Disturbance and subsequent recovery of mid-shore assemblages on seasonal, tropical, rocky shores

Abstract

Hong Kong experiences a strongly seasonal climate, with distinct hot, wet summers and cool, dry winters, which has a great influence on intertidal assemblages. The impacts and relative importance of disturbance events on assemblage structure and subsequent recovery in this environment were examined on semi-exposed rocky shores. In August 1997, Typhoon Victor affected Hong Kong coastal waters bringing high seas and strong winds. Effects on mid-shore assemblage structure were patchy, with an increase in free space and a decrease in the abundance of the dominant molluscan grazer Monodonta labio occurring on one 10 m site on a shore, but not at other areas 10s of m away. The long-term impacts of this pulse disturbance were, however, negligible, as at this time of year there is little algal cover and grazer abundances are low, due to predictable annual disturbance caused by an increase in temperature with the onset of summer. Monitoring of plots artificially disturbed at different times of the year showed that recovery to undisturbed conditions was rapid following pulse disturbance events such as typhoons. Such disturbances had no lasting (> 6 mo) effect, as the die-off of species in the summer caused assemblages on shores to dissipate, and any long-term impacts of these disturbances were not obvious after one summer. It appears that the short-term effects of pulse disturbances on Hong Kong shores are rapidly eclipsed by annual, summer die-off events.