Macrocystis

Macrocystis is a monospecific genus; the sole species is M. pyrifera. Some individuals are so huge that the thallus may grow to up to 60 m (200 ft). The stipes arise from a holdfast and branch three or four times from near the base. Blades develop at irregular intervals along the stipe. M. pyrifera grows to over 45 m (150 ft) long. The stipes are unbranched and each blade has a gas bladder at its base. Macrocystis pyrifera is the largest of all algae. The stage of the life cycle that is usually seen is the sporophyte, which is perennial and individuals persist for many years. Individuals may grow to up to long or more. The kelp often grows even longer than the distance from the bottom to the surface as it will grow in a diagonal direction due to the ocean current pushing against the kelp. The stalks arise from a basal meristem, with as many as 60 stalks in older well protected individuals. Blades develop at irregular intervals along the stipe, with a single pneumatocyst (gas bladder) at the base of each blade. It grows to only long. It is found on intertidal rocks or shallow subtidal rocks along the Pacific coast of North America (British Columbia to California) and South America. In New Zealand M. pyrifera is found in the subtidal zone of southern North Island, the South Island, Chatham, Stewart, Bounty, Antipodes, Auckland and Campbell Islands. The species can be found on rock and on sheltered open coasts. File:Giant Kelp - Macrocystis pyrifera (29296895168).jpg File:Macrocystis pyrifera.jpg File:Kelp forest Channel Islands.JPG| M. pyrifera growing in the Channel Islands File:Bryozoans on Macrocystis01.jpg|Macrocystis integrifolia File:Sanc0063 - Flickr - NOAA Photo Library.jpg|Giant kelp File:Alger, Macrocystis pyrifera, Nordisk familjebok.png| File:Giantkelp2 300.jpg| File:CAS Macrocystis 2.JPG| File:CAS Macrocystis 4.JPG| File:Kelpharvest 300.jpg| File:Seaweed, Santa Cruz Harbor.JPG| File:Paralabrax clathratus - Tokyosealifepark - 2019 1 8.webm| ==Life cycle==

The macroscopic sporophyte has many specialized blades growing near the holdfast. These blades bear various sori containing sporangia, which release haploid spores, which will grow into microscopic female and male gametophytes. These gametophytes, after reaching the appropriate substrata, grow mitotically to eventually produce gametes. Females release their eggs (oogonia) along with a pheromone, the lamoxirene. This compound triggers sperm release by males. The Macrocystis sperm consists of biflagellate non-synthetic antherozoids, which find their way to the oogonia following the lamoxirene. The egg is then fertilized to form the zygote, which, through mitosis, begins growth. Macrocystis integrifolia is found on intertidal rocks or shallow subtidal rocks along the Pacific coast of North America from British Columbia to California. It prefers water about to deep and exposed to the open sea and normal salinities, yet sheltered from full wave action. Macrocystis integrifolia alternates heteromorphic phases from a macroscopic sporophyte to dioecious microscopic gametophytes. ==Growth==

) Macrocystis pyrifera is one of the fastest-growing organisms on Earth. They can grow at a rate of a day to reach over long in one growing season. Juvenile giant kelp grow directly upon their parent female gametophyte. To establish itself, a young kelp produces one or two primary blades, and begins a rudimentary holdfast, which serves to anchor the plant to the rocky bottom. As the kelp grows, additional blades develop from the growing tip, while the holdfast enlarges and may entirely cover the rock to which it is attached. Growth occurs with lengthening of the stipe (central stalk), and splitting of the blades. At the growing tip is a single blade, at the base of which develop small gas bladders along one side. As the bladders and stipe grow, small tears develop in the attached blade. Once the tears have completed, each bladder supports a single separate blade along the stipe, with the bladders and their blades attached at irregular intervals. ==Ecology==

Macrocystis typically grow forming extensive beds, large "floating canopies", on rocky substrata between the low intertidal. Macrocystis pyrifera is found in North America (Alaska to California), South America, South Africa, New Zealand, and southern Australia. It thrives in cooler waters where the ocean water temperature remains mostly below . In high-density populations, giant kelp individuals compete with other individuals of the species for space and resources. Giant kelp may also compete with Pterygophora californica in these circumstances. Where surface waters are poor in nutrients, nitrogen in the form of amino acids is translocated up the stipe through sieve elements that very much resemble the phloem of vascular plants. ==Species==

Initially, 17 species were described within the genus Macrocystis. In 1874, Hooker, following blade morphology, put them all under the same taxon, Macrocystis pyrifera. In modern times, the large number of species were re-classified based on the holdfast morphology, which distinguished three species (M. angustifolia, M. integrifolia, and M. pyrifera) and on blade morphology, which added a fourth species (M. laevis) in 1986. In 2009 and 2010, however, two studies that used both morphological and molecular Morphs Although Macrocystis is a monospecific genus, some split it into the four morphs, or sub-species, described below, following pre-2010 taxonomy: • Macrocystis pyrifera, known as giant kelp, most widely distributed Macrocystis species, found in intermediate-to-deep water ==Distribution==

Macrocystis is distributed along the eastern Pacific coast from Alaska to Mexico and from Peru and along the Argentinian coast as well as in Australia, New Zealand, South Africa and most sub-Antarctic islands to 60°S. ==Aquaculture==

Macrocystis pyrifera has been utilized for many years as a food source; it also contains many compounds such as iodine, potassium, other minerals vitamins and carbohydrates and thus has also been used as a dietary supplement. In the beginning of the 20th century California kelp beds were harvested as a source for soda ash. With commercial interest increasing significantly during the 1970s and the 1980s this was primarily due to the production of alginates, and also for biomass production for animal feed due to the energy crisis during that period. Recently, M. pyrifera has been examined as a possible feedstock for conversion into ethanol for biofuel use. ==Conservation==

In recent years, the kelp forests have decreased dramatically throughout Japan, Chile, Korea, Australia and North America. Harvesting of kelp as a food source and other uses may be the least concerning aspect to its depletion. In the Northwest Pacific kelp forests in waters near large population centres may be most affected by the sewer/stormwater discharge. The natural phenomenon known as El Niño cycles warm, tropical water from the South Pacific to Northern waters. This has been known to kill off M. pyrifera, due to its need for cold waters it would usually find in the North Pacific Ocean. In California, El Niño also brought along a population bloom of purple sea urchins which feed on the giant kelp. Tasmania Off the coast of Tasmania, kelp forests have been significantly affected by several factors, including warming waters, shifting of the East Australian current (EAC), and invasion of long-spine sea urchins. Locals have noticed significant effects on the population of abalone, a food source for the Aboriginal Tasmanians for thousands of years. These changes have also affected the oyster farming industry. By saving oysters that have survived disease outbreaks, they have been able to continue their way of life. It was estimated that by 2019, 95 per cent of the giant kelp forests along Tasmania's east coast had been lost within just a few decades. Macrocystis pyrifera has become Australia's first federally-listed endangered marine community. Scientists and conservationists are continuously looking into ways to restore the once heavily populated species to its original state. Methods include artificial reefs, reducing numbers of purple sea urchins in overpopulated areas, and planting roots along the ocean floor. New Zealand Macrocystis pyrifera have begun to decline in New Zealand, and has been classified as having the "At Risk, Declining" conservation status under the New Zealand Threat Classification System. ==See also==