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

Nutrient enrichment and the ultrastructure of zooxanthellae from the giant clam Tridacna maxima

The separate and combined effects of ammonium (10 mu M) and phosphate (2 mu M) on the ultrastructure of zooxanthellae (Symbiodinium sp.) from giant clams, Tridacna maxima, were examined in the held. Nitrogen addition significantly changed the ultrastructure of the zooxanthellae inhabiting the clams. After 9 mo exposure, the cross-sectional area of zooxanthellae from N-treated clams was significantly lower than that from other treatments [N = 39.3 mu m(2); C = 47.9 mu m(2); P = 43.2 mu m(2); N + P = 44.5 mu m(2); (P = 0.001)]. There was also a significant decrease in the size of starch bodies, especially around the pyrenoid of the zooxanthellae from N and N+P treatments [N = 1.2 mu m(2); C = 2.0 mu m(2); P = 1.8 mu m(2); N + P = 1.2 mu m(2); (P = 2.08E-11)]. This presumably occurs as a result of the mobilization of organic carbon stores in response to stimulated amino acid synthesis under enriched nutrient conditions. These data strongly suggest that the symbiotic zooxanthellae of clams are limited to some extent by the availability of inorganic nitrogen, and that relatively minor changes to the nutrient loading of the water column can have substantial effects on the biochemistry of symbioses such as that which exists between clams and zooxanthellae

Confidence relations as a basis for uncertainty modeling, plausible reasoning and belief revision

International audienceThe aim of this position paper is to outline a unified view of plausible reasoning under incomplete information and belief revision, based on a ordinal representation of uncertainty. The information possessed by an agent is suppposed to be made of three items: sure observations, generic knowledge and inferred contingent beliefs. The main notion supporting this approach is the confidence relation, a partial ordering of events which encodes the generic knowledge of an agent. Plausible inference is achieved by conditioning. The paper advocates the similarity between plausible reasoning with confidence relations and probabilistic reasoning. The main difference is that the ordinal approach suppports the notion of accepted beliefs forming a deductively cloded set, while probability theory is not tailored for it. The framework of confidence relations sheds light on the connections between some approaches to non-monotonic reasoning methods, possibilitic logic and the theory of belief revision. In particular the distinction between revising contingent beliefs in the light of observations and revising the confidence relation is laid bare