Mangrove Propagule Tidal Dispersal

Tidal Forcing

Tidal current amplitude U₀ 0.28 m/s

Tidal period T 50 s

Propagule Physics

Drag response time τ 2.0 s

Root capture density 0.55

Live Readouts

Stranded

Mean drift (afloat)

0.0 m

Tide elevation η(t)

0.00 m — slack

How it works

A viviparous mangrove propagule (e.g. Rhizophora, Ceriops) detaches from the parent tree already germinated, floats on the tidal creek surface, and is transported passively by hydrochory — dispersal by water — until it strands somewhere it can root.

Tide elevation:  η(t) = A·sin(2πt/T)
Tidal current:   u(t) = U₀·cos(2πt/T)   (flood +x, ebb −x)
Drag relaxation: dv/dt = (u(t) − v)/τ + turbulent kick
Local depth:     h(z,t) = h₀ − k·|z| + η(t)
Stranding:       if h(z,t) < h_strand and |z| in root fringe →
                  captured with probability ∝ root density · dt

U₀, T — set the strength and period of the flood/ebb current that advects propagules back and forth along the channel.
τ — how tightly a propagule's velocity follows the local water velocity. Small τ (small, well-coupled propagule) tracks the current almost instantly; large τ (buoyant, higher-drag propagule) responds sluggishly and drifts more independently between reversals.
Root capture density — the probability per unit time that a propagule sitting over exposed, shallow root fringe at low tide gets mechanically trapped by pneumatophores and mud, ending its dispersal.
Only propagules over shallow, low-tide-exposed fringe can strand — one still in the deep central channel keeps drifting until a future low tide brings it close enough to a bank.

This mirrors field/hydrodynamic studies of mangrove propagule dispersal (e.g. Van der Stocken et al.), where residence time near suitable banks at the right tidal phase — not just current speed — governs whether a propagule establishes nearby or is exported far downstream.

Flood tide

Afloat propagule Stranded propagule Root fringe

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