Competition among introduced and indigenous submerged macrophytes in a southern mediterranean shallow system

In Termini Imerese H. stipulacea has been recorded inside artificial basins, located near the harbour, built arranging breakwater barriers along the coast in order to protect the coastal road. From July until the beginning of November the seagrass formed beds with cover values ranging from 70% to 80%, and it was in contact either with the seagrass Cymodocea nodosa (Ucria) Ascherson (cover values of 20-25%) or the green alga Caulerpa prolifera (Forsskål) Lamouroux (cover values of 10-15%). H. stipulacea in good health conditions showed a clear competition strategy with C. nodosa as proved by registered cover values. But during natural denudations occurring in winter, C. racemosa var. cylindracea, showing a faster spreading ability than that of H. stipulacea and a very high invasive potential, negatively interferes with the rhizomes of H. stipulacea not only preventing them from spreading and forming new leaves, but also causing their regression.