Abstract
Anthropogenic nutrient enrichment and increased seawater temperatures are responsible for coral reef decline. In particular, they disrupt the relationship between corals and their dinoflagellate symbionts (bleaching). However, some coral species can afford either high temperatures or nutrient enrichment and their study can bring new insights into how corals acclimate or adapt to stressors. Here, we focused on the role of the nutrient history in influencing the response of the Mediterranean scleractinian coral Cladocora caespitosa to thermal stress. Colonies living naturally in nutrient-poor (<0.5 µM nitrogen, <0.2 µM phosphorus, LN) and nutrient-rich (ca. 10–20 µM nitrogen, 0.4 µM phosphorus, HN) locations were sampled, maintained under the right nutrient conditions, and exposed to a temperature increase from 17 °C to 24 °C and 29 °C. While both HN and LN colonies decreased their concentrations of symbionts and/or photosynthetic pigments, HN colonies were able to maintain significant higher rates of net and gross photosynthesis at 24 °C compared to LN colonies. In addition, while there was no change in protein concentration in HN corals during the experiment, proteins continuously decreased in LN corals with increased temperature. These results are important in that they show that nutrient history can influence the response of scleractinian corals to thermal stress. Further investigations of under-studied coral groups are thus required in the future to understand the processes leading to coral resistance to environmental perturbations.
Highlights
The health of scleractinian reef-building corals is rapidly declining, in particular due to heat wave events, which have been increasing in frequency and intensity due to global change
We have investigated the thermal tolerance of the coral C. caespitosa acclimated to two different nutrient environments, in order to assess the effect of nutrient supply on the response of such coral species to thermal stress
This is explained by the fact that HN-corals presented lower rates of gross photosynthesis and needed more carbon to compensate the higher levels of nitrogen input
Summary
The health of scleractinian reef-building corals is rapidly declining, in particular due to heat wave events, which have been increasing in frequency and intensity due to global change. A reduced susceptibility to bleaching was noticed[29], in particular in regions with small-scale upwelling[31] Overall, these antagonistic observations suggest that more research has to be done to better understand the adaptation or acclimation of corals to nutrification. These antagonistic observations suggest that more research has to be done to better understand the adaptation or acclimation of corals to nutrification Mediterranean corals, such as the scleractinian symbiotic coral Cladocora caespitosa, are among the few examples of corals that can be found both in nutrient-poor (Levantine basin, Cyprus32) or nutrient-rich environments[20,33,34,35]. We hypothesize that the main physiological traits of the coral colonies will be different between nutrient-enriched and poor conditions and that the colonies will present a different response to thermal stress
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