Seasonal production of Oithona nana Giesbrecht, 1893 (Copepoda: Cyclopoida) in temperate coastal waters off Argentina

Oithona nana (Copepoda: Cyclopoida) is a widely distributed but poorly known species. The objective of this study was to estimate the seasonal variation of O. nana secondary production in temperate coastal waters off Argentina, South West Atlantic. The species occurred throughout the year, with higher abundances in spring and winter (9692-10132 ind m(-3)) than in summer and autumn (5537-8635 ind m(-3)). Sex ratio was highly skewed toward females. Total length of adults and immature stages was inversely related with temperature. Clutch size (mean +/- SD = 12 +/- 2 eggs sac(-1)) and egg diameter (mean +/- SD = 45 +/- 2 mu m) did not change throughout the year. Embryonic duration was inversely related to temperature (r(2) = 0.99). Mean (+/- SD) population-specific egg production rate (0.07 +/- 0.03 day(-1)) did not show a clear seasonal pattern; however, slightly higher values were observed in the warmest months. Oithona nana integrated annual production was 9.8 mg C m(-3), 94% of which was represented by copepodite somatic growth. The key role played by O. nana in the coastal waters of the Argentine Sea warrants further ecological studies under different oceanographic conditions.