Caulerpa racemosa
Encyclopedia
Caulerpa racemosa is a species
of 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. There are a number of different forms and varieties, and one that appeared in the Mediterranean Sea in 1990 is giving cause for concern as an invasive species
.
, showing different growth forms in different habitats which makes them difficult to identify. Caulerpa racemosa, C. laetevirens and C. peltata form a species complex
. A number of forms and varieties for C. racemosa are listed but further study is needed to clarify their exact phylogenetic relationships.
s which are anchored to the sandy substrate
by rhizoid
s. The branches are a few centimetres apart and can grow to a height of 30 centimetres (11.8 in). Many spherical or ovate side-shoots branch off these and give the seaweed its name of sea grapes. Like other members of the order Bryopsidales
, each C. racemosa plant consists of a single enormous cell with a large number of nuclei. The chloroplast
s containing chlorophyll
are free to migrate from any part of the organism to another and there is a network of fibrous proteins that helps movement of organelle
s.
, possibly an immigrant from the Red Sea
, and this later spread to much of the eastern Mediterranean Sea
. In 1990, a new, larger form with two vertical rows of branches on opposite sides of the stem was found off Libya
. It spread widely, invading much of the Mediterranean Sea and becoming more widespread than the invasive species, Caulerpa taxifolia
. It is known as C. racemosa var. cylindracea and may have originated from Australian waters. In America C. racemosa is found in shallow water in the Caribbean Sea
, around Bermuda
and along the eastern seaboard of America from Florida
to Brazil
.
C. racemosa reproduces vegetatively
by fragmentation. When pieces of the plant get broken off they develop into new plants. Small pieces of tissue only a few millimetres across are capable of doing this.
C. racemosa can also reproduce sexually and in so doing exhibits holocarpy. This means that all the organism's cytoplasm
is used up in the creation of the gamete
s and only a husk remains at the site of the original plant. The plants are monoecious with male and female gametes being produced by the same plant and liberated into the water column where they unite to give spherical zygote
s. These settle and after five weeks produce germ tube
s which elongate and branch to develop into new plants. Mass spawnings
sometimes take place in the Caribbean Sea
and normally do so just before dawn. There were 39 such mass spawnings during a period of 125 days and the days on which they took place showed no relation to the tidal or lunar cycles. The gametes remain motile for about 60 minutes. Mass spawning is advantageous to the plant in increasing the chances of fertilisation. Underwater visibility can be reduced to less than one metre by the green cloud produced in the process. Similar mass spawnings take place in the Mediterranean Sea causing a cloud of green gametes to be released in the water approximately 14 minutes before sunrise.
, of which caulerpenyne is the most abundant. These deter animals from consuming the plants. A study has been done on herbivore
s that graze on meadows of the invasive C. racemosa var. cylindracea in the north west of its range in the Mediterranean. The sea breams Boops boops
and Sarpa salpa
were found to feed on the algae, as did the sea urchin
s Paracentrotus lividus
and Sphaerechinus granularis
. Other herbivore
s also grazed occasionally, but the total amount consumed was compensated for by the rapid growth of the plant and it was considered that these organisms were not likely to play a valuable role in bio-control
of the plant.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of green alga
Green algae
The green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
, a seaweed
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
in the family Caulerpaceae
Caulerpaceae
In taxonomy, the Caulerpaceae are a family of algae, specifically of the Bryopsidales....
. It is commonly known as sea grapes and is found in many areas of shallow sea around the world. There are a number of different forms and varieties, and one that appeared in the Mediterranean Sea in 1990 is giving cause for concern as an invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
.
Taxonomy
There are about 75 species of Caulerpa. Many of them exhibit polymorphismPolymorphism
Polymorphism or dimorphism may refer to:-Biology:* Polymorphism , including:** having multiple phenotypes within a population; the switch that determines which phenotype an individual displays can be genetic or environmental...
, showing different growth forms in different habitats which makes them difficult to identify. Caulerpa racemosa, C. laetevirens and C. peltata form a species complex
Species complex
A species complex is a group of closely related species, where the exact demarcation between species is often unclear or cryptic owing to their recent and usually still incomplete reproductive isolation. Ring species, superspecies and cryptic species complex are example of species complex...
. A number of forms and varieties for C. racemosa are listed but further study is needed to clarify their exact phylogenetic relationships.
Description
A plant of C. racemosa consists of a number of branches linked to stolonStolon
In biology, stolons are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external skeletons.-In botany:...
s which are anchored to the sandy substrate
Substrate (biology)
In biology a substrate is the surface a plant or animal lives upon and grows on. A substrate can include biotic or abiotic materials and animals. For example, encrusting algae that lives on a rock can be substrate for another animal that lives on top of the algae. See also substrate .-External...
by rhizoid
Rhizoid
Rhizoids are thread-like growths from the base or bottom of a plant, found mainly in lower groups such as algae, fungi, bryophytes and pteridophytes, that function like roots of higher plants ....
s. The branches are a few centimetres apart and can grow to a height of 30 centimetres (11.8 in). Many spherical or ovate side-shoots branch off these and give the seaweed its name of sea grapes. Like other members of the order Bryopsidales
Bryopsidales
Bryopsidales is an order of green algae, in the class Bryopsidophyceae.-Characteristics:The thallus is filamentous and much branched and may be packed into a mass. It is coenocytic, having multi-nucleate cells consisting of cytoplasm contained within a cylindrical cell wall...
, each C. racemosa plant consists of a single enormous cell with a large number of nuclei. The chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
s containing chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
are free to migrate from any part of the organism to another and there is a network of fibrous proteins that helps movement of organelle
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....
s.
Distribution
C. racemosa is widely distributed in shallow temperate and tropical seas. In 1926 a new form of the alga was reported off TunisiaTunisia
Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...
, possibly an immigrant from the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
, and this later spread to much of the eastern Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
. In 1990, a new, larger form with two vertical rows of branches on opposite sides of the stem was found off Libya
Libya
Libya is an African country in the Maghreb region of North Africa bordered by the Mediterranean Sea to the north, Egypt to the east, Sudan to the southeast, Chad and Niger to the south, and Algeria and Tunisia to the west....
. It spread widely, invading much of the Mediterranean Sea and becoming more widespread than the invasive species, Caulerpa taxifolia
Caulerpa taxifolia
Caulerpa taxifolia is a species of seaweed, an alga of the genus Caulerpa. Native to the Indian Ocean, it has been widely used ornamentally in aquariums. The alga has a stem which spreads horizontally just above the seafloor, and from this stem grow vertical fern-like pinnae, whose blades are flat...
. It is known as C. racemosa var. cylindracea and may have originated from Australian waters. In America C. racemosa is found in shallow water in the Caribbean Sea
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
, around Bermuda
Bermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
and along the eastern seaboard of America from Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
to Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
.
Biology
In the Mediterranean, growth begins in April when new stolons develop and erect branches start growing, and continue till December, after which the plants decline and become dormant.C. racemosa reproduces vegetatively
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
by fragmentation. When pieces of the plant get broken off they develop into new plants. Small pieces of tissue only a few millimetres across are capable of doing this.
C. racemosa can also reproduce sexually and in so doing exhibits holocarpy. This means that all the organism's cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
is used up in the creation of the gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s and only a husk remains at the site of the original plant. The plants are monoecious with male and female gametes being produced by the same plant and liberated into the water column where they unite to give spherical zygote
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
s. These settle and after five weeks produce germ tube
Germ tube
A germ tube is an outgrowth produced by spores of spore-releasing fungi during germination.The germ tube differentiates, grows, and develops by mitosis to create somatic hyphae....
s which elongate and branch to develop into new plants. Mass spawnings
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
sometimes take place in the Caribbean Sea
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
and normally do so just before dawn. There were 39 such mass spawnings during a period of 125 days and the days on which they took place showed no relation to the tidal or lunar cycles. The gametes remain motile for about 60 minutes. Mass spawning is advantageous to the plant in increasing the chances of fertilisation. Underwater visibility can be reduced to less than one metre by the green cloud produced in the process. Similar mass spawnings take place in the Mediterranean Sea causing a cloud of green gametes to be released in the water approximately 14 minutes before sunrise.
Ecology
Caulerpa species contain secondary metabolites that are cytotoxicCytotoxicity
Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are a chemical substance, an immune cell or some types of venom .-Cell physiology:...
, of which caulerpenyne is the most abundant. These deter animals from consuming the plants. A study has been done on herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
s that graze on meadows of the invasive C. racemosa var. cylindracea in the north west of its range in the Mediterranean. The sea breams Boops boops
Boops boops
Boops boops, called the bogue, is a species of seabream native to the eastern Atlantic. Its scientific name, and its common names in many languages, refers to its large eyes. It is found off the coasts of Europe, Africa, the Azores and the Canary Islands, from Norway to Angola, and in the...
and Sarpa salpa
Sarpa salpa
Sarpa salpa, also known as the Salema porgy, is a species of bream, recognisable by the golden stripes that run down the length of its body, and which can cause hallucinations when eaten....
were found to feed on the algae, as did the sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
s Paracentrotus lividus
Paracentrotus lividus
Paracentrotus lividus is a species of sea urchin in the family Parechinidae commonly known as the purple sea urchin. It is the type species of the genus and occurs in the Mediterranean Sea and eastern Atlantic Ocean.-Description:...
and Sphaerechinus granularis
Sphaerechinus granularis
Sphaerechinus granularis is a species of sea urchin in the family Toxopneustidae, commonly known as the purple sea urchin. Its range includes the Mediterranean Sea and eastern Atlantic Ocean.-Description:...
. Other herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
s also grazed occasionally, but the total amount consumed was compensated for by the rapid growth of the plant and it was considered that these organisms were not likely to play a valuable role in bio-control
Biological pest control
Biological control of pests in agriculture is a method of controlling pests that relies on predation, parasitism, herbivory, or other natural mechanisms...
of the plant.