Seasonality of epiphytic development of the hydroid Obelia geniculata on cultivated Saccharina japonica (Laminariaceae, Phaeophyta) in Korea

The occurrence of encrusting colonies of the hydroid Obelia geniculata on farmed Saccharina japonica was examined between December 2007 and July 2008 at a Saccharina farm at Wando on the southwestern coast of Korea. The growth stages of S. japonica can be divided into two phases: an active growth phase from February to the end of May and a decay phase from June to July. There was a significant increase in the level of incrustation by colonies on fronds (measured as the percentage of fronds with encrusting colonies) between February and July (p?Saccharina frond, and a rapid increase in reproduction and growth of O. geniculata coinciding with rising seawater temperature.