''Rhodactis howesii'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of marine

cnidarian Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that th ...

in the order

Corallimorpharia Corallimorpharia is an order of marine cnidarians closely related to stony or reef building corals (Scleractinia). They occur in both temperate and tropical climates, although they are mostly tropical. Temperate forms tend to be very robust, wit ...

, a

sea anemone Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...

-like corallimorph found on

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock out ...

s in tropical regions of the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

. It is commonly known as the green fuzzy mushroom, elephant ear mushroom coral, giant anemone, giant mushroom anemone and giant cup mushroom.Animal-World: Green Fuzzy Mushroom
/ref> This species is toxic when eaten raw and ingestion can cause fatal poisoning.Observations on the Toxic Sea Anemone, ''Rhodactis howesii'' (Coelenterata)
/ref>

Description

This coral mushroom is essentially a coral without a skeleton and its internal structure is similar to a

stony coral Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a ...

. The upper surface is the oral disc. It has a short stalk or column below which is the pedal disc which adheres to the substrate. It can detach itself and drift to another location. It is either green or brown, and five to eight centimetres high. The tentacles are very short and somewhat knobbly, giving the oral disc a fuzzy appearance. They tentacles at the edge of the disc are longer and contain toxins which damage other corals close by but which are harmless to humans. ''R. howesii'' is a

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...

and catches

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

and other micro particles that float past its oral disc. It also obtains nutriments from its

endosymbiotic An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within" ...

alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...

Reproduction

There are three asexual means of

reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual or ...

Budding Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is know ...

can occur when new individuals are formed from pieces that divide off from the pedal disc. Fragmentation can occur when the individual moves slowly over the substrate and leaves small pieces of itself behind which eventually grow into new individuals. Division or fission can also occur when the corallimorph divides down the centre to form two new individuals. Sexual reproduction also sometimes occurs and

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

and

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...

are released into the water. They unite and form free-swimming

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e which are initially planktonic. Later they settle and adhere to the substrate, growing into new individuals.

Toxicity

American Samoans call ''R. howesii'' "matamalu" and are aware that consuming it uncooked can be fatal. Such ingestion has been recorded and may have happened accidentally or may have been used as a means of committing

suicide Suicide is the act of intentionally causing one's own death. Mental disorders (including depression, bipolar disorder, schizophrenia, personality disorders, anxiety disorders), physical disorders (such as chronic fatigue syndrome), and s ...

. Cooking seems to destroy the poison and cooked "matamalu" is commonly eaten by the

Samoa Samoa, officially the Independent State of Samoa; sm, Sāmoa, and until 1997 known as Western Samoa, is a Polynesian island country consisting of two main islands (Savai'i and Upolu); two smaller, inhabited islands (Manono Island, Manono an ...

ns. The three patients who had been poisoned by ''R. howesii'' and who were observed in a hospital in Samoa, fell into a prolonged stupor which lasted from 8 to 36 hours. During this time the

knee jerk reflex The patellar reflex, also called the knee reflex or knee-jerk, is a stretch reflex which tests the L2, L3, and L4 segments of the spinal cord. Mechanism Striking of the patellar tendon with a reflex hammer just below the patella stretches the mus ...

and the

pupillary light reflex The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retinal ganglion cells of the retina in the back of the eye, there ...

were absent but the

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...

and

pulse rate In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the nec ...

remained normal. All three developed prolonged shock and later died from

pulmonary oedema Pulmonary edema, also known as pulmonary congestion, is excessive liquid accumulation in the tissue and air spaces (usually alveoli) of the lungs. It leads to impaired gas exchange and may cause hypoxemia and respiratory failure. It is due to ...

. The

medical history The medical history, case history, or anamnesis (from Greek: ἀνά, ''aná'', "open", and μνήσις, ''mnesis'', "memory") of a patient is information gained by a physician by asking specific questions, either to the patient or to other peo ...

and the course of their illness resembled the paralytic poisoning caused by shellfish.

Invasiveness

Under some circumstances, ''R. howesii'' may become an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

. In 1991, a hundred-foot vessel was

shipwreck A shipwreck is the wreckage of a ship that is located either beached on land or sunken to the bottom of a body of water. Shipwrecking may be intentional or unintentional. Angela Croome reported in January 1999 that there were approximately ...

ed on Palmyra Atoll National Wildlife Refuge. Thirteen years later it was observed that ''R. howesii'' had colonised the area around the wreck. Over the next few years, the population increased rapidly close to the vessel and by 2008 had reached high concentrations and a

phase shift In physics and mathematics, the phase of a periodic function F of some real variable t (such as time) is an angle-like quantity representing the fraction of the cycle covered up to t. It is denoted \phi(t) and expressed in such a scale that it v ...

had occurred in the

ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...

of the

. Around the ship, ''R. howesii'' covered the sea bed overgrowing and directly competing with the few remaining corals (mainly

Montipora ''Montipora'' is a genus of Scleractinian corals in the phylum Cnidaria. Members of the genus ''Montipora'' may exhibit many different growth morphologies. With eighty five known species, ''Montipora'' is the second most species rich coral genus ...

sp.,

Pocillopora ''Pocillopora'' is a genus of stony corals in the family Pocilloporidae occurring in the Pacific and Indian Oceans.Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townville, Australia. They are commonly called c ...

sp. and

Acropora ''Acropora'' is a genus of small polyp stony coral in the phylum Cnidaria. Some of its species are known as table coral, elkhorn coral, and staghorn coral. Over 149 species are described. ''Acropora'' species are some of the major reef corals r ...

sp.). Close to the wreck there were as many as 288 individuals per square metre and it extended for up to 1100 metres from the vessel. Quite why ''R. howesii'' has flourished so abundantly at this location is not fully understood, but it is possible that

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

is leaching from the ship and promoting its growth. This

hypothesis A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...

is supported by the fact that similar explosive growth in numbers of ''R. howesii'' has occurred around the mooring chains of three

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 anchored some distance from the wreck. Iron is an essential

trace element __NOTOC__ A trace element, also called minor element, is a chemical element whose concentration (or other measure of amount) is very low (a "trace amount"). They are classified into two groups: essential and non-essential. Essential trace elements ...

for growth of

e and

nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...

, and much of the Pacific Ocean is extremely low in available iron which is a limiting resource for many marine organisms. Iron may also stimulate the growth of the symbiotic

zooxanthellae Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus ''Sy ...

in the polyps.Kuguru B, Winters G, Beer S, Santos S, Chadwick N (2007) Adaptation strategies of the corallimorpharian ''Rhodactis rhodostoma'' to irradiance and temperature. Marine Biology 151: 1287–1298.

References

External links

''Rhodactis howesii''
at ZipCodeZoo {{Taxonbar, from=Q3328097 Animals described in 1893 Discosomidae Taxa named by William Saville-Kent