BIOENERGETIC AND GENETIC-PARAMETERS IN RELATION TO SUSCEPTIBILITY OF BLUE MUSSELS, MYTILUS-EDULIS (L.) TO SUMMER MORTALITY

Our study examined whether the differences in susceptibility to summer mass mortality of two stocks of mussels from the Magdalen Islands (Qu ebec, Canada) are related to bioenergetic and/or genetic factors. The relative importance of maintenance and maximal metabolic rates, scope for growth (SFG) and the O:N ratio were followed over time to assess w hether the increased incidence of mortality in late summer reflects a decrease in bioenergetic status at this period. The stock of mussels w hich was more susceptible to summer mortality had higher values of V-O 2. Furthermore this stock had a more negative scope for growth and low er O/N ratio in early August. These parameters are Likely to reflect u nfavourable environmental conditions, which led the mussels to rely up on protein catabolism. We also observed a negative correlation between multiple-locus heterozygosity and standard V-O2. The more susceptible stock of mussels had a lower degree of multiple-locus heterozygosity. Thus, we suggest that the periodic, but irregular, outbreaks of summe r mortality are the result of a synergistic interaction involving diet ary deficiencies, temperature, a possible post-spawning, stress and th e genetic characteristics of the stock. The higher metabolic demand as sociated with a reduced degree of heterozygosity will impose a supplem entary stress and render such stocks more vulnerable to summer mortali ty. The results are in agreement with the hypothesis that high levels of heterozygosity are related with lower costs of maintenance. (C) 199 8 Elsevier Science B.V.