Ecological variations and El Nino effects off the southern coast of the Korean Peninsula during the last three decades

To explore ecosystem response to environmental changes, we investigated int erannual and decadal changes in the marine ecosystem using data collected f rom the southern coast of the Korean Peninsula during the 1960s-1990s. Wate r properties such as sea surface temperature (SST) and salinity in April di d not show large variation during the 1970s, but a relatively cool water ma ss appeared from the early to mid 1980s and a warm water mass replaced it a fter 1989. Chl a concentration in April, which was converted from Secchi di sc 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 1 32 mg m(-3), but abundance was frequently high after 1984 and low during 19 72-1982. The most representative pelagic fishes in the South Sea seemed to respond to the increase in planktonic organisms. Anchovy, mackerel and sard ine 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 Osc illation Index (SOI) exhibited a high correlation with SST in December in t he study area (P < 0.05). Catches of anchovy and mackerel were positively c orrelated with chl a and zooplankton during their early life periods, as we ll as with SST in December.