Autoecological studies of Salvinia auriculata Aubl. / David Searle Mitchell.

Tese (Ph.D.) - University of London, 1970

Investigations of the taxonomy, anatomy, morphology and reproduction of the neotropical species of Salvinia invading Lake Kariba show that it is a sterile pentaploid, capable of rapid vegetative reproduction and well adapted to a free-floating aquatic life; doubt is expressed that it is S. auriculata. The environment provided for the plant by Lake Kariba is described. In culture, growth of Salvinia increased with increase in temperature from 22ºC to 30ºC but was inhibited at 35ºC and above. Deficiency symptoms for nitrogen, phosphorus, sulphur, calcium, magnesium and potassium were produced in nutrition experiments and described. Addition of nitrate-nitrogen was shown to promote the production of leaf primordia. Lake-enrichment experiments demonstrated that nitrate-nitrogen is likely to limit growth on Lake Kariba. Salvinia is dispersed over water by winds and currents and between water bodies mainly by man. When colonising an area, population increase is exponential. Calm water and anchorage are the main requirements for mat formation. Lake Kariba initially provided large areas of nutrient rich water with these conditions and consequently Salvinia underwent explosive growth. The lake began to form in 1958 and, by 1962, the total area of Salvinia was 1000 km² (21.5% of the lake's surface). Further rise in lake level increased wave action and limited mats to sheltered inlets; thus the area of weed decreased and, since 1964, has fluctuated between 600 km² and 850 km². Many inlets are river estuaries subject to flash floods, which periodically disturb the Salvinia mats. Salvinia is an integral and valuable parte of the Kariba ecosystem. Permanent mats support sudd plants but inhibit other plant growth. Salvinia is an important habitat for invertebrates and consequently significant in many food chains. It is also a large reservoir of nutrients which are released differentely on decay. The future of Salvinia on Kariba will depend on the lake's nutrient status, particularly in the sheltered areas. Nitrogen availability may become especially important.