Data and code from: Ocean deoxygenation and warming disrupt cooperation in coral reef fish mutualisms

Climate change is intensifying ocean deoxygenation and warming,
compounding stressors that threaten tropical marine ecosystems. On coral
reefs, cleaner wrasses sustain fish health and community stability by
removing ectoparasites from client species during cooperative
interactions. However, the mutualism is inherently unstable, as cleaners
prefer to feed on clients’ protective mucus—a behaviour considered
cheating. To maintain cooperation, clients use partner control strategies,
while cleaners employ sophisticated social techniques to manage conflict
and maximize food intake. In this study, cleaner wrasses (Labroides
dimidiatus) and their clients (Naso elegans) were exposed for at least 33
days to projected climate scenarios of ocean deoxygenation (90 % O2 sat),
warming (+3 °C), and the combination of both stressors. We assessed the
resilience of the mutualistic interaction through a cooperativeness task
(feeding against preference test), measuring learning and cooperation, and
through cleaning interactions. Deoxygenation and warming significantly
reduced the proportion of time spent in cleaning interactions and led to
the breakdown of behavioural strategies, including tactile stimulation and
clients’ retaliation. Notably, dishonesty persisted at similar levels
during natural interactions, likely due to altered client responses rather
than maintained self-control. Clients under stress were more tolerant to
dishonesty, allowing cheating to go unpunished. This is supported by the
cooperativeness test, in which cleaners exposed to deoxygenation exhibited
reduced cooperation and diminished ability to suppress preferred but
non-cooperative behaviour, suggesting impaired cognitive control. Our
results reveal that climate stressors impair cognitive and behavioural
mechanisms underpinning cleaning mutualisms, potentially destabilising key
trophic interactions on coral reefs under future ocean conditions.