Corals are the main reef builders through the formation of calcium carbonate skeletons. In recent decades, coral calcification has however been impacted by many global (climate change) and local stressors (such as destructive fishing practices and changes in water quality). In this particular context, it is crucial to identify and characterize the various factors that promote coral calcification. We thus performed the first investigation of the effect of nickel and urea enrichment on the calcification rates of three coral species. These two factors may indeed interact with calcification through the activity of urease, which catalyzes the hydrolysis of urea to produce inorganic carbon and ammonia that are involved in the calcification process. Experiments were performed with the asymbiotic coral Dendrophyllia arbuscula and, to further assess if urea and/or nickel has an indirect link with calcification through photosynthesis, results were compared with those obtained with two symbiotic corals, Acropora muricata and Pocillopora damicornis, for which we also measured photosynthetic rates. Ambient and enriched nickel (0.12 and 3.50 μg L⁻¹) combined with ambient and enriched urea concentrations (0.26 and 5.52 μmol L⁻¹) were tested during 4 weeks in aquaria. We demonstrate in the study that a nickel enrichment alone or combined with a urea enrichment strongly stimulated urea uptake rates of the three tested species. In addition, this enhancement of urea uptake and hydrolysis significantly increased the long-term calcification rates (i.e. growth) of the three coral species investigated, inducing a 1.49-fold to 1.64-fold increase, respectively for D. arbuscula and P. damicornis. Since calcification was greatly enhanced by nickel in the asymbiotic coral species – i.e. in absence of photosynthesis – we concluded that the effect of increased urease activity on calcification was mainly direct. According to our results, it can be assumed that corals in some fringing reefs, benefiting from seawater enriched in nickel may have advantages and might be able to use urea more effectively as a carbon and nitrogen source. It can also be suggested that urea, for which hotspots are regularly measured in reef waters may alleviate the negative consequences of thermal stress on corals.

珊瑚是碳酸钙骨架形成过程中主要的礁石建造者。然而，近几十年来，珊瑚钙化受到了全球（气候变化）和局部压力（例如破坏性捕鱼行为和水质变化）的影响。在这种特定情况下，至关重要的是确定和表征促进珊瑚钙化的各种因素。因此，我们对镍和尿素富集对三种珊瑚钙化速率的影响进行了首次调查。这两个因素确实可能通过尿素酶的活性与钙化相互作用，尿素酶的活性催化尿素水解产生钙化过程中涉及的无机碳和氨。用非共生珊瑚树突藻进行了实验并且，为了进一步评估尿素和/或镍是否与通过光合作用的钙化作用有间接联系，将结果与使用两种共生珊瑚-紫罗兰（Acropora muricata）和Po（Pocillopora damicornis）获得的结果进行了比较，我们还测量了它们的光合速率。环境镍和富集的镍（0.12和3.50μgL ^-1）与环境和富集的尿素浓度（0.26和5.52μmolL ^-1））在水族箱中进行了4周的测试。我们在研究中证明，单独的镍富集或与尿素富集相结合会强烈刺激三种被测物种的尿素吸收率。此外，尿素吸收和水解的这种增强显着提高了所研究的三种珊瑚的长期钙化速率（即生长），分别导致了D. arbuscula和P. damicornis的增长了1.49倍至1.64倍。。由于镍在非共生珊瑚物种中的钙化作用大大增强（即在没有光合作用的情况下），因此我们得出结论，脲酶活性增加对钙化的影响主要是直接的。根据我们的研究结果，可以假设某些边缘礁中的珊瑚受益于富含镍的海水，这可能具有优势，并且可能能够更有效地利用尿素作为碳和氮源。也可以建议定期在珊瑚礁水域中测量热点的尿素可以减轻热应力对珊瑚的不利影响。