Age and individual growth of Mesodesma mactroides (Bivalvia) in the southernmost range of its distribution

FIORI, S. M.; MORSÁN, E. M.

ICES JOURNAL OF MARINE SCIENCE

Oxford University Press

Lugar: Copenhagen; Año: 2004 vol. 61 p. 1253 - 1259

1054-3139

The yellow clam, Mesodesma mactroides, is an intertidal bivalve typical of sandy beaches of the South American Atlantic coast. Its distribution ranges from Brazil to Argentina. Growth parameters of southernmost populations of M. mactroides were studied and compared with other populations. The study area was located at Isla del Jabalí , and Monte Hermoso. Thin shell sections were examined to describe internal shell layers and to contrast with external shell transparency. Periodicity of deposition of external growth increments was studied recording the degree of transparency of the shell border. Growth patterns were determined using modal progression analysis from size-frequency distributions, analysis of external shell increments, and size-at-age data derived from inner shell layers. Growth parameters were described using the von Bertalanffy growth model. Both internal and external patterns were coincident and exhibited a succession of one translucent and one opaque region. The transparent region was deposited during summer. Growth differences found between populations may be related to unequal size of first ring in both beaches. This feature may originate from asynchrony in spawning and recruitment. The monthly analysis of shell length size-frequency distribution from Isla del Jabalí, show that growth of M. mactroides is seasonal. Estimations of asymptotic size of studied populations and other located at the southern (coldest) half of the geographical range of distribution suggest a negative relation with latitude.