the marine herbivorous snail, Littorina littorea. Polysiphonia lanosa (L.) T.A. Christensen is a small red alga, commonly found growing in dense tufts on Ascophyllum whose rhizoids penetrate the host. It is considered by some as parasitic; however, as it only receives structural support from knotted wrack (not parasitically), it acts as an epiphyte. Distribution This species has been recorded in Europe from Ireland, the White Sea, the Faroe Islands, Norway, Britain and Isle of Man, Netherlands, and North America from the Bay of Fundy, Nova Scotia, Baffin Island, Hudson Strait, Labrador, and Newfoundland. It has been recorded as an accidental introduction near San Francisco, California, and eradicated as a potential invasive species. Uses Ascophyllum nodosum is harvested for use in alginates, fertilisers, and the manufacture of seaweed meal for animal and human consumption. It has long been used as an organic and mainstream fertilizer for many varieties of crops due to its combination of both macronutrients, (N, P, and K) and micronutrients (Ca, Mg, S, Mn, Cu, Fe, Zn, etc.). It also contains cytokinins, auxin-like gibberellins, betaines, mannitol, organic acids, polysaccharides, amino acids, and proteins which are all very beneficial and widely used in agriculture. Ireland, Scotland and Norway have provided the world's principal alginate supply. Ascophyllum nodosum is frequently used as packaging material for baitworm and lobster shipments from New England to various domestic and international locations. Ascophyllum itself has occasionally been introduced to California, and several species frequently found in baitworm shipments, including Carcinus maenas and Littorina saxatilis, may have been introduced to the San Francisco Bay region this way. Toxicological uses Because the age of the different parts of A. nodosum can be identified by its shoots, it has also been used to monitor concentrations of heavy metals in seawater. A concentration factor for zinc has been reported to be of the order 104. Chemistry Ascophyllum nodosum contains the phlorotannins tetraphlorethol C and tetrafucol A. Harvesting controversy Controversy exists over impacts of commercial harvesting of A. nodosum for use in garden or crop fertilizers and livestock feed supplements in North America and Europe. Some research has been focused on bycatch and impact on intertidal zone communities. Opponents of its wild harvest point to the algae's high habitat value for over 100 marine species, including benthic invertebrates, commercially important fish, wild ducks, shorebirds, and seabirds. Shoreland owners in Maine, as well as federal, state, and local agencies in