Delving for clues to help fish and hippos thrive
Efforts to help fish and animals like hippos survive and thrive were boosted by insights from EU-funded project AQUAHYDRO. With the support of the Marie Curie programme, Spanish ecologist Dr David Soto from KU Leuven, Belgium, used a cutting-edge method to investigate two of the most understudied food webs in the world. The funding took him to the banks of Lake Edward, which stretches between Uganda and the Democratic Republic of the Congo (DRC), for fieldwork with Belgian researchers and local fishermen. He also applied his new method to fish and plant samples previously collected at the Congo River in DRC. “The most striking finding was the high dependency of the Congo River fish, which feed the villages in the region, on the plants and the whole terrestrial ecosystem itself,” said Dr Soto, post-doctorate research fellow, supervised by Professor Steven Bouillon. “This connectivity stresses the importance of protecting the terrestrial environment as well as the river and of management on a wider scale.” Unweaving the web Dr Soto’s new approach was to analyse the lake and river food webs, using measurements of hydrogen-stable isotopes on samples of fish, small invertebrates and plants. Dr Soto and other ecologists increasingly use ‘stable isotope analysis’ of animal tissue to determine what food an animal has taken in over the last few months, rather than only examining stomach contents which tends to show what they have eaten during the last few hours. Through the project AQUAHYDRO he went further, using hydrogen isotope analysis, in addition to measuring carbon and nitrogen isotopes. The measurement of hydrogen isotopes has, until now, proved difficult because the hydrogen in organic materials like plants and animals exchanges with ambient moisture. The isotopic composition of this moisture varies depending on factors like geographical location and the time of year. The AQUAHYDRO team developed techniques to overcome those impediments for the samples collected. The approach helps distinguish the contribution of food from the land from that produced integrally in the river or lake, making for a sophisticated understanding of how organisms eat or rely on each other in the food web. “If aquatic animals depend on plant material like leaves from the land by the river or lake to grow, human developments like damming or deforestation can negatively impact those communities,” said Dr Soto. The results could prove invaluable in helping halt falling fishing yields at Lake Edward. The team is investigating whether there is a link between these fish communities and reductions in the numbers of hippopotamuses. One village on the lake, Ishango, used to have 10 000 hippotamus and had just 14 left last year, according to the Congolese Institute for the Conservation of Nature (ICNN), cited in Global Press Journal. “Hippo dung can fertilise the lake, and changes on these terrestrial inputs over time could have affected the whole food web,” says Dr Soto. The researchers are now looking to use the method to understand other ecosystems better – in the Kenyan mangroves and, closer to home, in Belgium’s River Scheldt.
Keywords
AQUAHYDRO, Afrotropical lakes, rivers, stable hydrogen isotopes, fish, hippopotamuses, Congo River, Lake Edward
