Use of internal growth bands for measuring individual and population growth rates in Mytilus edulis from offshore production platforms

Abstract

Age and growth rates of M y t h s eduiis from the Forties Bravo oil production platform in the North Sea and the Morecambe Flame gas exploration platform in the Irish Sea were assessed using internal growth patterns in shell sections. Clear annual growth lines in the nacreous layer were used to determine the age of mussels, whilst the tidally induced microgrowth bands in the prismatic layer enabled both the age and linear growth rate of individual mussels to be established. Considerable variation in individual growth rates occurred both within and between populations. No consistent relationship was observed between population growth rate and water depth on the 2 platforms. Age estimates of individuals taken from population subsamples showed that the Morecambe Flame and Forties Bravo platforms contained 3 and 11 year classes respectively but that these did not coincide with any obvious size classes present in the populations studied. The use of internal growth bands provides a reliable method in which individual and population growth rates can be accurately determined from a single sample of the population. Their use is especially valuable in habitats such as offshore platforms or water intake pipes where conventional methods involving repeated sampling of the population are difficult or impracticable.