Floating ability, shoot length and abundance facilitate hydrochorous dispersal of moss and liverwort fragments

Abstract

Question: Vegetative diaspores are pivotal to the ability of bryophytes to colonize new areas, but life-history traits and other factors facilitating vegetative hydrochorous dispersal are largely unknown. Here, we ask whether hydrochorous dispersal of vegetative bryophyte fragments can be predicted by specific traits in addition to discharge and abundance of species in the vegetation. Location: The Twentekanaal, a navigation canal in the Netherlands. Methods: Over a one-year period, viable bryophyte fragments dispersed in the canal were quantified using a 200-μm net and related to five potentially predicting variables. These variables are fragment buoyancy, shoot length, growth form, abundance in the vegetation and discharge. Buoyancy of fragments including regeneration was determined experimentally for all species found; other traits were derived from the literature. A Generalized Linear Mixed Model approach was adopted to identify the traits and trait–discharge interactions best explaining the presence of fragments in water. Results: Of the 144 samples collected, 77% contained bryophyte fragments. A total of 54,514 fragments were counted, representing 18 species. The free-floating Riccia fluitans was the most abundant species, followed by Brachythecium rutabulum. In total, 55% of the variation in diaspore presence of sessile species could be explained by abundance in the vegetation, buoyancy and shoot length. Of the sessile species of which fragments were trapped, mean floating time (T50) was 5.9 days and mean shoot length 79 mm. Species that occurred in the vegetation, but were not found in the water had a significantly lower buoyancy and shoot length. Conclusions: We conclude that abundance in the vegetation, buoyancy and shoot length are significant predictors for vegetative hydrochorous dispersal of aquatic and riparian bryophytes. As fragments of species found are able to regenerate after being in water for weeks, they may contribute to colonization of new favourable substrate patches along water bodies after being dispersed.