Predation on propagules regulates regeneration in a high-density reforested mangrove plantation

Abstract

Seedling recruitment underpins natural regeneration and contributes to the restocking of forest stands, which in the long term determines the structure and functioning of mangrove ecosystems. Propagule predation (among other factors) has been found to play an important role in determining seedling distribution patterns in many mangrove stands. The role of propagule predation in influencing the observed regeneration in a Rhizophora mucronata reforested stand (9 yr old) with various spontaneously established mangrove species was investigated by looking at the effects of pruning, position (planted/vertical or prone/horizontal on the forest floor to simulate stranding) and species (Rhizophora mucronata, Ceriops tagal and Bruguiera gymnorrhiza) found to be spontaneously growing in the plantation. Predation intensity was higher (p = 0.05) in the pruned part of the stand than in the unpruned part. Prone propagules were preyed on more (p = 0.05) than the planted category, while R. mucronata was the species least preyed on compared to C. tagal and B. gymnorrhiza, suggesting that predation favors the recruitment of R. mucronata into this conspecific stand. Significant differences among prone and planted propagules suggest that predation is intense during the stranding phase, and this may play a critical role in limiting seedling establishment and subsequent recruitment. Predation is suggested to be a regulator of competition in this high-density stand by eliminating or reducing potential competitors, alluding to a ‘mutual relationship’ between crab predators and mangrove trees.