# De Novo Transcriptome Assembly Reveals Insights Into Osmoregulation and Oxidative Stress Response in the Gills of the Southern King Crab (Lithodes santolla)

## TL;DR

This study uses transcriptome data to explore how Southern king crabs adapt to environmental stressors like salinity and temperature changes.

## Contribution

The first de novo transcriptome of Lithodes santolla is assembled, revealing molecular mechanisms of osmoregulation and oxidative stress response.

## Key findings

- Differential gene expression between two localities highlights distinct stress response strategies.
- Key genes like HSPs, NKA, NHE, and V-ATPase are linked to osmoregulation and redox control.
- WGCNA identifies hub genes as potential biomarkers for environmental stress monitoring.

## Abstract

Understanding the molecular mechanisms underlying physiological adaptations in marine species is crucial for assessing their resilience to environmental stressors. The Southern king crab (Lithodes santolla), an ecologically and commercially important species in sub‐Antarctic waters, inhabits dynamic fjord ecosystems characterized by fluctuating salinity, temperatures, and oxygen levels. However, the molecular basis of its adaptive responses remains largely unexplored. In this study, we assembled the first de novo transcriptome of L. santolla and compared gene expression between two localities in the Strait of Magellan (Ballena Sound and Choiseul Bay). Sequencing yielded 731,879,912 clean reads, which were assembled into 210,093 transcripts, of which 56,064 contigs were successfully annotated. Differential expression analysis identified 4474 differentially expressed genes (DEGs), with individuals from Ballena Sound exhibiting upregulation of heat shock proteins (HSPs) and Na

+

/K

+

‐ATPase (NKA), consistent with proteostasis support and ion‐transport demands. Conversely, individuals from Choiseul Bay showed higher expression of Na

+

/H

+

exchanger (NHE), V‐type proton ATPase (V‐ATPase), and antioxidant enzymes, indicating enhanced pH/ion regulation and redox buffering. Gene Ontology and KEGG enrichment analyses further highlighted ion transport, oxidative stress mitigation, and energy metabolism. Weighted gene co‐expression analysis (WGCNA) recovered modules associated with locality and allowed the identification of high‐connectivity hub genes as candidate biomarkers, yielding a panel for environmental stress monitoring. Taken together, these results reveal the gill‐level coregulation of ion/osmotic regulation, proteostasis, and redox control, enhancing our understanding of L. santolla's physiological plasticity. This transcriptomic resource and biomarker candidates provide a valuable molecular framework for hypothesis‐driven experiments and for monitoring the resilience and conservation status of sub‐Antarctic crustaceans under ongoing environmental change.

The Southern King Crab (Lithodes santolla), an ecologically and commercially important species in sub‐Antarctic waters. In this study, we assembled the first gill de novo transcriptome of L. santolla to characterize gene expression related to environmental responses. Gene Ontology and KEGG enrichment analyses further highlighted key pathways involved in ion transport, oxidative stress mitigation, and energy metabolism. This study enhances our understanding of L. santolla's physiological plasticity and provides a valuable molecular framework for future research on environmental resilience and conservation of sub‐Antarctic marine species.