RELATIVE IMPORTANCE OF RECRUITMENT VERSUS REGENERATION IN MAINTAINING THE POPULATIONS OF SARGASSUM HENSLOWIANUM IN PING CHAU, HONG KONG

Populations S. henslowianum dominate the shallow subtidal waters of Ping Chau Island, Hong Kong. A study was carried out to evaluate the relative importance of recruitment vs regeneration from the holdfast in the maintenance of these populations. The number of recruits on clearings, artificial and natural substrata as well as the density of the natural populations were evaluated on a periodic basis from March 1998 to March 2000. The results indicated that although up to 85 to 100% of the individuals of this species may be reproductive during the winter reproductive season (Nov to Feb), only up to a maximum mean density of 17 recruits 0.25 m⁻² were found in the cleared areas or artificial substrata provided. Less than 10% of these eventually survived the following growth season. In the natural stands, new individuals (recruits) constituted only less than 15% of the mean density. The number of new recruits was particularly low around older individuals. Thus, these populations were mainly made up of older individuals regenerating from their perennating holdfasts. It appears that regeneration from the holdfast is a far more important strategy than recruitment in the maintenance of these populations.