Sargassum setifolium is an endemic species from the Galápagos Islands. Prior to 1983, reported from: Fernandina: Punta Espinosa (1972 UC, K.A. Miller, pers. comm; Wellington 1975). Isabela: Caleta Black (Taylor 1945) and Caleta Tagus (Taylor 1945; also many 1966 UC specimens from 0.5 mile NW of Caleta Tagus and 1 mile N of Caleta Tagus; K.A. Miller, pers. comm.). Floreana: Champion (Wellington 1975), Black Beach Anchorage (1972 UC, K.A. Miller, pers. comm). San Cristóbal: (Albatros Espedition); Wreck Bay (1972 UC, K.A. Miller, pers. comm). Santiago: Bartolome (Taylor 1945). Santa Cruz. After 1983, reported from: Santa Cruz: Tortuga Bay (1995 CDS). Isabela: Las Marielas (CDRS record 2001).
Habitat and Ecology
Habitat and Ecology
S. setifolium has been reported from the low intertidal to 7.2 m depth.
IUCN Red List Assessment
Red List Category
Red List Criteria
Miller, K.A., Garske, L. & Edgar, G.
Stuart, S.N. & Carpenter, K.E. (Global Marine Species Assessment Coordinating Team)
Little reliable information on population trends is available for this species, and some problems exist with taxonomic identification. Regardless, populations of this species have clearly declined in recent decades since the alga was formerly abundant and recent collections have yielded only a single specimen. Because of some identification uncertainty, this species could be assessed as Data Deficient. However, because the locations that it was previously found in the central archipelago are no longer suitable Sargassum habitat as a consequence of herbivore overgrazing, the historical area of occupancy clearly has contracted dramatically. This represents a contraction of available habitat from about 20,000 km2 to one small area that is difficult to define because only drift material is known, but is estimated to be substantially less than 500 km2 AOO and less than 5,000 km2 EOO. Therefore this species is assessed as Endangered.
There is little information on population trends for S. setifolium, although Wellington (1975) reported it as one of the most prevalent brown algae at Punta Espinosa (along with S. albemarlense). At present, populations are almost exclusively restricted to the western archipelago. Recent surveys (2000 to 2004) have failed to find populations of S. setifolium from San Cristóbal, Bartolome, and Santa Cruz. This represents a contraction of available habitat from about 20,000 km² to one small area; estimated to be substantially less than 500 km² in area of occupancy, and less than 5,000 km² in extent of occurrence. Population trend: unknown over the past decade; declining over the past three decades.
Presumably El Niño and climate change. Ecosystem interactions involving these two factors appear to have caused widespread decline in algal populations because of an increase in density of grazing sea urchins and other herbivores, following overexploitation of predators along with ENSO disturbances.
S. setifolium is present within the Galápagos Marine Reserve (IUCN category VI); Galápagos Archipelago Particularly Sensitive Sea Area (PSSA); Galápagos Island World Heritage Site (UNESCO N (i)(ii)(iii)(iv)), and Galápagos Island Man and Biosphere Reserve (UNESCO).