Studies on jellyfish blooming in marine coastal waters : mechanisms for the population increase and technical development for the countermeasures

月亮水母奥雷利亚aurita是世界沿海沃茨最常见的schyphomedusae之一，并且高度推测该物种的人口在过去几十年中一直在增加。在日本内海，该物种的增加在过去10年中集中发生，可能是由于以下因素的组合：1）由于富营养化或营养供应的改变，水母的食物供应增加2）冬季水温升高，使水母种群越冬3）由于改变了水前和建筑，水螅附着面积增加4）由于过度捕捞，食鱼性鱼类种群数量减少。监测奥雷利亚aurita种群的技术已经建立，使用复合航空照片，a塞斯纳和地面实况网调查。通过对2000-2003年4年的监测，发现乌波海水母总生物量的年变化幅度在一个数量级以上，但造成这种年变化的原因尚不清楚。据渔民反映，日本内海水母聚集的滋扰十分严重，本研究通过测量耳奥雷利亚的呼吸、摄食和生长速率，估计水母对浮游动物种群的生态影响。根据水母的密度，每天的摄食压力从浮游动物生物量的百分之几到几百%不等。对策之一是使用水母分解细菌分解水母。从日本内海分离出几种对分解有效的细菌菌株。初步建立了奥雷利亚腐解试验装置。

The moon jelly Aurelia aurita is one of the most common schyphomedusae in the world's coastal waters, and the population of this species is highly speculated to have been increasing for the last decades. In the Inland Sea of Japan, the increase of this species occurred intensively in the last 10 years, due probably to the combination of the following factors:1) increase in food supply for the jellyfish owing to eutrophication or the modification of nutrient supply2) elevation of water temperature in the winter to allow the population overwintering3) increase in the polyp attachment area owing to the modification of the water front and construction4) decrease in planktivorous fish stock size owing to overfishing.The technique to monitor the Aurelia aurita population has been established using composite airphotographs from a Cessna and groundtruthed net surveys. The monitoring in the Uwa Sea for 4 years (2000-2003) reveals that the total jellyfish biomass varies more than one order magnitude year to year, although the causes for such annual difference are not known. According to fishermen, the nuisance of jellyfish aggregation is very severe in the Inland Sea of Japan.By measuring the respiration, feeding and growth rates of Aurelia aurita, the ecological impact of the jellyfish upon the zooplankton populations has been estimated. The daily feeding pressure ranges from a few % to several hundreds % of the zooplankton biomass, depending on the density of the medusae.One of the countermeasures is to decompose the medusae using jellyfish decomposing bacteria. Several bacterial strains which are effective to the decomposition have been isolated from the Inland Sea of Japan. A preliminary test plant for the decomposition of Aurelia aurita has been established.