Abstract
The attached diatom flora in the aquaculture facility, Kochi Prefectural Deep Seawater Laboratory, Muroto, Japan, in which Pacific deep seawaters (DSW) were pipelined from depths of 320 m and 341 m, was studied using light microscopy. A total of 37 species in 21 genera were recorded from the tanks (10-16°C). The popular identified species were Navicula agnita, Craspedostauros decipiens, Nitzschia laevis, Gomphoseptatum aestuarii, Diploneis papula, Tabularia fasciculata and T. investiens; among them, C. decipiens, G. aestuarii and D. papula recorded the highest relative frequency rank (> 50%) in at least one sample. Some diatom species were previously reported from aquaculture facilities in Toyama prefecture, Sea of Japan coast, in which colder (< 10°C) DSW is used. Among six examined tanks, one tightly covered outdoor tank was prepared for the present study by running DSW for forty days before sampling. Two samples collected from a wall and detached colonies floating in the tank, included only 4 species, showing the cleanliness of DSW. Other samples were collected from five tanks of a variety of size, period and cultured organisms. Five samples collected from a wall or other substrata in three abalone (two outdoor and one indoor) tanks included 12 to 24 species; the richest flora (24 species) was recorded from a net cage in the indoor tank in which surface seawater (SSW) was also mixed for adjusting water temperature. The other two samples, collected from one outdoor kelp tank and one indoor shrimp tank (with some seaweed), included 8 and 4 species, respectively. We concluded that the inclusion of organisms, particularly abalone, as well as mixing of SSW increase the species richness of attached diatoms in DSW and that diatom species occurring in high frequency are adequate for high production in culture in DSW.
