Prey preference of the common long-armed octopus Octopus minor (Cephalopoda: Octopodidae) on three different species of bivalves

Octopus minor is widely distributed along the northern coast of China. To date, there is little information on the prey selection process of this species. To understand this process, several experiments were carried out. Three types of bivalves, namely, Ruditapes philippinarum, Mactra chinensis, and Mytilus galloprovincialis, were used to observe the prey selection of O. minor and to analyze the potential causes of prey selection from three aspects: prey profitability, adductor muscle tension and handling time. Under single-prey conditions, we found that the average (±SD) predation rates of O. minor on R. philippinarum, M. chinensis, and M. galloprovincialis were 1.73±0.50, 1.27±0.42, and 0.8±0.2/d, respectively. Under different prey combinations, octopods actively selected one type of prey over the other(s), and the order of prey preference was R. philippinarum, followed by M. chinensis and lastly M. galloprovincialis. Furthermore, the shells of the consumed prey showed that O. minor only consumed bivalves by pulling them apart since there was no evidence of drill holes on the shells. The prey selection of O. minor was related to the prey profitability and handling time; O. minor appeared to select preys with a higher profitability and a shorter handling time. However, the difficulty in opening the bivalve was not consistent with the prey preference of the octopods. These results suggest that O. minor prefers to consume R. philippinarum possibly due to a high profitability and a short handling time that supports the optimum Foraging Theory.