Seasonal reproductive rates of Oithona nana (Copepoda: Cyclopoida): first record in temperate coastal waters off Argentina

TEMPERONI, BRENDA; VIÑAS, MARIA DELIA

Victoria

Encuentro; 3rd GLOBEC Open Science Meeting; 2009

GLOBEC

Oithonids are the most successful free-living cyclopoids in the marine pelagic ecosystem. Oithona nana (Copepoda: Cyclopoida) is a widely-distributed neritic species, which often comprises up to 90% of the zooplankton in many coastal areas. However, no detailed studies have been made so far on its reproductive biology. The objective of this study was to estimate, for the first time, the seasonal variation of O. nana reproductive rates, in a temperate region: coastal waters off Buenos Aires province, Argentina. Population density was low in late fall and winter (1800-3424 ind m-3), and high in early spring and summer (3709-12209 ind m-3). Sex ratio was highly skewed for females. Female prosome length changed inversely with temperature (r2=0.63 ; p=0.0011), while egg diameter (mean= 45.01 µm) did not change throughout the year. The number of eggs contained in a pair of sac (mean= 24 ± 3.6 eggs sac-1) was higher during the spring. Embryonic time was inversely related to the temperature (r2= 0.98; p= 0.125), while the interclutch time was independent of it (0.68 ± 0.07 days). Mean population specific egg production rate (0.129 ± 0.10 day-1) did not show a clear seasonal pattern. However, slightly higher values were observed in the warmest months. It was not significantly correlated with temperature (r2=0.08; p=0.37) or chlorophyll a (r2=0.12; p=0.27).