Fucoidans are sulfated polysaccharides extracted from brown seaweeds. They have a wide spectrum of activity in biological systems. Besides their well-known anticoagulant and anti-thrombotic activity, fucoidans modulate inflammation, possess antiproliferative and anti-adhesive effects on cells, protect cells from viral infection, and interfere with mammalian fertilization. Fucoidans are now used as raw material for development of drugs and are also widely used as a health-promoting food component. However, studies on the toxicity of fucoidans from different brown algae are limited. The present study examined the acute toxicity of varying levels of fucoidan extracted from Okinawa mozuku, a brown alga (Cladosiphon okamuranus), in Wistar rats after oral administration. No significant toxicological changes were induced by fucoidan at a dose of 600 mg/kg of body weight/day. However, with concentrations at and above 1,200 mg/kg of body weight/day, clotting time was significantly prolonged. No other signs of toxicity were observed.

The antibacterial properties of the three seagrasses namely Cymodocea serrulata, Halophila ovalis and Zostera capensis were tested against the human pathogens Staphylococcus aureus, Bacillus cereus, B. subtilis, Escherichia coli, Salmonella paratyphi, Salmonella typhimurium and Micrococcus luteus, using six different solvents namely, petroleum ether, chloroform, ethyl acetate, acetone, methanol and water. Ethyl acetate and methanol extracts showed maximum activity against most of the pathogens when compared to other solvents. Experiments are underway to isolate active compound(s) implicated in controlling the growth of the pathogens in vitro.