Abstract
Plankton is an integral part of wetland biodiversity and plays a vital role in the functioning of wetlands. Diversity patterns of plankton in wetlands and factors structuring its community composition are poorly understood, albeit important for identifying areas for restoration and conservation. Here we investigate patterns in local and regional plankton richness and taxonomic and functional community composition in riverine papyrus swamps, river mouth wetlands, and lacustrine wetlands in the Lake Tana sub-basin, Ethiopia. Data on phytoplankton, zooplankton, and environmental variables were collected from 12 wetlands during the dry and wet seasons of 2018. Redundancy analysis, and linear mixed effect models, were used to investigate differences in local environmental conditions and variation in plankton community richness and composition between wetland types. We also assessed the ecological uniqueness of the plankton community by calculating the contribution of a single wetland: local contributions to overall beta diversity (LCBD) and contributions of individual species (SCBD) to overall beta diversity (BDTotal). Beta regression models were used to investigate the relationships of LCBD and SCBD to environmental variables, wetland, and taxa characteristics. A total of 85 phytoplankton taxa, distributed among 18 Reynolds functional groups, and 57 zooplankton taxa were observed over the entire set of samples. Local plankton taxon richness was significantly higher in riverine papyrus swamps (mean taxa of 30 phytoplankton and 21 zooplankton) compared to river mouth wetlands (mean taxa of 27 phytoplankton and 13 zooplankton). Several local environmental variables and the composition of the plankton community differed significantly between the three wetland types. The highest phytoplankton ecological uniqueness (LCBD) was detected in lacustrine wetlands, whereas the riverine papyrus swamps had the highest zooplankton ecological uniqueness. Based on our analyses, we recommend protecting the wetlands with high LCBD values and stress the importance of various wetland types for preserving the diverse plankton communities of Lake Tana wetlands.
Highlights
Wetlands are one of the most productive habitats and are of immense socio-economic and ecological importance (De Groot et al, 2012) because they provide a wide range of ecosystem services such as groundwater recharge, water purification, nutrient cycling, shoreline stabilization, cultural, recreational, and educational resources, flood protection, and carbon storage (Everard et al, 2019)
The concentration of dissolved oxygen, pH and concentration of total phosphorus were significantly higher in river mouth wetlands compared to riverine papyrus swamps and lacustrine wetlands (Figures 4B, D, I)
Our findings revealed that water depths were shallower in river mouth wetlands than in riverine papyrus swamps and lacustrine wetlands, which might be another reason for the lower phytoplankton richness in the former wetland type
Summary
Wetlands are one of the most productive habitats and are of immense socio-economic and ecological importance (De Groot et al, 2012) because they provide a wide range of ecosystem services such as groundwater recharge, water purification, nutrient cycling, shoreline stabilization, cultural, recreational, and educational resources, flood protection, and carbon storage (Everard et al, 2019). Phytoplankton form the base of the food chain in aquatic ecosystems and play an important role in overall wetland productivity (Chengxue et al, 2019), while zooplankton are recognized as the main primary consumers. Due to their short life cycle and potentially rapid response to anthropogenic disturbance and environmental changes, planktonic organisms are regarded as ideal bioindicators for assessing the environmental status of wetlands (Wijeyaratne and Nanayakkara, 2020; Chaparro-Herrera et al, 2021). The plankton community structure differs between tropical and temperate lakes, but research on wetlands is still limited One of these differences is that smaller zooplankton species (including rotifers) often predominate in tropical lakes, whereas large cladocerans are dominant in temperate lakes (Fernando, 1980; Green, 1994). Wide temperature and light intensity fluctuations are widely regarded as the primary drivers of variation in plankton community structure in temperate systems, whereas hydrological conditions are important in the tropical systems (Loverde-Oliveira et al, 2009; Shatwell et al, 2016)
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