Abstract
Abstract. 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 finite-volume 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 oval-shaped 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.
Highlights
IntroductionThe understanding of mangrove autoecology, the patterns of reproduction, propagule distribution and establishment, as well as the human-mangrove relationships, is vital within the design and implementation of any successful mangrove restoration project (Bosire et al, 2008; Lewis III and Marshall, 1998; Lewis III, 2005; Primavera, 1993, 1991, 1998; Primavera et al, 2012a, b; Stevenson et al, 1999)
Dispersal of seeds and propagules can strongly influence the population dynamics and community structure in vegetated systems dominated by water dispersal (Honnay et al, 2001; Jansson et al, 2005; Nilsson et al, 2002)
The sensitivity analysis revealed that the dispersal of smaller, oval-shaped propagules is more sensitive to a variation in retention schemes and buoyancy period than the dispersion of larger, torpedo-shaped propagules
Summary
The understanding of mangrove autoecology, the patterns of reproduction, propagule distribution and establishment, as well as the human-mangrove relationships, is vital within the design and implementation of any successful mangrove restoration project (Bosire et al, 2008; Lewis III and Marshall, 1998; Lewis III, 2005; Primavera, 1993, 1991, 1998; Primavera et al, 2012a, b; Stevenson et al, 1999). In this study we focus on mangrove propagule dispersal within its ecological context and in view of shrimp pond restoration projects. We examined to what extent the removal of certain parts of outer pond
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