Effect of Salinity on Buoyancy of Mangrove (Rhizophora racemosa) and Nypa Palm (Nypa fruticans) Seedlings in the Niger Delta, Nigeria

摘要

Seed dispersal is a major factor of species distribution and propagation. It was hypothesized that Nypa palm seed will float more than mangrove seeds in water due to its outer fiber coat. An experiment was conducted with 30 seeds each of both mangrove (Rhizophora racemosa) and Nypa palm (Nypa fruticans). Buoyancy experiment was conducted in the laboratory. The weights of all the seeds were recorded. A small basin full of water was placed in an empty bigger basin. The seeds of each species were sequentially placed inside the inner container that was full of aqueous media. The amount of water spilled was collected and measured in milliliter (ml). The weight of the seed and the weight of the water spilled were then used to calculate the floatability of each seed. If the weight of the seed is greater than the mass of water spilled the seed floats while if the weight of the seed is less than the mass of water spilled the seed sinks. The result indicates that there was no significant difference in the amount of spill between tap and river water (F1,119=3.76, p>0.05). But there was a significant difference in the amount of spill between mangrove and Nypa palm seeds (F1,119=163.2, p<0.0001). Five Nypa palm seeds floated in tap water while one floated in river water, as for mangrove none of the seeds floated in both water types. Nypa palms seeds were heavier (0.13 ± 0.01 kg) than mangrove seeds (0.026 ± 0.001 kg). This implies that Nypa palm seed has higher buoyancy than mangrove seeds. Similarly, salinity influenced seed floatation, as the tap water (control) had higher floatation than river (saline) water.