Modelling drivers of mangrove propagule dispersal and restoration of abandoned shrimp farms

Propagule dispersal of four mangrove species Rhizophora
mucronata, R. apiculata, Ceriops tagal and Avicennia
officinalis in the Pambala-Chilaw Lagoon Complex (Sri
Lanka) was studied by combining a hydrodynamic model
with species-specific knowledge on propagule dispersal behaviour.
Propagule transport was simulated using a finitevolume
advection-diffusion model to investigate the effect of
dispersal vectors (tidal flow, freshwater discharge and wind),
trapping agents (retention by vegetation) and seed characteristics
(buoyancy) on propagule dispersal patterns. Sensitivity
analysis showed that smaller propagules, like the ovalshaped
propagules of Avicennia officinalis, dispersed over
larger distances and were most sensitive to changing values
of retention by mangrove vegetation compared to larger,
torpedo-shaped propagules of Rhizophora spp. and C. tagal.
Directional propagule dispersal in this semi-enclosed lagoon
with a small tidal range was strongly concentrated towards
the edges of the lagoon and channels. Short distance dispersal
appeared to be the main dispersal strategy for all four
studied species, with most of the propagules being retained
within the vegetation. Only a small proportion (max. 5 %)
of propagules left the lagoon through a channel connecting
the lagoon with the open sea. Wind significantly influenced
dispersal distance and direction once propagules entered the
lagoon or adjacent channels. Implications of these findings
for mangrove restoration were tested by simulating partial removal
in the model of dikes around abandoned shrimp ponds
to restore tidal hydrology and facilitate natural recolonisation
by mangroves. The specific location of dike removal, (with
respect to the vicinity of mangroves and independently suitable
hydrodynamic flows), was found to significantly affect
the resultant quantities and species of inflowing propagules
and hence the potential effectiveness of natural regeneration.
These results demonstrate the value of propagule dispersal
modelling in guiding hydrological restoration efforts that aim
to facilitate natural mangrove regeneration.

Jaar van publicatie:2013

Trefwoorden:sea level rise