PRECIOUS CORAL (Corallium rubrum, Linnaeus, 1758)

Animal description 

Identity :

Sub-Kigdom        : Cnidarians          

Class                    :Anthozoans       

Order                     :Gorgonacea          Famille                   :Coralliidae

Genre                     :Corallium

Scientific name :

    Corallium rubrum

Local name : Marjane 

Key of identification:stiff, treelike colony, comprising ramifications directed according to several irregular, cylindrical plans and relatively short and arranged everywhere  on twigs. Axial skeleton completely mineralized by red color, whitish pink in deepwater and exceptionally white.White polyps (5 mm) very protuberant, topped with an oral disk surrounded with 8 poor urticant cells tentacles. Visible sclereids in the microscope (50-100 µm), as" bone of dog ".

Distribution & Habitat

More or less endemic species of the Mediterranean Sea, it is essentially located in the western part. It was reported as well on the Atlantic Coast between Portugal and Cape Verde. This species was present in the Mediterranean Sea in the upper Cretaceous, there are approximately 8 million years. It is a sessile and benthic species. It lives fixed to hard substrata. We find the red coral in shallow depths, in the ceiling of caves, when the luminosity decreases gradually under rocky overhangs, in the excavations or in the border of cracks, on flat slopes. It is met from 5 m of depth nowadays, but it evolves more spontaneously by 30 or 40 m of depth, until 100 m. It can grow until 400 m depth.

In Morocco, the red coral is present in big concentrations between SpartelCape and Larache. Low densities are observed in the Moroccan Mediterranean Sea (Tofinio and Topo Zones).

                                                    

Biology-Ecology

It is a microphage zoophage predator (= carnivorous) who captures small plankton preys by means of the tentacles of the polyps which constitute a fine network which filters the sea water and holds eggs, larvaes, shellfish copepods and inert organic particles. It is a passive filtrator(= suspension feeding). The internal cavities of polyps communicate between them, The products of the digestion benefit the rest of the colony.


It reproduces by sexual way, given that colonies are hermaphrodite. The fertilization is external and the egg gives birth to a ciliated larva or planula which settles on a hard substratum and gives a small polyp which forms by budding a colony. Thus there is no medusa stage in the development of this animal. The red coral also reproduces by asexual way by budding. The growth is slow. The genitalia of the coral are inside polyps. The sexes are normally separated. The maturation of the male sex cells is made in one year; it begins at the beginning of the summer. On the other hand, the maturation of the female gonads occurs over two years. This begins slowly the first year to be completely achieved at the beginning of the summer of the 2nd year (Vighi, 1972).After their issue by the male polyp, sperm cells swim to the female polyp meeting. The fertilization comes true inside the polyp. The young larva, called planula, develops during 20 in 30 days in the polyp before going out in the water: the red coral is thus viviparous animal. The issue of larvae is spread out between July and beginning of October according to the depth. Larvae swim from 4 to 15 days, at first in ascending direction, in search of a cave ceiling. If they find nothing, their swimming becomes downward, until they meet a substratum favorable to their metamorphosis, among which mechanisms and control are totally unknown. It seems on the other hand that the larva is not sensible to light, so suggesting that the red coral’sdistribution regarding  the light results from an absence of convenient site to the metamorphosis in enlightened zones, or a problem of young colonies growth (due to competition with seaweeds for example). After its metamorphosis, the young larva begins to build a skeleton: a new colony of coral is born. The sexual maturity of the first polyps will be reached after 2 years approximately. It would seem that the growth of the young coloniesis initially fast then it slows down after a few years.

The colonies of the red coral are the oldest alive animals of the world. Their longevity exceeds by far that of the turtles living more than 210 years or of that quahogs that live more than 405 years. Some colonies could have more than for hundreds even thousands of years according to NOAA experts.

Jewelry exploitation  

Harvested since the highest antiquity, the calcareous axis is used in jewelry(the red gold).

Exploitation Modes

The exploitation of the red coral is made by scuba diving (Scuba), onboard 9 coderisive boats (Barjavel, Mimosa, Karama, Bora, Monica, Bonito, Samia, Argo 1 and Argo II). Approximately 20 - 35 mn of diving is the duration that spend a diver under the water for the coral collection. Generally this operation is realized by one or two divers who cross a surface between 30 and 50 m², using to dive bottles containing generally compressed air at around 200 bars.

The harvest by hands using a hammer is the mode of exploitation authorized by the Moroccan law. This method seems much more selective and capable of respecting the limitations of sizes of the exploited colonies.

Stock State
        • The stock biomass in decrease between Spartel cape and Larache since 2010. 
        • Degraded stock in the Mediterranean Sea (Tofinio and Topo zones)

 

Regulations in Force  

        • Institution of a 500 kg/coral fisher/year quota for a maximal duration of 3 years (2014-2016).
        • Limitation of the fishing effort in the zone of Spartel Cape from the latitude 35°36 ' North.
        • Institution of market size for colonies whose diameters is lower than 7 mm.