Ecological significance of a new record of Vallisneria americana Michx. in the conservation and sustainability of the Usumacinta Fluvial System

The American eelgrass Vallisneria americana is a submersed rooted macrophyte that is widely distributed throughout North America. As a structured habitat, it shelters a high biodiversity of aquatic fauna and acts like a carbon sink. However, its populations have drastically decreased or disappeared in the free-flowing Usumacinta Fluvial System. Physicochemical parameters in water, measurements of quantitative habitat complexity, and records of fish collected were quantified for a V. americana patch. A low average density of 96 ± 48 stems/m2, 61.7 ± 0.9 gash free dry weight/m2 of biomass, and 192 ± 42.3 male inflorescences/m2 were recorded for this 14 m2 patch. Six fish species of the Poeciliidae and Cichlidae families were collected, with an average density of 19 ± 1.9 org/m2, all smaller than 6.3 cm standard length. This first record of V. americana in the transitional longitudinal zone (20–60 MASL) of the Usumacinta Fluvial System reinforces the importance of the Wanhá Biosphere Reserve (WBR), which was decreed mainly for its relict inland red mangrove populations and high diversity of tropical swamp woody communities. Moreover, the American eelgrass patch is a nursery area for at least six native poeciliids and cichlids. These are the two most diverse fish families in Mesoamerica. In addition, the cichlid fishery is an important component for environmental sustainability.