University of Tasmania, Australia

Nyctiphanes australis

Sars 1883

Taxonomy

Distinguishing characteristics

• Only truly coastal euphausiid found in the coastal waters of south-east Australia.
• Because it aggregates in very large swarms, it is a key prey species, being fed upon by many species of fish, seabirds, squid and whales.
• The name, Nyctiphanes australis, means southern winking light and refers to the bioluminescence produced by a series of photophore organs along the length of the body. These organs are typical of euphausiids.

Distribution

• South-eastern Australian waters (Dakin and Colefax 1940, Sheard 1953, Blackburn 1980). Southern New Zealand (Mauchline 1969, 1980,).
• Nyctiphanes australis range extends from approximately Sydney round the southern coast through Bass Strait to central South Australia, and throughout all Tasmanian coastal waters (Nyan Taw 1978, Ritz and Hosie 1982): approximately 31 to 44º S and between 132 and 156ºE.

Ecology

• When abundant it can be found at the surface during the daytime, causing the water to appear reddish. This may seem at odds with the more common habit among zooplankters of avoiding the surface in daytime because of the risk of predation. The reason it is viable for Nyctiphanes australis may be because swarming itself affords some protection to individuals in the group, and staying in the surface provides some feeding benefits.
• Sheard (1953) noted that it had a preferred temperature range of 12 to 18 ºC, with an overall range of 10 to 23 ºC.
• Nyctiphanes australis is one of the key species in the pelagic food webs of the coastal waters of south-eastern Australia and southern New Zealand.
• Krill occurs at times in very high numbers, especially in areas of high productivity such as the upwelling region off western Victoria.
• A number of predators take advantage of the high abundance and productivity of Nyctiphanes australis and feed on this species almost exclusively, e.g. muttonbirds Puffinus tenuirostris, Australian salmon Arripis trutta, barracouta Leionura atun, jack mackerel Trachurus declivis and pigmy blue whale (Balaenoptera musculus).
• Fluctuations in Nyctiphanes australis numbers can dramatically affect abundance or distribution patterns of dependent predators.
• Nyctiphanes australis feeds primarily on phytoplankton but it will also feed on zooplankton, detritus, flocculent organic matter and faeces. In doing so, it plays a key role in recycling organic matter, which would otherwise sink to the bottom, back into flesh available for higher order predators. Numerous other species feed on Nyctiphanes australis opportunistically.
• Most euphausiid species release their eggs, often in thousands, directly into the water. In contrast, female Nyctiphanes australis lay eggs into a temporary ovisac attached to the thoracic legs. The females with ovisac should not be confused with mysids with their marsupium. Only one or two hundred eggs are deposited in the
  ovisac, but a female will produce a number of broods in a season.
• The eggs hatch in the ovisac and develop through the early naupliar stages before being released at the metanauplius stage.
• The larvae continue their development through 3 calyptopis stages, which bear some resemblance to copepods, and 3 furcilia stages, in which there is an increased development of thoracic and abdominal legs, and which begin to resemble the adult stage. Nyctiphanes australis reaches maturity approximately four months from egg release.
• There is a main peak of spawning from early spring to late autumn, but reproduction continues through all months with as many as three generations produced each year.
• The developmental stages are particularly abundant and conspicuous in coastal samples throughout the year.
• Continuous reproduction through the year coupled with its high growth rate means that Nyctiphanes australis has very high productivity.