Can a scavenging gastropod with a mussel conspecific diet induce anti-predator defence in the mussel Perna viridis?

This study investigated whether a mussel predator (the swimming crab Thalamita danae) and a scavenger (the gastropod Babylonia lutosa) could induce anti-predator response in the green-lipped mussel Perna viridis by chemical means. The crabs and gastropods had been either starved or recently fed with the mussels. We examined the number, diameter, length and volume of byssus threads produced by the mussels in order to compare the intensity of anti-predator responses when they were exposed to different stimuli. Our results showed that the mussels produced a significantly larger volume of byssus threads when they were exposed to a crab that had recently consumed conspecifics than the mussels in the control group. The starved crab had a weak effect on increasing the number, length, diameter and volume of byssus threads. Furthermore, the scavenging gastropods failed to increase byssus thread production in the mussels, no matter they had been starved or consumed conspecifics. Indeed, byssus thread production is energetically costly. It would be maladaptive for the mussels to increase byssus thread production in response to a low predation risk presented by a scavenger.