Radiant Environment within the Sea in a Marine Cultivation Region for the Alga, 'Okinawa-mozuku'

The annual amount of 'mozuku' production in Okinawa Prefecture was in a wide range of from　5,000 to 20,000 tons in the second half of the 1990's and then about 15,000 tons in recent years. Its productivity and quality are remarkably dominated by environmental factors especially the ra...

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Bibliographic Details
Published inJournal of Agricultural Meteorology Vol. 60; no. 5; pp. 841 - 844
Main Authors HATAKEDA, Hirohisa, MASUDA, Atsunori, HORAGUCHI, Kimitoshi, KOSAKA, Shinichi, KUDO, Akihide, MOROMIZATO, Satoshi, MURAKAMI, Katsusuke
Format Journal Article
LanguageEnglish
Published The Society of Agricultural Meteorology of Japan 2005
Subjects
Aquaculture
Cladosiphon okamuranus
Daylight
Spectral absorbance
Spectral reflectance
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Summary:The annual amount of 'mozuku' production in Okinawa Prefecture was in a wide range of from　5,000 to 20,000 tons in the second half of the 1990's and then about 15,000 tons in recent years. Its productivity and quality are remarkably dominated by environmental factors especially the radiant environment within the sea. 　The radiant environment was observed within the sea in an 'Okinawa-mozuku' aquaculture area. Both direct daylight transmission within the sea and daylight reflecting from the sea bottom were observed. Spectral reflectance from coral-sands on the sea bottom and spectral absorbance of a few kinds of algae were also determined with a spectrophotometer. 　Not only the direct daylight but also the daylight reflecting from the sea bottom existed as growth environmental factors. In a horizontal plane at 2.5m below the sea surface, relative illuminance and PPFD for the direct daylight were 82 and 77% and for the reflecting daylight, relative illuminance was 113% and relative PPFD was 87%. In the area, the illuminance and PPFD for direct daylight within the sea from the sky decreased with depth from the sea surface, but for daylight reflecting from the sea bottom, the illuminance increased with the depth and the attenuation pattern through the sea of PPFD differed from that of illuminance. Characteristics of spectral reflection from coral-sands on the sea bottom were similar to that of spectral absorption by 'Okinawa-mozuku'.
ISSN:0021-8588
1881-0136
DOI:10.2480/agrmet.841