The colonization, regeneration, and growth rates of macrophytes from fragments: a comparison between exotic and native submerged aquatic species

Abstract

The propagation of most aquatic macrophytes occurs vegetatively, via fragments. After dispersal, the fragments may exhibit two survival strategies: colonization (the ability to develop roots) and regeneration (the ability to develop new propagules that can disperse). Invasive species, for example, Hydrilla verticillata, are known to have a high potential for dispersal and growth. We experimentally evaluated the colonization and regeneration abilities and growth rates of this species in the early stage of development and compared these properties to the corresponding characteristics of two native species of Hydrocharitaceae (Egeria densa and Egeria najas). The following hypotheses were tested: (1) fragments with apical tips have greater colonization and regeneration abilities and higher growth rates than fragments without apical tips and (2) H. verticillata has greater colonization and regeneration abilities and higher growth rates than other native species of Hydrocharitaceae. Our results showed that both types of fragments had the same ability to colonize, whereas fragments without tips had a higher ability to regenerate. However, fragments with apical tips showed higher growth rates. It is probable that these higher growth rates resulted from apical dominance. H. verticillata had the greatest propagation potential. Its colonization and regeneration abilities and growth rates were greater than those of the native species. These differences can produce competitive advantages for the exotic species in the early stages of development in new habitats and may contribute to understanding the success of the exotic compared to the native species.