Ecological Investigation On The Decline Phase Of Jellyfish Bloom And Preliminary Research Of Stimulation On Bacterial Proliferation By Jellyfish Metabolic Product

In order to reveal the abundance relationship between the small jellyfish and micro-zooplankton,a field investigation was conducted in Nanhu Park of Xiamen in the spring of 2012.For further understanding of the function jellyfish have in marine ecosystem,a spectroscopic analysis of metabolic product released from Aurelia sp.was carried out by using excitation-emission matrix fluorescence spectroscopy-parallel factor analysis(EEMs-PARAFAC for short)united technology.The method of DAPI staining was used to figure out the variations of bacterial abundance under the stimulation of metabolic product released fromAurelia sp..Meanwhile,the tracking of bacterial abundance was also conducted in the jellyfish metabolic product under photo-degradation.TThe preliminary results are as following:The species of small jellyfish outbroke in Nanhu Park was Blackfordia virginica,and 2 taxa consisting of 13 groups were identified in micro-zooplankton,in which planktonic larvae were the most predominant group in aspect of both species number and abundance.There were 9 groups in planktonic larvae and accounted for 93.00%in total abundance of micro-zooplankton.Copepod nauplius was the main group in planktonic larvae which was followed by Gastropoda larvae and Bivalvia larvae.The other taxon was Copepoda.which had 4 groups including Cyclopoida and Pseudodiaptomus spp.in majority,accounted for 7.00%in total abundance of micro-zooplankton.Through the investigation for 44 days,there was nearly no explicit relationship between B.virginica and micro-zooplankton in abundance variations during the decline phase of jellyfish bloom.The abundance of jellyfish experienced two rises and tihree falls;meanwhile,the abundance of micro-zooplankton kept increasing till the end of investigation.Regarding April 9 as a dividing point,after then,the water temperature increased faster,while the abundance of jellyfish began to fall into a decline till 0 ind·mL-1,at the end;simultaneously,the abundance of micro-zooplankton remained increasing at a more rapid rate.During the 12 h metabolism experiment in the dark,chromophoric dissolved organic matter in metabolic product released from Aurelia sp.was collected for EEMs-PARAFAC analysis.Three independent fluorescent components were identified,including two protein-like components(tyrosine-like C1:275/298 nm;tryptophan-like C2:<240,310/354 nm)and one humic-like component(C3:<240,355/410 nm).In metabolic group,the fluorescent intensity of C1 component kept increasing conspicuously,only a little increment of fluorescent intensity was observed in C3 component,while the fluorescent intensity of C2 component remained almost stable during the metabolic process.There were two indices applied in the study,the humification index(HIX)rised gradually with a maximum of 7.36;the biological index(BIX),whose value were all above 1 except in the first hour,could reflect a strong signal of CDOM from autochthonous origin,but the value of which fluctuated unstably.The natural bacteria in seawater were incubated in fresh metabolic product released from Aurelia sp.in this study,the bacterial abundance was stimulated by metabolic product immediately and reached the peak on the 2nd day,after then the value started to drop until the 5th day,since then,the abundance stayed relatively steady till the end;the bacterial abundance from control group also experienced a rising period whose peak was one day later than experimental group;and the value of the peak,as well as the growth rate of the control group were all lower than those in the experimental group.During the photo-degradation experiment,the bacterial abundance from the experimental group had an obvious increase compared to the control group.Comparison between different light exposure durations(3 days and 7 days)indicated that,the bacterial abundance from 3 days photo-degradation had an apparent increase,while the bacterial abundance in experimental group and control group from 7 days photo-degradation were very close.In the experiment combined with micro-degradation and photo-degradation,the bacterial abundance from experimental group had an evident increment.