Phaeophyceae in the context of Macrocystis

Ascophyllum nodosum is a large, common cold water seaweed or brown alga (Phaeophyceae) in the family Fucaceae. Its common names include knotted wrack, egg wrack, feamainn bhuí, rockweed, knotted kelp and Norwegian kelp. It grows only in the northern Atlantic Ocean, along the north-western coast of Europe (from the White Sea to Portugal) including east Greenland and the north-eastern coast of North America. Its range further south of these latitudes is limited by warmer ocean waters. It dominates the intertidal zone. Ascophyllum nodosum has been used numerous times in scientific research and has even been found to benefit humans through consumption.

Macrocystis is a monospecific genus of kelp (large brown algae) with all species now synonymous with Macrocystis pyrifera. It is commonly known as giant kelp or bladder kelp. This genus contains the largest of all the Phaeophyceae or brown algae. Macrocystis has pneumatocysts at the base of its blades. Sporophytes are perennial and the individual may live for up to three years; stipes/fronds within a whole individual undergo senescence, where each frond may persist for approximately 100 days. The genus is found widely in subtropical, temperate, and sub-Antarctic oceans of the Southern Hemisphere and in the northeast Pacific. Macrocystis is often a major component of temperate kelp forests.

Despite its appearance, it is not a plant; it is a stramenopile. Giant kelp is common along the coast of the northeastern Pacific Ocean, from Baja California north to southeast Alaska, and is also found in the southern oceans near South America, South Africa, Australia, and New Zealand. Individual algae may grow to more than 45 metres (150 feet) long at a rate of as much as 60 cm (2 ft) per day. Giant kelp grows in dense stands known as kelp forests, which are home to many marine animals that depend on the algae for food or shelter. The primary commercial product obtained from giant kelp is alginate, but humans also harvest this species on a limited basis for use directly as food. It is rich in iodine, potassium, and other minerals. It can be used in cooking in many of the ways other sea vegetables are used, and particularly serves to add flavor to bean dishes.

Sargassum is a genus of brown macroalgae (seaweed) in the order Fucales of the class Phaeophyceae. This brown macroalgae comes from the Sargasso Sea, which was named because it hosts large amounts of Sargassum. Sargassum can extend for kilometers across the ocean surface, forming golden brown drifting mats that move with the currents and wind; in recent years, Sargassum has been known for arriving in large quantities throughout the Caribbean region. More recently, scientists have found using satellite data that a new hotspot has been forming from western Africa and extends into the Caribbean Sea, called the Great Atlantic Sargassum Belt (GASB).

Most of the macroalgae species inhabit shallow coastal waters and coral reefs, but some are planktonic (free-floating) or pelagic after being detached from reefs during storms. Sargassum includes two holopelagic species, Sargassum natans and Sargassum fluitans, with other species interconnected. These species are distinguished to reproduce solely by clonal reproduction through fragmentation. Sargassum plays an important ecological role in the open ocean because they provide a vital habitat for a variety of marine species, including fish, crabs, sea turtles, migratory birds and other organisms. However, when large amounts of Sargassum accumulate in the shore and start to decompose it forms what is known as Sargassum brown tides (SBT). SBT alters the water column by changing the appearance of the water and in addition alters the water quality by reducing light penetration, decreasing dissolved oxygen and changing the pH of the coastal waters. As a result, it affects seagrass meadows, corals, mangroves and coastal communities that depend on tourism.