Micronekton organisms are ubiquitous in the world's oceans and they can be divided into broad taxonomic groups. The distinction between micronekton and micro-, meso- and macro- zooplankton is based on size. Micronekton typically ranges in size from 2 to 20 cm, macro-zooplankton from 2 mm to 2 cm, meso-zooplankton from 0.2 to 2 mm and micro-zooplankton from 20 μm to 0.2 mm. Micronekton represents 3.8-11.8 billion tons of mesopelagic fishes worldwide, approximately 380 million tons of Antarctic krill in the Southern Ocean and a global estimated biomass of at least 55 million tons of a single group of Ommastrephid squid. This diverse group assemblage is distributed between the sea surface and approximately 1000 m deep (in the mesopelagic zone). Micronekton shows a diverse range of migration patterns including diel vertical migration over several hundreds of metres from below 400 m (deeper layers) to the top 200 m (shallower layers) of the water column at dusk and inversely at dawn, reverse migration (organisms stay in the shallow layer during the day) mid-water migration (organisms stay in the intermediate layer, i.e. between 200 and 400 m) or non-migration (organisms stay in the deep layer at night and shallow layer during the day). Micronekton plays a key role in the oceanic biological pump by transporting organic carbon from the euphotic zone to deeper parts of the oceansHidaka, K., Kawaguchi, K., Murakami, M., Takahashi, M., 2001. Downward transport of organic carbon by diel migratory micronekton in the western equatorial Pacific: its quantitative and qualitative importance. Deep-Sea Res. I. 48: 1923-1939. It is also preyed upon by various predators such as tunas, billfishes, sharks, marine birds and marine mammals.Romanov, E. V., Nikolic, N., Dhurmeea, Z., Bodin, N., Puech, A., Norman, S., ... & Potier, M. (2020). Trophic ecology of albacore tuna (Thunnus alalunga) in the western tropical Indian Ocean and adjacent waters. Marine and Freshwater Research, 71(11), 1517-1542.Filmalter, J. D., Cowley, P. D., Potier, M., Ménard, F., Smale, M. J., Cherel, Y., & Dagorn, L. (2017). Feeding ecology of silky sharks Carcharhinus falciformis associated with floating objects in the western I ndian O cean. Journal of fish biology, 90(4), 1321-1337.
