Identifying internal shell growth bands in the Patagonian scallop Zygochlamys patagonica (King and Broderip, 1832) in Reclutas bed (39º24'S,

LOMOVASKY, B; LASTA, M; BRUSCHETTI, M; IRIBARNE, O

Coquimbo, Chile

Congreso; XXIV CONGRESO DE CIENCIAS DEL MAR; 2005

Universidad de Chile

IDENTIFYING INTERNAL SHELL GROWTH BANDS IN THE PATAGONIAN SCALLOP ZYGOCHLAMYS PATAGONICA (KING AND BRODERIP, 1832) IN RECLUTAS BED (39º24’ S – 55º56’ W), ARGENTINA.   Lomovasky Betina J. 1, 2*, Mario Lasta 3*, Martín Bruschetti 1, 2 and Oscar Iribarne 1, 2   *E-mail : lomovask@mdp.edu.ar; mlasta@inidep.edu.ar   1 Laboratorio de Ecología, Dpto. Biología, FCEyN, Universidad Nacional de Mar del Plata. CC 573 Correo Central (B7600WAG) Mar del Plata, Bs. As. Argentina. 2 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). 3 Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP). Paseo V. Ocampo N° 1, (B7602HSA) Mar del Plata, Argentina.     Abstract The Patagonian scallop is widely represented in the extreme south of South America reaching 42ºS in the Pacific and 36º 15’S in the Atlantic between 40-200 m depth. It is an important economic resource in the Atlantic where most productive beds are located along the 100 m isobath under influence of the shelf-break front. Accurate age determination is essential to the assessment of population dynamics of Z. patagonica; thus, studies to identify internal growth bands are necessary to confirm the external growth rings and no underestimate the age. Analysis of acetate peels of shell sections were carried out and revealed the presence of alternating broad opaque and narrow translucent internal growth bands. The internal growth pattern was clearly observed in the umbo, but it was more difficult to interpret them along the cross section of the shell. For the first 2 or 3 bands, which were always very difficult to observe, the pattern observed was different from other growths bands. Each external surface ring was associated with a cluster of small internal growth bands. Thus, these clusters are the result of slowed growth rate within the year. The acetate peels technique gave the possibility to identify the internal growth bands closer to the shell edge which are very difficult to be identified on the exterior surface. Thus, using this technique it will be possible to obtain new information about the maximum age of the species. This study is the first describing the internal growth band of Z. patagonica.