Whereas close relatives (Ceiba aesculifolia, Ceiba pentandra, and Pseudobombax ellipticum) create a silk-like, cotton like “kapok” to surround the seeds, the Pachira aquatica has a soft gel-like white substance (which reminds me of the pulp around cacao seeds).
Kapok allows the seeds of ceiba and comparable trees to float through the air, driven by the wind, to find new places to grow. In distinction, the zapoton tree prefers to grow along the shore of rivers or lakes so can often best survive if the seeds fall directly onto the shore (or into the water when water level rises during the rainy season).
I have seen healthy seedlings of Pachira aquatica growing in water about 10 to 15 cm deep along Lake Izabal.
Yet there was an equally healthy fully grown Pachira aquatica tree nowhere near water, in the central park of Chisec (until it was cut down two years ago in order to pour cement on the surface). There is also a healthy Pachira aquatica tree in the botanical garden at the end of Avenida Reforma (where the office of of CECON is).
We at FLAAR have about four healthy Pachira aquatica trees in our garden at 1500 meters elevation: no lake, no river, and a long dry season. The trees are healthy and happy (but do very much prefer to be alongside a river or lake or in an eco-system with lots of water).