In 2005, an unrecorded bryozoan, Bantariella sp., invading on black corals was observed at Munseom in Jejudo Island. An intensive study was performed in the portion of 180 m width and $10{sim}30m$ deep of Hangae-chang at Munseom during the period from Jan. to Nov. 2006. The following two black corals, Antipathes japonica and A. lata are occurring in this area. To investigate the quantitative change of invasion rates, 26 colonies with initial invasion rate of 0%, 30%, 70% and 100% respectively were individually tagged at the beginning of this study. After that, the change of reinvasion rates was monitored in a timely manner with the pictures taken by underwater camera and ensile observation. These data were analyzed as to host species, depth and initial invasion rates. According to host species, the removal effect was higher in A. lata than A. japonica. The reinvasion rate of black corals showed a maximal effect at $20{sim}30m$ deep, and the most successful removal effect appeared in the colonies of initial invasion rates of $30{sim}70%$. Especially, the invasion of Bantariella sp. on black corals is related to seawater temperature in seasonal manner and this appearance was limitedly observed at Munseom. This study is to document the impact by bryozoan proposing removal methods and its proper time of removal. It could contribute to the conservation of black corals and furthermore help to predict the change of marine environments.