Age-dependence of metabolism in mussels Mytilus edulis (L.) from the WhiteSea

Age structure, natural mortality and growth, as well as age- and size-depen dent changes in parameters of energy metabolism were studied in blue mussel s Mytilus edulis (L.) from the White Sea. Mussels were sampled in August (S ummer sample, SS) and October (Autumn sample, AS) and contained animals of three size groups, 2-9 years old. Field data showed an increase of mortalit y of mussels and strong decrease in growth rates after 6 years of age. Abso lute tissue growth increment (AI) reconstructed from winter growth marks on the shells decreased with age and was strongly size-dependent, while relat ive tissue growth increment (RI) did not depend on size of the animals. Res piration rates and citrate synthase activity demonstrated power regression versus tissue weight with regression coefficients - 0.231 and - 0.170, resp ectively. After weight correction both parameters showed a decrease with in creasing age. ATP and phosphagen levels also showed a pronounced decrease i n animals older than 5-6 years despite considerable differences in the abso lute values of both parameters in SS and AS. pH(i) in mussels was also age- dependent and decreased with increasing age after 5 years. In air exposed m ussels, pH(i) was reduced only at young age such that pH(i) was low and con stant within the whole age range. Our data give evidence that aerobic metab olic rate in M. edulis from the studied population declines when animals re ach an age of about 6 years. The decrease in oxygen consumption reflects th e drop in mitochondrial respiration, which is mirrored by the decrease in C S activity. A concomitant fall in ATP turnover may include a downregulation of the mechanisms of acid-base regulation. pH(i) will then approach equili brium indicated by lower pH(i) values in older animals. Our data suggest th at intrapopulational comparisons of physiological parameters in mussels sho uld take into account age composition of compared samples. (C) 2001 Elsevie r Science B.V. All rights reserved.