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

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

Absorption et devenir du phosphore au sein de la symbiose corallienne

Symbiotic Scleractinian corals survive in oligotrophic reef waters owing to their efficient uptake of nutrients such as phosphorus and nitrogen. Although the use of nitrogen by corals has often been studied, this is not the case for phosphorus. The main aim of this work was to examine the use of dissolved inorganic and organic phosphorus (DIP, DOP) by corals under various environmental conditions, and to assess their metabolic demand for phosphorus. Results showed that DIP and DOP uptake, measured respectively with depletion experiments and with alkaline phosphatase activity assays, are dependent upon light, the presence of symbiotic Dinoflagellates within coral tissues, the availability of inorganic nitrogen, and the nutritional status of the host (repletion in particulate organic phosphorus, POP, ingested as plankton). During a temperature stress, alone or combined with a pH decrease, DIP uptake was affected. Upon DIP enrichment, coral calcification and photosynthesis increased, thus suggesting that, under oligotrophic conditions, phosphorus limits the symbiosis. Finally, nuclear magnetic resonance analyzes showed that phosphorus occurs as phosphate within the symbiosis, but also as phosphonates in the host, and as polyphosphates and phosphate esters in the symbionts. A first budget of the relative importance of DIP, DOP and POP was established at the end of this work, as well as a critical evaluation of the tools used to assess phosphorus limitation of the symbiosis.Les Scléractiniaires symbiotiques (coraux) qui se développent dans des eaux oligo-trophes survivent grâce à une utilisation optimale des nutriments tels que le phosphore et l'azote. Alors que l'utilisation de l'azote par les coraux a été bien étudiée, ce n'est pas le cas du phosphore. L'enjeu principal de cette thèse a été d'évaluer l'utilisation du phos-phore inorganique et organique dissous (PID, POD) par les coraux dans diverses condi-tions environnementales, ainsi que leurs besoins métaboliques en phosphore. Les résul-tats obtenus ont montré que l'absorption de PID, mesurée par déplétion dans le milieu, et de POD, mesurée via l'activité de l'alcaline phosphatase, dépendent de l'éclairement, de la présence de Dinoflagellés symbiotiques dans les tissus coralliens, de la présence d'azote inorganique, et du statut nutritionnel de l'hôte (réplétion en phosphore organique particulaire, POP, ingéré sous forme de plancton). Lors d'un stress de température, seul ou combiné à une acidification du milieu, l'absorption de PID a été affectée. Sous l'effet d'un enrichissement du milieu en PID, la photosynthèse et la calcification corallienne ont été augmentées, suggérant qu'en conditions oligotrophes, la symbiose est limitée par le phosphore. Enfin, des analyses en résonance magnétique nucléaire ont montré que le phosphore se trouve principalement sous forme de phosphate dans la symbiose, mais aussi de phosphonates chez l'hôte, et de polyphosphates et esters de phosphate chez les symbiotes. Un premier bilan de l'importance relative du PID, POD et POP a été établi à l'issue de ce travail, et un examen critique des outils permettant d'évaluer la limitation par le phosphore a été réalisé

Phosphate excretion by anemonefish and uptake by giant sea anemones: demand outstrips supply

International audiencehigh biodiversity on coral reefs results in part from tight nutrient cycling among symbiotic organisms, such as within the obligate associations among some damselfishes, cnidarians, and zooxanthellae. Some anemonefish excrete ammonia 20-50× faster than host anemones can absorb this nutrient, leading to significant growth of the anemones and their zooxanthellae. In contrast, little is known about phosphate transfer in this major coral reef mutualism. We determined rates of phosphate excretion by anemonefish and uptake by giant sea anemones under laboratory conditions, and compared them with known rates of ammonia transfer in this symbiosis. Immediately after feeding with a phosphate-rich diet, anemonefish excreted phosphate at slow rates of 0.07 ± 0.01 µmol P g-1 d-1 , which did not vary significantly with body size. Starved anemones that had been cultured with phosphate supplements absorbed phosphate at a significantly slower rate (0.18 ± 0.03 µmol P g-1 d-1) than did those cultured with either no supplements or with anemonefish, which absorbed phosphate at similarly rapid rates (0.54 ± 0.01 and 0.51 ± 0.14 µmol P g-1 d-1 respectively). We conclude that under laboratory conditions, anemones absorb phosphate up to 6.6× faster than the rate at which it is excreted by their anemonefish, and thus fish do not appear to provide sufficient phosphate to their hosts through this pathway. Anemones may get most of their phosphorus via ingestion of fish feces and/or mucus, or via the ingestion of prey

On the use of 31P NMR for the quantification of hydrosoluble phosphorus-containing compounds in coral host tissues and cultured zooxanthellae

31P Nuclear Magnetic Resonance (NMR) was assessed to investigate the phosphorus-containing compounds present in the tissues of the scleractinian coral Stylophora pistillata as well as of cultured zooxanthellae (CZ). Results showed that phosphorus-containing compounds observed in CZ were mainly phosphate and phosphate esters. Phosphate accounted for 19 ± 2% of the total phosphorus compounds observed in CZ maintained under low P-levels (0.02 μM). Adding 5 mM of dissolved inorganic phosphorus (KH2PO4) to the CZ culture medium led to a 3.1-fold increase in intracellular phosphate, while adding 5 mM of dissolved organic phosphorus led to a reduction in the concentration of phosphorus compounds, including a 2.5-fold intracellular phosphate decrease. In sharp contrast to zooxanthellae, the host mainly contained phosphonates, and to a lesser extent, phosphate esters and phosphate. Two-months of host starvation decreased the phosphate content by 2.4 fold, while bleaching of fed corals did not modify this content. Based on 31P NMR analyses, this study highlights the importance of phosphonates in the composition of coral host tissues, and illustrates the impact of phosphorus availability on the phosphorus composition of host tissues and CZ, both through feeding of the host and inorganic phosphorus enrichment of the CZ.This research was supported by the government of the Principality of Monaco. Financial support to C.G. was provided by the École Normale Supérieure and the Centre Scientifique de Monaco.peer-reviewe

Control of phosphate uptake by zooxanthellae and host cells in the scleractinian coral Stylophora pistillata

International audienceDepletion experiments were used to assess the uptake rates of phosphate by the tropical coral Stylophora pistillata and its symbiotic zooxanthellae under different conditions. Our results showed the presence of active phosphate carriers both in the animal and the algal fractions, since uptake kinetics followed uniphasic saturationcurves in both compartments (Michaelis–Menten shape). Transporters in the animal and the algae presented different affinities for phosphate, with higher half-saturation constants for the animal compartment than for the isolated zooxanthellae (K 5 1.08 6 0.42 vs. 0.57 6 0.18 mmol L21). The velocity of phosphate absorption increased in the light, suggesting a relationship with the photosynthetic activity of the zooxanthellae. Acorrelation was found between phosphate uptake rates and the organic or inorganic feeding history of the corals; rates were indeed 4.6 times higher in 8-week starved than in fed corals and depended on the repletion status of phosphorus stocks within the symbionts. We report evidence showing that zooxanthellae act as a sink of phosphate within the symbiosis

Seawater carbonate chemistry, nutrient uptake and biological processes of coral Stylophora pistillata during experiments, 2011

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

Alkaline phosphatase activity of reef-building corals

Extracellular alkaline phosphatase activity (APA) was measured in four tropical (Stylophora pistillata, Pocillopora damicornis, Pavona cactus, Galaxea fascicularis) and two Mediterranean (Oculina patagonica, Cladocora caespitosa) symbiotic coral species, both in the coral host and associated symbionts, as well as in one tropical non-symbiotic coral (Tubastraea sp.). The effects of light, feeding, and bleaching (loss of symbionts) were also tested in S. pistillata. Host APA increased with long-term starvation, irradiance, and bleaching, suggesting that APA is linked to the metabolic activity of the host and symbionts, and to their phosphate limitation or repletion status. The comparison of APA between coral species containing different symbiont clades suggests that clade C is less efficient than clades A and B, but this result remains to be confirmed. At environmental phosphate concentrations, if the total amount of phosphate generated by APA is taken up by the coral colony, it can supply 0.3-1.6 mmol P m(-2) d(-1). In comparison, dissolved inorganic phosphorus and particulate organic phosphorus have been shown to supply 0.2-1.6 and 0.9 mmol P mm(-2) d(-1), respectively, highlighting the importance of APA in symbiotic corals

High phosphate uptake requirements of the scleractinian coral Stylophora pistillata

International audienceSUMMARY Several untested aspects of the regulation of inorganic nutrient uptake were examined using nutrient depletion experiments with the symbiotic coral Stylophora pistillata. The total inhibition of phosphate uptake in artificial seawater lacking sodium indicates the involvement of a sodium/phosphate symporter for the uptake of phosphate across host membranes. Addition of ammonium or nitrate (up to 6.0 μmol l–1) did not enhance saturated phosphate uptake rates, thus indicating that corals, or their symbiotic algae, were not, or not sufficiently, nitrogen limited to modify their phosphate needs. Conversely, the saturated uptake rate of ammonium increased by 2.5-fold in the presence of 3.0 μmol l–1 of phosphate, thus indicating that the corals or their symbionts were lacking intracellular phosphate to take advantage of the inorganic nitrogen compounds dissolved in their surrounding medium. Overall, these results highlight some greater limitation in phosphate rather than in nitrogen. Finally, the rate of phosphate uptake decreased with particulate feeding of the host (organic phosphate source). Indeed, corals that were fed 1 and 3 days before the uptake experiment took up phosphate 42 and 19% slower, respectively, than corals that were fed 21 days before. This result provides additional evidence of phosphate limitation in S. pistillata. This study therefore brings new insights into the relationships between nutrients and symbiotic corals, and may provide a rapid and effective tool to investigate which nutrient is the most limiting for coral metabolism