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 m−2 d−1, respectively, highlighting the importance of APA in symbiotic corals.