## 3 Results  
### Hydrodynamic Characteristics  
The hydrodynamic data from the well-established hydrodynamic model are essential for the particle-tracking modeling of the green macroalgae, because tidal currents are the fundamental driving force of the macroalgae drifting. In order to obtain a general sense of the Bohai Sea tidal environment, which provides the outer tidal energy for the detailed study area at Jinmeng Bay, four cotidal charts of M2, S2, K1, and O1 are provided by harmonic analysis, as shown in Figure 6. The semi-diurnal constituents of M2 and S2, and the diurnal constituents of K1 and O1, are the four primary constituents accounting for most of the tidal energy in the Bohai Sea, which is derived from the tidal waves in the Yellow Sea. As shown in Figure 6a, two anticlockwise amphidromes are formed under the Coriolis force of the Northern Hemisphere, with one amphidromic point near the coast of Qinhuangdao and another near the Yellow River estuary. According to the amplitude of different locations in the Bohai Sea, the descending order is listed as Liaodong Bay in the north, Bohai Bay in the west, Bohai Strait in the east, and Liazhou Bay in the south. Because M2 is the strongest tidal constituent, the two amphidromic points near the Qinhuangdao coast and the Yellow River estuary make these two areas low-energy zones in terms of hydrodynamics. In Figure 6c, only one amphidromic point appears in the Bohai Strait, which means that this location has the smallest amplitude, and for the other three locations the descending order is the same as M2, i.e., Liaodong Bay > Bohai Bay > Laizhou Bay. The cotidal charts of S2 and O1 present similar patterns to M2 and K1, respectively, with minor changes in amphidromic point locations, but with smaller amplitudes. The simulated cotidal charts of the Bohai Sea in this research correspond to results obtained by other scholars, and further prove that the hydrodynamic model is reliable for particle-tracking modeling [46; 55; 56; 57; 58]. It is concluded that the amphidromic point of M2 near the Qinhuangdao coast causes this to be an area with low tidal energy, which is not helpful for nutrient dispersion and the migration of green macroalgae. In order to seize the hydrodynamic characteristics in more detail locally within the coastal waters of Jinmeng Bay, the current fields of a representative spring tidal cycle on 10 August 2021, for the moments of flood slack, maximum ebb, ebb slack, and maximum flood are presented in Figure 7. From the time series of the water level at the measuring point JVMP during August 2021 (Figure 7f), it demonstrates that the tides in the Jinmeng Bay area are of a regular diurnal type. From the time series of the current speed and direction at JVMP from 00:00 9 August 2021, to 00:00 11 August 2021, it demonstrates that the tidal currents in the Jinmeng Bay area are of a regular semi-diurnal type. The currents present a reciprocating pattern in the SW-NE direction substantially parallel to the isobath, the flood current is in the SW direction, and the ebb current is in the NE direction. At the moments of flood slack and ebb slack, the current speed is generally small in the study area, except for some patches near Lianhua Island and Hailuo Island. Even at the moments of maximum flood and ebb, the largest current speed is less than 0.3 m/s at the farthest point  
Figure 5: Comparison between the observed and simulated biomass concentration of green macroalgae for the particle-tracking model in the Jinmeng Bay domain. offshore. The nearshore area enclosed by artificial structures presents a lower current speed, but at the narrow channels on the northeast and southwest side of Hailuo Island enhanced currents appear due to the constraining effect of the channels. In general, the hydrodynamic environment in the Jimmeng Bay waters is low-energy, and, as it is additionally surrounded by multiple artificial structures, it is adverse for water exchange and thus the dispersion of nutrients.