Size matters in the murky depths of thepolar oceans and oxygen, not low water temperatures, is the reason why, scientists saidearly this week. Sea spiders in the Antarctic measure in excess of 30 centimetres (12 inches) across and are up to 1,000 times heavier than their cousins living in seas off Europe. Isopods, animals related to woodlice, grow up to 13 or 14 centimetres and are 20 to 50 times the weight of those living in warmer oceans. 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.