Cleaning symbioses on tropical coral reefs are typically documented between two species: a single client fish and one or more conspecific cleaners. However, multiple Caribbean cleaner species often live sympatrically and have been anecdotally reported to simultaneously clean the same client. The patterns and processes driving these interactions are poorly understood and cleaning interactions involving multiple cleaner species may be subject to different driving forces than those involving a single cleaner species. Here we used remote underwater videography on three reefs in Honduras to record simultaneous cleaning interactions involving Pederson’s cleaner shrimp (Ancylomenes pedersoni) and cleaner gobies (Elacatinus spp.). Our multi-year dataset shows cleaner gobies joined 28% of all interactions initiated at A. pedersoni cleaning stations with cleaner gobies residing nearby, and 9% of all cleaning interactions across our study sites. Client body size significantly predicted simultaneous cleaning interactions, with 45% of interactions simultaneous for clients >20cm total body length compared to only 8% for clients <20cm. We also found that simultaneous cleaning interactions were over twice as long as solitary shrimp-only interactions. Moreover, interactions were always initiated by a shrimp with gobies joining simultaneously and we recorded no observations of aggression between the two cleaners. We suggest the possibilities of cooperative and exploitative relationships between the two cleaners.

Remote underwater video observations were collected from A. pedersoni cleaning stations on three reefs in Honduras: (i) Coral View, Utila, (ii) an unnamed reef,  Cayos Cochinos Marine Protected Area, and (iii) Banco Capiro, in the mainland bay of Tela (15°51′48.71′′N, 87°29′42.90′′W).

At each reef location, B. annulata cleaning stations hosting A. pedersoni were located and tagged, and any evidence of Elacatinus spp. residing nearby was noted. We use Elacatinus spp. due to difficulties with accurate identification from video, although diver observations suggest most, if not all, were Elacatinus evelynae. Anemones were measured using the tentacle crown surface area approach to provide a reference scale to estimate client fish size. GoPro cameras were placed approximately 1-1.5m from each cleaning station and were left to record for the duration of their battery life (ca. 120-210 min). Cameras were deployed between 7am and 3pm and time was recorded to include in analyses. Once deployed, all divers exited the water to mitigate the effects of diver presence.

Video footage was analysed for: client fish species, client feeding guild and predatory category (whether they pose a predation risk to shrimp only, goby only, both, or neither), clean duration, and whether the interaction was solitary (shrimp only) or simultaneous (participation by at least one shrimp and one goby). Client body size was classified as small (<20cm total length) or large (>20cm), with more accurate measurements not deemed feasible due to the challenges of measuring size from single, stationary video footage, and the need for clients to be consistently positioned side-on. A cleaning interaction was defined as physical contact between A. pedersoni or Elacatinus spp. and a client fish.