Reef manta ray cephalic lobe movements are modulated during social interactions

Abstract

Reef manta rays (Mobula alfredi) are social elasmobranchs that have structured societies and actively interact with preferred social partners. Being able to detect cues and signals produced by conspecifics is vital in enabling social behavior. Many elasmobranch species communicate via body and fin postures, but it is not yet known if or how mobulid rays communicate or respond to cues produced by conspecifics. These rays have specialized cephalic lobes that are highly flexible and used in feeding, but may have other functions such as gestural communication. In this study, we developed a standardized method to assess manta ray behavior in the wild via focal sampling and frame-by-frame video analysis. From observations recorded at cleaning stations in Raja Ampat, West Papua, we described various types of cephalic lobe positioning and movements made by free-ranging M. alfredi and investigated these in different behavioral contexts. We found that cephalic lobe curls were modulated when approaching both conspecifics and human divers, as well as during interactions with cleaner fish, suggesting that these lobes may be used in sensing water movements, olfactory sensing, and/or gestural communication. Cephalic lobes were moved independently of one another, but we found no evidence of individual laterality. The lack of chemosensory capacity on the lobes suggests that gestural communication is the most likely function, but further research is required to determine this. These results are informative in understanding the function of gestural communication in manta ray social interactions and add to our growing understanding of elasmobranchs’ sophisticated social behavior. Social animals rely on communication and cues produced by conspecifics to respond to opportunities and threats. Many elasmobranch species use body and fin postures as gestural signals during competitive, courtship, and other social interactions. Reef manta rays (Mobula alfredi) are social elasmobranchs that form groups in near-shore, shallow water habitats. They possess paired, flexible cephalic lobes positioned on the side of the head which are specialized for feeding but may have a variety of functions. Here, we describe, quantify, and suggest likely explanations for the movement and positioning of cephalic lobes during various manta ray social behaviors, including conspecific, human, and cleaner fish interactions. Our results suggest that lobe movements may be used in detecting water movements, olfactory sensing, and/or gestural communication, and are an important aspect of social behavior in this species.