A checklist of aquatic macrophytes of the Guaraguaçu river basin reveals a target for conservation in the Atlantic rainforest

Abstract

Describing and understanding distribution of species in natural ecosystems is the first step to establish conservation efforts. In aquatic habitats, macrophytes play a central role in promoting biodiversity and ecosystem functioning. This study aimed to create the first checklist of aquatic macrophyte species occurring in the Guaraguaçu river, the largest river in Paraná State coast, Brazil. Species herborized, identified and incorporated into the Herbarium collection of the Universidade Federal do Paraná. A total of 47 species were registered corresponding to 37 genera and 29 botanical families; Cyperaceae and Poaceae were the most representative families. In addition, the wide invasion of the non-native species Urochloa arrecta (Hack. ex T. Durand & Schinz) Morrone & Zuloaga was registered and the presence of the floating-leaved non-native species Nymphaea caerulea Savugny was recorded. Even so, the inventory shows a noteworthy richness of aquatic macrophytes species in the Guaraguaçu river, and it is clear macrophyte species reflect a gradient of anthropic impact and salinity in this tidal estuarine river. Our study contributes to the creation of public policies to aid in the protection of this river that represents a central site for biological conservation efforts, yet is constantly threatened by anthropic activities.

The invasive tropical tanner grass decreases diversity of the native aquatic macrophyte community at two scales in a subtropical tidal river

“…By digging further within our data, we argue that effects observed depended on the beta diversity facet (i.e., turnover and nestedness, see also Angeler 2013), and may also depend on sampling period, which demonstrates the complexity in describing impacts of invasive species. Compared to a recent checklist reporting 47 species for this basin (Araújo et al 2021), our samplings did not fully represent the aquatic community of the river. This can be explained by the fact that only paired and welldeveloped beds were sampled in our study, excluding unique macrophytes that commonly colonize several small patches of the river margins.…”

“…Following this rationale, comparing plots within beds would be an extremely small spatial scale, but we argue that is an informative strategy given the structuring role of macrophytes, and given the fact that many invertebrates perceive the habitat at very local scales (Thomaz & Cunha 2010). Complementarily, comparing beds over the spatial gradient of the river (the other scale addressed here) may inform how the invasive plant changed the regionalization along the river, which is indeed very observable in the Guaraguaçu River for multiple biological groups (Vitule 2008;Araújo et al 2021). By digging further within our data, we argue that effects observed depended on the beta diversity facet (i.e., turnover and nestedness, see also Angeler 2013), and may also depend on sampling period, which demonstrates the complexity in describing impacts of invasive species.…”

“…Independently of the seasonal variation, human occupation along the river margins has been increasing near the roadside, which also coincides with a region with high input of untreated sewage leachate from a landfill (Singo et al 2020), and with intense tropical tanner grass invasion (see Fig. 1), although this invasive species occurs along most of the navigable stretch of this river (Araújo et al 2021). Apart from the impacted sites, the Guaraguaçu River waters are naturally transparent and black-red due to the large amounts of organic matter and humic compounds received from the forests, which acidify the waters, particularly in the rainiest periods (Vitule 2008).…”

“…This river is highly invaded by the African tropical tanner grass Urochloa arrecta (Hack. Ex t. Durand & Schinz) Morrone & Zuloaga (Araújo et al 2021). The Guaraguaçu River is a subtropical tidal aquatic ecosystem that is highly dynamic considering the two daily tidal changes in water level; reaching c. 3 m in extreme maritime conditions and depending on the moon phase (personal observation), which means that flora and fauna are subject to such varying water level conditions.…”

“…Such temporal variation can affect biodiversity and likely the effects of nuisance macrophytes in biodiversity. Just after summer, macrophyte beds are particularly highly developed (Araújo et al 2021) likely attributed to the high temperatures and leaching of nutrients in water following a combination of frequent rainfall and high human occupation during summer holidays that attract tourists to coastal cities (Vitule 2008).…”