Abstract

The connection of habitats is critical to support freshwater biodiversity, especially in regulated hydrological systems where the occurrence of natural flow regimes is disturbed. The paper examines fish habitat connectivity at lotic-lentic boundaries, based on an integrated multi-layered model, which integrates structural, hydrological, and ecological indicators. An experiment on a dataset of different levels of connectivity was conducted to determine the effects of fragmentation on fish diversity and ecosystem well-being. The analysis incorporates global-scale geospatial data and connectivity metrics to quantify fragmentation patterns and hydrological alterations. The statistical analysis indicated that there are a lot of differences in the species richness among the connectivity gradients, with high connectivity areas having a maximum of 45 species and low connectivity areas having 18 species, representing nearly a 60% reduction in biodiversity. The percentage of migratory species decreased significantly between highly connected habitats (62) and fragmented systems (19). Correlation analysis showed that barrier density and species richness had a good negative relationship (r = -0.78, p < 0.01), and hydrological connectivity index had a good positive relationship with biodiversity (r = +0.74, p < 0.01). Regression results further demonstrated strong predictive relationships, with a high coefficient of determination (R² ≈ 0.96), confirming the influence of connectivity on ecological responses. The results of the regression further supported the hypothesis that an increase in fragmentation causes significant loss of biodiversity, and better hydrological connectivity creates stability in the ecosystems. The conclusions stress that physical obstacles, as well as a change in flow processes, have a significant impact on aquatic ecosystems. The suggested framework is able to represent these intricate interactions and give a detailed connectivity measurement tool. The paper concludes that the restoration of hydrological connectivity and structural fragmentation reduction are the key measures to preserve fish diversity and ecological balance of the regulated river systems.

Keywords: Fish habitat connectivity, Hydrological connectivity index (HCI), Barrier density, Freshwater biodiversity, Habitat fragmentation, Migratory fish species, River–Lake ecosystems