Changes in drag and drag coefficient on small Sargassum horneri (Turner) C. Agardh individuals

Sargassum horneri (Turner) C. Agardh is used to restore, create, and recreate seaweed beds along the coastlines of East Asia. Drag produced by waves is a bulk force that can detach thalli from substrata during the early growth stages from substrata. In this study we measured drag forces on small S. horneri thalli (10-40 cm long). Unidirectional steady flow was controlled from 20 to 130 cm s−1 in increments of 10 cm s−1 in a recirculating water tank. Drag force on individuals ranged from ∼0.3 N to ∼3 N. Drag (Fdrag) and water velocity (U) produced the following exponential empirical approximations: Fdrag = 0.0168 × U0.8925. The drag coefficient (Cd) was plotted as a function of Reynolds number (Re) as follows: Cd = 4744.7 × Re−0.93. Cd converged to 0.037 at Re of 105−6 suggesting that small thalli exhibit optimal morphological adaptations to withstand high current speeds.