Abstract
The aqueous fractions of the dry methanol extracts (500 ppm) of sixty marine algal species were screened for molluscicidal activity against Biomphalaria glabrata, which is an important host of the bilharzia-causing Schistosoma species. The majority of the extracts tested were inactive at the concentration used, but those of Fucus serratus, F. vesiculosus, Pelvetia canaliculata, Ascophyllum nodosum, Halidrys siliquosa, Bifurcaria bifurcata, Dictyota dichotoma and Halopithys incurva all showed significant molluscicidal activity. Treatment with polyvinylpolypyrrolidone (PVPP) either removed or drastically reduced the activity of the extracts of F. serratus, F. vesiculosus, P. canaliculata, A. nodosum, Halidrys siliquosa and Halopithys incurva, which suggested that the active compounds in the extracts of these species were polyphenolic in nature. The active extracts of the other two seaweed species did not appear to be affected by treatment with PVPP. Dialysis of the active extracts against distilled water separated them into high and low molecular weight fractions. In the case of the two Fucus species, P. canaliculata and A. nodosum, the activity resided in the high molecular weight fraction, whereas with all the other species, the activity was found in the low molecular weight fraction. 1H NMR spectroscopic examination of the active extracts confirmed that the molluscicidal components of the extracts of the Fucus species, P. canaliculata and A. nodosum were high molecular weight polyphenols.