Temporal changes in the abundance and growth of intertidal Thalassia hemprichii seagrass beds in southern Taiwan

A bimonthly study of temporal changes in abundance and growth of the tropical seagrass Thalassia hemprichii on intertidal reef flats was conducted in southern Taiwan from October 1995 to December 1996. Thalassia hemprichii showed a marked temporal pattern in percentage cover, shoot density, and specific growth rate. There were no significant differences in the variables of T. hemprichii between the study sites. The percentage cover showed a unimodal or bimodal pattern in which one peak occurred in June or August and the other occurred in October. The shoot density was highest in June and lowest between December and February. The specific growth rate peaked in October or December, but declined in February or April. However, the temporal patterns in root:shoot ratio of biomass were different. Higher root:shoot ratios were observed in December or February, and lower between April and August. The above-ground biomass was always smaller than the below-ground biomass. Canonical correlation analysis indicated that temperature, water-column nutrient concentration and rainfall were positively correlated, and daylight exposure time and wind speed negatively correlated, with the dynamics of T. hemprichii. Among these variables, wind speed and rainfall were most responsible for the observed temporal changes in southern Taiwan, which has a monsoonal climate and distinct wet and dry seasons.