For the first time, use of the flooding dose technique using 3H-Phenylalanine is validated for measuring wholeanimal
and tissue-specific rates of protein synthesis in the blue mussel Mytilus edulis (61 mm shell length;
4.0 g fresh body mass). Following injection, the phenylalanine-specific radioactivities in the gill, mantle and
whole-animal free poolswere elevated within one hour and remained elevated and stable for up to 6 h following
injection of 3H-phenylalanine into the posterior adductor muscle. Incorporation of 3H-phenylalanine into body
protein was linear over time following injection and the non-significant intercepts for the regressions suggested
incorporation into body protein occurred rapidly after injection. These results validate the technique formeasuring
rates of protein synthesis inmussels. There were no differences in the calculated rates following 1–6 h incubation
in gill,mantle orwhole-animal and fractional rates of protein synthesis fromthe combined time course datawere
9.5 ± 0.8% d−1 for the gill, 2.5 ± 0.3% d−1 for the mantle and 2.6 ± 0.3% d−1 for the whole-animal, respectively
(mean values ±SEM). The whole-animal absolute rate of protein synthesis was calculated as 18.9± 0.6mg protein
day−1. The use of this technique inmeasuring one of themajor components ofmaintenancemetabolismand
growthwill provide a valuable and convenient tool in furthering our understanding of the proteinmetabolism and
energetics of this keystone marine invertebrate and its ability to adjust and respond to fluctuations, such as that
expected as a result of climate change.