Moderately intensive selective fish removal enhances biodiversity and promotes ecosystem restoration: a whole-lake...

Biomanipulation through selective fish removal (SFR) has been widely applied to shallow lake rehabilitation. However, studies on SFR in plateau lakes remain limited, and evaluating its ecological effects is critical for guiding restoration efforts in these globally significant freshwater ecosystems. Caohai Lake, a highland plateau lake, experienced severe ecological degradation since 2016, with submerged macrophyte coverage collapsing from ∼70% to below 10% by 2019. From February 2022 to July 2023, a moderate-intensity SFR intervention targeting benthic omnivores, herbivores, and zooplanktivores removed approximately 55 kg/ha (∼20-40% of standing biomass). We assessed multiple responses across fish, benthic macroinvertebrates, submerged macrophytes, phytoplankton, and water quality before and after the intervention. Consistent with the Intermediate Disturbance Hypothesis, the SFR was associated with significant increases in alpha diversity in both fish and benthic macroinvertebrate communities, accompanied by compositional shifts as dominant species (Carassius auratus, Hemiculter leucisculus) declined and previously suppressed taxa reassembled. A synergistic ecosystem recovery was observed: submerged macrophyte coverage and biomass increased by 29% and 428 g/m², respectively, while phytoplankton biomass (-6.7 mg/L), chlorophyll a (-38.3 μg/L), and water transparency (+15 cm) improved markedly. PLS-PM modeling suggested that attenuation of fish-mediated top-down pressure on macrophytes represented a plausible mechanistic pathway driving this recovery. Our findings demonstrate that moderate SFR enhances biodiversity, disrupts dominance structures, and triggers trophic cascades conducive to macrophyte recovery, supporting its application as an effective tool for lake ecosystem restoration and sustainable management. Nevertheless, long-term monitoring is needed to further evaluate functional stabilization and the persistence of the observed recovery.