A continuous culture system for a benthic food diatom Nitzschia sp. was established by using properties of high nutrient and clean of deep seawater (DSW). DSW collected from 320 m depth in Muroto City, Japan, was introduced into a glass-pipe bioreactor (14 cm length, 3 cm diam.) containing glass beads of 0.5 cm diam. as substrata for the alga, and it was incubated at 18 degrees C, 80 mu Em(-2)sec(-1), L:D=14:10. The chlorophyll a yield of benthic diatoms in a reactor as a unit of surface area of the substratum was only 0.001-0.003 mu g cm(-2) when the flow rate of DSW was 0 (batch culture conditions). However, when DSW was supplied continuously to a reactor, the yield increased to 1.4 mu g-chl.a cm(-2) along with the increase in flow rate of DSW. Moreover, amounts of chl.a washed out of the system were negligible, 0.0014 to 0.0045%, even though the flow rate of DSW was as much as 25 times/h, suggesting that sloughing of benthic diatoms from the substratum was minimized. Although the yield of diatoms fluctuated significantly at the time that the DSW was collected, the variation could be minimized by increasing the flow rate of DSW. These results indicate that the continuous culturing system with DSW supports the stable and effective mass culture of benthic food diatom.
(Kochi Univ., Lab. Aquat. Environm. Sci. Laques, Nankoku, Kochi 783, Japan)
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