Trophic adaptation strategies of deep-Sea fish in cold seep environments

The diversity of marine habitats influences fish trophic niches and adaptation strategies. This study investigated fish trophic niches in cold seep and adjacent areas of the South China Sea in August 2023 using stable isotope techniques. It examined these niches across different depths and compared trophic strategies between cold seep and non-cold seep habitats. The δ 15 N values of fish in the cold seep area increased with depth, indicating shifts in trophic levels, while the δ 13 C values increased solely in the cold seep area. Bayesian analysis revealed that deeper fish in the cold seep area preferred shrimp, whereas those in the control area leaned towards cephalopods. At depths exceeding 500 ​m, the trophic niche of the fish community in the cold seep area was broader than that in the control area, although the individual niches of shared species were narrower. This finding suggests a balance between resource diversity and individual feeding specialization within the cold seep fish community at greater depths. In contrast, individual niches in the control area expanded to adapt to a resource-limited environment. Additionally, the overlap of trophic niches between deep-sea and shallow-water fish diminishes with increasing depth in both regions. We hypothesize that beyond a certain depth, mesopelagic fish either cease vertical migration or modify their patterns of vertical migration. These results underscore the essential role of cold seep ecosystems in sustaining deep-sea biodiversity and intricate trophic structures, thereby enhancing our understanding of adaptive strategies in deep-sea fish communities. • Stable isotope analysis reveals that fish δ 15 N values in cold seep areas rise with depth, indicating trophic level shifts, and δ 13 C values increase only with depth in cold seep areas, suggesting chemosynthetic products add carbon sources and enrich deep-sea food diversity. • Bayesian analysis shows deep cold seep fish mainly eat shrimp, while control area fish prefer cephalopods, highlighting distinct diets. Over 500 m, cold seep fish community has broader trophic niche, shared species have narrower niches, indicating diverse resources and individual specialization. • As Depth increased, trophic niche overlap between deep- and shallow-water fish decreased in both areas, suggesting cessation of migration beyond a certain depth. • This study emphasizes the crucial role of cold seep ecosystems in deep-sea biodiversity and trophic structure, offering insights into the adaptive strategies of fish communities and providing a scientific basis for deep-sea ecosystem management.