Morphometric variations and internal shell growth patterns of the Patagonian scallop Zygochlamys patagonica across their SW Atlantic distribution range.

BETINA JUDITH LOMOVASKY; MARIO LASTA,; MACARENA VALIÑAS; MARTÍN BRUSCHETTI,; SILVANA CAMPODÓNICO; OSCAR IRIBARNE,

Mooloolaba, Queensland, Australia

Workshop; 15th International Pectinid Workshop; 2005

We compared morphometry, internal shell growth patterns of the Patagonian scallop Zygochlamys patagonica from four different beds across their SW Atlantic distribution range. The northern beds (Uruguay; 36º17’S and Reclutas; 39°20’S to 39°30’S) showed lower shell height, length and shell mass than the southern populations (i.e., Tango B bed: 42º30’S and Beagle bed: 55º10’S). Mean height, length, and width increased following a N-S latitudinal gradient. Acetate peels revealed the presence of internal growth bands with alternating broad opaque and narrow translucent growth bands. In Reclutas bed, the simple translucent band was formed in all seasons but the “cluster of translucent bands” representing external rings was formed principally in winter coincident with a higher gonadal condition index; thus, the energy input to gamete proliferation could be the cause of decrease in shell growth and posterior formation of external rings. The growth pattern observed for the first 2 or 3 growth bands was less pronounced than other growths bands, with sizes of these individuals corresponding to first maturity of the species; thus, the difference found can be due to differential allocation of energy investment between juvenile and adult organisms to shell production. The internal growth patterns differed between beds. Our study provides evidence of variation of growth in Z. patagonica in four beds across their SW Atlantic distribution range.