Tropical cleaner wrasse changes its clients as it moves poleward

A large portion of the ocean has undergone significant warming as a consequence of ongoing climate change. Tropical marine species, from corals to fish, are expected to move polewards, keeping track of seawater temperature increase. However, species differ in their dispersal abilities. For example, species that have highly specialized food or habitat requirements may shift their distribution slower than species that use a broader array of resources.

The cleaner wrasse, Labroides dimidiatus, is a tropical coral reef fish that ‘cleans’ other fish by removing and eating parasites from other fish, which are called the cleaner wrasse’s ‘clients’. This interaction involves highly specialized signalling behaviour from both the cleaner wrasse and client fishes, which is assumed to have evolved together. Recently, the high specialization level of this interaction has been challenged by some of our recent work, led by Osmar Luiz and colleagues [article], which photographed cleaner wrasses cleaning seven typical temperate fish species during a couple of expeditions to the Solitary Islands, a tropical-temperate transition zone on Australia’s east coast. The previously unreported ability to clean temperate fishes has important implications, as it turns the table on the cleaner wrasse’s potential for warming-induced distribution shifts.

Transition zones between tropical and temperate zones are ideal ‘natural laboratories’ that can be used to further our understanding of species traits’ plasticity. Suboptimal environmental conditions and mixed assemblages comprising species from both tropical and temperate regions may push specialist species to their limits, revealing variability in ecological and behavioural traits that are only apparent in such areas. These areas may, therefore, inform predictive models of future species distributions for other specialized tropical guilds.