Octopuses could lose vision and struggle to survive due to heat stress by the end of the century if ocean temperatures continue to rise at the projected rate, a new study has found.
While previous research has suggested octopuses are highly adaptable, the latest research found heat stress from global heating could result in impaired eyesight and increased deaths of pregnant mothers and their unborn young.
The researchers said loss of vision would have significant ramifications for octopuses as they are highly reliant on sight for survival. About 70% of the octopus brain is dedicated to vision, and it plays a crucial role in communication and detecting predators and prey.
Researchers exposed unborn octopuses and their mothers to three different temperatures: a control of 19C, 22C to mimic current summer temperatures, and 25C to match projected possible summer temperatures in 2100.
Octopuses exposed to 25C were found to produce significantly fewer proteins responsible for vision than those at other temperatures.
“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,” Dr Qiaz Hua, a recent PhD graduate from the University of Adelaide’s School of Biological Sciences and the study’s lead author, said.
The study also found that higher temperatures were associated with higher rates of unborn offspring and an increased rate of premature deaths of pregnant mothers.
Eggs did not hatch for two of the three octopus breeds kept at 25C. The researchers said this was due partly to the deaths of mothers while eggs were in early development stages.
Less than half the eggs hatched for the third brood kept at this temperature. The scientists said the mother of this brood displayed “visible signs of stress” not observed in mothers exposed to lower temperatures. They found the hatchlings that survived exhibited an “immense amount of thermal stress and are unlikely to survive into adulthood”.
Hua said it meant “global warming could have a simultaneous impact on multiple generations”.
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She said the research highlighted that “even for a highly adaptable taxon like octopuses, they may not be able to survive future ocean changes”.
Bronwyn Gillanders, the head of biological sciences at the University of Adelaide and a co-author of the study, said of the research: “It’s only a change of three or so degrees and you’re starting to see the impairment of organisms.”
Gillanders noted the study was not a direct reproduction of what would happen with global heating, as the octopuses were exposed to a more rapid increase than what would happen over coming decades, and she said it was “hard to tell” if the study’s results would mimic reality in 2100. But she said it was clear that rising temperatures would be bad for octopuses.
Jasmin Martino, an aquatic ecologist at the University of New South Wales who was not involved in the study, said the findings contradicted previous literature, which had suggested that cephalopods – a group including octopuses and squids – may be relative “winners” during the climate crisis due to their adaptability.
“This study reveals that in regions of inescapable heat stress, like the tropics, thermal stress responses may overwhelm octopuses’ capacity to cope,” she said.
