Biological and hydrographical responses to tropical cyclones (typhoons) in the continental shelf of the Taiwan Strait

A survey on the changes of chemical and biological parameters in the continental shelf of the south East China Sea, northwest of Taiwan was conducted shortly after the passage of tropical cyclone Herb in the summer, 1996. A transect with four sampling stations was visited twice to explore temporal and spatial variability. Data collected from the same transect in the summer of 1994 and 1997 indicated that the study area was a typical oligotrophic system with lack of typhoon disturbance. The results showed that after the cyclone event, all the values of the measured chemical and biological parameters were much greater than those derived from normal summer periods. The depth (40 m) integrated values of chlorophyll-a, nitrate and particulate organic nitrogen concentrations increased 18, 169 and 73%, respectively. More significantly, primary production, particulate organic carbon concentrations and bacterial production as well as biomass increased at least two-fold. Wind mixing, re-suspension and terrestrial runoff which resulted from cyclone passage probably were the three major processes resulting in these phenomena, although their relative importance could not be distinguished clearly in this study. The magnitude of the enhancement of measured parameters varied with time and space, suggesting that the study area was at a highly unsteady status after the passage of the typhoon. This study demonstrated that the shelf ecosystem became more productive after the cyclone event, but more research is required to explore the fate of these newly formed organic substances.