Native versus invasive crab effluent effects on byssal thread production in the mussel, Mytilus trossulus (Gould, 1950)

Mussels have evolved many adaptations to protect themselves, including the production of byssal threads. These are strong, proteinaceous fibres that mussels secrete to adhere themselves to rocks, preventing detachment by waves and predators. These byssal threads may be strengthened if mussels can recognize potential threats, such as native crabs, as their populations have a long history of coevolution. Unfortunately, the introduction of invasive predators poses a challenge for prey, which may not be capable of recognizing them. In this study, byssal thread production in the Pacific blue mussel (Mytilus trossulus ) was observed when exposed to effluent from the native red rock crab (Cancer productus) or the invasive European Green crab (Carcinus maenas). M. trossulus  were placed in closed systems with effluent from either C. productus , C. maenas  or control (no predator), over a 24-hour time period. Final measurements of number, length and diameter of byssal threads were recorded. M. trossulus  exposed to effluent from C. productus produced byssal threads at a statistically significantly faster rate than in the control group over the first 7.5 hours. M. trossulus exposed to effluent from C. maenas  produced byssal threads at a statistically significantly faster rate than both the C. productus and control groups. However, after 24 hours, there was no statistically significant difference between the mean number of byssal threads for any treatment. Additionally, we found no statistically significant difference between the mean diameter of byssal threads produced or length of byssal threads produced for any treatment.