The Influence Of Jellyfish Decomposition On Marine Environments

In recent years, the jellyfish population increased has been reported in China marginal seas. Decomposition of jellyfish blooms has large influence on marine eco-environments. The study on effect and mechanism of jellyfish decomposition shows great significance for early warning and prevention of the ecological disaster caused by jellyfish bloom. This paper focused on the decomposition of jellyfish and its relationship coupling with marine environment. We illustrated the release and transformation characteristics of different forms of carbon(C), nitrogen(N) and phosphorus(P) in water column during jellyfish decomposing by simulation experiments, and clarified the pathway of jellyfish decomposition on marine environment. We also expounded the variation characteristics of amino acids and fatty acids in suspended particulate matters from jellyfish decomposition and discussed the coupling relationship between them and the biogenic elements. On this basis, we investigated the composition, distribution and variation of particulate nitrogen and phosphorus during three growth stages of jellyfish(the period before bloom, during bloom and during decomposition) in Yellow Sea and East China Sea, explored the response of particulate biogenic elements to jellyfish decomposition after bloom, and discussed the indicative significance of particulate biogenic elements for jellyfish abundance. Major results and conclusions are as following:1. The release characteristics of biogenic elements during jellyfish decomposing and its influence on water environment were revealed. The accumulation of released biogenic elements varied between different jellyfish species. The results showed that jellyfish decomposed with the rapid release of biogenic elements. The release rate of C, N and P reached the maximum at the beginning of decomposing. The concentrations of dissolved matters released by jellyfish decomposition were much greater than that of particulate matters, and the dissolved C, N and P accounted for 51.8- 81.9%, 86.0- 97.9% and 53.6- 86.3% of total amount respectively. Furthermore, the quantity of C, N, and P releasedby dead jellyfish was much greater than that excreted by living jellyfish. Jellyfish decomposition resulted in high C and N loads. In addition, jellyfish decomposition led to relative acidification and hypoxia/anoxia. However, sediments can relieve the changes of p H and oxygen caused by jellyfish decomposition.Jellyfish decomposition was a continuous and rapid process, which varied with jellyfish species. The times of jellyfish decomposition were 7 days for Nemopilema nomurai and 14 days for Cyanea nozakii, with a foul stench throughout the whole incubation time. The biogenic elements released by jellyfish were dominated by dissolved ones. The net release rates of dissolved organic carbon(DOC) reached a maximum value of 103.77 ± 12.6 mg kg-1 h-1, and the concentration of DOC released by dead jellyfish was 253- 288 times greater than that excreted by living jellyfish. NH4+ occurred predominantly for dissolved N, accounting for 72.2- 75.2% of total nitrogen(TN), whereas PO43- increased with the decrease of dissolved organic phosphorus(DOP), accounting for 39.3- 40.7% and 34.9- 43.1%, respectively. The release rate of NH4+ and PO43- was 3- 5 and 8- 13 times higher than that of living jellyfish. As for particulate matters, the net release rate of particulate organic carbon(POC) attained the maximum of 1.52 ± 0.37 mg kg-1 h-1 and it had a significant positive correlation with DOC. Particulate organic nitrogen(PON) and inorganic phosphorus(PIP) was the major component of particulate N and P, accounting for 73.9- 95.2% of total particulate nitrogen(TPN) and 52.5- 83.4% of total particulate phosphorus(TPP). During jellyfish decomposing, the TC/TN ratios and DC/DN ratios were lower than the Redfield ratios and the C/N ratios of jellyfish tissues(4.3- 4.5), with the ranges of 2.1- 3.3 and 1.2- 2.9, whereas the TN/TP ratios and DN/DP ratios were higher than the Redfield ratios and N/P ratios of jellyfish tissues(22), with the ranges of 29.5- 35.8 and 28.5- 69.0. The decrease of C/N ratios and increase of N/P owing to jellyfish decomposition resulted in the relative high C, high N and low P, which aggravated the unbalance of C, N and P in China marginal seas. Additionally, the study demonstrated that jellyfish decomposition led to the decrease of p H and theconsumption of dissolved oxygen(DO), with the drop of 0.77- 0.96 units for p H and the maximum DO consumption of 7378.9- 5550.8 μmol kg-1 d-1. The sediments were beneficial to recover from acidification and hypoxia/anoxia and had buffer action to the change of seawater environment.2. The release characteristics of amino acids(AA) and fatty acids(FA) in particulate matters during jellyfish decomposing were observed, and the coupling relationships between AA/FA and biogenic elements of particulate matters were explained. Particulate AA in greater quantity during decomposing process were neutral AA and acidic AA, accounting for 37% and 23% of total amino acids(TAA), while particulate FA were dominated by saturated fatty acid(SFA), constituting 67.2% ± 10.9% of total fatty acids(TFA). The study suggested that particulate AA composition changed from predominant basic AA including arginine(Arg) and histidine(His) to more acidic AA including aspartic acid(Asp) and glutamic acid(Glu), while particulate FA composition changed from predominant SFA to more monounsaturated fatty acids(MUFA). Furthermore, TAA had a significant correlation with POC and PON, whilst TFA significantly correlated with POC, indicating that particulate AA and FA released by dead jellyfish were principal sources of organic C and N for aquatic organism.17 AA were detected in particulate matters during jellyfish decomposing,which can compensated the deficiencies of AA in marine water and sediment. The highest percentage of TAA was observed for glutamic acid, which contributed 10.7- 17.2% of TAA, then followed by aspartic acid, which accounted for 8.8- 13.9%. The glutamic acid, aspartic acid and glycine(Gly) were always found among the main AA which determined the overall trend of TAA. The acidic AA(Glu + Asp) in particulate matters increased by 23% owing to the addition of jellyfish, which may resulted in the decreased of p H in water column. In addition, a significantly positive correlation with TAA for POC and PN was observed, and it suggested that AA were important sources of POC and PN. 12 FA were detected in particulate matters during jellyfishdecomposing. SFA were the most abundant FA in particulate matter, which accounted for 57.6- 83.3% of TFA. The decline of proportion of SFA and increase of MUFA in particulate matters indicated that the FA composition changed from predominant SFA to more MUFA as jellyfish decomposed. Palmitic acid(16:0) and stearic acid(18:0) dominated the SFA with values ranging between 25.2% and 42.9% and between 15.0% and 40.9% of TFA, respectively, while palmitoleic acid(16:1ω9) dominated in MUFA groups with values ranging from 2.7% to 17.6% and PUFA were mostly rich in linoleic acid(18:2ω6), which ranged from 1.2% to 1.8%. The increase of bacterial fatty acids(BFA) including ISO14:0, 15:0 and 18:1ω7 and the fungal fatty acids(FFA) including 18:1ω9 and 18:2ω6 in particulate matters represented the significant increase of bacterial and fungal population. Most of individual FA, with the exception of 16:1ω9, 18:1ω7 and 20:0, were significantly correlated with POC, therefore, it suggested that FA may be the important sources of POC. The release of AA and FA contributed to the accumulation of C and N. The increase of AA and the decline of FA combined decrease of C/N during jellyfish decomposing indicated that jellyfish decomposition made the particulate matters of seawater transform from C-rich to N-rich.3. The temporal and spatial variation of particulate nitrogen and phosphorus in Yellow Sea(YS) and East China Sea(ESC) during three phases(jellyfish pre-bloom phase, jellyfish boom phase and jellyfish decomposing phase) were analyzed. The results showed that particulate organic nitrogen(PON) and particulate inorganic phosphorus(PIP) were the major constitutions of total particulate nitrogen(TPN) and phosphorus(TPP), occupied 75.7% of TPN and 67.0% of TPP, respectively. The distribution of high concentrations of particulate nitrogen and phosphorus were under direct control of Jiangsu coastal current and Yangtze diluted water, which also related with the seasonal variation of phytoplankton and jellyfish population. The concentrations of particulate nitrogen and phosphorus of bottom water in autumn was higher than that in other seasons due to jellyfish decomposition(mainly Nemopilema nomurai). Theinput of TPN and TPP during jellyfish decomposing accounted for 15.3% of total input of particulate nitrogen and 4.5% of the total particulate phosphorus, while the input of PIN, PIP, PON, and POP accounted for approximate 92.1%, 51.3%, 12.5% and 7.2%. It indicated that jellyfish decomposition contributed to the input of particulate nitrogen and phosphorus to bottom water.In Yellow Sea and East China Sea, particulate nitrogen was dominated by PON, accounting for 72.5- 77.6% of TPN, while PIP was the major components of particulate phosphorus, accounting for 66.3- 67.8%, which was in accordance with that of jellyfish decomposition. The distribution of particulate nitrogen and phosphorus illustrated that Jiangsu costal current and Yangtze River were the main sources of particulate matters. The high value area of particulate nitrogen and phosphorus transferred from Jiangsu coastal area to Yangtze estuary from summer to autumn. In early summer, Jiangsu coastal current input was the main source of particulate phosphorus, while PIN was from phytoplankton input. The high value of PIP and POP concentrated in continental shelf margin waters of 28.5- 34 oN due to the input of resuspended sediment taken by Jiangsu coastal current from Yellow River delta. Jellyfish had little influence on particulate matter in early growth period. In later summer, the high value area transferred into Yangtze estuary due to the increase of Yangtze River runoff, while low value area occurred in offshore. The sediments from Yangtze River were the major sources of particulate matters of inshore, so the particulate nitrogen and phosphorus were mainly from terrestrial input. The high value area of surface water was found in Yangtze estuary and adjacent area, while the high value area of bottom water still occurred in Jiangsu coastal area and Yangtze estuary. The concentrations of particulate nitrogen and phosphorus in August were higher than that in June, which affected by marine organism including phytoplankton and jellyfish. The average biomass of Nemopilema nomurai in August reached 12140 kg km-2, and the excretion of jellyfish was one of the sources of particulate matters. In autumn, the content of particulate nitrogen and phosphorus of surface water in Yangtze estuary and adjacent area decreased owing to the reduce of discharge ofYangtze River, but the content in bottom water increased due to the sink of sediments. Furthermore, the reduction of primary production in autumn resulted in the decrease the input of particulate nitrogen and phosphorus from phytoplankton. However, the contents of PON, PIP and POP in bottom water in autumn were higher than that in other seasons and the contents in transect with abundant jellyfish were higher than that in transect of less jellyfish. The maximum biomass of Nemopilema nomurai reached 2.0 × 105 kg km-2 in autumn, on the basis of that, we calculated the release rate of TPN, TPP, PON and POP of Nemopilema nomurai, which was equivalent to 2.83 mg m-2 d-1, 0.67 mg m-2 d-1, 2.06 mg m-2 d-1 and 0.19 mg m-2 d-1. Therefore, we can evaluate the contribution of jellyfish decomposition to particulate nitrogen and phosphorus in YS and ECS. The results showed that Nemopilema nomurai decomposition could supply about 15.3% of TPN, 4.5% of TPP, 12.5% of PON and 7.2% of POP in YS and ECS, indicating the important contribution of jellyfish decomposition to particulate nitrogen and phosphorus in bottom water in YS and ECS system.