Sargassum C. Agardh
“[T]halli are highly differentiated into holdfast, cylindrical main axis, leaflike blades, and airbladders in the axil of blades. This genus is widely spread in temperate, tropical, and subtropical waters in both intertidal and subtidal zones. Some forms are free-floating, sometimes occurring in extensive rafts that harbor distinctive communities of organisms adapted to the buoyant Sargassum habitat. These occur in the Sargasso Sea off the western coast of Africa. During the 1940s, Sargassum muticum spread from Japan to the northern pacific coast of the US, and by the 1970s had made its way south to California. This species of Sargassum has also spread to Europe, probably on oysters destined for aquaculture operations. Sargassum forms nuisance growths in harbors and on beaches, and it can quickly spread to new areas due to the floatation capabilities conferred by its many air bladders. Other features contributing to rapid spread include fast growth rate, fertility in the first year and monoecious reproduction.” (Graham & Wilcox, 2000)
Sargassum do not show alternation of generations, as do many other brown algae. Tiny gametophytes (“gametangia”) are retained within the thallus of the larger sporophyte. Gametes are formed in the gametophyte via meios followed by mitotic divisions. The multicellular, macroscopic thalli are diploid (though many cases of polyploidy occur). (Lee, 1999; Graham & Wilcox, 2000)
Parenchymatous, with growth from an apical cell
Branching monopodal, with lateral branch systems consisting of leaf-like blades, air bladders, and recepticles
Haploid generation reduced to the egg and sperm
Gametes retained in conceptacles
Gamete union is oogamous
(Lee, 1999; Graham & Wilcox, 2000).
The Sargussum of the Sargasso Sea never develop holdfasts, and all reproduction is vegetative (Graham & Wilcox, 2000).
Rocky subtidal and intertidal; also pelagic, creating large rafts floating on the sea surface, e. g., the Sargasso Sea.
“Because of their worldwide distribution and capacity to alter native communities, non-indigenous algae are potentially important agents of global ecological change.” (Britton-Simmons, 2004)
Sargassum occurs in temperate to tropical waters. Since the 1940s, Sargassum muticum has spread from Japan to Canada, the United States, and Europe where it can have a significant impact on the composition of the native flora and fauna, either via direct or indirect effects.
(Critchley et al., 1983; Stæhr et al., 2000; Britton-Simmons, 2004)
Sexual (with gametes as only haploid phase) and/or vegetative (Lee, 1999; Graham & Wilcox, 2000)
Sargassum rafts are habitat and/or food for many species of larval and adult fish and invertebrates (Stoner & Greening, 1984; Coston-Clements et al., 1991; Hoffmayer et al., 2005; Casazza & Ross, 2008)
Sargassum acinarium (Linnaeus) C. Agardh, Sargassum agardhianum J. Ag., Sargassum albermarlense Taylor, Sargassum bacciferum (Turner) Agardh, Sargassum bermudense, Sargassum boryi C. Ag., Sargassum carpophyllum J. Ag., Sargassum cinctum J. Ag., Sargassum coriifolium J. Ag., Sargassum crassifolium J. Ag., Sargassum cristaefolium C. Agardh, Sargassum cymosum, Sargassum desvauxii (Mertens) C. Ag., Sargassum duplicatum J. Ag., Sargassum echinocarpum J. Ag., Sargassum filifolium C. Ag., Sargassum filipendula C. Agardh, Sargassum fissifolium (Mertens) C. Ag., Sargassum flavicans (Mertens) C. Ag., Sargassum fluitans (Børgesen) Børgesen, Sargassum hystrix, Sargassum ilicifolium (Turner) C. Ag., Sargassum linifolium, Sargassum lophocarpum J. Ag., Sargassum muticum Yendo, Sargassum myriocystum J. Ag., Sargassum natans (Linnaeus) Gaillon, Sargassum obtusifolium, Sargassum oligocystum Mont., Sargassum palmeri Grun., Sargassum piluliferum, Sargassum polyacanthum J. Ag., Sargassum polyceratium, Sargassum polycystum C. Ag., Sargassum polyphyllum, Sargassum pteropleuron, Sargassum scabripes J. Ag., Sargassum spathulaefolium J. Ag., Sargassum spinuligerum Sonder, Sargassum stenophyllum J. Ag., Sargassum torvum J. Ag., Sargassum turbinarioides Grunow, Sargassum verruculosum (Mertens) C. Ag., Sargassum vulgare