Seasonal variations in proteins, fat and glycogen of the wedge clam <i>Donax cuneatus</i>

85-87Variations in proteins, fat and glycogen along with water in Donax cuneatus were studied for 1 yr. Water content remained at high level during monsoon (July to September) and at a moderate level from October to January followed by slight decrease during February to June. Protein content remained relatively high throughout the year with a decrease during the breeding period and the maturation period. Glycogen content showed peak values when the clams were in gametogenic phase. It decreased during the breeding period but the increase in the glycogen content during December-January was due to the absence of resting stage in the gonad. The decline in glycogen content in September might be due to its utilization under unfavourable conditions. Glycogen content during the maturation period declined showing the utilization in sexual cells production and development. Fat content remained at a moderate level during the gametogenic period and increased during the period of active formation of sexual cells. It then decreased during the spawning period

Population structure, growth and production of the wedge clam Donax hanleyanus (Bivalvia: Donacidae) from northern Argentinean beaches

Donax hanleyanus Philippi, 1847 (Bivalvia: Donacidae) dominates fine to coarse sandy beach communities of the northern Argentinean Atlantic coast. The population biology of this intertidal wedge clam was studied by determining population structure, growth and production at the three locations Santa Teresita, Mar de las Pampas (both from December 2005 to December 2006) and Faro Querand&#305;Ž (from March 2005 to December 2006). Von Bertalanffy growth functions were established from length-frequency distributions using an asymptotic length (LN) of 44 mm and the growth constants (K) of 0.46 and 0.47 y1 respectively of Mar de las Pampas and Faro Querand&#305;Ž. Compared with growth studies four decades ago, D. hanleyanus today is growing more slowly, but is reaching a higher maximum length. Longevity is estimated to be approximately five years. The present study confirms that the overall growth performance index is habitat-specific, grouping Donacidae into tropical/subtropical, temperate and upwelling species. The intertidal biomass of D. hanleyanus ranged between 0.04 and 1.32 g ash-free dry mass (AFDM) m2yr1. Individual production revealed the highest value at 30 mm length (0.16 g AFDM m2yr1) and annual production ranged between 0.08 and 0.99 g AFDMm2yr1, resulting in renewal rate values (P/B) between 0.82 and 2.16. The P/B ratios of D. hanleyanus populations increased with decreasing latitude from temperate to tropical regions. Only at Santa Teresita D. hanleyanus was found living with the sympatric yellow clam Mesodesma mactroides. A significant negative correlation between abundances of both surf clams suggests that abundance peaks of D. hanleyanus are related with population crashes of M. mactroides. Spatial differences in abundance are significantly related to sand texture as confirmed by nonmetrical multidimensional scaling, but not to sea surface temperature. However, the decrease of D. hanleyanus seems to be principally related to human activities