Spatio-temporal distribution of Acartia (Copepoda: Calanoida) species along a salinity gradient in the Seomjin River estuary, South Korea

The spatio-temporal distribution of four coexisting Acartia (Copepoda: Calanoida: Acartiidae) species, A. hudsonica, A. omorii, A. ohtsukai and A. forticrusa was examined along a salinity gradient in the Seomjin River estuary, during the spring tide of each month for one year from January to December 2000. Most of the Acartia species were found in mesohaline (5-18 psu) and polyhaline regions (>18 psu), but their densities varied seasonally both along the salinity gradient and with chlorophyll a concentration. Acartia hudsonica showed a high density in mesohaline and polyhaline regions in March and April when chlorophyll a concentration was >20 mu g l(-1), but A. omorii showed high density only in the polyhaline region in April. Acartia ohtsukai occurred both in mesohaline and polyhaline regions after June, but its peak density occurred in the polyhaline region in October when there was an autumn diatom bloom in the mesohaline. Acartia forticrusa showed peak density in the mesohaline in June when the water temperature was >20 degrees C. These results indicate that food can be an important factor in controlling spatio-temporal distributions in the Seomjin River estuary, in addition to other environmental factors.