Bioenergetic model predictions of actual growth and allometric transitions during ontogeny of juvenile blue mussels Mytilus edulis

The growth rates of blue mussels Mytilusedulis on ropes in the Great Belt (Denmark) have been studied during the growth season of one year, from settling to about 30 mm shell length mussels, covering >4 decades of body mass. Measured shell length (L, mm) and dry weight of soft parts (W, μg) for L > 10 mm followed a power-law (W =
2.15L^3.40) which supplemented an existing power-law for L < 10 mm (W = 24.7 L^2.42) to establish that somatic growth changes character at L ≈ 10 mm and W ≈ 10 mg. Results of specific growth rates based on dry weight of soft parts (μ = dlnW/dt) compared well with predictions based on a previously developed bioenergetic growth model (BEG) for W> 10 mg (μ =aW^b, a = 0.871× C – 0.986; b = –0.34, with μ in % d⁻¹ and W in g) which explicitly takes into account the prevailing chla concentration C (μg L⁻¹). Results for W< 10 mg also correlated well by the power-law (μ =aW^b), now with exponent b = −0.13 close to the suggested value (b ≈ −0.1) from experimentally established correlations for filtration and respiration rate of post-metamorphic mussels. Using the stated W(L)-relation for L> 10 mm the growth model has been expressed in terms of shell length specific growth rate (μL ≡ dlnL/dt = αL^β) by which data on shell length was well correlated, including the influence of chla concentration. Supplementary growth data from mussels in suspended net-bags at the same site illustrated differences ascribed to lack of competition for space and food, and literature data on shell length from cage-growth of mussels in the brackish Baltic Sea support the present correlations. It is argued that the allometric transitions that take place around W ≈ 10 mg and L ≈ 10 mm during the ontogeny of M. edulis is most likely universal and not restricted to first
year growth of juvenile (young) mussels during the productive season.