[Release and supplement of carbon, nitrogen and phosphorus from jellyfish (Nemopilema nomurai) decomposition in seawater].

Abstract: Jellyfish bloom has been increasing in Chinese seas and decomposition after jellyfish bloom has great influences on marine ecological environment. We conducted the incubation of Nemopilema nomurai decomposing to evaluate its effect on carbon, nitrogen and phosphorus recycling of water column by simulated experiments. The results showed that the processes of jellyfish decomposing represented a fast release of biogenic elements, and the release of carbon, nitrogen and phosphorus reached the maximum at the beginning of jellyfish decomposing. The release of biogenic elements from jellyfish decomposition was dominated by dissolved matter, which had a much higher level than particulate matter. The highest net release rates of dissolved organic carbon and particulate organic carbon reached (103.77 ± 12.60) and (1.52 ± 0.37) mg · kg⁻¹ · h⁻¹, respectively. The dissolved nitrogen was dominated by NH4⁺-N during the whole incubation time, accounting for 69.6%-91.6% of total dissolved nitrogen, whereas the dissolved phosphorus was dominated by dissolved organic phosphorus during the initial stage of decomposition, being 63.9%-86.7% of total dissolved phosphorus and dominated by PO4³â»-P during the late stage of decomposition, being 50.4%-60.2%. On the contrary, the particulate nitrogen was mainly in particulate organic nitrogen, accounting for (88.6 ± 6.9) % of total particulate nitrogen, whereas the particulate phosphorus was mainly in particulate. inorganic phosphorus, accounting for (73.9 ±10.5) % of total particulate phosphorus. In addition, jellyfish decomposition decreased the C/N and increased the N/P of water column. These indicated that jellyfish decomposition could result in relative high carbon and nitrogen loads.

Jellyfish (Cyanea nozakii) decomposition and its potential influence on marine environments studied via simulation experiments.

A growing body of evidence suggests that the jellyfish population in Chinese seas is increasing, and decomposition of jellyfish strongly influences the marine ecosystem. This study investigated the change in water quality during Cyanea nozakii decomposition using simulation experiments. The results demonstrated that the amount of dissolved nutrients released by jellyfish was greater than the amount of particulate nutrients. NH4(+) was predominant in the dissolved matter, whereas the particulate matter was dominated by organic nitrogen and inorganic phosphorus. The high N/P ratios demonstrated that jellyfish decomposition may result in high nitrogen loads. The inorganic nutrients released by C. nozakii decomposition were important for primary production. Jellyfish decomposition caused decreases in the pH and oxygen consumption associated with acidification and hypoxia or anoxia; however, sediments partially mitigated the changes in the pH and oxygen. These results imply that jellyfish decomposition can result in potentially detrimental effects on marine environments.

[Causes of jellyfish blooms and their influence on marine environment].

Jellyfish blooms have damaged the normal composition and function of marine ecosystem and ecological environments, which have been one of the new marine ecological disasters. In this study, we summarized the possible inducements of jellyfish blooms, and the influences of jellyfish blooms on biogenic elements, dissolved oxygen, seawater acidity and biological community were discussed emphatically. The results showed that jellyfish blooms had a close contact with its physiological structure and life history, which had favorable characteristics including simple body struc- ture, rapid growth, thriving reproduction and short generation interval to tolerate harsh environment better. Jellyfish abundance increased rapidly when it encountered suitable conditions. The temperature variations of seawater might be the major inducing factor which could result in jellyfish blooms. Jellyfish blooms may benefit from warmer temperature that could increase the food availability of jellyfish and promote jellyfish reproduction, especially for warm temperate jellyfish species. Eutrophication, climate change, overfishing, alien invasions and habitat modification were all possible important contributory factors of jellyfish blooms. Jellyfish could significantly influence the form distribution and biogeochemical cycling of biogenic elements. Jellyfish excreted NH4+ and P04(3-) at a rate of 59.1-91.5 micromol N x kg(-1) x h(-1) and 1.1-1.8 micromol P x kg(-1) x h(-1), which could meet about 8%-10% and 21.6% of the phytoplankton primary production requirement of N and P, respectively. Live jellyfish released dissolved organic carbon (DOC) at a rate of 1.0 micromol C x g(-1) x d(-1). As jellyfish decomposing, the effluxes of total N and total P were 4000 micromol N x kg(-1) x d(-1) and 120 micromol P x kg(-1) x d(-1), respectively, while the efflux of DOC reached 30 micromol C x g(-1) x d(-1). Jellyfish decomposition could cause seawater acidification and lowered level of dissolved oxygen and finally made the ambient water become acidic and hypoxic. The pH decreased by 1.3, while the mean dissolved oxygen demand reached 32.8 micromol x kg(-1) x h(-1). Jellyfish blooms also influenced the marine organism community, which might reduce the biomass of some fish and zooplankton, increase the amount of bacterioplankton, indirectly .increase the quantity of phytoplankton and lead to abnormal primary production.