Cabomba (cabomba Caroliniana) Invasion Of The Features Of The Ecosystem

Cabomba caroliniana (cabomba, fanwort) is a perennial aquatic plant originated from the United States, Brazil and other places of in South America. Since it was reported as a new record in 1993,C.Cabomba has been widely spread in the water bodies in eastern China, and becomes the dominance in the submerged plant communities of Taihu lake region in Jiangsu Province, Hangjiahu region and Ningshao Plains in Zhejiang Province. In order to find out the basic characters of the ecosystems invaded by C.Cabomba, community investigation through quadratic method, habitat record, and water quality test had been conducted in 19 typical sites and 6 fixed sites. The results show that:1 Cabomba was an aggressive invader into small or middling rivers or lakes which are slow flowing, most with silt substrate, esp. if they were nutrient rich or middling.2 Cabomba had been the dominant or co-dominant species in the most investigated submerged plant communities, and its dominance negatively correlated with the number of species markedly. Most similarity coefficients of nineteen communities put forward by Spate are 15~40%, and it is related to the number and composing ratio of various species observably.3 The biomass of fanwort has significantly positive correlation with transparency, and its biomass and dominance has markedly negative relationship with dissolved oxygen in the water. The biomass and dominance of Vallisneria natans have significantly positive correlation with dissolved oxygen. But the biomass and dominance of Ceratophyllum demersum and Hydrilla verticillata have no significantly correlation with water quality.4 The maximum biomass of native species and Cabomba were occurred in different depth of water. The suitable depth for Cabomba was approximately 1.2-1.6 meters, while it was approximately 0.8~1.0 meters for native species {Ceratophyllum demersum, Vallisneria natans and Hydrilla verticillata, etc.).5 The main coexisting plants of the communities were Ceratophyllum demersum, Hydrilla verticillata, and Vallisneria natans, Potamogeton crispus and Myriophyllum spicatum were often found as well. It was noteworthy that these species were dominant in many submerged plant communities in the subtropics of China. The dominance of Cabomba negatively correlated with H. verticillata and V. natans observably, it indicated that the invasion of fanwort influenced the existence of the two species.6 The dominant species of the communities were only occasionally changed with seasonsin some places, including the communities of Taihu, Daochang, and Taoyan. Where fanwort always dominated in the Taihu community except it was replaced by Potamogeton crispus in winter season.7 The dominance of Cabomba was also changed with seasons, however it kept a high level (importance value >50%) if the community was simple in species composition. Which means species simple communities can be easily invaded and quickly dominated by Cabomba.8 The maximum biomass of native species and Cabomba were occurred in different depth of water. The suitable depth for Cabomba was approximately 1.2-1.6 meters, while it was approximately 0.8-1.0 meters for native species (Ceratophyllum demersum and Vallisneria natans, etc.).And Hydrilla verticillata was approximately 0-0.4 meter. The suitable depth of Cabomba was always deeper than that of native species with the season changed, which means Cabomba can occupy a unique niche in the submerged plant communities.9 The seasonal dynamics showed that fanwort and Vallisneria natans had more compact correlation with water quality, in six factor of water quality, dissolved oxygen had most compact correlation with the biomass and dominance of fanwort and Vallisneria natans. Especially the biomass of fanwort had positive correlation with dissolved oxygen in 4 fixed sites.