Heat stress brought about by rising temperatures may cause impaired eyesight and more deaths of pregnant mothers and their unborn young. 

In a study by the University of Adelaide, unborn octopuses and their mothers were exposed to three different temperatures: a control temperature of 19°C, 22°C to mimic current summer temperatures, and 25°C to match projected summer temperatures in 2100.

Negative impact on eyesight

Compared to the other two groups, octopuses that were exposed to 25°C produced significantly fewer of some proteins responsible for vision. 

Lead author Qiaz Hua, a PhD graduate from the University’s School of Biological Sciences, elaborated, “One of them is a structural protein found in high abundance in animal eye lenses to preserve lens transparency and optical clarity, and another is responsible for the regeneration of visual pigments in the photoreceptors of the eyes.” 

The fact that the octopuses in the third group had less of these proteins suggested that the eyesight of octopuses would be impaired due to the higher temperature. This would make the octopus more vulnerable to attacks and also become a less effective predator.

In addition, higher temperatures were also found to lead to more unborn offspring and the premature deaths of pregnant mothers.

Higher mortality and stress

For two of the three octopus breeds kept at 25°C, the mothers had perished while the eggs were in the early development stages, subsequently leading to the deaths of the unborn offspring as well. As for the third brood at this temperature, less than half of the eggs hatched; with both the mothers and offspring showing visible signs of stress.

Co-author Bronwyn Gillanders, Head of Biological Sciences, said in The Guardian article that it was hard to tell whether the study’s results would mimic the reality in 2100, as the octopuses in the lab had experienced a more rapid rate of temperature increase than what would occur in the coming decades.

Nonetheless, she said it was clear that rising temperatures would be bad for octopuses. “It’s only a change of three or so degrees and you’re starting to see the impairment of organisms,” she said.

"Our study shows that even for a highly adaptable taxon like octopuses, they may not be able to survive future ocean changes."

– Dr Qiaz Hua, University of Adelaide