How deep can seals go?
The gold medal goes to a bull southern elephant seal, recorded at an incredible 2,388m. While this is extreme, the species frequently dives to depths of 400–800m, staying under for 20–30 minutes. Motivated by food, elephant seals plumb the depths for squid and rays, often at nutrient-rich boundary zones where different oceanic waterbodies meet. Since it takes time to get down, hunt and resurface, these seals have astounding breath-holding abilities – up to two hours is known. They can carry three times more oxygen in their blood than humans, also storing it in their tissues. So the precious oxygen lasts even longer, the seals lower their heart rate to slow the pace at which it is used, and are able to tolerate very low levels of blood oxygen at the end of dives.
Many do, yet there are fascinating exceptions. ‘Harry Potter’ usually conjures up images of wizards, children in cloaks and banquet-style meals, but the series has also inspired the name of a spider: Eriovixia
gryffindori, whose tiny body resembles a Hogwarts sorting hat. The spider’s unusual shape protects it from predators by disguising it as dried foliage. Adopting a non-rotund body like this has worked for other spiders too. Jumping spiders in the genus Myrmarachne, for example, have turned their abdomen into what looks like two separate body parts – a bit like wearing a tight belt. The resulting ant-like silhouette deters predators that find ants noxious, and allows ant-eating species to approach their prey undetected. Such a slimline body limits how many eggs a female spider can lay. A fat, round body clearly has something going for it.
Strange discs of bare red earth swarm across the sparse grasslands of south-west Africa, forming pockmarked patterns that stretch for miles along the arid Atlantic strip. Spaced so evenly they appear to have been stamped, the ‘fairy circles’ are often the size of a garden trampoline, but in some areas reach 20m wide. For half a century, the formations have had scientists scratching their heads. Leading theories to explain them include feeding activity by termite colonies, or competition for scarce water between different species of clump-forming grass.