So-called twilights zone, also known as the disphotic zone or the mesopelagic zone, is thought to house vast populations of unexploited fish, which makes it extraordinarily interesting to marine researchers and conservationists. Environmental DNA metabarcoding may prove useful for unearthing which organisms live down in ocean twilight zones and how, if at all, these species migrate. Equally as important, using environmental DNA for sampling can preserve the ecological processes and fragile species that inhabit these middle ocean zones.

What Is The Twilight Zone?

The disphotic zone is a layer of water depth that is penetrated by significantly less light than what can be found closer to the water’s surface. For this reason, the twilight zone is cold and quite dark, making it unsuitable for most photosynthetic plant species. Twilight zones can be found around the world and are not unique to any body of water. According to National Oceanic and Atmospheric Administration, the twilight zone can be found at a depth of about 200 meters to 1000 meters (650 to 3,300 feet) beneath the water’s surface. This layer range is below the water’s photic layer- the sunlit area, and just above the midnight range.

EDNA Metabarcoding Animal Samples In The Mesopelagic Zone

While some species spend their lives in this undisturbed zone range, many animals move in and out of it. Species fish, squid and plankton likely swim in darkness to find food or to keep away from predators. These traveling carry environmental DNA signatures with them, which reveals detailed information about the creature. A new study by researchers, Elizabeth Andruszkiewicz Allan, Michelle H. DiBenedetto, Andone C. Lavery, Annette F. Govindarajan and Weifeng G. Zhang simulates the physical environmental conditions that cause environmental DNA samples to move through the twilight zone. Their findings propose that environmental conditions like currents, wind, and mixing do not significantly impact the vertical distribution of DNA samples. To be precise, their computer generated model demonstrates that eDNA samples didn’t move beyond a 20 meter range of where it was released into the environment. If this model reflects the actual conditions of marine ecosystems in twilight zones, perhaps changes eDNA concentrations can be used to determine which fish species are present at a sea depth or how long species spend at varying depths. This has groundbreaking implications for tracking marine species travel patterns and migration more generally in aquatic ecosystems.

DNA double helix molecule strands
DNA double helix

More On Conservation

There is still much to learn about carbon sequestration potential, the ecological processes and biologicals diversity profiles of the middle ocean twilight zones. Piercing the complexities of these mostly mysterious regions depends on advancements in measuring technologies- acoustic, eDNA metabarcoding and species tagging methods. Here at eco Treatise, we are quite vocal about the need to protect ecosystems during sampling missions, ultimately disturbing them as little as possible. One of the best methodologies for achieving this standard is by implementing eDNA wherever possible, and avoiding practices like trawling, bait camera trapping and other fish capture techniques. Twilight zones likely provide ecological services to the network of species that migrate in and out of them, and there more permanent inhabitants. In order to preserve these functions, we must prioritize the wellbeing of these environments and their species.

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