Population dynamics of a brackish water clam, Corbicula japonica, in the Seomjin River estuary, Korea

Abstract

The population dynamics of a clam Corbicula japonica were investigated in the Seomjin River estuary during two years (2016 to 2017). Samples for analysis were monthly collected at 3 stations 5 times per station using a small grab. The distribution of C. japonica population was mostly restricted at middle-to-upper region of the estuary (station 11 to 15), where the average values of salinity at the bottom waters during the investigation period was 21.9 psu, 15.7 psu and 3.8 psu at station 11, 13 and 15, respectively. The sediments at all stations were mostly composed of coarse sands including some granules, and the mean grain size of the sediments at station 11, 13 and 15 was 1.4 Ф, 0.7 Ф and 0.1 Ф, respectively. Overall, the density of C. japonica was the highest in the upper region of the estuary (station 15, 3,163 ind.m-2) and the lowest in the middle region (station 11). Interestingly, an discernible annual variation in the recruitment of C. japonica was observed: the recruitment of 2016 cohort started in June, whereas that of 2017started in April at most stations. The density of a newly recruited cohort was recorded as 4,280 ind.m-2 at station 15 in July, 2017, but 368 ind.m-2 in July, 2016. The duration of recruitment and the number of newly recruits in 2017 were longer than those in 2016. Such difference in the density and recruitment strength between 2016 and 2017 cohorts of C. japonica in the Seomjin Riveribution of C. japonica population was mostly restricted at middle-to-upper region of the estuary (station 11 to 15), where the average values of salinity at the bottom waters during the investigation period was 21.9 psu, 15.7 psu and 3.8 psu at station 11, 13 and 15, respectively. The sediments at all stations were mostly composed of coarse sands including some granules, and the mean grain size of the sediments at station 11, 13 and 15 was 1.4 Ф, 0.7 Ф and 0.1 Ф, respectively. Overall, the density of C. japonica was the highest in the upper region of the estuary (station 15, 3,163 ind.m-2) and the lowest in the middle region (station 11). Interestingly, an discernible annual variation in the recruitment of C. japonica was observed: the recruitment of 2016 cohort started in June, whereas that of 2017started in April at most stations. The density of a newly recruited cohort was recorded as 4,280 ind.m-2 at station 15 in July, 2017, but 368 ind.m-2 in July, 2016. The duration of recruitment and the number of newly recruits in 2017 were longer than those in 2016. Such difference in the density and recruitment strength between 2016 and 2017 cohorts of C. japonica in the Seomjin River