Examining the Density Gradient Along the Rhizophora mangle Propagule
Keywords:
mangrove; propagule; densityAbstract
Mangroves grow in tropical regions around the globe, but these dense forests have been declining due to agriculture, industry, and climate change. While of great ecological and economic importance, mangrove restoration is costly and has high failure rates. More research is needed to determine how these plants function. Mangrove propagules are not seeds but the seedlings themselves that grow on the parent tree until they reach maturity and fall. They are water dispersed, floating horizontally in seawater and vertically in brackish water. This study investigated the change in density longitudinally along the Rhizophora mangle propagule. Propagules were cut into one-centimeter sections and the density of each section calculated. The data shows that the density of the propagules increases from the plumule end to the radicle end until around 80-90% of the length of the propagule, at which point the density decreases. This density gradient is consistent with a propagule floating vertically with the radicle end below the plumule end. A cross-section of the propagule shows an inner medulla surrounded by a cortex. Towards the radicle end of the propagule, the cortex sinks while the medulla continues to float.
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