Antipredatory responses of Perna viridis (Linnaeus, 1758) under acute hypoxia and low salinity

The antipredatory responses/attachment behaviour of the green-lipped mussel Perna viridis were studied under combined stresses of hypoxia and low salinity in the presence/absence of its predator, the swimming crab Thalamita danae. There were two oxygen concentrations (1.5 mg l^-1 O₂ = hypoxic and 6.0 mg l^-1 O₂ = normoxic) and two salinity levels (15‰ = low, 30‰ = normal). Byssus production performances (including byssal-thread number, byssal-thread diameter, byssal-thread length, cumulative byssal-thread length and volume and frequency of stalk-shedding) were evaluated after 48 h. All variables were significantly affected by dissolved oxygen (DO), salinity and predator presence. Interactive effects of these three factors on byssus production were also observed. Byssus production and frequency of stalk-shedding were lowest in hypoxia × low salinity, followed by normoxia × low salinity, hypoxia × normal salinity, while normoxia × normal salinity exhibited the highest values in both predator-presence and non-predator-presence groups. At each treatment of DO and salinity, all parameters in predator-presence groups were significantly higher than in non-predator-presence groups. Our results indicate that the environmental hypoxia and low salinity impair anti-predatory/attachment behaviour and show some synergistic effects. Since reduced byssus production makes the mussels more vulnerable to crab predators, the co-occurrence of hypoxia and low salinity may increase the rates of crab predation on P. viridis in the field. © 2013 The Author.