Transcriptomic profiling of Helice tientsinensis reveals its adaptation mechanisms to different salinity levels

Helice tientsinensis is a typical species in the intertidal ecosystem, which is easily affected by fluctuations in salinity. This study systematically investigated the physiological and molecular responses of H. tientsinensis under freshwater (0 ‰), low-salinity (15 ‰, control group), and high salinity (30 ‰) stress conditions at 24 and 48 h, using histological observation, enzyme activity detection, and transcriptome sequencing. The results showed that there were relatively few differentially expressed genes between different salinity groups, indicating that H. tientsinensis has a certain degree of adaptability to salinity fluctuations, which is consistent with its intertidal lifestyle. The gill tissue shows structural damage in the freshwater environment, and immune-related genes were downregulated, indicating that freshwater stress damages the gill tissue and suppresses the immune response. At the same time, H. tientsinensis responds to salinity stress through strategies related to energy metabolism, such as enhancing glycolysis, lipid metabolism, and purine synthesis. The study further reveals that H. tientsinensis adopts a tissue-specific osmoregulation strategy: osmoregulation-related genes (e.g., SLC34A, nptA) are significantly upregulated in gill tissue to enhance ion transport efficiency; in contrast, ion transport-related osmoregulation genes (e.g., ABCA1, ABCC2, ABCC3) are downregulated in the hepatopancreas to reduce metabolic load by saving energy consumption. The gene expression patterns of the two tissues act synergistically to maintain the overall osmotic balance homeostasis of the organism. The purpose of this study was to systematically elucidate the physiological and molecular mechanisms underlying the adaptation of H. tientsinensis to different salinity stresses, thereby filling the gap in current research on its molecular response to salinity changes and providing molecular evidence for the environmental adaptation of intertidal crustaceans.