Extreme Environment, Darkness And Fascinating Deep-Sea Creatures At Depths Greater Than 6,000 Meters

Eddie Gonzales Jr. – MessageToEagle.com – The deep sea, covering 65% of Earth’s surface, is often seen as a biological desert. In the hadal zone, beyond 6, 000 meters deep, organisms face immense pressure over one ton per square centimeter, near-freezing temperatures, low oxygen levels, and constant darkness.

Sampling information and morphological characteristics of 11 deep-sea species. Credit: Institute of Hydrobiology

China’s advanced deep-sea exploration technology revealed that the hadal zone is a cradle of evolutionary marvels. Creatures like the hadal snailfish thrive and form unique ecosystems in this extreme environment.

In a new study, Prof. HE Shunping’s team from the Institute of Hydrobiology, along with researchers from other institutions, have revealed the evolutionary history and genetic mechanisms that allow deep-sea fish to survive in extreme conditions, shedding light on how life endures in such environments.

This study was based on extensive sampling conducted by the motherships Tansuo Yihao (Exploration I) and Tansuo Erhao (Exploration II), which are equipped with the manned submersibles Shenhai Yongshi (Deep-Sea Warrior) and Fendouzhe (Striver), respectively.

The sampling covered the western Pacific to the central Indian Ocean, including trenches, basins, fracture zones, and hydrothermal vents. It spanned deep-sea fish habitats (1, 218–7, 730 meters) and yielded 11 species from six major groups.

The researchers analyzed genetic data from these deep-sea fish, and reconstructed their evolutionary history, revealing how vertebrates conquered the deep sea through distinct processes and mechanisms, thereby reshaping our understanding of deep-sea adaptation.

Researchers confirmed a century-old hypothesis about deep-sea fish evolution, identifying two pathways: “Ancient survivors,” which colonized the deep sea before the Cretaceous mass extinction, and “new immigrants,” representing most modern species emerging after it 60 million years ago. This model reveals how vertebrates adapted to the deep sea through distinct evolutionary processes.

One finding of this study challenged the traditional TMAO hypothesis of deep-sea adaptation. Although TMAO levels rise with depth in fish from 0 to 6,000 meters, this trend doesn’t continue beyond 6,000 meters. Researchers identified a conserved mutation in the rtf1 gene in all fish beyond 3,000 meters, which enhances transcription efficiency and presents a new genetic mechanism for pressure adaptation.

The team detected high concentrations of polychlorinated biphenyls (PCBs) in hadal snailfish liver tissues from the Mariana Trench and Philippine Sea Basin. These pollutants have reached Earth’s deepest trenches, highlighting human activity’s pervasive impact and raising concerns about deep-sea conservation.

The study comprehensively investigates deep-sea fish adaptation, from genetic to ecological levels. It uncovers mechanisms for thriving in extreme environments and establishes an interdisciplinary approach for future research in biology, ecology, and deep-sea conservation.

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Written by Eddie Gonzales  Jr. – MessageToEagle.com Staff Writer