Photo: Peter Rask Møller, University of Copenhagen

Twilight Zone can feed the world

Wednesday 09 Mar 16
by Line Reeh


Michael St. John
Senior Researcher
DTU Aqua
+45 21 79 89 32

Life in the twilight zone

The twilight zone is the zone in the sea, where daylight can not reach. The most common fish here is lanternfish (Myctophiids), which consists of 245 species of 10-15 cm big fish, which is widespread poles to equator. 

Together with squid and crustaceans can be ‘seen’ on acoustic surveys 500 meters under the surface over large areas during the day. At night they migrate walk into the water to the surface to approximately 150 meters from surface. 

There is huge untapped resources of protein in the deep sea, but any potential exploitation should be done with caution, warns research.

The deep ocean contains a huge untapped source of protein. An international research group estimated last year that the so-called twilight zone (200 to 1,000 meters), nurses a community of fish, squid and crustaceans whose biomass far surpasses all the world's current fisheries. According to the study, the twilight zone up to 90 percent of the world's total fish biomass.

There are so many creatures here that if estimates hold, it would be equivalent to 1.3 tons of fish biomass per person on earth, and that excludes squid and krill, explains oceanographer and professor Michael St. John DTU Aqua:

"Life in the twilight zone is a huge potential source of fishmeal and Omega 3 to feed the world's population. But we have also to deal with a kind of "no man's water", where there are no rules for fishing. We know so little about the biological processes in the twilight zone, that it is impossible to accurately estimate how large a fishing stocks it can sustain. It is estimated that there are more than 1 million undescribed species in the zone, which we do not even know about yet."

An international group of researchers from Denmark, UK, Portugal and Spain published the outlook on the Twilight Zone community in a Perspective article in the journal Frontiers in Marine Science.

"Of all the research I've done in my career, this is the most important, I'm sure. We need fundamental knowledge on fish biology and spawning success in order to define the limits of sustainable exploitation. The investigation would focus on the role they play as food for other species, such as tuna and sharks, and we would like to preserve that function. Life in the twilight zone plays a huge role as a buffer in relation to climate change, because they remove carbon from the atmosphere when the community feeds on carbon-carrying marine snow in the water and then swim back into the depths where the carbon is stored and thus can not contribute to global warming, "says Professor St. John.

"Of all the research I've done in my career, this is the most important, I'm sure. "
Professor Michael St. John, DTU Aqua

At present, there is no great fishing effort on this community because there are no economically viable ways to exploit the resource, but this will change soon, assesses DTU Aqua professor:

"As coastal stocks are overexploited, alternative marine resources in the twilight zone will be of greater interest, I'm sure. There have already been several attempts to exploit the mesopelagic community and the fear is that it may lead to unregulated “gold rush”, as soon as the technology is available and the cost justified. Therefore, the world community is faced with a major challenge."

Read more
St. John MA, Borja A, G Chust, Heath M, Grigorov I, Martin AP, Serrão Santos R and P Mariani (2016).
'A Dark Hole in our Understanding of Marine Ecosystems and sina Services: Perspectives from the mesopelagic community', Front. Mar. Sci. 3:31. doi: 10.3389/fmars.2016.00031