Effects of wave energy on the residence times of a fluorescent tracer in the canopy of the intertidal marine macroalgae,Sargassum fusiforme (Phaeophyceae)

We determined the relationship between the residence times of water within the canopy of the intertidal macroalgae, Sargassum fusiforme (Harvey) Setchell to the energy caused by hydrodynamic mixing. We measured the residence times (t) of fluorescein dye injected into the canopy (31 ± 9 ind/quadrat; canopy plan form area 6 × 1 m²) to estimate the length of time gametes persist within the canopy. The total kinetic energy (TKE) and wave energy (WE) was measured during dye dispersal, which ranged from 0.002 to 0.009 m²/s² and 0.001 to 0.016 m²/s², respectively. The experiments revealed that the canopy significantly (P < 0.0001) increased t, which was 56 ± 35 s inside of the canopy compared with 14 ± 4 s outside. Moreover, the relationship between t and energy could be statistically modeled with a power function, and for the results inside of the canopy, t = 3.67 TKE^?0.50 for turbulent kinetic energy and t = 1.83 WE^?0.38 for wave energy. Outside of the canopy, t = 0.98 TKE^?0.50 and t = 1.83 WE^?0.38 Based on the values of t determined for within the canopy, we developed a dispersion model to explore how gametes dispersed within the canopy. The estimated dispersion coefficient (D) with respect to WE, could be modeled as D = 403 WE^0.55 and ranged from 10 to 42 cm²/s for the WE examined in the study. Areal gamete densities modeled in the canopy increased in density for increasing WE at short (0.5 h) durations of gamete discharge; however, the relationship reversed above 2 h of discharge.