al 2011). Further, high pCO 2 has no effect on F v /F m in S. pistillata (Godinot et al 2011), or chlorophyll content (a ? c 2 ) and Symbiodinium density in P. australiensis (Iguchi et al 2011).…”

“…Hermatypic corals depend on Symbiodinium to provide photosynthetically fixed carbon to fuel metabolism (Muscatine et al 1984). Some studies with corals suggest OA reduces net photosynthesis (P net ) (Reynaud et al 2003;Anthony et al 2008), and the maximum rate of photosynthesis (i.e., P net max ) (Crawley et al 2010), although some corals show no response of photosynthesis to pCO 2 enrichment (Leclercq et al 2002;Godinot et al 2011). OA has also been reported to induce bleaching in at least two corals, both alone and in concert with elevated temperature (Anthony et al 2008).…”

“…Anthony et al (2008) hypothesized that the mechanism of OAinduced bleaching involved the disruption of carbon-concentration mechanisms used by Symbiodinium (Weis et al 1989;Leggat et al 1999), or impaired photoprotective mechanisms, such as photorespiration (Crawley et al 2010) and nonphotochemical quenching (Hill et al 2005). Support for these hypotheses is limited; however, as effects of OA on the photophysiology of Symbiodinium in hospite have not been studied in detail, and where these effects have been investigated, the outcomes are equivocal (Godinot et al 2011;Iguchi et al 2011;Edmunds 2012) and may be specific to Symbiodinium phylotypes (Brading et al 2011).…”

Modeling photoinhibition‐driven bleaching in Scleractinian coral as a function of light, temperature, and heterotrophy

“…Previous studies have shown that under non-stress conditions, increasing DIN concentration in the environment may lead to increasing symbiont growth, as well as the ability to sustain the host when feeding is limited (Muller-Parker et al 1994). However, corals under temperature stress have been found to have a reduced DIN uptake rate from the environment (Godinot et al 2011). Additionally, elevated DIN concentrations in the water column have been found to increase symbiont expulsion rate (Zhu et al 2004), and corals exposed to high DIN river run-off have been found to have a lower thermal tolerance threshold (Wooldridge and Done 2009).…”