Numerous species of small invertebrates and even fish can be found living in the holdfasts of Macrocystis pyrifera. In a study in M. pyrifera forests around Navarino Island, Chile, Ojeda and Santelices (1984) found 42 species of invertebrates and 1 fish living in kelp holdfasts. Five invertebrate phyla were represented, but especially prominent were crustaceans (especially decapods), echinoderms, and molluscs. The authors note that in a similar study in California, over 100 invertebrate taxa, mostly amphipods, polychaetes, and isopods, were found dwelling in M. pyrifera holdfasts (Ghelardi 1971, cited in Ojeda and Santelices 1984).
In giant kelp forests, shade from the canopy of M. pyrifera negatively affects understory algae. Because these algae compete for space with sessile (i.e., stationary) invertebrates, the shade from the giant kelp indirectly benefits the sessile invertebrates. In a study off San Clemente, California (USA), this indirect positive effect turned out to be quite substantial (Arkema et al. 2009).
Hernandez-Carmona et al. (2006) reviewed the literature on long-distance dispersal of giant kelp (Macrocystis pyrifera). Long-distance dispersal is believed to occur via drifting sporophytes. Drifting M. pyrifera sporophytes (kelp rafts) are created following sporophyte detachment from benthic substrates; in California, this occurs primarily during the winter months (November–February). Kept afloat by numerous pneumatocysts (gas-filled bladders), M. pyrifera sporophytes may remain alive and adrift for more than 100 days. Zoospore germination rates remain fairly high even after several months of floating. Based on their investigation of the rate of fertility decline while afloat, Hernandez-Carmona et al. (2006) conclude that the reproductive longevity of drifting M. pyrifera sporophytes is long enough to support effective long-distance dispersal of over 1000 km. Drifter reproductive viability is maintained at relatively high levels so long as enough biomass is present to promote the production of spore-bearing sori.
Kelp rafts disperse kelp, but they may also disperse an enormous diversity of kelp forest fauna among isolated kelp forests. Some pelagic species with larval dispersal may even complete a cycle of larval settlement, growth, and reproduction before kelp rafts sink or wash ashore (Hobday 2000).
Macrocystis is the most widely distributed kelp genus in the world, with an amphitropical distribution that spans the west coasts of North and South America and also includes Argentina, South Africa, Australia, New Zealand, and most of the sub-Antarctic islands (Neushul 1971, cited in Hernandez-Carmona et al. 2006). Macrocystis pyrifera forms dense forests in many parts of the world, including parts of the northeast Pacific (but not north of San Francisco, California), the southern shores of South America, many Southern Ocean islands, and isolated areas of South Africa, Australia, and New Zealand (Dayton 1985).
According to Abbot and Hollenberg (1976), M. pyrifera occurs on the west coast of North America from Alaska to Baja California.
Kelp forests experience irregular cycles of growth and deforestation. The biotic (biological) and abiotic (physical) factors driving these changes, both "natural" and anthropogenic, have been the subject of much study by ecologists over many decades and in several parts of the world (see, e.g., Dayton et al. 1998). Steneck et al. (2002) review the major factors controlling the development and disappearance of kelp forests, including M. pyrifera forests. They find that between about 40 and 60 degrees north in both hemispheres, well developed kelp forests are most threatened by herbivory, usually by sea urchins. Overfishing and loss of apex vertebrate predators such as sea otters have repeatedly led to increased herbivore (e.g., urchin) populations and consequently deforestation of kelp forests. In southern California, however, home to extensive forests of M. pyrifera, widespread deforestation is rare. Steneck et al. suggest that this relative stability may result from functional redundancies among both predators and herbivores (in contrast to less species-rich regions to the north).
Nearly all kelp forests occur on hard substrata, an exception being Macrocystis pyrifera in some protected fjords in Chile and New Zealand (Dayton 1985). Abbot and Hollenberg (1976) describe the habitat of this species as "on rocky substrata or occasionally anchoring in coarse sand, subtidal (6-20 (80) m)"
The life history of Macrocystis pyrifera involves a complex alternation of generations between large diploid (spore-producing) sporophytes and microscopic haploid (gamete-producing) gametophytes. Meiosis within the sporangium of the diploid sporophyte produces haploid microscopic flagellated zoospores, which settle and germinate into male or female haploid gametophytes. These gameteophytes produce male and female gametes, which combine via fertilization to form diploid sporophytes which then grow from microscopic to macroscopic size (Dayton 1985; Ladah and Zertuche-Gonzalez 2007). Based on studies of M. pyrifera in La Jolla, California (USA), Neushul (1963) estimated the minimum time required to complete the sexual cycle to be 12 to 14 months.
Macrocystis pyrifera produces spores year round, but with seasonal peaks (Reed et al. 1997).
In a study near San Diego, California (USA), maximum lifespan recorded for a Macrocystis pyrifera plant was about five years (Dayton et al. 1992).
Dayton et al. (1998) and Steneck et al. (2002) review (and speculate about) how human activities (hunting marine mammals, harvesting urchins, polluting the seas, etc.) from prehistoric times to the present have likely impacted the dynamics of kelp forests, including M. pyrifera forests, in several geographic regions.
Macrocystis pyrifera plants consist of a holdfast, which anchors the plant to the substrate, bundles of fronds analogous to the branches and leaves of a land plant, and reproductive structures called sporophylls located just above the holdfast (Tegner et al. 1996). Like most kelp species, M, pyrifera is perennial. It may exceed 45 m in length and the holdfasts of old plants are conical and may reach a meter in height (Abbot and Hollenberg 1976). Macrocystis pyrifera occurs in extensive stands (kelp forests) throughout its range, providing the basis for biologically diverse ecological communities.
Macrocystis is a monospecific genus[3] 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;[4] stipes/fronds within a whole individual undergo senescence, where each frond may persist for approximately 100 days.[5] The genus is found widely in subtropical, temperate, and sub-Antarctic oceans of the Southern Hemisphere (e.g. Chile, New Zealand, Australia, Falkland Islands, Auckland Islands, etc.) and in the northeast Pacific from Baja California to Sitka, Alaska. Macrocystis is often a major component of temperate kelp forests.
Despite its appearance, it is not a plant; it is a heterokont. 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, as 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.
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).[6] The stipes arise from a holdfast and branch three or four times from near the base. Blades develop at irregular intervals along the stipe.[7][8] M. pyrifera grows to over 45 m (150 ft) long.[8][9] The stipes are unbranched and each blade has a gas bladder at its base.[10]
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 50 m (160 ft) 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.[11]: 201 The stalks arise from a basal meristem, with as many as 60 stalks in older well protected plants.[12] Blades develop at irregular intervals along the stipe, with a single pneumatocyst (gas bladder) at the base of each blade.[10] At the base of each stalk a cluster of blades that lack pneumatocysts, instead they develop small sacks on the blade that release the biflagellated zoospores these are the sporophylls.[12]
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 1 centimetre (0.39 in) wide to 30 metres (98 ft) long) come from the rhizome which is up to 0.1 metres (3.9 in) at the widest. Periodically 5 centimetres (2.0 in) wide and 35 centimetres (14 in) 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.[13] It grows to only 6 m (20 ft) 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.[8][14] 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.[15] The species can be found on rock and on sheltered open coasts.[15]
.jpg)
M. pyrifera growing in the Channel Islands
Macrocystis integrifolia
Giant kelp
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.[16]
Females release their eggs (oogonia) along with a pheromone, the lamoxirene.[17][18] 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.[1][19][20] It prefers water about 7 metres (23 ft) to 10 metres (33 ft) deep and exposed to the open sea and normal salinities, yet sheltered from full wave action.[21]
Macrocystis integrifolia alternates heteromorphic phases from a macroscopic sporophyte to dioecious microscopic gametophytes.[20] It has been studied as a plant fertilizer, increasing bean yields up to 24% and chemical studies indicate presence of phytohormone-like substances.[22]
.jpg)
Macrocystis pyrifera is one of the fastest-growing organisms on Earth.[23][24]: 8 They can grow at a rate of 60 cm (2 ft) a day to reach over 45 m (150 ft) long in one growing season.[8][25][26]
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.[7][27]: 226–227
Macrocystis typically grow forming extensive beds, large "floating canopies", on rocky substrata between the low intertidal.[8][16] It was harvested by barges which used large blades to harvest up to 300 tons a day along the coast of California.[28]
Macrocystis pyrifera is found in North America (Alaska to California), South America, South Africa, New Zealand, and southern Australia.[29] It thrives in cooler waters where the ocean water temperature remains mostly below 21 °C (70 °F).[26] 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".[8] 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.[30]: 158
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.[31][32]
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.[30]: 151–153 [11]: 204 Translocation of nutrients along the stipe may be as rapid as 60 cm (24 in) per hour.[27] 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.
Initially, 17 species were described within the genus Macrocystis.[33] In 1874, Hooker, following blade morphology, put them all under the same taxon, Macrocystis pyrifera.[34] 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.[35] In 2009 and 2010, however, two studies that used both morphological[36] and molecular[3] assessments demonstrate that Macrocystis is monospecific (as M. pyrifera), which is currently accepted by the phycological community (see AlgaeBase).[37]
Although Macrocystis is a monospecific genus, some split it into the four morphs, or sub-species, described below, following pre-2010 taxonomy:[38][39]
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.[16]
Macrocystis pyrifera has been utilized for many years as a food source;[44][45] it also contains many compounds such as iodine, potassium, other minerals vitamins and carbohydrates and thus has also been used as a dietary supplement.[46][47]: 58 In the beginning of the 20th century California kelp beds were harvested as a source for soda ash.[44][48][49] 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.[48][49] However the commercial production of M. pyrifera never became reality. With the end of the energy crisis and the decline in prices of alginates, the research into farming Macrocystis also declined.[45]
The demand for M. pyrifera is increasing due to the newfound uses of these plants such as fertilizers, cultivation for bioremediation purposes, abalone and sea urchin feed.[45] There is current research going into utilizing M. pyrifera as feed for other aquaculture species such as shrimps.[50] Recently, M. pyrifera has been examined as a possible feedstock for conversion into ethanol for biofuel use.[51]
In recent years, the kelp forests have decreased dramatically throughout Japan, Chile, Korea, Australia and North America.[52] 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.[53]
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.[54] In California, El Niño also brought along a population bloom of purple sea urchins which feed on the giant kelp.[55] By the late 2000s most of the onshore giant kelp in California was practically nonexistent.
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.[56] 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.[57] Some of this loss was attributed by locals to the harvesting of the forests by Alginates Australia, which opened its factory near Triabunna in 1963, shutting down operations 10 years later as uneconomical. However, expert in marine ecosystems Craig Johnson says that the loss of the forests "is almost certainly the result of climate change". Water temperatures along the east coast of Tasmania have been rising at nearly four times the average rate globally. The EAC brings warmer waters, which are also nutrient-poor compared to the previously usual cold water around the coast. Common kelp (Ecklonia radiata) is better at nitrogen storage than giant kelp, so has been taking over the areas formerly occupied by giant kelp.[58]
Macrocystis pyrifera has become Australia’s first federally-listed endangered marine community.[58][59] 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.[52] Scientists had built 28 artificial reefs off Maria Island by 2019, and were hopeful of bringing the kelp forests back.[57]
{{cite web}}: CS1 maint: url-status (link) 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 (e.g. Chile, New Zealand, Australia, Falkland Islands, Auckland Islands, etc.) and in the northeast Pacific from Baja California to Sitka, Alaska. Macrocystis is often a major component of temperate kelp forests.
Despite its appearance, it is not a plant; it is a heterokont. 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, as 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.
