How can a longer seed be an advantage to the Red Mangrove?

Mangroves have one of the most unique reproductive strategies in the plant world. Mangroves are viviparous (bringing forth live young), just like most mammals. Rather than producing dormant resting seeds like most flowering plants, mangroves disperse propagules via water with varying degrees of vivipary or embryonic development while the propagule is attached to the parent tree.The red mangrove flowers mostly during the summer months. The long cigar shaped propagules are often found hanging on the tree all year long. The black mangrove flowers all summer long with the lima bean shaped propagules produced during late summer and early fall. The white mangrove flowers mid to late summer with small green pea shaped propagules produced a month later. Once the propagule drops from the parent tree there is an obligate dispersal period which each species’ propagule must remain in the water. During this period embryonic development continues. For the red mangrove this dispersal period is the longest at 40 days. The black mangrove propagule must drift for at least 14 days. The white mangrove dispersal period is the shortest at 5 days, which also includes germination. If the propagule strands in a “favorable” area, there is an obligate stranding period before the primary roots and cotyledons (primary leaves) emerge. The red mangrove has the longest obligatory stranding period of 15 days. However, the propagule may be lying horizontally on the sediment or vertically “standing up” and may be covered by water during this time.