Our emissions of carbon dioxide lead to the world’s oceans becoming increasingly acidic. Now scientists have discovered unexpected side effects of this in octopuses – their brains shrink drastically.
It is known that acidification can in the long run lead to essentially catastrophic conditions for many marine organisms. Currently, the pH value – the measure used for acidity – in the oceans is around 8.1. But there is an obvious risk that this will drop to around 7.8 by the year 2100, which means a sharp increase in acidification.
Fatal
What the consequences of this would be is unclear, but at least for many octopuses it could be fatal, judging by experimental studies by scientists at Acadia University in Canada and Academia Sinica in Taiwan. They examined the sensitivity to increasing acidification of a common decapod species, the bigfin reef squid (Sepioteuthis lessoniana), which is common in coastal waters of the Indian and Pacific oceans.
The octopuses were placed in two different water pools, one with a pH of 7.8 and one with a pH of 8.2. After 90 days, the animals were taken up and the effects examined.
Shrinking brains
Immediately, something striking was discovered – the brains were markedly smaller in the octopuses that had been in the more acidic pool. No effect could be seen on the other organs, but the brain volume decreased incredibly much, in total by around 50 percent, probably as a result of so-called oxidative stress. The greatest reduction was seen in the regions that control vision, the optic lobes and the optic nerve.
Octopuses hunt mainly with their sight, and the animals showed a clear reduced tendency to want to search for prey after the stay in the more acidic water. What the consequences may be in the long term is unclear, but if the brain is not capable of handling information from the outside world, the result may be abnormal behaviour. Octopuses are recognized intelligent creatures that have a particularly great need for a functioning thinking apparatus. At present, many species are numerous, but if carbon dioxide emissions are not reduced, the future may be dark for them.
Octopuses
The cephalopods, with approximately 900 living, known species, form a class of their own among the molluscs. They have existed for at least 500 million years.
Today they are divided into three main groups, pearl boats (which are the only ones with an outer shell), ten-armed octopuses and eight-armed octopuses. They have by far the largest brains among the invertebrates.
Source: Nature
