Induction of anti-predator responses in the green-lipped mussel Perna viridis under hypoxia |
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Authors: | Youji Wang Menghong Hu P K S Shin S G Cheung |
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Institution: | (1) City University of Hong Kong, Kowloon, Hong Kong; |
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Abstract: | Hypoxia due to the over enrichment of waters by nutrients is becoming a global problem. In mussels, enhanced byssus thread
production is an important adaptation to the presence of crustacean predators and to energetic hydrodynamic regimes. Thread
production is an energy-consuming process, so this study used the green mussel Perna
viridis (L.) to examine the response to predator exposure combined with hypoxia. Hypoxia is common in sheltered bays in Hong Kong,
and the mussels were collected in one such bay, Lok Wo Sha (latitude/longitude: 22o18′ N/114o10′ E) in January, 2009. The
predator used in the experiments was the swimming crab Thalamita danae. Oxygen concentrations used in the 48-h experiments ranged from hypoxic to normoxic (1.5 ± 0.3 mg l−1, 3.0 ± 0.3 mg l−1 and 6.0 ± 0.3 mg l−1). Fewer byssus threads which were also shorter and thinner were produced at reduced oxygen levels, no matter if the predator
was present or not; the frequency the mussels shed stalks was also lower. Mussels exposed to the predator, however, have enhanced
byssus thread production at all oxygen levels when compared with the control. This has highlighted the significance of anti-predator
responses for the survival of individuals even under a stressful environment in which energy supply is limited by aerobic
metabolism. Interactive effects between oxygen level and predator exposure were observed for the byssus thread production
(frequency of shed stalks, mean byssus thread length, cumulative byssus thread volume), with values obtained at 1.5 and 3.0 mg
O2 l−1 being statistically indistinguishable for the control group without predator but not for the predator group. The lack of
differences in the byssus thread production at lower oxygen levels in the absence of predator may indicate the minimum amount
of byssus that is required for settlement on a substrate. |
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