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Aquaculture of giant kelp, ''
Macrocystis pyrifera ''Macrocystis pyrifera'', commonly known as giant kelp or bladder kelp, is a species of kelp (large brown algae), and one of four species in the genus ''Macrocystis''. Despite its appearance, it is not a plant; it is a heterokont. Giant kelp is ...
'', is the cultivation of kelp for uses such as food,
dietary supplements A dietary supplement is a manufactured product intended to supplement one's diet by taking a pill (pharmacy), pill, capsule (pharmacy), capsule, tablet (pharmacy), tablet, powder, or liquid. A supplement can provide nutrients either extr ...
or potash. Giant kelp contains
iodine Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
,
potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
, other minerals vitamins and
carbohydrates In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or may ...
.


History

At the beginning of the 20th century California kelp beds were harvested for their
potash Potash () includes various mined and manufactured salts that contain potassium in water-soluble form.
. Commercial interest increased during the 1970s and the 1980s due to the production of
alginate Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. With metals such as sodium and calcium, its salts are known as alginates. Its colou ...
s, and also for biomass production for animal feed due to the
energy crisis An energy crisis or energy shortage is any significant bottleneck in the supply of energy resources to an economy. In literature, it often refers to one of the energy sources used at a certain time and place, in particular, those that supply n ...
. However commercial production for ''M. pyrifera'' never developed. With the end of the energy crisis and the decline in
alginate Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. With metals such as sodium and calcium, its salts are known as alginates. Its colou ...
prices, research into farming ''
Macrocystis ''Macrocystis'' is a monospecific genus of kelp (large brown algae). 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 indiv ...
'' declined. The supply of ''M. pyrifera'' for alginate production relied heavily on restoration and management of natural beds during the early 1990s. Other functions such as substrate stabilization were explored in California, where the “Kelp bed project” transplanted 3-6m adult specimens to increase the stability of the harbor and promote diversity.


Twenty-first century

Research is investigating its use as feed for other
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
species such as fish.
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
and
Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
are the largest producers of aquatic plants, each producing over 300,000 tonnes in 2007. How much of this total can be attributed to ''M. pyrifera'' is unclear. Both countries culture a variety of species; in Chile 50% of the production involves ''Phaeophytes'' and the other 50% is ''
Rhodophytes Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...
''. China produces a larger variety of seaweeds including chlorophytes. Experiments in Chile are exploring hybrids of ''M. pyrifera'' and '' M. integrifolia''. Kelp farming development has been ongoing in Oregon and British Columbia. Startups have begun leasing water in Alaska to cultivate ''M. Pyrifera'' at a large scale.


Kelp forest restoration in California

In the 2010s, Northern California lost 95% of its kelp ecosystems due to marine heatwaves. Kelp bed recovery efforts in California are primarily focusing on
sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...
removal, both by scuba divers, and by
sea otters The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of the weasel family, but among the smalle ...
, which are natural predators. A brown algae, ''
Sargassum horneri ''Sargassum horneri'' is a species of brown macroalgae that is common along the coast of Japan and Korea. It is an annual algae which has a varying fertile season along the coast. In Wakasa Bay it began to grow in early autumn through winter, bec ...
'', an invasive species first spotted in 2003, has also been a concern. Researchers at the Bodega Marine Laboratory of UC Davis are developing replanting strategies, and volunteers of the Orange County Coastkeeper group are replanting giant kelp. Humboldt State University began cultivating bull kelp in its research farm in 2021. Research efforts at the state level to prevent kelp forest collapse in California were announced in July 2020. At the federal level, H.R. 4458, the Keeping Ecosystems Living and Productive (KELP) Act, introduced July 29, 2021, seeks to establish a new grant program within
NOAA The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...
for kelp forest restoration.


Methods

The most common method of cultivating ''M. pyrifera'' was developed in China in the 1950s. It is called the long line cultivation system, where the sporelings are produced in a cooled water greenhouse and then planted in the ocean attached to long lines.Mariculture of Seaweeds The depth at which they are grown varies. This species alternates generations in its life cycle, cycling between a large
sporophyte A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote pr ...
and a microscopic
gametophyte A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...
. The sporophyte is harvested as seaweed. The mature
sporophytes A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote pro ...
form the
reproductive The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...
organs called sori. They are found on the underside of the leaves and produce the motile
zoospores A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mor ...
that germinate into the gametophyte. To induce
sporulation In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...
, plants are dried for up to twelve hours and placed in a seeding container filled with
seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...
of about 9-10 °C; salinity of 30% and a pH of 7.8-7.9.
Photoperiod Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...
is controlled during sporulation and growth phases. A
synthetic Synthetic things are composed of multiple parts, often with the implication that they are artificial. In particular, 'synthetic' may refer to: Science * Synthetic chemical or compound, produced by the process of chemical synthesis * Synthetic o ...
twine of about 2 – 6mm in diameter is placed on the bottom of the same container after sporulation. The released
zoospores A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mor ...
attach to the twine and begin to germinate into male and female
gametophytes A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the sex ...
. Upon maturity these gametophytes release sperm and egg cells that fuse in the water column and attach themselves to the same substrate as the gametophytes (the twine). These plants are reared into young sporophytes for up to 60 days. These strings are either wrapped around or are cut up into small pieces and attached to a larger diameter cultivation rope. The cultivation ropes vary, but extend approximately 60m with floating
buoy A buoy () is a floating device that can have many purposes. It can be anchored (stationary) or allowed to drift with ocean currents. Types Navigational buoys * Race course marker buoys are used for buoy racing, the most prevalent form of yac ...
s attached. The depths vary. In
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
, ''M. pyrifera'' is cultivated on the surface with floating buoys attached every 2-3m and the ends of the rope attached to a wooden peg anchored to the substrate. Individual ropes are usually hung at 50 cm intervals. In Chile ''M. pyrifera'' is grown at a depth of 2m using buoys to keep the plants at a constant depth. These are then let alone to grow until harvest. Problems that afflict this method include management of the transition from spore to gametophyte and
embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
nic sporophyte which are done on a terrestrial facility with careful control of water flow, temperature, nutrients and light. The
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
ese use a forced cultivation method where 2 years of growth is achieved within a single growing season by controlling inputs. In China a project for offshore/deep water cultivation used various farm structures to facilitate growth, including pumping nutrients from deep water into the beds. The greatest benefit for this approach was that the algae were released from size constraints of shallow waters. Issues with operational and farm designs plagued deep water cultivation and ended further exploration.


Harvesting

The duration of cultivation varies by region and farming intensity. This species is usually harvested after two growth seasons (2 years). ''M. pyrifera'' which is artificially cultivated on ropes is harvested by a pulley system that is attached to boats that pull the individual lines on the vessels for cleaning. Other countries such as the US rely primarily on naturally grown ''M. pyrifera,'' use boats to harvest the surface canopy several times per year. This is possible due to fast growth while the vegetative and reproductive parts are left undamaged.


Applications

In the UK, legislation defines giant kelp as a nuisance. Invasive specimens are mechanically removed. The demand for ''M. pyrifera'' centers on
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s,
bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluent ...
and feed for
abalone Abalone ( or ; via Spanish , from Rumsen ''aulón'') is a common name for any of a group of small to very large marine gastropod molluscs in the family (biology), family Haliotidae. Other common name In biology, a common name of a taxon o ...
and
sea urchins Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...
.


Carbon sequestration

Offsetting current carbon emissions would require some 50 trillion trees. An alternative offset would be to cultivate kelp forests. Kelp can grow at 2 feet per day, 30 times faster than terrestrial plants. Planting kelp across 10% of the oceans (4.5 x the area of Australia) could provide the same offset. Additionally, the kelp would support a fish harvest of 2 megatons per year and reduce
ocean acidification Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
. Large scale open ocean forestry would require engineered substrate and added nutrients. A Maine startup, Running Tide Technologies, seeks to grow large quantities of kelp which would sequester carbon in the ocean floor.


Biofuel

A kelp nursery and planting program is under development near Catalina Island. Cultivation techniques using a "kelp elevator" have shown promise for biofuel production using thermochemical liquefaction. This research effort is supported by
ARPA-E ARPA-E, or Advanced Research Projects Agency–Energy is a United States government agency tasked with promoting and funding research and development of advanced energy technologies. It is modeled after the Defense Advanced Research Projects Agenc ...
.


Food

Small-scale cultivation uses kelp as a replacement for
kale Kale (), or leaf cabbage, belongs to a group of cabbage (''Brassica oleracea'') cultivars grown for their edible leaves, although some are used as ornamentals. Kale plants have green or purple leaves, and the central leaves do not form a head ...
. Organizations such as Connecticut-based
GreenWave GreenWave is a North American nonprofit focused on the development of regenerative farming techniques for aquaculture, called "3D ocean farming", to create blue carbon. Their focus is on developing polyculture practices for farming shellfish ...
connect ocean farmers with kelp buyers in an effort to support the ocean greens market.


See also

*
Edible seaweed Edible seaweed, or sea vegetables, are seaweeds that can be eaten and used for culinary purposes. They typically contain high amounts of fiber. They may belong to one of several groups of multicellular algae: the red algae, green algae, and ...
*
Kelp forest Kelp forests are underwater areas with a high density of kelp, which covers a large part of the world's coastlines. Smaller areas of anchored kelp are called kelp beds. They are recognized as one of the most productive and dynamic ecosystems on Ea ...
*
Seaweed farming Seaweed farming or kelp farming is the practice of cultivating and harvesting seaweed. In its simplest form, it consists of the management of naturally found batches. In its most advanced form, it consists of fully controlling the life cycle of ...
*
Ocean fertilization Ocean fertilization or ocean nourishment is a type of technology for carbon dioxide removal from the ocean based on the purposeful introduction of plant nutrients to the upper ocean to increase marine food production and to remove carbon dioxid ...
*
Blue carbon Blue Carbon refers to organic carbon that is captured and stored by the world's oceanic and coastal ecosystems, mostly by algae, seagrasses, macroalgae, mangroves, salt marshes and other plants in coastal wetlands. The term Blue Carbon was coined ...


Notes


References

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Giant Kelp ''Macrocystis pyrifera'', commonly known as giant kelp or bladder kelp, is a species of kelp (large brown algae), and one of four species in the genus ''Macrocystis''. Despite its appearance, it is not a plant; it is a heterokont. Giant kelp is ...