Integrating movement data and behavioural observations to assess the spatial functional role of sympatric cleaner fishes

The ecosystem role of mobile organisms is intimately linked with the way they use space. However, explicitly incorporating movement data in functional assessments of marine fishes has yet to become a common procedure. Here, we combine behavioural observations with detailed short-term movement data sourced from GPS tracks for two related and sympatric cleaner wrasses Labroides dimidiatus and Labroides bicolor. We reveal how these complementary sources of information may help clarify the functional roles of these species. Comparing indicators from the cleaners' movement trajectories revealed differences between species in both path tortuosity and area covered, but not for the total distance travelled. In support of previous literature, we also found that these two species differ sharply in their overall cleaning behaviour (e.g. number, identity and size of clients inspected and interaction time). Regardless of their size, L. dimidiatus established cleaning stations in relatively small areas and cleaned predominantly small client species. In contrast, L. bicolor exhibited size-specific cleaning strategies, travelled across vastly larger areas and cleaned primarily larger client species. Interestingly, despite covering areas that differed vastly in magnitude, both species swam similar cumulative distances. Thus, although the ‘territorial’ versus ‘roving’ cleaning strategies of L. dimidiatus and L. bicolor imply ecosystem roles that contrast in spatial scale and predictability, the similar distances swum suggest that the energetic requirements of these strategies may be less dissonant. Overall, our study highlights the opportunities and implications of incorporating movement when assessing the functional role of species.