Biomass estimates for the ocean’s second layer have been revised from one thousand million tonnes to a figure at least ten times the size – ten thousand million.
The figure appears in the journal Nature Communications and is based on acoustic surveying of mesopelagic fish, species found between 200 and 1000 metres below sea level.
At this depth, little commercial fishing is done. Lantern fish (Myctophidae) and cyclothonids (Gonostomatidae) are commonplace.
The study was undertaken as part of the 32,000 nautical mile Malaspina Expedition 2010, an interdisciplinary research project assessing global change on oceans and biodiversity.
Renewed fish stocks mean a drastic alteration to oceanic carbon absorption estimates. Instead of CO2 sinking from the surface, more carbon will be rapidly transported 500 and 700 metres below and released in the form of faeces.
This is according to Xabier Irigoien, research leader, and he added: "Mesopelagic fish actively accelerate the flow for transporting organic material from the upper layers of the water column where the bulk of the organic carbon from the flow of sediment particles is lost.”
The role of fish in the biogeochemical cycles of ocean ecosystems and global ocean has to be reconsidered, as it is likely to be breathing between 1 per cent and 10 per cent of primary production in deep water, "said Mr Irigoien.
The study posited that excretion of material from the surface may help explain unexplained microbial respiration recorded in deep oceans.
Mesopelagic fish therefore could represent a link between plankton and top predators, the paper added.
Furthermore, the study stated that efficiency of energy transfer could be higher than experts previously thought.
The report also showed the close relationship between primary fishing production and ocean fish biomass.
