Description: 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 Querandí (from March 2005 to December 2006). Von Bertalanffy growth functions were established from length-frequency distributions using an asymptotic length (L∞) of 44 mm and the growth constants (K) of 0.46 and 0.47 y-1 respectively of Mar de las Pampas and Faro querandí. 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) m-2yr-1. Individual production revealed the highest value at 30 mm length (0.16 g AFDM m-2yr-1) and annual production ranged between 0.08 and 0.99 g AFDM m-2yr-1, resulting in renewal rate values (P/) between 0.82 and 2.16. The P/ 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.

Description: 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 QuerandıŽ (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 QuerandıŽ. 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.

Description: Ovigerous females of Cancer setosus are present year-round throughout most of this species extended distributional range along the Chilean/Peruvian Pacific coast (46°S 2°S). However, their annual number of egg-masses remains speculative and as such hasnt been considered in latitudinal comparisons of this species reproduction. To reveal the effect of temperature on egg-mass production and egg-development female C. setosus were held in through-flow aquaria under natural seasonal temperature conditions (16 23 °C) in Antofagasta (23°S), Northern Chile (06/2005 - 03/2006), and at three fixed temperatures (09/2006 - 02/2007) in Puerto Montt (41°S), Central-Southern Chile. Female crabs uniformly produced up to 3 viable egg-masses within 4 1/2 months in Antofagasta and in Puerto Montt (at 19.3 °C). The second oviposition followed the first, and the third the second, after 62.5 d (± 7.6, N = 7) and 73.5 d (± 12.5, N = 11) in Antofagasta and 64.4 d (± 9.8, N = 5) and 67.0 d (± 2.8, N = 2) in Puerto Montt. At the two lower temperatures in Puerto Montt of 15.9 °C and 12.1 °C the production of a second egg-mass was observed after 82.8 d (± 28.9; N = 4) and 137 d (N = 1) respectively. The duration of egg- development from oviposition until larval hatching decreased from 65 d at 12.5 °C to 22.7 d at the observed upper temperature threshold of 22.0 °C. Based on the derived relationship between temperature and the duration of egg-development (y = 239.3175e-0.107x; N = 21, r2 = 0.83) and reports on monthly percentages of ovigerous females from field studies the annual number of egg-masses of C. setosus was calculated. This analysis revealed an annual output of about one egg-mass close to the species northern and southern distributional limits in Casma (9°S) and Ancud (43°S), respectively, while around Coquimbo (29°S) about two and in Concepción (36°S) more than 3 egg-masses are produced per year.

Description: Previous study on Cancer setosus Molina, 1782 showed that latitudinal changes in temperature control the number of annual egg masses. This study focused on the effects of preoviposition temperature and female size on egg traits in C. setosus from northern (Antofagasta, 23° S) and central-southern (Puerto Montt, 41°S) Chile. Blastula eggs produced in nature ranged in dry mass (DM) from 9.1 to 15.1 μg, in carbon (C) from 4.8 to 8.4 μg, in nitrogen (N) from 1.0 to 1.6 μg, in C:N ratio between 4.7 and 5.4, and in volume (V) between 152 and 276 mm3 × 104 per female. Blastula eggs from females caught early in the reproductive season in Puerto Montt (September 2006) were significantly higher in DM, C, N, and V than those of females caught 2 mo later, reflecting a seasonal increase in water temperature. In Puerto Montt early and late season blastula eggs were higher in DM, C, N, and V than eggs from Antofagasta by about 32 and 20%, respectively. Subsequent egg masses produced in captivity in Puerto Montt followed this pattern of smaller eggs with lower DM, C, and N content at higher pre-oviposition temperatures. In Antofagasta no significant difference in DM, C, N, and V between eggs produced in nature and subsequent eggs produced in captivity was found and all egg traits were significantly positively affected by maternal size. Reproductive plasticity in C. setosus helps to explain the species wide latitudinal distribution range.