Trophic niche and gut microbiota of Dosidicus gigas in the eastern equatorial Pacific Ocean

Understanding the adaptation of important marine species to environmental changes is critical for evaluating the effects of fisheries and climate change on marine services. The jumbo squid, Dosidicus gigas, is a keystone species in the eastern Pacific, which plays an intermediate role in the marine food web. Better understanding of their responses to climate change would be a big step to understand their population dynamics. In this study, stable isotope and high-throughput 16S rRNA sequencing were used to compare the variation of trophic niche, gut length, and gut microbiota of D. gigas in the eastern equatorial water during normal and El Niño periods. The results showed a significant variation in δ¹³C values for D. gigas in different periods, indicating differences in their food sources. The main phylum-level gut microbiome included Actinobacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Proteobacteria, and Tenericutes. There was no significant difference in the gut microbial composition during normal and El Niño periods, but differences in gut microbial diversity and relative abundance of some phyla bacteria. El Niño events could decrease the trophic niche breadth of D. gigas, and positively impact gut length and gut microbial diversity and richness. Firmicutes, Bacteroidetes, Spirochaetes, WPS-2, and Kiritimatiellaeota had a significant increase in the gut microbiota of D. gigas combined with a more concentrated intraspecific rank of distance during El Niño, suggesting that the changes of habitat and food sources caused by El Niño events could limit the distribution range of D. gigas. D. gigas might change their digestive system to improve the digestive and absorption capacity and enhance their immunocompetence. Such a climate-driven alteration might help D. gigas rapidly adapt to the changes of environmental conditions and food resources under El Niño.