Bivalve Shell Utilization by Juvenile Octopus vulgaris in Sandy Substrates

Abstract

The early life stages of Octopus vulgaris face significant challenges in sandy environments, where shelter is limited and predation risk is high. This study examines how juvenile octopuses adapt to these conditions, focusing on their use of empty bivalve shells as shelters. Between May 2022 and June 2023, through four SCUBA diving expeditions in the Cíes Islands, NW Spain, nine juvenile octopuses were found inhabiting bivalve shells. The juveniles preferentially selected shells that fit their body size, providing protection and minimizing exposure. They manipulated the shells for security and positioned themselves strategically for optimal visual surveillance. Additionally, they used camouflage techniques, blending with the sandy substrate. When threatened, some octopuses displayed bipedal locomotion to enhance their escape. This study highlights the adaptive flexibility of juvenile O. vulgaris in response to predation pressures in sandy habitats, adding to the growing but limited knowledge of habitat-specific behaviors that can help contribute to the conservation strategies of wild populations.

Keywords: Octopus vulgaris; bivalve shells; camouflage; juvenile behavior; sandy habitats; shelter use.

FIGURE 1

Juvenile octopuses ( Octopus vulgaris ) photographed in sandy bottoms off the Cíes Islands (NW Spain) using bivalve shells as shelters. The white arrows indicate the position of the octopus's eye. (a) Octopus hidden inside clam shells ( Laevicardium crassum ) with the shells almost closed. (b) Octopus hidden inside clam shells ( Dosinia exoleta ) with the shells separated. (c) Octopus attempting to emerge from the clam shell ( Dosinia exoleta ). (d) Octopus camouflaged inside a spiny cockle shell ( Acanthocardia aculeata ). (e) Octopus hidden inside razor clam shells (Ensis sp.) with the shells separated.

FIGURE 2

Juvenile octopus ( Octopus vulgaris ) abandoning its shelter (clam shell; Dosinia exoleta ) and moving away from the divers. (a) Octopus emerging from inside the clam shell. (b) Octopus showing a cryptic display, raising two of its arms above its head while sitting on the remaining 6 arms. (c) Octopus initiating bipedal locomotion. (d) Octopus finishing bipedal locomotion just before starting to swim by jet propulsion.