Combining shading and lipid-enriched diets as an adaption tool to reduce coral bleaching

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https://www.sciencedirect.com/science/article/pii/S0022098124000030

Authors

Conor Hendrickson, Peter Butcherine, Alejandro Tagliafico, Sophia L. Ellis, Daniel P. Harrison, Brendan P. Kelaher

https://doi.org/10.1016/j.jembe.2024.151988

29 January 2024

Highlights

•Hydnophora exesa did not respond positively to increased abundance of PUFAs.

•PUFA enrichment may not be appropriate for some coral species.

•Light was likely not a significant stress factor due to low irradiance levels.

•Higher irradiance levels are needed to evaluate coral shading techniques.

Abstract

Mass coral bleaching driven by climate change impacts coral reefs globally. As net zero emissions and a return to pre-industrial global temperatures are unlikely to occur in the near future, there is an urgent need to engineer intervention methods that can mitigate the risk of coral bleaching at different scales. Coral dietary enrichment and shade-based irradiance reduction have each been shown to reduce coral bleaching. Here, we tested the hypothesis that combining these two intervention methods could further reduce the risk and impact of bleaching using an outdoor experiment with fragments of the coral Hydnophora exesa. The experiment was set up over three orthogonal factors: shade (2 levels – 4 h of 30% shade and no shade), temperature (2 levels – 32.6 °C and 26.4 °C) and food type (2 levels – fatty-acid enriched and non-enriched Artemia). The provision of 30% shade for 4 h did not significantly affect any of the measured bleaching response variables, likely due to the low natural irradiance for all treatments throughout the experiment. Significant bleaching of H. exesa fragments occurred in the high-temperature treatments after 18 days of thermal stress. Feeding the corals Artemia enriched with omega-3 and omega-6 fatty acids had a minor impact on the proportion of fatty acids in the corals and resulted in a decline in chlorophyll a content and symbiont density. Overall, these results suggest that coral PUFA enrichment may have limited potential as a mitigation tool to minimise the risk of mass coral bleaching as numerous factors such as species and lipidome composition must be considered. In addition, we recommend that irradiance values higher than the natural light levels recorded during our experiment are required to effectively test the ability of shading technologies designed to reduce mass bleaching of coral reefs.

Conclusions

A lipid-enriched diet did not limit bleaching in H. exesa and may have had a detrimental effect on the species due to the PUFA-heavy formulation of the diet not being appropriate for the species, especially during thermal stress, or due to coral lipidome interactions in the omega-3 and omega-6 biosynthesis chain. Currently, there is no practical method to deliver live or formulated diets to corals at reef-level scale and such a deployment could have a variety of impacts on other reef species. In contrast, shading at a reef-wide scale may be possible with marine cloud brightening and fogging (Bay et al., 2019; Baker et al., 2021). Although the provision of 30% shade for 4 h daily did not significantly impact any of the measured bleaching responses, the moderate ambient light levels in our experiment were likely insufficient to influence bleaching in H. exesa. Further research is needed on coral shading using rigid structures, fogging, or marine cloud brightening sprayer designs under light conditions more representative of those that typically occur in shallow depths during bleaching events (500–700 μmol m−2 s−1 peak). Our experiment highlights several possibilities and challenges with proposed bleaching mitigation tools. The long-term conservation of coral reefs will depend on both the application of innovative conservation solutions at the reef level, as well as a steadfast commitment to global emission reductions.

Source: ScienceDirect