![Sample our Earth Sciences journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5930/TOC-Subject-Sample-2021-Earth-Sciences.jpg"})
Abstract
The lower reservoir of the Karori Wildlife Sanctuary (Wellington) has experienced cyanobacterial blooms for the last 8 years. In this study, we sought to test the role of nutrient resources (bottom‐up) versus cascading effects of zooplanktivorous perch (Perca fluviatilis) (top‐down) in controlling cyanobacteria in this lake. A 2×2 factorial field experiment was performed within plastic enclosures positioned in the lake, using four treatments: (1) the addition of juvenile perch; (2) the addition of nitrogen and phosphorus; (3) the addition of juvenile perch and of nitrogen plus phosphorus; and (4) a control treatment of no perch or nutrient addition. Four species of Anabaena were found with the dominant species being A. lemmermannii. Cyanobacterial abundance was significantly higher in treatments with perch. The addition of nutrients had no significant effect on cyanobacterial densities, but there was a weak fish × nutrient interaction on cyanobacteria abundance. There was no overall difference in total zooplankton abundance in any of the treatments. However, zooplankton species diversity was increased and large crustaceans were at higher densities in treatments without perch. Community composition of both phytoplankton and zooplankton species was altered by the addition of juvenile perch and nutrients. Our results suggest that an eradication of perch may cause a reduction in cyanobacteria abundance with the plankton being dominated by both larger phytoplankton and zooplankton species.
