A study conducted by James Cook University has found that a species of reef fish has impaired learning and memory when exposed to warmer-than-usual water temperatures. Spiny Chromis, Acanthochromis polyacanthus, are common on inshore and offshore coral reefs in Indo-Australian waters and are famed for their cichlid-like parental care. They naturally inhabit and thrive in waters as warm as 28C, but when researchers raised the temperature to 32C, their cognitive skills were impaired, which could impact their decision-making, memory, and survival in the wild.
Previous studies have shown that Damselfish like the Spiny chromis have advanced spatial cognitive skills. In the wild, they map their environment, have social interactions with conspecifics, and can remember negative interactions, where they happened, and with whom. But according to predictions for the next 50–100 years, the Earth’s surface temperature is projected to rise by 2?4 °C, Spiny chromis are territorial and non-migratory, so they stand to be directly affected by warming water. Researchers needed to find out how it will affect them.
Learning tests
30 fish were split into three groups – a control group, held at 28-28.5C, a moderate warming group, held at 30-30.5C, and a high, held at 31.5-32C. Learning and memory were tested by placing the fish into a maze-like square tank with grey PVC walls, halls, and a colored cue card. Over 20 trials, the damselfish did indeed learn a spatial task and remember it five days later. But when warmed up, both learning and memory were compromised, which shows that these clever fish will be negatively affected by warming oceans.
The effects of rising CO2 levels have also been tested on Spiny Chromis, (again at James Cook University,) and they showed a reduced ability to avoid predators. With oceans at risk of both rising temperatures and rising levels of carbon dioxide, the future looks bleak for the Spiny Chromis.
Citation
Silveira MM, Donelson JM, McCormick MI, Araujo-Silva H, Luchiari AC. 2023. Impact of ocean warming on a coral reef fish learning and memory. PeerJ 11:e15729 https://doi.org/10.7717/peerj.15729
Image credit Rickard Zerpe, CC BY 2.0 https://creativecommons.org/licenses/by/2.0, via Wikimedia Commons
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