Ecological variations and El Niño effects off the southern coast of the Korean Peninsula during the last three decades
To explore ecosystem response to environmental changes, we investigated interannual and decadal changes in the marine ecosystem using data collected from the southern coast of the Korean Peninsula during the 1960s–1990s. Water properties such as sea surface temperature (SST) and salinity in April did not show large variation during the 1970s, but a relatively cool water mass appeared from the early to mid 1980s and a warm water mass replaced it after 1989. Chl a concentration in April, which was converted from Secchi disc information, was low (mean=1.18 mg m−3) during the period 1968–1980 excluding 1974, but there was a period of greater biomass for 7 years from 1981 (mean=2.78 mg m−3). A negative correlation (r=−0.387, P < 0.05) between SST and chl a in April matched high chl a during the low-SST period in the early and mid 1980s. Annual zooplankton biomass ranged from 37 to 132 mg m−3, but abundance was frequently high after 1984 and low during 1972–1982. The most representative pelagic fishes in the South Sea seemed to respond to the increase in planktonic organisms. Anchovy, mackerel and sardine increased in abundance since the mid 1970s. High catches of anchovy and mackerel lasted until the 1990s, whereas sardine decreased after the early 1990s. From the matrix of simple correlation coefficient, the Southern Oscillation Index (SOI) exhibited a high correlation with SST in December in the study area (P < 0.05). Catches of anchovy and mackerel were positively correlated with chl a and zooplankton during their early life periods, as well as with SST in December.
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