Friends for their own benefit

Native to the northeast Atlantic and Mediterranean, European conger (Conger conger) is largest extant eel species thought be semelparous, with adults migrating deep ocean spawn (J Fish Biol 2020; doi.org/10.1111/jfb.14223). As juveniles, congers inhabit coastal areas where they act as top predators, feeding on fish, cephalopods, decapods Mar Assoc UK 2010; doi.org/10.1017/S0025315409990555). Given their nocturnal lifestyle, juveniles typically remain inside rock crevices during day venture into open after dark. While scuba diving in Cíes Islands (northwest Spain), we observed this individual within a crevice alongside up seven different crustacean (Maja brachydactyla, Homarus gammarus, Cancer pagurus, Galathea strigosa, Palaemon sp, Inachus Necora puber). Our observation – admittedly of only one represents unique case interspecific association. The crustaceans potentially gain safety from predation while close proximity conger; for instance, large such M N puber, or C pagurus are important prey common octopus (Octopus vulgaris). However, what benefits hosting diversity associated species, which indeed components its own diet? What ecological consequences high density around single conger? Associations at small spatial scales commonly overlooked but may have fitness outcomes individuals.