Scallop shells used as test plates were hung from an oyster culture raft in Isahaya Bay, Nagasaki, Japan, for different periods from May/June to November/December each year from 2008 to 2010. Marine organisms that attached to the plates were studied. Twenty-nine species or higher taxonomic categories of fouling organisms were observed, including 2 macroalgal groups (Ceramiales and Ulvales) and 5 invasive species. In general, total wet weights of fouling organisms on 1-month plates increased with increasing water temperature, reaching 45–111 g/100 cm² in August/September, and decreased after October. Hydroids and ascidians were dominant from May to July, while barnacles became dominant in August/September. Amphibalanus reticulatus and Fistulobalanus kondakovi were dominant in 2008 and 2009, resepectively. In 2010, F. kondakovi and A. amphitrite were the dominant barnacles. On plates immersed for 2 weeks, only barnacles with aperture diameters (AD) smaller than 4 mm were observed from May to July, but the percentage of larger barnacles (AD>4 mm) increased in August and September, indicating that barnacles could reach reproductive maturity within 2 weeks during these periods. Thus, oyster farmers in Isahaya Bay should focus their antifouling measures on the barnacles that become abundant in August and September every year.

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Cooling efficiency at coastal industrial plants with seawater-based cooling systems is often reduced due to water flow blockage caused by marine biofouling. Maintenance of a residual chlorine concentration of 0.1–0.3 mg/L for 18 h/day is known to be an effective countermeasure, but it is often impossible to maintain so high a concentration because of chlorine-induced corrosion and/or environmental considerations. There have been only a few reports examining the effects of low concentrations of residual chlorine, so we carried out a study to evaluate the marine biofouling potential at residual chlorine concentrations of 0.05 mg/L or less, and to identity any related problems. The study was conducted at a factory on the shore of Ise Bay, Japan, at which no residual chlorine was detected in the discharge water. For 63 days (27 Apr. to 29 Jun. 2010) we regularly observed the extent of marine biofouling on a coarse-mesh vinylon net placed parallel to the water flow inside a cooling-water pipe through which seawater with a total residual chlorine concentration averaging 0.055 mg/L (range: 0.02–0.12 mg/L) was run continuously. We also checked the condition of the net on 6 Dec. 2010 after 30 days of uninterrupted exposure to the water flow. In both cases, much biofouling was observed on the test net. Thus, low levels of residual chlorine, even when applied continuously, appear insufficient to prevent biofouling and an attendant reduction in cooling efficiency.

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