Review of the biology of the krill genus Nyctiphanes G.O. Sars, 1883 (Euphausiacea: Euphausiidae): challenges for future research on environmental change

The genus Nyctiphanes G.O. Sars, 1883 (Euphausiacea, Euphausiidae) includes four extant species. These species are a conspicuous component of trophic webs of coastal marine ecosystems due to their abundance, the formation of dense aggregations, swarms, and schools, fast growth, and high reproductive rates. They dominate the bulk biomass in eutrophic Eastern Boundaries System and subtropical mesotrophic habitats, with estimates of 30-40% of the total zooplankton biomass. Species of Nyctiphanes are efficient omnivores and conversely prey for a large number of zooplanktonic and nektonic species. We review current knowledge of the biogeography, reproductive biology, physiology, biochemistry, ecology, and parasitology of the four species of Nyctiphanes. Most published information on Nyctiphanes focuses on the two species from the Pacific Ocean, N. australis G.O. Sars, 1883 and N. simplex Hansen, 1911, and considerably less is known on the biology and ecology of N. couchii (Bell, 1853) and N. capensis Hansen, 1911 from the Atlantic Ocean. Knowledge on the biology and ecology of the species of Nyctiphanes is still behind what is currently known for species of krill, particularly compared to Euphausia Dana, 1850 and Thysanoessa Brandt, 1851, and new multi-focal studies on the effects that environmental variables have on reproductive aspects, survival, growth, and physiology are especially critical to address under future environmental change.