FIELD STUDY OF ALGAL RECRUITMENT BY CLEARING EXPERIMENT IN PING CHAU, HONG KONG SAR, CHINA

Abstract

Recruitment, the entry of new individuals into a population, was investigated by a clearing experiment along the shore of A Ma Wan (AMW) in Ping Chau, Hong Kong SAR, China. Two types of clearing, with all the existing vegetation removed (cleared) and with the top 2 to three mm of the rock surface removed (hammered), were carried out monthly in AMW from November 1997 to June 1999. Observations were made one month after clearing and on a monthly basis thereafter. The number of algal species present on the cleared areas and their percentage cover were recorded. The experimental results showed that more algal species were recruited during March and April in 1998 (n=10) but in 1999, the number of species was found higher in February and March (n=8). Species richness dropped after May (more obvious in 1998), indicating that recruitment greatly declined in summer. A tuft complex composed of several filamentous algal species dominated over the others in all clearing areas (coverage mostly over 90%) but recruits of Caulerpa peltata, Colpomenia sinuosa, Enteromorpha sp., Hypnea charoides, Padina spp., Sargassum sp., Spyridia filamentosa, Ulva sp., etc. also were observed during the study period. Generally, there were no significant differences in terms of species richness and composition of the recruits between the two treatments (cleared vs. hammered) as well as with the controls. This implied that algae in AMW were more likely to be recruited de novo from elsewhere rather than regenerated from remnants of the previous year's growth.