Size matters in the murky depths of the polar oceans and
oxygen, not low water temperatures, is the reason why,
scientists said on Wednesday, May 12, 1999.
Sea spiders in the Antarctic
measure in excess of 30
centimeters (12 inches) across and
are up to 1,000 times heavier than
their cousins living in seas off
Isopods, animals related to
woodlice, grow up to 13 or 14
centimeters and are 20 to 50 times
the weight of those living in warmer
Scientists had thought gigantism, the ability to grow very
big under the right conditions, was a phenomenon limited to
a few species.
But Belgium-based Gauthier Chapelle and Lloyd Peck have shown
size is dependent on oxygen availability, which is greater in
cooler and less saline locations like the Antarctic ocean.
"The maximum size that these animals can grow at any site is
limited by the amount of environmental oxygen available to
them," Peck, of the British Antarctic Survey, said in a
"The physiological limit is the amount of oxygen they can
get into their blood because the more oxygen they can get
into their blood the longer the path they can have for
their circulatory system and the bigger they can grow."
Peck and Chapelle, of the Institut Royal des Sciences
Naturelles de Bruxelles, reached their conclusions after
comparing the relationship between size and oxygen of
1,853 species of amphipods, crunchy sea creatures with
lots of legs, from 12 sites worldwide.
Their finding, published in the science journal Nature,
explains gigantism in a large group of animals including
sea spiders, sponges, jelly fish, and anemones, which grow
much larger at low temperatures because of oxygen availability.
The researchers also believe oxygen supply may have led to
the giant insects recorded in the Carboniferous period
around 350 million years ago when the oxygen content of air
on Earth was 33 to 34 percent instead of 20 percent.
"We know that they disappeared from the Earth at about the
same time that oxygen levels came down to 20 percent," Peck said.
"Under many of the expected scenarios of global changes over
the next 50 to 100 years the places where you will see
extinction of species is likely to be in polar seas," he added.