Though not a true plant, Sargassum is a brown seaweed or macroalgae that floats along the surface of the ocean. It has long leafy-branches with small round berry-like balls called pods attached and forms large “mats” that can stretch for miles.
Dr. Sylvia Earle has likened large mats or accumulations of Sargassum “the golden rainforest of the ocean” because of all of the organisms that rely on this species. Open ocean Sargassum provides an important marine community to many species, some of which only exist because of it. These organisms include: Sargassum fish, Sargassum sea mat, Sargassum pipefish, Sargassum snail, Sargassum swimming crab, Sargassum nudibranch and Sargassum shrimp.
Along with these species, more than 145 invertebrate species such as shrimp, nudibranch, seahorses, crabs, snails and fish have been documented is association with Sargassum. These smaller invertebrate species attract larger species in the food web such as sharks, mahi-mahi, wahoo and tuna. The food web does not stop at fish-- tropical birds such as Audubon’s shearwater, masked booby, red-necked phalarope and terns, have been known to feed on the fish in Sargassum.
Sargassum not only provides food for many species but provides refuge, breeding grounds and nursery habitat as well. According to Wells and Roocker (2004), around 36 species of fish spawn or use Sargassum as their nursery such as swordfish, flying fish, white and blue marlin, bluefin tuna and yellowfin tuna. Along with fish, sea turtles such as the loggerhead use Sargassum as a nursery habitat.
So what’s in it for Sargassum? All of the organisms that use Sargassum in various ways produce waste that nourishes the seaweed in return. Even when Sargassum is washed ashore, it provides benefits for the beach community. One way that Sargassum is beneficial is that it becomes food for many invertebrates. Once invertebrates feed on this seaweed, they then become food for shorebirds. According to Thomas (2004), Sargassum is critical for stabilizing the shoreline by adding nutrients to coastal soils and promoting the growth of dune plants.
Oil from oil spills tends to aggregate towards Sargassum because both float. When oil coats the seaweed, other marine life that consume and swim around this oil filled seaweed are at risk.Pollution such as microplastics is also a threat to Sargassum and all of the organisms associated with it.
Doubilet, David, et al., “Life in the North Atlantic Depends on This Floating Seaweed.” In the Sargasso Sea, Life Depends on Floating Sargassum Seaweed, 15 May 2019, https://www.nationalgeographic.com/magazine/2019/06/sargasso-sea-north-atlantic-gyre-supports-ocean-life/#close.
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Wells, R.J.D. and J.R Rooker 2004 Spatial and temporal habitat use by fishes associated with Sargassum mats in the NW Gulf of Mexico. Bulletin of Marine Science 74: 81–9
Last updated: December 12, 2019