Survivorship and production of Aurelia aurita ephyrae in the innermost part of Tokyo Bay, Japan
2004
Ishii, H. (Tokyo Univ. or Marine Science and Technology (Japan)) | Kojima, S. | Tanaka, Y.
The survivorship and daily production rate of the Aurelia aurita ephyrae population in Tokyo Bay was estimated. A disc growth index, expressed as the ratio of the diameter of the central disc to the diameter over lappet tips, was used to describe the developmental process and morphological changes in the ephyrae. The number of days spent of the arbitrary developmental stages as defined by disc growth index group was also calculated, and it appears that newly liberated ephyrae become young medusae after 20-28 days. Survivorship in each stage was estimated from the changes in the total number of ephyrae belonging to each stage that were produced in the survey area over the whole observation period. Survivorship of ephyrae metamorphosing into young medusae compared to the number of newly liberated ephyrae was only 0.95%. Field observations revealed that the number of individuals, biomass and daily production rate of ephyrae was highest on March 13, being 2.8 inds m sup(-3), 0.084 mgC m sup(-3) and 0.021 mgC m sup(-3) day sup(-1), respectively. Total production of ephyrae over the observation period was 0.47 mgC m sup(-3). Daily P/B ratio of ephyrae was higher than other zooplankters and decreased significantly with increasing size of the ephyrae. How the population of A. aurita is maintained through the ephyra developmental process is discussed.
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