''Millepora dichotoma'', the net fire coral, is a species of

hydrozoan Hydrozoa (hydrozoans; ) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specialize ...

, consisting of a colony of polyps with a

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an ad ...

skeleton.

Description

''M. dichotoma'' is a colonial

hermatypic coral Hermatypic corals are those corals in the order Scleractinia which build reefs by depositing hard calcareous material for their skeletons, forming the stony framework of the reef. Corals that do not contribute to coral reef development are referred ...

with a calcareous endoskeleton. They form colonies up to 60 cm wide, but clumps of colonies may be several meters across. They initially build as encrusting coral, adhering themselves to hard substrate. The encrusting formations further develop into other growth forms, such as lace-like, leaf-like blades, and box-work. What growth form an individual develops into is highly dependent on the depth and location of growth as well as on the turbidity of the water in a given location. More fragile structures, such as lace-like, succeed better in deeper, less turbulent waters, whereas box-work forms are able to better succeed in harsher environments. As in other hermatypic corals, part of the

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run c ...

of fire corals relies on

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 ''S ...

. Symbiotic zooxanthellae give ''M. dichotom''a their vibrant colors, support structural growth, and assist with nutrient cycling. ''M. dichotoma'' is within the phylum

cnidaria 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 ...

, which means they have

nematocysts A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this c ...

. Their nematocysts carry venom and are fatal to many organisms, but have not been found to be fatal to humans. However, they can cause humans extreme pain, burn-like wounds, and skin irritation that may continue for up to two weeks.

Distribution

''M. dichotoma'' can be found in the

Republic of Mauritius Mauritius ( ; french: Maurice, link=no ; mfe, label=Mauritian Creole, Moris ), officially the Republic of Mauritius, is an island nation in the Indian Ocean about off the southeast coast of the African continent, east of Madagascar. It incl ...

, the

Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...

, and the

Indo-West Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

region. They are a benthic dwelling species that is most commonly found at depths of 0.2–3 meters.

Diet

''M. dichotoma'' are carnivorous suspension feeders.

Polyps A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral (opposite to oral) end i ...

snare

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

and detritus from the surrounding waters and process their intake in their

gastrovascular cavity The gastrovascular cavity is the primary organ of digestion and circulation in two major animal phyla: the Coelenterates or cnidarians (including jellyfish and corals) and Platyhelminthes (flatworms). The cavity may be extensively branched into a ...

Reproduction

Reproduction occurs between April and May, but

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

s can be present through June. A synchronized release of gametes is used to facilitate

external fertilization External fertilization is a mode of reproduction in which a male organism's sperm fertilizes a female organism's egg outside of the female's body. It is contrasted with internal fertilization, in which sperm are introduced via insemination and then ...

. Male gametes are broadcast slightly before females release their eggs in order to achieve a higher success rate. During their multi-month reproduction period, there are multiple distinct times of gamete release. Fertilized gametes will disperse with currents and eventually settle on the seafloor to establish or add to colonies. After their planktonic stage, the polyps will settle and adhere to hard substrates, become hosts to symbiotic zooxanthellae, and build calcareous skeletons.

Threats

''M. dichotoma'' does not currently have an extinction concern but does encounter human caused harm. They can sustain damage from humans walking, snorkeling, and diving on and around them. Fragmentation of their colonies can create distinct structural changes. Growth may change from more fragile forms, such as lace-like, to a thicker and less fragile form, like box-work. Additionally, areas with anthropogenic nutrient addition have seen lower numbers of ''M. Dichotoma'' when observed over long periods of time. Similar to other coral species that are supported by symbiotic zooxanthellae, ''M. Dichotoma'' responds to increases in ocean temperatures with bleaching events.

References

External links

* {{Taxonbar, from=Q2294231 Milleporidae Animals described in 1775 Taxa named by Peter Forsskål