Long-term Changes Of Zooplankton Functional Groups In Jiaozhou Bay

Climate change and human activities are destabilizing coastal marine ecosystems.During the past several decades,eutrophication,frequent occurrence of harmful algal blooms,increasing abundance of gelatinous zooplankton,outbreaks of macrobenthos(e.g.starfish),and decline of fishery resources that reported in Jiaozhou Bay,indicating that the structure and function of marine ecosystem has significant changed.Zooplankton play a central role in marine ecosystems,variations in the zooplankton abundance and species composition will alter the whole ecosystem.Different zooplankton species have different ecological function,we concern about the long-term changes in zooplankton taxa.For example,what happened to the fodder zooplankton,like copepods;whether gelatinous zooplankton(e.g.jellyfish,chaetognaths)increase continuously.In order to effectively simplify the food webs,and comprehensively and accurately simulate the ecological processes of zooplankton community,we classify the zooplankton into different functional groups.In this paper,based on the ZooScan Intergrated System and eleven-year(2003-2013)zooplankton samples collected by Jiaozhou Bay Marine Ecosystem Research Station(JBMERS)in north,middle and outside region of the Jiaozhou Bay,we studied the long-term changes in abundance of zooplankton functional groups,long-term change in copepod size,and population dynamics of Noctiluca scintillans.From the perspective of Jiaozhou Bay marine ecosystem responded to the typical ecological disasters in recent years,we studied the impacts of the outbreaks of moon jellyfish(Aurelia sp.1)and green tide(Ulva prolifera)on zooplankton community.It aims to deepen people's understanding of coastal ecosystem evolution,and provide theoretical basis for scientific management of the Jiaozhou bay.During the period of 2003-2013,we found that copepods dominated the zooplankton community,their abundance decreased,with the decrease in spring,summer and autumn.The abundance of appendicularians decreased,with the decrease in spring and summer.Chaetognaths showed a fluctuated variation trend.The abundance of medusae increased at the sampling station that outside the bay,mainly caused by the increase in spring.Noctiluca scintillans exhibited an increasing trend in spring in middle and outside bay.Other zooplankton increased from 2003 and reaching the peak value in 2008-2009,and then decreased.By analyzing the relative abundance of two size ranks of copepods during the period of 2004-2012 at the sampling stations in north,middle and outside part of the Jiaozhou Bay,we found that the relative abundance of 300-500 ?m size rank increased,while that of >500 ?m size rank decreased.The interannual difference between the two size ranks was caused by the variation in summer,with the average volume of total copepods decreased,which was significantly negative correlated with the increased water column averaged temperature.These changes are consistent with predictions of the impact of warming on aquatic ectotherms.Seasonal variations in numerical abundance,cell diameter and population carbon biomass of the heterotrophic dinoflagellate Noctiluca scintillans were studied for 10 years from 2004 to 2013 in middle and outside region of the Jiaozhou Bay.In both areas,N.scintillans occurred throughout the year and demonstrated an essentially similar seasonality;the cell abundance increased rapidly from the winter minimum to an annual peak in late spring and early summer,and decreased gradually toward the autumn-winter minimum.The cell diameter also showed a seasonal fluctuation,being larger in spring and early summer than the other seasons.Temperature was an important factor that affected the seasonal phenology of N.scintillans.The peak abundance of phytoplankton in late winter and early spring preceded the massive occurrence of N.scintillans,indicating that phytoplankton provided the energy for the massive occurrence of N.scintillans.Estimated carbon biomass of N.scintillans population reached to a peak as high as 90.3 mg C m-3,and occasionally exceed over phytoplankton and copepod biomass.Our results demonstrate that N.scintillans in northwestern Yellow Sea displays the seasonal phenology almost identical to the populations in other temperate regions,and play important trophic roles as a heterotroph to interact with sympatric phytoplankton and copepods.In the summers of 2009 and 2011,moon jellyfish(Aurelia sp.1)massive occurred in Jiaozhou Bay.In order to find out the impacts of bloom of this large jellyfish on zooplankton community,we analyzed the seasonal variation of zooplankton functional groups from 2003-2013 at the sampling station in north part of the bay.Compared with non-moon jellyfish bloom years,the seasonal peak abundance of total zooplankton in the years of massive occurrence of moon jellyfish significantly decreased.Meanwhile,during the massive occurrence months(May-August)in jellyfish bloom years,the mean abundance of zooplankton also significantly decreased.The blooms of moon jellyfish have significant impacts on copepods and appendicularians,but not chaetognaths and medusae.The abundance of 300-1000 ?m size rank of total zooplankton and copepods significant decreased during the jellyfish bloom period,indicating the moon jellyfish exerted severe pressure on this size rank of zooplankton.Small-sized copepods,such as Acartia bifilosa and Paraclanus parvus are the dominate species in late spring and summer,which match the massive occurrence of the moon jellyfish,thus we speculate that small-sized copepods provide the energy for the outbreaks of moon jellyfish.From 2008,Ulva prolifera ongoing outbreak in summer in western coastal Yellow Sea and invasion into Qingdao coast,causing a serious impact on local environment and marine ecosystem.In order to find out the impacts of green tide on zooplankton community,we analyzed the seasonal variation of zooplankton functional groups from 2005-2013 at the sampling station outside the bay.Compared with non-green tide bloom years,the abundance of zooplankton in the years with green tide significant decreased,mainly reflected by the dramatic decrease in the abundance of copepods and nauplii.Meanwhile,the abundance of bivalve larvae and decapod larvae decreased 84.7% and 54.6%,respectively,echinoderm larvae increased 95.6%.In addition,compared with non-green tide bloom years,zooplankton community structure in the years with green tide also significant changed.The relative abundance of copepods decreased 10%,gelatinous zooplankton(including appendicularians,chaetognaths and medusae)and other zooplankton increased 6.3% and 3.5%,respectively.In the meroplankton composition,the relative abundance of bivalve larvae reduced a half,polychaeta larvae tripled and replaced the bivalve larvae became the dominant species;moreover,echinoderm larvae increased by 6 times.