We studied the propagules of two widespread mangrove species, Ceriops tagal and Rhizophora mucronata, that are similar in shape but differ in other morpho-anatomical features (average length is 23.1 ± 2.2 cm and 44.4 ± 4.3 cm, resp., n = 180). We hypothesized the propagules of both species to have a different hydrodynamic behavior and establishing capacity, resulting in a different dispersal strategy. More specifically, we hypothesized that C. tagal propagules have a larger dispersal capacity than those of R. mucronata. The dispersal strategies of C. tagal and R. mucronata propagules were elucidated through a combination of a propagule tracking (n = 180 per species), predation (n = 20 per species) and root-growth experiment (n = 120 per species), carried out in the field. C. tagal and R. mucronata adopted two different dispersal strategies. C. tagal releases a large number of propagules and disperses fast, having a slender morphology and low density (average ?: 985.29 ± 19.02 g L-1), as well as 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 thicker, longer and denser R. mucronata propagules (average ?: 1003.92 ± 8.52 g L-1; t = 8.90, p < 0.0001, n = 197). C. tagal have, however, lower establishment chances due to slower root-growth, desiccation sensitivity and smaller size. In contrast to Ceriops’ tactic of releasing high numbers of propagules 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 (Mann–Whitney U: p < 0.0001, nCt = 59, nRm = 57). Overall, propagule characteristics of both species result in different and alternative dispersal strategies on a local scale, contradicting our initial hypothesis. On a global scale, we hypothesize this might lead to a similar capacity for long-distance dispersal, ending in successful establishment. |
