Proximity to research centers, fluvial accessibility, and dams presence drive sampling efforts for phytoplankton, zooplankton, and macrophytes in freshwater ecosystems

Abstract

Understanding biodiversity and monitoring ecosystems require robust sampling eforts for important bioindicators like phytoplankton, zooplankton, and aquatic macrophytes. This study quantifed sampling eforts for these aquatic groups across the Tocantins-Araguaia Basin in Central Brazil, evaluating the infuence of geographic and environmental factors such as human development, fuvial and terrestrial accessibility, elevation variation, and proximity to protected areas and research centers. These variables align with the appeal and accessibility hypotheses, which help explain sampling patterns observed across regions. A systematic review compiled 2,307 unique feld collection records, allowing analysis of spatial and temporal sampling patterns. The sampling efort was quantifed based on geographic coordinates per grid cell, with predictors analyzed using generalized linear mixed models. Results showed sampling was concentrated in the centralsouthern region, with phytoplankton covering 28.83% of the area, macrophytes 16.13%, and zooplankton 11.9%. Key drivers of sampling efort included proximity to research centers, dam presence, and fuvial accessibility. Additionally, protected areas and human development infuenced sampling efort for specifc biological groups. Despite these eforts, vast regions, especially in the northern Araguaia River, remain under-sampled, highlighting the need for comprehensive long-term sampling strategies to address critical biodiversity knowledge gaps.