Size does matter, but not only size: Two alternative dispersal strategies for viviparous mangrove propagules

Abstract

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.

Mangrove Vegetation Dynamics of the Tanbi Wetland National Park in The Gambia

“…These are in line with recent findings indicating that vegetation cover in TWNP is seemingly intact with no noticeable growth since pre-independence days (1965) [23]. This is a uniquely bizarre ecological situation that has not been reported elsewhere and is explicable by the long-term lack of rejuvenation stemming from low growth and seedlings survival in estuaries with unstable hydrological regimes [52].…”

“…All of these indicate mangrove species' response to long-term seasonal hyper-salinity, in the form of reduced growth and decreased success in seedling [50,51,52]. In a study in Pichavaram (India), natural causes of mangrove degradation were attributed to high salinity, low levels of available nutrients and low microbial counts [10].…”

Propagule size is not a good predictor for regional population subdivision or fine-scale spatial structure in lichenized fungi

“…In plants, species with small seeds (i.e. low seed mass) are more efficient at dispersing over long distances than those with larger seeds, but establishment success is higher in species possessing large seeds (Morse & Schmitt 1985;Greene & Johnson 1993;Gravuer et al 2003;Greene & Quesada 2005;Skarpaas et al 2010;De Ryck et al 2012). Hence, there is a tradeoff in propagule size, where high dispersal capability excludes high establishment success.…”

Application of remote sensing and GIS for detection of long-term mangrove shoreline changes in Mui Ca Mau, Vietnam

“…Most of propagules were found to disperse over a short distance up to tens of metres (McGuinness, 1997;Breitfuss et al, 2003;Sousa et al, 2007;De Ryck et al, 2012). However, some propagules dispersed over extensive ranges, even more than 50 km (Clarke, 1993).…”