Cleaning interactions under ocean acidification and warming

Chair: Elvira Poloczanska

José Ricardo Paula (1)*, Maria R. Pegado (1), Tiago Repolho (1), Alexandra S. Grutter (2), Rui Rosa (1)

1 MARE – Marine and Environmental Sciences Centre, Laboratório Marítimo da Guia, Faculdade de Ciências da Universidade de Lisboa, Av. Nossa Senhora do Cabo, 939, 2750-374 Cascais, Portugal
2 School of Biological Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia

Background
One of the key ecological components of coral reef ecosystems are the mutualistic interactions: from corals and zooxanthellae to cleaner fishes and their clients. A cleaning interaction involves a cleaner organism that removes and eats ectoparasites from their so-called “clients” in complex and cognitive demanding cooperative interactions that can involve tactile stimulation and partner control. The ubiquity of cleaning behaviour across marine ecosystems is well described and this mutualism is an essential key ecological component in coral reef ecosystems biodiversity. Nonetheless, until now, there is no knowledge on the potential effects of climate change on mutualistic interactions.

Methods
We investigated how cleaning interactions respond to acclimation to chronic conditions of high CO2 (ocean acidification, ΔpH 0.4) and warming (+3 °C). To accomplish such goal, we used cleaner wrasses Labroides dimidiatus and their clients Naso elegans. After 45 days of acclimation pairs of cleaners and clients were allowed to interact in an observation tank for 45 min. We then measured cleaner and client motivation to interact and cleaning interaction quality.

Findings
We observed a significant decrease in motivation to interaction at warming, high CO2 and warming + high CO2. We only observed a decrease in the proportion of interactions started by cleaners and an increase in the number of client posing displays when reared at high CO2 treatments. This shows that cleaners’ motivation to interact is affected by high CO2 but only warming produced impairment on both cleaners and clients’ motivation. We did not observe any significant effect on interaction quality.

Conclusions
In this study we’ve shown, for the first time, that near future oceanic conditions have huge effects on cleaner motivation for engaging in cleaning interactions. Our results provide the first evidence that ocean acidification also affects complex cognitive demanding interactions between two different cooperating species.