Humans need oxygen to turn light particles into visual information, and this is true with marine invertebrates as well. According to a recent study in the Journal of Experimental Biology, the amount of oxygen available to marine invertebrates like crabs, squids, and octopuses are more important to their eyesight than what was previously thought.
In the study that was published on April 24, the researchers saw a significant drop in retinal activity in four species of marine larvae, they are two crabs, a squid, and an octopus. When the animals were exposed to environments with reduced oxygen for 30 minutes, that was when the changes were observed.
For some species, even a small drop in oxygen levels resulted in an immediate vision loss and causing near-total blindness before the oxygen was put back up again.
According to lead study author Lillian McCormick, a doctoral candidate at the Scripps Institution of Oceanography in La Jolla, California, some form of vision impairment may be a reality for these species on a daily basis, which migrates between the ocean's highly oxygen-saturated surface and the low-oxygen depths during their feeding routines every day.
Ocean oxygen levels continue to drop around the world, in part due to climate change, so the risks to these creatures had intensified.
"I am concerned that climate change is going to make this issue worse," McCormick told Live Science, " and that visual impairment might happen more frequently in the sea."
According to a 2017 study in the journal Nature, the total ocean oxygen levels have dropped by 2% around the world in the last 50 years and are projected to decline by up to 7% more by the year 2100. The climate change is a significant factor that is driving these losses, the study found, especially in the upper parts of the ocean where the larvae that the researchers studied tend to spend most of their lives.
This deoxygenation, together with natural forces like water and wind circulation patterns that make near-surface oxygen levels inconsistent in the region, could result in more creatures losing their vision when they need it. These animals could be less effective at hunting for food near the surface and might miss the signs of predators lurking in their midst.
More research is needed to know the amount of oxygen-related vision loss it really takes before the animals make harmful mistakes.
"If I take out my contact lenses at home and walk around, I might stub my toe, but I'll get by," McCormick said. "The next question is, how much retinal impairment equals a change in visual behavior?"
