Energy transformations by the Iceland scallop, Chlamys islandica (O. F. Müller), from 70°N. I. The age-specific energy budget and net growth efficiency

Abstract

Age-specific production and net growth efficiency for the Iceland scallop, Chlamys islandica (O. F. Müller), have been calculated by combining laboratory and field data on oxygen consumption, growth, spawning, and byssus production. Faster growing scallops attain maturity at an earlier age than slower growing ones, thus indicating that in C. islandica maturation depends more on size than on age. Upon reaching maturity, growth rate of shell and somatic tissue decreases whereas reproductive output increases. The combined effects of starvation and reproductive drain seem to cause somatic growth to approach nil in individuals older than 20 yr. This probably limits the length of life in the species. Provided with an adequate food supply, all sizes of the Iceland scallop have the same potential for growth because the net growth efficiency during the main growth period is high and more or less the same in all age-groups. Age-specific differences in annual growth are, therefore, caused by the younger scallops' ability to maintain a high growth rate for a longer period than older scallops.