Organisms attaching to cathodically protected mild steel at the head of Tokyo Bay

The organisms attaching to cathodically protected mild steel and to control plates lacking catholic protection were investigated at two locations, Shinagawa and Funabashi, in the innermost coastal area of Tokyo Bay, which has shown progressive recent improvement in water quality. The results are compared to those of studies at Numazu in Suruga Bay. At Numazu, the quantity of attached organisms on cathodically protected plates was greater than that on control plate, but there was no clear difference between the two types of plate at the two locations in Tokyo Bay. The quantity of attached organisms at the latter two sites was about 10% of that found in Suruga Bay, and fewer than 50% of the Suruga Bay species were present. Typical attaching animals included Balanus eburneus and Mitylus sp. at Shinagawa and Caulibugula ciliata and B. improvisus at Funabashi. Of algal species, a small amount of green algae and Colpomenia sp. was observed at Shinagawa, while none was observed at Funabashi. Compared to Suruga Bay, the water quality of Shinagawa and Funabashi was marked by low pH and Cl- while resistivity was high. In addition, the extent of corrosion of the mild steel was about 1.5 times greater than that at Numazu, which may partly explain the lower quantity of attached organisms at the Tokyo Bay sites.