Abstract
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.
