Deep Sea fish
Deep Sea fish

Fish living in deep waters on the continental slope around the UK play an important role carrying carbon from the surface to the seafloor.

It has been assumed that deep water fishes all depend on particles that fall from the surface for their energy. These bottom-living deep water fishes never come to the surface and the carbon in their bodies stays at the seafloor. However, at mid-slope depths there is an abundant and diverse ecosystem where a huge volume of animals make daily vertical migrations to feed at the surface during the night. The animals conducting this migration then transport nutrients from the surface back to the deep.

Researchers from the University of Southampton and Marine Institute, Ireland used novel biochemical tracers to piece together the diets of deep-water fish revealing their role in transferring carbon to the ocean depths.

They found that more than half of all the fishes living on the seafloor get their energy from animals that otherwise go back to the surface, and not from settling particles. These bottom-living fishes therefore become a carbon capture and storage facility. Global peaks in abundance and biomass of animals at mid slope depths (between 500 and 1800 m) occur because this is the depth range where the vertically migrating animals are most easily captured by fishes that live at or near the seafloor.

Lead author, Dr Clive Trueman from the University of Southampton, says: “As fishing, energy extraction and mining extend into deeper waters, these unfamiliar and seldom seen fishes in fact provide a valuable service to all of us. Recognising and valuing these ecosystem services is important when we make decisions about how to exploit deep water habitats for food, energy or mineral resources.”

The study is published in the journal Proceedings of the Royal Society B.

Further Reading:
Proc. R. Soc. B 22 July 2014 vol. 281 no. 1787 20140669

Photo credit: Citron, CC BY-SA 3.0