Predation of the crab Acanthocyclus albatrossis on seeds of the bivalve Mytilus chilensis under different environmental conditions: Importance of prey and predator size

Abstract

Predation is one of the most important interactions in biology, playing a fundamental role in the ecology of populations and communities. In southern Chile, the mussel Mytilus chilensis supports a large aquaculture industry. This species cohabits with one of its predators, the crab Acanthocyclus albatrossis, both in wild bivalve beds and in suspended culture systems. In this investigation, we assessed the predator-prey interaction between these two species, addressing the following aspects: a) the vulnerability pattern of M. chilensis to predation by A. albatrossis; b) prey sizes that are free of predation (the refuge in size); c) the attack rate and d) the effects of temperature and salinity on predation by different-sized A. albatrossis crabs. The prey sizes most likely to be attacked were 7.5, 12 and 14 mm (valve length) respectively for the three predator size categories evaluated. The sizes of the mussels that are free of predation were > 12, > 18 and > 22 mm respectively for each predator size. The mean attack rate was affected by the size of M. chilensis, with the smallest prey (6–12 mm) exposed the highest predation pressure. Temperature exhibited a positive linear effect on the median attack rate only for crabs in the smallest size category; no pattern was observed for the effect of temperature on the other sizes of crabs. Salinity showed no evident effects on the median attack rate at any size category. Our results indicate that A. albatrossis could be an important predator of M. chilensis recruits in wild bivalve beds, and of seeds in suspended culture systems.