A team of researchers from Acadia University (Canada) presented the results of a study at the Society for Experimental Biology conference in Florence, Italy, revealing an alarming impact of ocean acidification on cephalopods. According to preliminary data, squid raised in waters with CO2 levels similar to those projected for the end of the century suffer a reduction in brain volume of up to 50% , directly affecting their ability to hunt and survive.
The study, led by Dr. Garett Allen, focused on the largefin reef squid ( Sepioteuthis lessoniana ), a species considered one of the most intelligent invertebrates on the planet, with a number of neurons comparable to that of a dog. Ocean acidification, caused by increased atmospheric CO2, was already known to be harmful to many marine species, but this finding reveals a previously unknown neurological effect that could jeopardize the entire subclass Coleoidea, which also includes octopuses and cuttlefish.
This is how the experiment was carried out
To simulate future conditions, scientists set up two parallel water tanks: one with the current ocean pH (8,2) and another with a pH of 7,8, which is the pH expected by 2100 according to the most pessimistic climate scenarios. Newly hatched squid were raised in these tanks for 90 days , and then their heads were removed for analysis using diffusion magnetic resonance imaging (dMRI).
When comparing the images, the team was in for a major surprise. “I immediately realized that their brains were half the size, and I had to revise the software's diagnostics,” Allen confessed. The average reduction in brain volume was 49% in the specimens exposed to higher CO2 levels , and no significant change in overall body size was observed, ruling out the possibility that the shrinkage was due to a smaller overall build.
Visual areas, the most affected
Detailed analysis revealed that the most affected areas are those responsible for processing visual information. The optic lobes were reduced by 52% and the optic tracts by 62% compared to the squid in the control group. Since these animals rely almost entirely on sight to locate and capture their prey, the consequence is immediate: their hunting behavior plummets.
In fact, the study builds on previous research by the same team that had already documented a 65% reduction in hunting behavior after just seven days of acute exposure to high levels of CO2 , and a 42% reduction after 90 days of chronic exposure from hatching. Allen believes the loss of visual acuity is not due to damage to the retina, which appears intact, but rather to shrinkage of the optic lobe, which hinders image interpretation.
Possible causes and future consequences
Researchers still don't have a definitive explanation for this phenomenon, but they are considering two main hypotheses. On the one hand, energy limitations within the brain could prevent neurons from functioning properly ; on the other, oxidative stress caused by excess CO2 could damage nerve cells. In either case, the result is that the brain is unable to transmit information adequately, leading to abnormal eating behavior.
These findings serve as a wake-up call regarding the future of cephalopods, a key group in marine food webs. If ocean acidification continues at the current rate, intelligent species like squid could see their cognitive and survival abilities diminished , with cascading effects throughout the ecosystem. Allen's team will continue investigating to determine if other marine invertebrates suffer similar damage and if there is any room for adaptation.