Illuminating the Twilight Zone: Biodiversity, Ecosystem Functioning and Conservation of Mesopelagic Fish Communities

The mesopelagic zone, stretching approximately between 200 and 1000 meters below the ocean surface, constitutes one of the least studied and most enigmatic ecosystems on Earth. Mesopelagic fish dominate the vertebrate biomass of the global ocean and are critical to its ecological balance through their diel vertical migrations, which connect surface and deep-water habitats. These migrations play a key role in the biological carbon pump, facilitating the transfer of organic carbon from productive surface waters to the ocean’s interior and sustaining numerous predators such as marine mammals, seabirds, and larger fish. Despite their pivotal role in global biogeochemical cycles and food webs, the mesopelagic realm remains poorly understood. Persistent knowledge gaps exist in taxonomy, functional diversity, population dynamics, biogeography, trophic networks, and responses to environmental variability. Growing interest in potential resource extraction from this zone has amplified the need for in-depth multidisciplinary research to ensure sustainable management and preservation of these fragile ecosystems.

This Research Topic aims to advance our understanding of the structure, functioning, and conservation of mesopelagic fish communities through a cross-disciplinary approach integrating ecology, physiology, oceanography, and conservation science. By addressing unresolved questions on species composition, ecological roles, and adaptive strategies, it seeks to quantify how mesopelagic organisms contribute to carbon sequestration, climate regulation, and ecosystem resilience. The Research Topic will also investigate the potential risks posed by anthropogenic stressors such as climate change, pollution, and industrial exploitation. Through the integration of novel observational tools and modelling frameworks, this effort strives to bridge fundamental ecological knowledge with actionable conservation and management solutions tailored to the twilight zone.

To gather further insights into the biodiversity and ecosystem functioning of mesopelagic fish communities in global oceans, we welcome articles addressing, but not limited to, the following themes:

- Patterns and drivers of mesopelagic fish biodiversity and distribution

- Trophic ecology and contributions to the biological carbon pump

- Adaptive physiology, bioluminescence, and sensory ecology

- Genetic, genomic, and microbiome analyses to elucidate life-history traits

- Advances in acoustic, optical, and environmental DNA (eDNA) methods

- Modelling approaches to species interactions and migration dynamics

- Responses to climate change, deoxygenation, and anthropogenic impacts

- Conservation strategies and governance frameworks for deep-sea ecosystems

Appendix: We invite Original Research, Review, Mini Review, Perspective, and Data Report articles.

Article types and fees

This Research Topic accepts the following article types, unless otherwise specified in the Research Topic description:

• Brief Research Report
• Case Report
• Classification
• Clinical Trial
• Editorial
• FAIR² Data
• General Commentary
• Hypothesis and Theory
• Methods
• ... View all formats

Articles that are accepted for publication by our external editors following rigorous peer review incur a publishing fee charged to Authors, institutions, or funders.

Article types

This Research Topic accepts the following article types, unless otherwise specified in the Research Topic description:

• Brief Research Report
• Case Report
• Classification
• Clinical Trial
• Editorial
• FAIR² Data
• General Commentary
• Hypothesis and Theory
• Methods
• Mini Review
• Opinion
• Original Research
• Perspective
• Review
• Systematic Review
• Technology and Code

Keywords: Mesopelagic fish, Twilight zone, Deep-sea biodiversity, Diel vertical migration, Biological carbon pump, Trophic ecology, Ecosystem functioning, Climate change impacts, Marine conservation, Sustainable management

Important note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.