| The Zhangzi Island area, an important farming area for Patinopecten yessoensisin the Northern Yellow Sea, locates in the south part of the Changshan Archipelago,abouth50km from the south coast of Liaodong Penisulla and150km from the YaluRiver Estuary. Due to clear seasonal variation of physical environment, it is alsosuggested as an ideal place for biological-physical coupling studies.The physicalpattern is determined by the Yellow Sea Cold Water Mess (YSCWM) and Yalu Riverfreshwater discharge in summer and by coastal currents and the Yellow Sea WarmCurrent (YSWC) in winter.In this study, monthly investgation was carried from July2009to June2010(except January and May for bad weather). Annual variation of zooplanktoncommunity was analyzed in relation to environmental conditions, includingtemperature regime, nutrient and Chlorophyll-a (Chl-a) concentrations. Long-termchange of zooplankton community was investigated through comparison withhistorical data in1959. Impacts of the YSCWM were emphasized on regimes ofnutrient and Chl a concentrations and population recruitment of Calanus sinicus,respectively.During the investigation, a total of29zooplankton species and7planktoniclarvae were indentified. Calanus sinicus and Saggita crassa were observed asdominant species in all months. Themisto gracilipes was sampled in each month, butrecorded as dominant species only in winter and spring. In spring, Labidocerabipinnata, Acartia clausi, Noctiluca scintillans and Ophiopluteus larvae were alsorecorded as dominant species. Penetia avirostris was recorded as dominant speciesonly in September. Zooplankton abundance (non-jellyfish) and biomass were highestin June and lowest in August, with annual averages of131.3ind/m3and217.5mg/m3. A ctenophores Beroe bloom was observed in October and November. Beroe biomasscorrelated negatively and significantly with other zooplankton abundance in October(P<0.05). Zooplankton species diversity was highest in October (1.56), and richnessindex was highest in April (1.81). The average value of eveness index was0.49. Thedomiant species of zooplankton community and annual variation of total abundance inthis study was similar to those recorded in the former study in1959, indicating lowpossibility of regime shift. The difference in species composition may result frominter-annual variation in freshwater discharge and warm currents intrusionRegimes of nutrient and Chl a concentration in summer and autumn wasdetermined mainly by the YSCWM. In2009, significant thermal stratificationpresented from July to October in open waters, and salinity decrease appeared in Julyand August in surface layers in mariculture area. Nutrient concentrations increasedwith depth in both areas in summer, but were similar through water column inNovember and December. On average, nutrient increased from summer to autumn inall components except ammonia. Nutrient concentrations lower than the minimumthresholds for phytoplankton growth presented only in upper layers in summer, butstoichiometric nitrogen limitation existed from July to December. Column averagedChl-a concentration was lower in open waters than in mariculture from July toDecember. It increased significantly in August and October in mariculture area, andwas less variable in open waters. Our results showed that nutrients limitation tophytoplankton growth presented mainly in upper layer in association withstratification caused by YSCWM in summer. Freshwater input and upwelling ofnutrients accumulated in YSCWM can stimulate phytoplankton production inmariculture area. Although phytoplankton bloom was induced by rainfall, littlecontribution was expected to food availability, as it was limited in surface layer.The Yellow Sea Cold Water Mass (YSCWM) was suggested an over-summeringsite of the dominant copepod species Calanus sinicus in coastal China Seas. In ourstudy, total abundance was lowest in October and highest in June, and sex ratio washighest in February and lowest in August. Evident spatial difference in abundance wasobserved during existence of the YSCWM. In June, total abundance averaged in 158.8ind/m3at well-stratified stations, and532.1ind/m3at the other stations. FromJuly to August, abundance decreased from50.4to1.9ind/m3outside the YSCWM, butsimilarly high abundance of322.0and324.4ind/m3was recorded inside. When theYSCWM disappeared in September, C. sinicus distributed evenly over the study area.Our results indicate that existence of YSCWM retarded population recruitment inspring but preserved a cohort with considerable abundance in summer. Theover-summered population was transported to neritic waters in autumn. Besides lowtemperature, stable vertical structure is also essential condition for preservation ofover-summer population. Comparing to the central YSCWM area, C. sinicus cansurvive summer condition with considerable abundance in marginal area, butpopulation structure was completely different in terms of C5proportion and sex ratio. |
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