Weeds and the Rotorua Lakes

Abstract

The Rotorua Lakes are of volcanic origin and they form an integral feature of the regions landscape. No other region in New Zealand has such an interesting combination of lakes in close proximity, each of which offers unique cultural values and a diversity of recreational activities. Rotorua lake weeds rose to public and political prominence in the 1960s and the first seminar addressing this issue was held in 1964. A second meeting followed in 1966 with a ‘Seminar on Water Weeds’. These seminars involved outside experts and many will remember Prof Val Chapman, University of Auckland, who had a prominent role supervising research on these weed problems with his students. I was his last PhD student before he retired in c. 1975. This talk will provide an outline of key changes in the Rotorua Lakes over time by focusing on the aquatic plants. The aquatic plants in a lake provide a window into understanding the health and condition of each lake and this talk explains how native and invasive plants can be used to assess or describe lake condition, enabling lakes to be ranked, monitored and compared. The native condition of each lake has been compromised by two key impacts; invasive plant species and declining water clarity. Other potential impacts are also discussed. Key invasive weed species will be illustrated and discussed, including their spread and ecological impacts. Some of the history of management response will be discussed along with some thoughts about the future.