Paula Moura

Appraisal of the usefulness of operculum growth marks for ageing Hexaplex trunculus (Gastropoda: Muricidae): Comparison between surface striae and adventitious layers

Abstract This study estimated the age of Hexaplex trunculus (Gastropoda: Muricidae) by analysing operculum growth marks. Surface striae and adventitious layers were counted in opercula of H. trunculus from the Ria Formosa Lagoon (southern Portugal) and from the Bizerte Lagoon (northern Tunisia), and in aquacultured individuals used for validation of the ageing technique. Operculum growth features were also compared between H. trunculus populations under contrasting environmental conditions (namely seawater temperature). Despite high inter-individual variability, all H. trunculus populations displayed a clear increasing trend in the number of striae and layers with increasing specimen size. The operculum marginal growth revealed that opercular deposition is not annual. Instead, a few growth marks are formed in the operculum each year, which was confirmed with reared specimens. In both ageing methods, considerable variation in the number of counts at a determined shell length indicates that operculum growth marks should be interpreted cautiously because they might not correspond accurately with individual age. Because of the subjectivity inherent to either method, counting striae and layers in opercula only provides rough age estimates of H. trunculus.

Morphometric relationships and relative growth of 20 uncommon bivalve species from the Algarve coast (southern Portugal)

This study reports the morphometric relationships and relative growth of 20 uncommon bivalve species collected along the Algarve coast (southern Portugal). Morphometric relationships were established between three linear variables (shell length, height and width) and one ponderal variable (total weight) and the relative growth between variables (isometry vs allometry) was analysed in order to assess their variation throughout ontogeny. In addition, morphometric indices (elongation, compactness, convexity and density) based on ratios of those linear and ponderal variables were calculated in order to further characterize morphologically the bivalve species. A total of 2512 individuals belonging to nine bivalve families were analysed, comprising specimens with broad ranges in both shell length (11.8–109.0 mm SL) and total weight (0.2–354.6 g TW). All morphometric relationships were highly significant ( P r = 0.727–0.998). Among a total of 60 morphometric relationships, 27 isometries, 25 positive allometries and 8 negative allometries were registered. The morphometric indices displayed a remarkable variation among taxa, reflecting the high morphological diversity of these miscellaneous bivalve species. Discriminant analysis provided a spatial visualization of the species morphometric variables that further evidenced their main shape features, the distinctness between some species and families (e.g. Pharidae and Cardiidae) and the morphological resemblance among some species belonging to other families (e.g. Veneridae and Tellinidae). Overall, this information is useful and has practical application in diverse research fields, including studies on systematics and taxonomy, physiology, biology, ecology, fisheries assessment and management.

Biochemical and energy dynamics throughout the reproductive cycle of the striped venus Chamelea gallina (Mollusca, Bivalvia)

The striped venus Chamelea gallina is an important commercial bivalve species in Europe. However, large inter-annual fluctuations in stock abundance and periodic recruitment failure threaten the biological and economic sustainability of this fishery. This study aimed to improve the knowledge of the reproductive cycle and reproductive strategies of this species from the Algarve coast (southern Portugal) in order to contribute to the establishment of management measures and to assess its potential for aquaculture. The reproductive cycle of C. gallina followed a seasonal cycle, significantly influenced by sea surface temperature and food availability. Gametogenesis took place in winter, coinciding with the phytoplankton bloom. Spawning occurred during summer, followed by a short period of sexual inactivity in autumn. Condition index did not reflect the reproductive cycle of C. gallina and generally, followed the same trend of chlorophyll a. Glycogen was positively correlated with gonadal index and chlorophyll a. High total lipid values were recorded throughout gonad ripeness and spawning, but decreased at the end of the spawning and in the rest period. The extended spawning period of C. gallina will allow larvae to be obtained for much of the year by artificial spawning of wild broodstock.