Body size-density relationship for Mytilus edulis in an experimental food-regulated situation

We grew mussels (Mytilus edulis) under two different food regimes and eight population density levels to estimate the joint effects of density and bio mass on their growth and survival and to determine the shape of the biomass -density (B-IV) relationship. Mussels were reared for 22 months, between De cember 1994 and October 1996, in 1-L experimental chambers supplied with na tural seston. Growth in shell length, individual wet mass and ash free dry mass (m) decreased with decreasing food availability and increasing populat ion density. Survival was negatively correlated with density but did not di ffer significantly between food regimes during the first year. Variations i n concentration of available food did not alter the effects of crowding on mussels, as judged from the slopes of the body size-density curves. The gen eral patterns exhibited by B-N curves were not consistent with expectations since we found 1) no classical competition-density (C-D) effect as reporte d in plants at intermediate competition levels, and 2) a slope of -0.648 fo r m-N curves in both food regimes, which was higher than expected from self -thinning (ST) theory. This value does not support present food-driven ST t heory. This study introduces an unusual m-N region which combines propertie s of both ST and C-D effect.