AUTHOR=Zheng Qiaojun , Wang Yunjian , Chen Jiao , Li Yunpeng , Zhao Feng , Liu Danwen , Wei Maokai , Kong Dexu , Chen Zongtao , Zhang Zhifeng , Ma Yubin 

TITLE=Effects of Salinity on the Growth, Physiological Characteristics, and Intestinal Microbiota of the Echiura Worm (Urechis unicinctus)

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 9 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.912023

DOI=10.3389/fmars.2022.912023

ISSN=2296-7745

ABSTRACT=Intertidal biota is subjected to significant fluctuations in salinity. Urechis unicinctus, a typical species thriving in intertidal sediments, have relatively simple anatomy structure and therefore could be considered as an ideal species for salinity acclimation. Moreover, due to the high nutrients, U. unicinctus has been became an emerging aquaculture species in China. In this study, we investigated the effects of salinity on the growth performance, coelomic fluid biochemical indices, antioxidant enzyme system, Na+/K+-ATPase and non-specific immune enzyme activities, as well as intestinal microbiota composition of this species in a 8-week experiment. The results indicated U. unicinctus is a euryhaline species that can tolerate salinities from 15‰ to 40‰ and demonstrated the highest growth performance at 30‰. Physiological characteristics analyses of coelomic fluid and intestine indicated range of 15‰ to 30‰ salinities are more suitable, while 10‰ and 40‰ salinities seem not suitable for U. unicinctus juvenile. Furthermore, intestinal microbiota analysis indicated salinity had a significant effect on the composition structure. KEGG pathway analysis indicated antioxidant related metabolic pathways and amino acid pathways may play important roles in gut microbiota under salinity stress. Comprehensive analysis of intestinal bacteria and enzyme activities indicated Unidentified Rhodobacteraceae, Vibrio and Shimia may play important roles in high salinity acclimation, while Legionellaceae may act as important microbiota in low salinity acclimation. Moreover, Ruminococcus, Oscillospira, Lachnospiraceae, Clostridiales and S24-7 showed negative correlations with the antioxidant and nonspecific immune enzymes, indicating that these bacteria can be considered as important candidates of probiotics for U. unicinctus aquaculture industry. The findings of this study will extend our understanding of the effects of salinity on the growth and health of U. unicinctus and contributes a better understanding of the salinity acclimation strategies of organisms in intertidal zone.