Abalone

K
rill is the term given to swarms of shrimp-
like creatures, called euphausids, that form
the staple food of whales and other Antarctic
marine life. Krill is a Norwegian whaling term
meaning ‘tiny fish’, but this is a misnomer as they
are not fish but crustaceans. Krill are large species
of plankton and have a collective mass many times
that of the global human population. They are a
concentrated source of energy-rich food which is
just starting to be tapped by humans.
Antarctic krill, Euphausia superba, is the largest and most
common species of krill in the Southern Ocean. It forms dense
schools between the Antarctic continent and Subantarctica.
Further north, in warmer waters, they are replaced by four
other Euphausia species and Thysanoessa macrura. Further
north in the subtropics they give way to Euphausia lucens
and Euphausia similis, species with antennae that light up so
that their swarms emit blue-green light.
Biology of Euphausids
Euphausids, together with crabs and rock lobsters, belong to
the superorder Eucarida in which a shield-like structure
called the carapace covers the whole of the head and
thorax, fusing it into a solid unit. Euphausids are per-
manently planktonic and swim using flaps
(pleopods)
C O A S TA L A N D M A R I N E L I F E – A N I M A L S : I N V E RT E B R A T E S – C R U S T A C E A N S
Krill 3B
on the abdomen. Their thoracic limbs are armed with stiff
hairs and are held to form a ventral basket through w h i c h
water is sieved as they swim along, enabling the capture of
smaller planktonic plants and animals on which they feed.
Thus they entrap their food in much the same way that baleen
whales feed on krill.
Antarctic krill survive the inhospitable Antarctic winters by
hiding for several months under the pack ice. Here, in icy
nooks and crevices, they feed on algal cells that grow in
dense concentrations in spite of the poor light conditions.
In the summer months, from about December to May, the
ice melts and the phytoplankton blooms due to the long light
hours and the upwelling of nutrient-rich water. The krill in
turn multiply into huge swarms that occupy a central position
in the Southern Ocean food web. Krill are the principal food
for at least five species of baleen whales, three species of
seals, twenty species of fish, three species of squid and
many different birds.
Lifecycle of Antarctic Krill
During spring, in October and November, males of the
Antarctic krill implant their sperm in newly moulted females,
while they still have soft shells. Each female stores the male’s
sperm and later releases it to fertilise her eggs. She produces
many sets of eggs, totalling more than 20 000 during the
summer spawning. When released into the sea, the eggs sink
hundreds of metres to depths where few predators dwell.
There they hatch into nauplii larvae which subsist initially on
the yolk from the eggs. Later they swim towards the surface to
find phytoplankton on which they feed. Antarctic krill develops
slowly through five larval moults to the adult form and re a c h e s
a mature length of 60 mm after three to four years.
Krill – staple food of the Southern Oceans