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

[摘要] Propagule dispersal of four mangrove species Rhizophora mucronata, R. apiculata, Ceriops tagal and Avicennia officinalis in the Pambala–ChilawLagoon Complex (Sri Lanka) was studied by combining a hydrodynamic modelwith species-specific knowledge on propagule dispersal behaviour. Propaguletransport was simulated using a finite-volume advection-diffusion model toinvestigate the effect of dispersal vectors (tidal flow, freshwaterdischarge and wind), trapping agents (retention by vegetation) and seedcharacteristics (buoyancy) on propagule dispersal patterns. Sensitivityanalysis showed that smaller propagules, like the oval-shaped propagules ofAvicennia officinalis, dispersed over larger distances and were most sensitive to changing valuesof retention by mangrove vegetation compared to larger, torpedo-shapedpropagules of Rhizophora spp. and C. tagal. Directional propagule dispersal in thissemi-enclosed lagoon with a small tidal range was strongly concentratedtowards the edges of the lagoon and channels. Short distance dispersalappeared to be the main dispersal strategy for all four studied species,with most of the propagules being retained within the vegetation. Only asmall proportion (max. 5%) of propagules left the lagoon through achannel connecting the lagoon with the open sea. Wind significantlyinfluenced dispersal distance and direction once propagules entered thelagoon or adjacent channels. Implications of these findings for mangroverestoration were tested by simulating partial removal in the model of dikesaround abandoned shrimp ponds to restore tidal hydrology and facilitatenatural recolonisation by mangroves. The specific location of dike removal,(with respect to the vicinity of mangroves and independently suitablehydrodynamic flows), was found to significantly affect the resultantquantities and species of inflowing propagules and hence the potentialeffectiveness of natural regeneration. These results demonstrate the valueof propagule dispersal modelling in guiding hydrological restoration effortsthat aim to facilitate natural mangrove regeneration.

[学科分类] 地球化学与岩石