Caulerpa | |
---|---|
Caulerpa prolifera | |
Scientific classification | |
(unranked): | Viridiplantae |
Division: | Chlorophyta |
Class: | Ulvophyceae |
Order: | Bryopsidales |
Family: | Caulerpaceae |
Genus: | Caulerpa J.V. Lamouroux, 1809 |
Type species | |
Caulerpa prolifera (Forsskål) J.V. Lamouroux, 1809 [1] | |
Species [2] | |
About 101 |
Caulerpa is a genus of seaweeds in the family Caulerpaceae (among the green algae). They are unusual because they consist of only one cell with many nuclei, making them among the biggest single cells in the world.
Referring to the crawling habit of its thallus, the name means 'stem (that) creeps', from the Ancient Greek kaulos ( καυλός , ‘stalk’) and herpo ( ἕρπω , ‘to creep’). [3]
First described by Jean Vincent Lamouroux in 1809, Caulerpa is the only genus under the family Caulerpaceae, from the order Bryopsidales, class Ulvophyceae, and phylum Chlorophyta. [4] Through the use of tufA gene sequencing, it was revealed that Pseudochlorodesmis F. Børgesen was a sister clade of Caulerpa. [5] Cremen et al. [6] proposed a new classification scheme in Bryopsidales, wherein Caulerpaceae and Halimedaceae were described as sister families.
Species discrimination via morphology-based identification is often hampered by the high degree of variation among traits. Thus, several species are often misidentified without the use of molecular analyses. [7] As of 2019, there are 101 accepted species, with 40 varieties and 67 forms. [8] [9]
Caulerpa species support their large cell size by having the cytoplasm circulate constantly, supported by a network of microtubules. This behavior was known in 1967. [10]
The cytoplasm does not leak out when the cell is cut. Regeneration is directional, with rhizoids at the bottom and fronds at the top. [11]
The genus produces a number of secondary metabolites thought to be related to its toxicity and peppery taste. These include the red pigment alkaloid caulerpin and its derivative caulerchlorin and the amine mixture caulerpicin.
The genus Caulerpa exhibits several different growth forms. They possess a stolon with rhizoids which grow downward, anchoring the plant to the substrate. The stolons support upright fronds or leaves known as assimilators. The structure of the assimilator may be ligulate (leaf-like, e.g. Caulerpa prolifera), or they may have a central axis known as a rachis. The rachis may have lateral branchlets known as ramuli which themselves come in different forms (terete, turbinate, clavate, peltate, falcate, vesiculate) and arrangements: distichous - ramuli are arranged evenly opposite each other (e.g. Caulerpa taxifolia), irregular - vesiculate ramuli with no distinct arrangement (e.g. Caulerpa racemosa), verticillate - whorled ramuli (e.g. Caulerpa cuppresoides). [4]
Caulerpa is coenocytic, meaning it has a multinucleate thallus organization. It is also siphonous, meaning unlike other algae, the thallus and the nuclei are not separated by cell walls. They are instead one long mass of protoplasm surrounded by a single cell wall. [12] The genus also possesses trabeculae, which are inward growing cell wall extensions that pass through the central lumen of siphons. It is hypothesized that these provide the thallus with structural support, facilitate diffusion to the inner cytoplasm, and can possibly help in determining cell shape - which may contribute to the diversity of growth forms found in the genus. [13]
Caulerpa is mostly found in tropical regions, however its distribution may also extend up to temperate locations. Diversity is highest in the Caribbean and the Indo-Malay region, as well as in southern Australia, where a majority of Caulerpa species are endemic. [14] [4]
The genus is typically found in shallow intertidal zones and can reach up to depths of 100 meters. They are known to be able to adapt and thrive in different environmental conditions, which contributes to their potential for becoming invasive species. Some of their traits include having a high tolerance for a wide range of temperatures, their capacity for asexual reproduction through rhizoid extension and fragmentation, their fast growth rate, as well as their capacity for nutrient intake from sediments through their rhizoids. [4] [15] This last trait gives them a competitive edge over other macroalgal species who mainly absorb nutrients from the water column. [16]
Many studies on the life cycle of Caulerpa have been found to contradict each other, leading researchers to conclude that it varies with species and geographical region. [4] Earlier research revealed that Caulerpa has a diplontic life cycle with a diploid vegetative phase and haploid biflagellate gametes. However, it was later found that ploidy status and genome size can vary within and between species. [17] [18] [19]
Some species of Caulerpa are edible. The two most commonly eaten are Caulerpa lentillifera and Caulerpa racemosa , both called "sea grapes" in English. Both are traditionally harvested in the wild and sold in local markets in Southeast Asia, Oceania, and East Asia. They are eaten raw in salads and have a characteristic "sea" flavor and a crunchy texture. [20]
Both species are cultivated in aquaculture. Their cultivation began in the 1950s in Cebu, Philippines, after accidental introduction of C. lentillifera to fish ponds. [21] Cultivation of C. lentillifera continued in Japan in 1986, where it was cultivated in tanks in the tropical waters of Okinawa. [22] Commercial cultivation has since spread to other countries, including Vietnam, Taiwan, and China (in Fujian and Hainan). Most are for domestic consumption, but they are also exported to Japan. [23]
Cultivation of Caulerpa is convenient because they can propagate through fragmentation. There are several farming techniques being used to cultivate Caulerpa, which typically involve tying fragments to different types of infrastructure. Many Pacific countries such as Japan, Philippines, Vietnam, and Samoa use the off-bottom method, where the seaweeds are grown a few meters above the ground on cages or trays. [24] The bottom-planting method is also used in the Philippines, and involves growing the Caulerpa on a substrate. [25] Land-based raceways in hatchery-type facilities offer a more controlled environment for cultures, and have been used more in recent years. [4] [24]
Caulerpa contains a high amount of iron (up to 81.3 mg per 100 g of dry matter in C. racemosa), [26] magnesium, and calcium. [24] Water content is species-specific and generally ranges from 75 - 94%. [24] The genus is known to have a high bioaccumulation rate, [27] [20] [28] which can make it less than ideal to consume on a regular basis. Carbohydrate content can range from 3.6 - 83.2% of dry matter depending on the species. [24] The main pigments of Caulerpa are chlorophyll a and b. [20] It has a high diversity of chemical compounds which have pharmaceutical potential. Although the genus is known to exhibit high toxicity, it was found to be of low risk to humans. [29]
Aside from being a source of food, Caulerpa has several uses from bioremediation, to fertilizer, and health and wellness. [4] The anti-oxidant compounds of Caulerpa have been well-studied, and these are used in treating various diseases and health conditions such as cancer and cardiovascular disorders. [26] [30] [31] [32] Caulerpa has been shown to be effective in filtering water used in culturing fish, mollusks, and shrimp [33] (in particular C. lentillifera [34] ). The use of Caulerpa as a biofertilizer has also been studied particularly in India, where fertilizers composed of 25% Caulerpa extracts enhanced the growth and reduced the total sugar content, among other things, of Vigna mungo. [35] [36] [37]
Another species, Caulerpa taxifolia , has become an invasive species in the Mediterranean Sea, Australia and southern California (where it has since been eradicated). In U.S. waters, the Mediterranean strain of Caulerpa taxifolia is listed as a federal noxious weed, under the Plant Protection Act. The Aquatic Nuisance Species Taskforce has also created a National Management Plan for the Genus Caulerpa. The state of California also prohibits possession of nine different species of Caulerpa.
It is thought that Caulerpa species have such invasive properties in these regions due to their capability to thrive in temperate waters, along with their freedom from natural predators. Most Caulerpa species evolved in tropical waters, where herbivores have immunity to toxic compounds (mainly caulerpicin) within the alga. Temperate water herbivores have no natural immunity to these toxins, allowing Caulerpa to grow unchecked if introduced to temperate waters.
C. racemosa has recently been found in waters around Crete, where it is thought to have contributed to a significant reduction in fisheries. The alga has invaded the area from the warmer waters of the Red Sea.
C. cylindracea , which is native to Australia, has also become an invasive species in the Mediterranean. [38]
Exotic seaweeds Caulerpa brachypus and Caulerpa parvifolia have been found in New Zealand waters at Great Barrier Island (Aotea) and Great Mercury Island (Ahuahu). [39]
Caulerpa is common in the aquarium hobby as a nitrate absorber because of its rapid growth under relatively adverse conditions. It may also be used in refugiums for a long-term nitrite absorber. Many introductions of invasive Caulerpa to the wild are thought to have occurred via aquarium dumping although there is no proof that this is so. For this reason, some aquarium hobbyists have begun using Chaetomorpha or an algae scrubber instead. [40] [41]
The species currently recognized are: [1]
Chlorophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it is a highly paraphyletic group of all the green algae within the green plants (Viridiplantae) and thus includes about 7,000 species of mostly aquatic photosynthetic eukaryotic organisms. In newer classifications, it is the sister clade of the streptophytes/charophytes. The clade Streptophyta consists of the Charophyta in which the Embryophyta emerged. In this latter sense the Chlorophyta includes only about 4,300 species. About 90% of all known species live in freshwater. Like the land plants, green algae contain chlorophyll a and chlorophyll b and store food as starch in their plastids.
Caulerpa taxifolia is a species of green seaweed, an alga of the genus Caulerpa, native to tropical waters of the Pacific Ocean, Indian Ocean, and Caribbean Sea. The species name taxifolia arises from the resemblance of its leaf-like fronds to those of the yew (Taxus).
Acetabularia is a genus of green algae in the family Polyphysaceae. Typically found in subtropical waters, Acetabularia is a single-celled organism, but gigantic in size and complex in form, making it an excellent model organism for studying cell biology. In form, the mature Acetabularia resembles the round leaves of a nasturtium, is 4 to 10 centimetres tall and has three anatomical parts: a bottom rhizoid that resembles a set of short roots; a long stalk in the middle; and a top umbrella of branches that may fuse into a cap. Unlike other giant unicellular organisms, which are multinucleate, members of this genus possess a single nucleus located in the rhizoid, which allows the cell to regenerate completely if its cap is removed. The caps of two Acetabularia may also be exchanged, even from two different species. In addition, if a piece of the stem is removed, with no access to the nucleus in the rhizoid, this isolated stem piece will also grow a new cap.
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 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.
Caulerpa racemosa is a species of edible green alga, a seaweed in the family Caulerpaceae. It is commonly known as sea grapes and is found in many areas of shallow sea around the world. Despite the name, it is not related to grapes. There are a number of different forms and varieties, and one that appeared in the Mediterranean Sea in 1990, which is giving cause for concern as an invasive species.
Halimeda is a genus of green macroalgae. The algal body (thallus) is composed of calcified green segments. Calcium carbonate is deposited in its tissues, making it inedible to most herbivores. However one species, Halimeda tuna, was described as pleasant to eat with oil, vinegar, and salt.
Codium is a genus of edible green macroalgae under the order Bryopsidales. The genus name is derived from a Greek word that pertains to the soft texture of its thallus. One of the foremost experts on Codium taxonomy was Paul Claude Silva at the University of California, Berkeley. P.C. Silva was able to describe 36 species for the genus and in honor of his work on Codium, the species C. silvae was named after the late professor.
Udotea is a genus of green algae in the family Udoteaceae.
Turbinaria is a genus of brown algae (Phaeophyceae) found primarily in tropical marine waters. It generally grows on rocky substrates. In tropical Turbinaria species that are often preferentially consumed by herbivorous fishes and echinoids, there is a relatively low level of phenolics and tannins.
Bifurcaria is a genus of brown algae seaweeds found on rocky North American and European shores and tidepools of the Atlantic Ocean. One species is also found on the shores of the Galapagos Islands in the Pacific Ocean.
Gelidium is a genus of thalloid red algae comprising 134 species. Its members are known by a number of common names.
Caulerpa lentillifera or sea grape is a species of ulvophyte green algae from coastal regions in the Asia-Pacific. This seaweed is one of the favored species of edible Caulerpa due to its soft and succulent texture. It is traditionally eaten in the cuisines of Southeast Asia, Oceania, and East Asia. It was first commercially cultivated in the Philippines in the 1950s, followed by Japan in 1968. Both countries remain the top consumers of C. lentillifera. Its cultivation has since spread to other countries, including Vietnam, Taiwan, and China. C. lentillifera, along with C. racemosa, are also known as sea grapes or green caviar in English.
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 brown algae. Seaweeds are also harvested or cultivated for the extraction of polysaccharides such as alginate, agar and carrageenan, gelatinous substances collectively known as hydrocolloids or phycocolloids. Hydrocolloids have attained commercial significance, especially in food production as food additives. The food industry exploits the gelling, water-retention, emulsifying and other physical properties of these hydrocolloids.
Sargassum muticum, commonly known as Japanese wireweed or japweed, is a large brown seaweed of the genus Sargassum. It is an invasive seaweed with high growth rate. It has an efficient dispersion thanks to its floats.
Ice-ice is a disease condition of seaweed. Ice-ice is caused when changes in salinity, ocean temperature and light intensity cause stress to seaweeds, making them produce a "moist organic substance" that attracts bacteria in the water and induces the characteristic "whitening" and hardening of the seaweed's tissues. Bacteria involved include those in the Vibrio-Aeromonas and Cytophaga-Flavobacteria complexes. The bacteria lyse epidermal cells and chloroplasts, turning the seaweed tissue white. The disease is known from seaweeds including Kappaphycus alvarezii and Eucheuma denticulatum, economically important sources of carrageenan. In countries where seaweed is harvested as a crop, ice-ice can wreak havoc on yields. Zamboanga, Philippines, had an outbreak of ice-ice in 2004, and Bali, Indonesia, experienced an outbreak in 2009. A rise in surface sea temperatures of 2–3 degrees Celsius can trigger ice-ice outbreaks.
Caulerpa prolifera is a species of green alga, a seaweed in the family Caulerpaceae. It is the type species of the genus Caulerpa, the type location being Alexandria, Egypt. It grows rapidly and forms a dense mass of vegetation on shallow sandy areas of the sea.
Caulerpa cylindracea is a species of seaweed in the Caulerpaceae family.
Dictyota is a genus of brown seaweed in the family Dictyotaceae. Species are predominantly found in tropical and subtropical seas, and are known to contain numerous chemicals (diterpenes) which have potential medicinal value. As at the end of 2017, some 237 different diterpenes had been identified from across the genus.
Ulva australis, the southern sea lettuce, is a species of bright green coloured seaweed in the family Ulvaceae that can be found in waters around Australia and was first described by Swedish botanist Johan Erhard Areschoug. It is an edible green algae, although sometimes designated as a seaweed. General characteristics of Ulva australis include a smooth surface, distromatic blades, lobed fronds, and thallus color from dark green to light grass green. It can be either free floating or attached by a single holdfast. Its cells appear to be irregularly arranged, have rounded edges, and have shapes such as rectilinear, square, and pentagonal.
Susan Brawley is an American marine ecologist at the University of Maine known for her research on algae, especially algal reproduction. She was elected a fellow of the American Association for the Advancement of Science in 2012.
This tropical alga is the world's largest single-celled organism. Yet it di›erentiates into a complex structure of leaves, stems and roots.