Gobally, aquaculture and fisheries play an important role in providing animal protein for human consumption. However, climate change poses a significant threat to these industries, with marine heatwaves becoming increasingly frequent and severe. Especially the effect of heat stress on the important symbiotic relationship of a host and the intestinal microbiome is understudied. In this study, we investigated the impact of short-term (3-day) and longer-term (3-week) marine heatwaves (+3°C) on the microbial community and molecular response of commercially important juvenile Malabar grouper.
Our findings indicate that both heatwave durations resulted in measurable effects on the fish, which are still detectable after a four-week recovery period. While the microbial richness in the stomach showed a decreasing trend post-heatwave, no significant increase in pathogenic Vibrio was observed. In contrast, the host transcriptome of the stomach, particularly to the 3-week heatwave, showed a response in the form of a downregulation of mitochondrial function and digestive processes. After recovery, these effects turn into an upregulation of tissue repair and extracellular matrix reorganisation. Contrastingly, the pyloric caeca showed minimal response to the heatwaves, suggesting maintenance of function during short-term heat stress.
These findings highlight the variable response of the Malabar grouper to marine heatwaves. While some aspects reveal resilience, such as the absence of increased Vibrio in the stomach and the stability of both microbiome and host transcriptome in the pyloric caeca, other indicators suggest negative impacts. Overall, the results indicate that while the fish can cope with the heatwave in certain aspects, others can pose challenges. Understanding these complex dynamics is crucial for assessing the full impact of climate change on both wild and cultured populations of economically important mesopredators.