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 (air bladders) at the base of its blades. Sporophytes, the macroscopic forms, are perennial and the individual may live for up to three years;W.J. North (1971) The biology of giant kelp beds. 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, but 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 long at a rate of as much as 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.
Description Macrocystis is a monospecific genus; the sole species is M. pyrifera. Some individuals are so huge that they may grow to up to 60 m (200 ft) long.C. van den Hoek, D.G. Mann and H.M. Jahns (1995) Algae An Introduction to Phycology. Cambridge University Press, Cambridge. The stipes arise from a holdfast and branch three or four times from near the base. Blades develop at irregular intervals along the stipe.Mondragon, Jennifer and Mondragon, Jeff (2003) Seaweeds of the Pacific Coast. Sea Challengers, Monterey, California. I.A. Abbott and G.J. Hollenberg (1976) Marine Algae of California. Stanford University Press, California. M. pyrifera grows to over 45 m (150 ft) long.A.B. Cribb (1953) Macrocystis pyrifera (L.) Ag. in Tasmanian waters Australian Journal of Marine and Freshwater Research, Vol 5, issue 1. The stipes are unbranched and each blade has a gas bladder at its base.Kain, J M (1991) Cultivation of attached seaweeds in Guiry, M D and Blunden, G (1991) Seaweed Resources in Europe: Uses and Potential. John Wiley and Sons.
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.Hoek, C van den; D G Mann & H M Jahns. (1995) Algae: An Introduction to Phycology. Cambridge: Cambridge University Press. 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. At the base of each stalk is a cluster of blades that lack pneumatocysts; instead they develop small sacks on the blade that release the biflagellated zoospores: these are the sporophylls.
The smaller morphs, formerly identified as Macrocystis integrifolia, have deep brown color on flattened rhizomes which are profusely dichotomously branched. Each is attached by branched root-like structures coming out of the sides of the rhizomes. Slender main stipes (about wide to long) come from the rhizome which is up to at the widest. Periodically wide and long flattened leaf-like branches derive from the stipe. They have furrowed surfaces and taper gradually, but then have an oval or rounded float where attached to the stipe. The blade-like branches have notched denticulate edges leading to the terminal blade at the tip of the stipe, which is separated by several smaller branches. Phylum: Phaeophyta, Class: Phaeophyceae, Order: Laminariales, Family: Lessoniaceae, Macrocystis integrifolia (Bory), Pearson College UWC. Retrieved 6 February 2013 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.AlgaeBase: Species: Macrocystis integrifolia 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.
Life cycle The macroscopic sporophyte has many specialized blades growing near the holdfast called sporophylls. 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.
What was previously known as Macrocystis integrifolia is found on intertidal rocks or shallow subtidal rocks along the Pacific coast of North America from British Columbia to California.Abbott, I. A. & G. J. Hollenberg. (1976) Marine Algae of California. California: Stanford University Press. Macrocystis integrifolia Bory, DeCew's Guide to the Seaweeds of British Columbia, Washington, Oregon, and Northern California, Center for Phycological Documentation, University Herbarium, University of California, Berkeley, 2002. 13 July 2007 It prefers water about to deep and exposed to the open sea and normal salinities, yet sheltered from full wave action.The Race Rocks Taxonomy, Macrocystis integrifolia, Pearson College UWC. Retrieved 6 February 2013
Macrocystis integrifolia alternates heteromorphic phases from a macroscopic sporophyte to dioecious microscopic gametophytes. It has been studied as a plant fertilizer, increasing bean yields up to 24% and chemical studies indicate presence of phytohormone-like substances.Temple, W. D., A. A. Bomke, Effects of kelp (Macrocystis integrifolia and Ecklonia maxima) foliar applications on bean crop growth, Plant and Soil, June 1989, Volume 117, Issue 1, pp. 85-92 (paywall)
Growth
Macrocystis pyrifera is one of the fastest-growing organisms on Earth.Fenner, Bob The Brown AlgaeWhite, L P & L G Plaskett, (1982) Biomass as Fuel. Academic Press. They can grow at a rate of a day to reach over long in one growing season.Cribb, A B. (1953) Macrocystis pyrifera (L.) Ag. in Tasmanian waters Australian Journal of Marine and Freshwater Research 5 (1):1-34.Davis, Chuck. (1991) California Reefs. San Francisco, California: Chronicle Books.
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.Prescott, G W. (1968) The Algae: A Review. Boston: Houghton Mifflin Company.
Ecology
Macrocystis typically grow forming extensive beds, large "floating canopies", on rocky substrata between the low intertidal. It was harvested by barges which used large blades to harvest up to 300 tons a day along the coast of California.Smith, G.M. 1955. Cryptogamic Botany. Volume 1. Algae and Fungi. McGraw-Hill Book Company, Inc.
Macrocystis pyrifera is found in North America (Alaska to California), South America, South Africa, New Zealand, and southern Australia.AlgaeBase: Species: Macrocystis pyrifera It thrives in cooler waters where the ocean water temperature remains mostly below . The species is also found near Tristan da Cunha in the Mid-South Atlantic Ocean.
Where the bottom is rocky and affords places for it to anchor, giant kelp forms extensive kelp beds with large "floating canopies". When present in large numbers, giant kelp forms kelp forests that are home to many marine species that depend upon the kelp directly for food and shelter, or indirectly as a hunting ground for prey. Both the large size of the kelp and the large number of individuals significantly alter the availability of light, the flow of ocean currents, and the chemistry of the ocean water in the area where they grow.Lobban, C S & P J Harrison. (1994) Seaweed Ecology and Physiology. Cambridge: Cambridge University Press.
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. Translocation of nutrients along the stipe may be as rapid as per hour. Most translocation occurs to move carbon-rich photosynthate, and typically transfers material from mature regions to actively growing regions where the machinery of photosynthesis is not yet fully in place. Translocation also moves nutrients downward from light-exposed surface fronds to sporophylls (reproductive fronds) at the base of the kelp, where there is little light and thus little photosynthesis to produce food.
Recent research has shown that Arctic kelp forests can steadily increase pH levels by 0.15 units over a 10-day period during extended daylight conditions in summer. This pH regulation, driven by sustained photosynthetic activity, helps mitigate the harmful effects of ocean acidification and supports calcifying organisms such as bivalves and sea urchins.
Species Initially, 17 species were described within the genus Macrocystis.W.J. North (1971) Review of Macrocystis biology. In Biology of Economic Algae, I. Akatsuka (ed.). Hague: Academic Publishing, 447–527. In 1874, Hooker, following blade morphology, put them all under the same taxon, Macrocystis pyrifera.J.D. Hooker (1874) The Botany of the Antarctic Voyage of H.M. Discovery Ships Erebus and Terror. I. Flora Antarctica. London: Reeve Brothers. 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 assessments demonstrate that Macrocystis is monospecific (as M. pyrifera), which is currently accepted by the phycological community (see AlgaeBase).AlgaeBase: Genus: Macrocystis
Morphs Although Macrocystis is a monospecific genus, some split it into the four morphs, or sub-species, described below, following pre-2010 taxonomy: