MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14750

ABSTRACT: Remoras are the most common symbiont of pelagic devil rays (Mobulidae). They attach to the host using a modified dorsal fin that acts as a suction cup, an adaptation to provide enhanced protection from predators and feeding opportunities, facilitate encounters with conspecifics, and save energy by reducing the remora’s cost of transport. Much less clear is whether mobulids obtain any benefits, or even if they are impacted by this symbiosis. These ecological interactions have only been addressed for some species (e.g., sharks, cetaceans and turtles) but not yet for the sicklefin devil ray (Mobula tarapacana). To understand the remora’s attachment body site preferences, the hydrodynamic influence on the site selection and the drag cost of transport to the host, the remora-devil ray association was investigated in the Azores archipelago (Portugal) by combining in situ surveys with animal-borne video monitoring and 3D fluid modelling analyses. Our study identifies the common remora (Remora remora) as the main symbiont of adult sicklefin devil rays and describes the number of remoras per host, their size structure and preferred attachment position, plus the hydrodynamic cost to the devil rays. We found that individual sicklefin devil rays usually carry 2 to 3 remoras (including large to small remoras) and remoras choose to attach to the head and the tail of the sicklefin devil rays, to benefit from minimised drag. Our results also highlight that the overall drag resulting from the transportation of remoras is a relatively low hydrodynamic burden to the sicklefin devil rays.