In the Supplemental Data of this article, the strain described as smu b571 was actually b641. The authors regret the error.

Whether or not mangroves function as buffers against tsunamis is the subject of in-depth research, the importance of which has been neglected or underestimated before the recent killer tsunami struck. Our preliminary post-tsunami surveys of Sri Lankan mangrove sites with different degrees of degradation indicate that human activity exacerbated the damage inflicted on the coastal zone by the tsunami.

To the present day, it is much debated whether long-distance dispersal (LDD) of mangrove propagules is an epic, rather than a frequent event, next to more local dispersal. In general, there is a knowledge gap on the whereabouts of a propagule between the moment it releases from the parent tree and its establishment after a certain dispersal period through water. We addressed the fundamental need to understand the dispersal behaviour of viviparous mangrove propagules, in relation to their morphological characteristics, the differences between genera and the link with their different position in the intertidal zone. We studied the propagules of two dominant mangrove species, Ceriops tagal and Rhizophora mucronata, that are similar in shape but differ in other morpho-anatomical features. We hypothesized the propagules of both species to have a different hydrodynamic behaviour, resulting in a different dispersal strategy. The dispersal strategies of C. tagal and R. mucronata propagules were elucidated through a combination of a propagule tracking, predation and root-growth experiment, carried out in the field. C. tagal and R. mucronata adopted two different dispersal strategies. C. tagal releases a large number of propagules, disperses fast (low density and slender morphology) and has a high agility (smaller size) when dispersing through dense root systems. C. tagal propagules have a theoretical advantage to disperse over longer distances over the denser, thicker and longer R. mucronata propagules. C. tagal propagules have, however, lower establishment chances due to slower root-growth, desiccation sensitivity and smaller size. In contrast to Ceriops' tactic of "few and fast" dispersal, R. mucronata has adopted a dispersal tactic of survival. Fewer propagules are released, but they are more resistant to predators due to their larger size and they can anchor themselves faster due to quicker root-growth. Overall, propagule characteristics of both species result in different and alternative dispersal strategies on a local scale. On a global scale, we hypothesize this might lead to a similar capacity for LDD, ending in successful establishment.

Abstract. Mangrove forests prominently occupy an intertidal boundary position where the effects of sea level rise will be fast and well visible. This study in East Africa (Gazi Bay, Kenya) addresses the question of whether mangroves can be resilient to a rise in sea level by focusing on their potential to migrate towards landward areas. The combinatory analysis between remote sensing, DGPS-based ground truth and digital terrain models (DTM) unveils how real vegetation assemblages can shift under different projected (minimum (+ 9 cm), relative (+ 20 cm), average (+ 48 cm) and maximum (+ 88 cm)) scenarios of sea level rise (SLR). Under SLR scenarios up to 48 cm by the year 2100, the landward extension remarkably implies an area increase for each of the dominant mangrove assemblages except for Avicennia marina and Ceriops tagal, both on the landward side. On the one hand, the increase in most species in the first three scenarios, including the socio-economically most important species in this area, Rhizophora mucronata and C. tagal on the seaward side, strongly depends on the colonisation rate of these species. On the other hand, a SLR scenario of + 88 cm by the year 2100 indicates that the area flooded only by equinoctial tides strongly decreases due to the topographical settings at the edge of the inhabited area. Consequently, the landward Avicennia-dominated assemblages will further decrease as a formation if they fail to adapt to a more frequent inundation. The topography is site-specific; however non-invadable areas can be typical for many mangrove settings.

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