Dispersal of propagules by water, or hydrochory, is a primary or secondary dispersal mode for many plant species that live in or near aquatic habitats. Buoyancy of seeds and fruits is a key attribute in hydrochory; the longer a propagule remains afloat, the greater the likelihood that it will be carried some distance from its source by flowing or pulsing water or by wind-generated surface currents (Shimamura et al. 2007). Studies of hydrochory in plants often initially focus on quantifying the buoyancy of propagules in laboratory settings to assess the water dispersal potential of a species (e.g., Williamson and Costa 2000).