Artificial reefs act as cleaning stations in temperate waters

Artificial reefs (ARs) are structures installed in aquatic habitats that serve as a substrate and/or shelter for organisms and are often used to restore or enhance fish populations. While a great deal of the research on ARs has focused on the abundance of fish species associated with these habitats, comparatively little is known about the behaviour of these fish. Cleaning symbiosis, where, following communication, a cleaner removes and consumes ectoparasites, mucus, dead tissue or unwanted particles that negatively impact a client, has been recorded in over 200 fish species from 36 families, four of which are species of Coris (Vaughan et al. 2017). Most cleaners occur in tropical marine waters, but there are examples from temperate areas, including five fish (Tilodon sexfasciatus, Siphonognathus beddomei, Cochleoceps bicolor, Austrolabrus maculatus and Enoplosus armatus) and one crustacean (Periclimenes aesopius) species on inshore rocky reefs in South Australia (Shepherd et al. 2005). Cleaning events are often associated with cleaning stations that typically develop at sites with vertical relief where fish aggregate.

ARs, each comprising 30 ‘Fish Box’ modules (3 m³) constructed from steel-reinforced concrete, were deployed in coastal waters off Bunbury, Dunsborough and Mandurah in south-western Australia to increase the abundance of recreationally-important fish species (Florisson et al. 2018). Fish assemblages were monitored using remote underwater video (Hero 2018, GoPro Inc.) at the three ARs and one natural site comprising sand with rocky outcrops 2 km from the Mandurah AR. This study was conducted in accordance with Murdoch University Animal Ethics Permit O3085/18. Female Coris auricularis (Western King Wrasse (Labridae)) were observed cleaning a range of clients, including teleosts such as the pelagic carangids Pseudocaranx georgianus and Seriola hippos and, less frequently, the epibenthic Aracana aurita, Neatypus obliquus, Acanthaluteres vittiger, Chelmonops curiosus, Upeneichthys lineatus and benthic elasmobranch Myliobatis tenuicaudatus (Fig. 1).

Fig. 1.

Extract from an underwater video showing a female Western King Wrasse (Coris auricularis) cleaning a Silver Trevally (Pseudocaranx georgianus) and another Silver Trevally adopting a head-up display to request an approach from a nearby cleaner.

Both the client and cleaner initiated cleaning interactions. Clients would swim around or through the modules slowly before entering a head-up or head-down approach, with erect fins and flared gills, or, in the case of M. tenuicaudatus, with their pectoral fins pointed to the surface (Supplementary material). Cleaners also adopted a head-up position individually or in groups. As gut content studies demonstrate that C. auricularis is an opportunistic zoobenthivore (Lek et al. 2011), it is most likely a facultative rather than obligate cleaner, similar to other cleaners in temperate waters (Shepherd et al. 2005). The presence of facultative cleaners provides additional benefits to resident and transitory fish, and may be an underreported benefit of ARs. These findings are important as ARs are increasingly being used to restore/enhance the abundance and diversity of aquatic fauna and as ecological offsets.

Supplementary material

Supplementary material is available online.