Distribution of sunken macroalgae against the background of tidal circulation in the coastal waters of Qingdao, China, in summer 2008

A high‐resolution, three‐dimensional, POM‐based numerical model is developed to study the distributional responses of sunken algae (SA) in a massive macroalgal bloom, which occurred in Qingdao coastal waters in summer 2008, to the barotropic tidal currents which dominate the dynamic circulation system. Validated by in situ observation of both sea level and buoy‐measured current data, the model shows satisfactory performance in reproducing the tidal system. An indicator BotDIV, the integral of velocity divergence of bottom flow over hours preceding the trawling of SA, is diagnosed on the basis of tidal modeling. It is found that the distribution of SA, captured by 16 tows of bottom trawling, is dependent on the BotDIV field. Basically, large (small) quantity of algae are caught at the sites where bottom currents converge (diverge). The influences of advective or diffusive process on the distribution of such heavy seaweeds settling on the seabed are probably limited.