By Asephelele Shabalala
In keeping with the traditions of Rhodes University, the inaugural lecture of Professor Julie Coetzee was held on 2 June 2022 in Eden Grove Red Lecture Theatre to honour her achievement of the title of Professor. There she presented her body of work and the most recent results of her research on the invasive water plant species Pontederia crassipes, commonly known as water hyacinth, and her efforts to understand and control it.
In her lecture titled Hoping on a hopper: the silver bullet for water hyacinth control? Professor Coetzee related the legend of how a random act of kindness performed by a generous plant enthusiast at the 1884 World’s Fair resulted in the spreading of water hyacinth around the world. The first invasive outbreaks of this water weed were recorded as early as the late 1800s, with its presence in South Africa being recorded in the early 1900s.
She then went on to explain the importance of the relationship and interplay of bottom-up effects and top-down pressures in aquatic ecosystems, where the amount of nutrients present in the waters of the ecosystem would usually limit the amount of plant growth from a bottom-up perspective. This, however, was not the case in South Africa.
In 2005, Professor Coetzee and others conducted research that showed that in all the water bodies where they had observed water hyacinth growing, they found high amounts of nutrients (phosphorus and nitrogen) that contributed to the rapid propagation of the weed in our country’s waters. She attributed this high nutrient saturation to a lack of water purification infrastructure and lax water policy that fosters nutrient-rich environments ideal for the invasive water hyacinth plant. The water hyacinth has no natural competitors in our ecosystem and is thus in the best position to take full advantage of those eutrophic water conditions and spread rapidly.
According to Professor Coetzee, the solution is to introduce those competitors into the ecosystem to act as biological control agents and exert top-down pressure on the invader. This is not a new concept even in combating water hyacinth in South Africa, with various bugs, mites, moths and fungi being migrated from South America (where water hyacinth itself originated) to try to get a grip on the weed. Unfortunately, the high amount of nutrients in the water, combined with the inability of most of the introduced control agents to survive the colder winters in South Africa, has thus far rendered most of these efforts only partially successful, although her most recent work, however, has yielded promising results.
Professor Coetzee discussed her work with the planthopper Megamelus scutellaris and the lessons learned in her efforts to use biological control to reduce the spread of water hyacinth on the Hartbeespoort Dam in the North West Province. Through her work with the Centre for Biological Control (CBC), where she serves as its Aquatic Weeds Programme Manager and Deputy Director, she coordinated a mass-rearing programme of the Megamelus, which were then released into the dam throughout 2019, with excellent results.
Through the efforts of the CBC’s Sisonke programme, various schools and community groups in the area surrounding Hartbeespoort Dam, she and her team reduced the water hyacinth coverage on the dam from 42% to under 2%. Professor Coetzee spoke of the work that still needs to be done, particularly with the population reduction Megamelus experiences during winter. However, the results of this augmented biological control programme have already far exceeded her expectations and have garnered a great deal of local and international attention.
In closing, she thanked those who had helped her to where she is today. Rhodes University congratulates Professor Coetzee for her fantastic achievement and thanks her for her many years of academic excellence.