Response of cladoceran assemblages to restoration of riparian vegetation: A case study in a tropical reservoir of Brazil

Abstract

In recent decades, riparian vegetation has been removed from important ecosystems around the world, in spite of its high ecological importance for aquatic biota. Nevertheless, the effects of catchment land use on zooplankton have been little studied. The present study investigated if replanting riparian vegetation in a tropical reservoir influences the richness and abundance of cladoceran communities, by addressing the question of whether cladocerans show differences in richness and abundance among four levels of riparian vegetation conditions: 1) native forest (NF); 2) 30 years after forest replanting (R1); 3) 10 years after forest replanting (R2); and 4) no forest (No-F). Zooplankton samples were obtained from 9 stations in the Volta Grande Reservoir, Minas Gerais, Brazil. Cladocerans in zones NF and R1 showed higher levels of richness and abundance than in zones No-F and R2. Ceriodaphnia reticulata, Ceriodaphnia laticaudata, and Diaphanosoma spinulosum showed higher abundances in zones NF and R1. Cladoceran community structure was influenced by the different levels of riparian vegetation. This study showed that the presence and age of riparian forest positively influence the abundance, richness and diversity of cladoceran assemblages. Furthermore, our results indicated that C. reticulata, C. laticaudata and D. spinulosum are more efficient than other cladocerans in exploiting allochthonous resources provided by riparian forest. Functional diversity was higher in zones NF and R1, suggesting that the trait composition of cladoceran assemblages responds positively to recovery of riparian forest. Overall, our research suggests that cladocerans are good indicators of riparian vegetation conditions and that restoration of riparian forest positively affects cladoceran assemblages of tropical reservoirs.

Introduction

Riparian vegetation is important for aquatic ecosystems, since it provides habitat for many species, controls fluvial erosion, and functions as a biological filter of pollutants between terrestrial and aquatic zones. Riparian vegetation also serves as wildlife habitat and ecological corridors, retains sediment, and protects aquatic ecosystems from agrochemical contamination (Lowrance, 1998; Micheli and Kirchner, 2002). Additionally, these vegetation strips shape habitat heterogeneity and modulate the input of dissolved organic matter, which is used as an allochthonous resource by aquatic organisms (Zalewski et al., 1995; France et al., 1996; Cecilio et al., 2004; Dodson et al., 2005; Tundisi et al., 2008; Seger et al., 2012).

Despite its ecological importance, riparian vegetation has been removed from the margins of waterbodies around the world, due to human occupation and development of industry and agriculture near aquatic systems (Basińska et al., 2014; Chen et al., 2019). Previous studies in subtropical areas have reported that input of dissolved inorganic matter from riparian forests positively affected the abundance and richness of zooplankton species (Carpenter et al., 2005; Czerniawski, 2013; Dodson et al., 2007; Watkins et al., 2011). However, no information is available concerning the effect of riparian forest on zooplankton communities of rivers modified by the construction of reservoirs in tropical ecosystems.

Replanting riparian vegetation is an effective strategy for restoration of impacted watersheds (Newaz et al., 2019; Tundisi et al., 2008). Some evidence shows that particulate organic carbon sourced from riparian grass can partly support aquatic food webs through the trophic link to zooplankton (Taipale et al., 2014). Cladocerans can dominate the zooplankton of freshwater systems such as reservoirs (Guevara et al., 2009) and are good indicators of environmental quality (Eyto et al., 2002; Seminara et al., 2016), especially in human-impacted ecosystems (Leppänen et al., 2018). In addition, changes in species composition as a response to environmental changes may cause shifts in functional groups, affecting ecosystem functioning (Nevalainen and Luoto, 2017). However, little is known about the responses of crustacean species to restoration of forest vegetation in areas impacted by human occupation, industry, and agriculture.

The relationship between riparian forest conservation and aquatic biota has been insufficiently studied in tropical freshwater systems (Zhao et al., 2014; Braghin et al., 2018). In addition, no information is available regarding whether replanting riparian forests has only short-term or longer-lasting effects on planktonic crustacean communities in tropical systems, and how riparian reforestation could affect the richness, abundance and functional diversity of crustacean species in reservoir systems. The present study tested the hypothesis that replanting riparian vegetation around an impacted reservoir may influence cladoceran communities, by addressing the question of whether cladocerans show differences in richness, abundance and contribution of species to functional groups, among four levels of riparian vegetation conditions: 1) preserved native forest; 2) forest 30 years after replanting; 3) forest 10 years after replanting; and 4) no forest.

Our sampling design allowed us to test, in a space-for-time substitution approach, the responses of cladoceran communities to riparian forest age and spatial distribution. We tested if a short period (10 years) and long period (30 years) after replanting might result in similar patterns of richness, total abundance, and relative contribution of functional groups of cladocerans, compared to an area where the riparian forest has never been removed (preserved native forest) in a tropical reservoir in Brazil. If cladoceran communities from restored zones (10 and 30 years old) have similar richness, abundance and relative contribution of functional groups compared to areas without riparian forest (no-forest zones), the effects of vegetation restoration should be considered negligible for cladoceran communities in this reservoir.