Propagule predators in Kenyan mangroves and their possible effect on regeneration

Abstract

Grapsid crabs can play a considerable role in the predation of mangrove propagules and possibly are a threat to the regeneration of mangroves, whether natural or artificial. Experiments consisting of artificial plantation of mangrove juveniles were set up in Gazi Bay (Kenya). Grapsid crabs, particularly Neosarmatium meinerti in the most landward fringe and N. smithii and Sesarma guttatum in the middle fringe of the mangrove forest, were found to be a regeneration-limiting factor. Almost 100% (n = 40) of the landward plantations were cleared. There was a slight initial preference for Rhizophora propagules lying horizontally on the mangrove floor, which simulates the position of a stranding propagule. In Mida Creek (Kenya) the snail Terebralia palustris was observed predating mangrove propagules. This study shows that crabs may affect the regeneration potential of mangroves, and snails might also be a factor in predation. A need to actively search for ways to protect re-afforestation plots from predators of mangrove tree juveniles is necessary.