Helen Scales
We ask the marine biologist about her Ladybird Expert book on octopuses.
Why are we fascinated by octopuses?
Octopuses are instantly captivating, I think, because they look and behave so differently from any other animals. All those arms and suckers that twist and hold onto things, their ability to change shape and colour, the way they can squeeze into tiny spaces then peep out with those big eyes. Everything about them is strange and enchanting.
How intelligent are they compared to other species?
Octopuses are highly intelligent, especially compared to all the other animals without backbones. They have complex nervous systems with about 500 million nerves, half of them clustered in their heads and the rest in their arms, controlling their agile limbs and super-sensitive suckers.
How are their three hearts used?
One heart pumps blood around the body and the other two pump blood to the gills. It’s thought this arrangement has evolved because of the composition of octopuses’ blood. They have a copper-rich pigment, haemocyanin, dissolved in their blood, unlike vertebrates, which have iron-rich haemoglobin inside their red blood cells. Haemocyanin turns an octopus’s blood blue. It’s also less efficient at transporting oxygen compared to haemoglobin. The three hearts compensate for this by pumping blood at a higher pressure, helping to supply enough oxygen for the octopuses’ active lifestyle.
How many species are there?
There are about 300 known species of octopus, most of them living close to the seabed in shallow seas and down into the deep. Some also spend their whole lives swimming and floating through open water. My favourites are the argonauts, which are the only octopuses that make shells. The octopuses’ ancestors lost their shells millions of years ago, but this group re-evolved the ability.
What surprises you about octopuses?
One of the really surprising things about octopuses is the fact that most species live for at most one or two years. It’s odd that these complex, intelligent animals should live such rich lives, but for such a short time. It’s not quite clear why they’ve evolved to live fast and die young.
What are their greatest threats?
Octopuses are actually faring well at the moment. They seem to be able to quickly adapt to changing climate and habitats, perhaps because of their short generation time. Their numbers worldwide seem to have been increasing.