Effects of low dissolved oxygen on planula settlement, polyp growth and asexual reproduction of Aurelia aurita
Effects of low dissolved oxygen on planula settlement, polyp growth and asexual reproduction of Aurelia aurita
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DOI：
10.3800/pbr.3.107
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发表时间：
2008-05
影响因子：
0.6
通讯作者：
H. Ishii;T. Ohba;Takeshi Kobayashi
中科院分区：
文献类型：
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作者：
H. Ishii;T. Ohba;Takeshi Kobayashi
东京湾是日本富营养化最严重的海湾之一，随着富营养化的加剧，经常观察到舟形水母Aurelia aurita的大量出现。在沿海环境中，通过围垦，适合金线虫生长的基质丰度明显增加。然而，最适合沉降的基质，除了东京湾最内侧的底层外，都被其他固着生物占据，如贻贝、藤壶或海鞘。底层的特点是溶解氧浓度低（≤2.0 ml O2 L−1），在夏季会出现缺氧，导致其他固着生物的补充和生长缓慢。为了阐明水母大量发生的机制，对浮浪幼虫和水螅期的缺氧适应行为进行了实验研究。在本研究中，溶解氧浓度的降低促进了浮藻沉降，并且即使在低氧水中培养的息肉中，也观察到息肉的明显生长和通过无性出芽产生子代息肉。此外，在缺氧条件下培养的A. aurita息肉在DO浓度水平恢复后开始颤动，并且释放出碟状体。表明缺氧水域的出现有利于金鲫鱼的生存、生长和无性繁殖，可直接促进东京湾内次年春季金鲫鱼的产生。
Tokyo Bay is one of the most eutrophicated bays in Japan, and mass occurrences of scyphozoan jellyfish Aurelia aurita have often been observed with progress of eutrophication. In the coastal environment, the abundance of substrates suitable for A. aurita polyps are obviously increasing by reclamation. However, most suitable substrates for settling, except in the bottom-layer in the innermost part of Tokyo Bay, are occupied by other sessile organisms such as mussels, barnacles or ascidians. The bottom layer is characterized by low DO concentrations (≦2.0 ml O2 L−1) that turn to hypoxia during summer, resulting in low recruitment and low growth of other sessile organisms. To elucidate the mechanism by which mass occurrence of jellyfish occurs, adaptative behavior to hypoxia in planula larvae and the polyp stage was experimentally studied. In the present study, planula settlement was promoted by a decrease in DO concentrations, and apparent growth of polyps and production of daughter polyps by asexual budding were also observed, even in the polyps cultured in hypoxic waters. Moreover A. aurita polyps cultured under hypoxic conditions began strobilation and ephyrae were liberated after the DO concentration levels were restored. It is suggested that the occurrence of hypoxic waters is rather favorable for the survival, growth and asexual reproduction of A. aurita polyps, and it can directly contribute to the consequent production of A. aurita ephyrae in the next spring within Tokyo Bay.