Influences of the Jellyfish Bloom of Aurelia aurita upon Plankton Production including Fish Larvae

本研究的目的是量化的影响，大量发生的水母，奥雷利亚aurita浮游生物群落，包括鱼卵和仔鱼。东京湾是日本富营养化程度最高的海湾之一，平均丰度为0.32个/只。M3. A.aurita种群的估计摄食率介于0.7和7 mg C/m3/天之间。由于浮游动物中最具优势的桡足类--戴氏剑水蚤（Oithona davisae）的生产率约为100%，因此，金眼鲷种群的平均丰度对浮游动物种群数量的摄食影响并不显著。100 mg C/m3/天。然而，当A.aurita的丰度超过1 ind./ m ~ 3，其密度多见于春、夏两季，种群摄食量占浮游动物日生产量的10%以上。虽然食饵性鱼类与水母竞争浮游动物，但水母可能超过食饵性鱼类，因为水母是昼食性鱼类，而不是从早到晚摄食。最具代表性的浮游动物，戴氏剑水蚤不吃硅藻，而硅藻通常是最主要的浮游植物。硅藻死亡后向海水中释放大量DOC，导致细菌数量增加，从而形成了微生物食物链，进而通过细菌-HNF-纤毛虫-微型桡足类，将原本用于鱼类生产的能量转化为水母生产的能量（Oithona davisae）。当水母食物链发展起来时，预计马面鱼和收获鱼等食草鱼类将增加，然而，微生物和水母本身大量再生的营养物质将加速海湾的富营养化。

Aim of the present study is to quantify the impact of massive occurrence of a jellyfish, Aurelia aurita on plankton community including fish eggs and larvae. In the case of Tokyo Bay, one of the most eutrophicated embayment in Japan, average abundance of A.aurita was 0.32 ind./m3. Estimated feeding rates of the A.aurita population ranged between 0.7 and 7 mg C/m3/day. The feeding impact of the average abundance of A.aurita population on the zooplankton assenmblages is not so significant because the production rates of a copepod, Oithona davisae which was the most dominant zooplankton were estimated to be ca. 100 mg C/m3/day. However, when the abundance of A.aurita exceeds 1 ind./m3, which density was frequently found during spring and summer, the population feeding is calculated to correspond to >10% of the daily production of zooplankton.Although planktivorous fishes compete with jellyfish for zooplankton, jellyfish may surpass the planktivourous fishes considering that these fishes are day light feeder in a contrast to jellyfish that feeds from morning to night.The most representative zooplankton, Oithona davisae ingest no diatoms which are usually the most dominant phytoplankton. Microbial food chain is also developed by the increase of bacteria which was caused by abundant DOC released into seawater from dead diatoms, and then the energy that previously went into production of fishes may be switched over to the production of jellyfish via bacteria-HNF-ciliates-micro copepod (Oithona davisae).When the jellyfish food chain is developed, medusivorous fishes such as filefish and harvest fish are expected to increase, however, eutrophication of embayment will be accelerated by huge regeneration of nutrients via microbes and jellyfish itself.