Sea urchins or urchins are commonly called sea hedgehogs and are small, spiny, globular animals that, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinodermata phylum. About 950 species of echinoids inhabit all oceans from the intertidal to 5000 m deep. Sea urchins will be harvested once they reached 7-9 cm. Depending on market considerations
Sea urchins, locally known as “swaki, santol-santolan, maritangtang, are invertebrates that look like a ball of spines which feed on sea grasses and seaweeds particularly Sargassum sp. or Aragan.
Sea urchins can grow up to 7-9 cm with an average weight of 1 pound. They are usually found in colder off-shore water. Sea urchins are harvested mainly for their internal roe or gonads known locally as “alige or bugi”. Stomopneustes variolaris, Toxopneustes pileolus, Temnopleurus toreumaticus are common species used for aquaculture.
Phylum : Echinodermata
Subphylum : Eleutherozoa
Class : Echinoidea
Echinus is a benthonic animal found abundantly in the coastal waters. It prefers areas with rocky bottom. The body is globular or hemispherical in shape and thickly covered with cylindrical movable spines. The oral and aboral surface are distinct. The body does not possess arms.
Mouth is situated at the Centre of the oral surface and the aboral surface bears the anus. Sea urchin possess a unique and complicated masticatory apparatus, called ‘ Aristotle’s latern ‘. Sea urchins are omnivorous and feed mainly on marine weeds and algae with the help of this scraping organ. Sea urchins are gonochoric, and the majority display no sexual dimorphism. Reproduction is sexual and fertilization is external. The development involves a free swimming echinopluteus larva.
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Anatomy of Seaurchin
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Reproduction
Sea urchins are dioecious, having separate male and female sexes, although distinguishing the two is not easy, except for their locations on the sea bottom. Males generally choose elevated and exposed locations, so their milt can be broadcast by sea currents. Females generally choose low-lying locations in sea bottom crevices, presumably so the tiny larvae can have better protection from predators. Indeed, very small sea urchins are found hiding beneath rocks. Regular sea urchins have five gonads, lying underneath the interambulacral regions of the test, while the irregular forms have only four, with the hindmost gonad being absent.
Development
In most cases, the female's eggs float freely in the sea, but some species hold onto them with their spines, affording them a greater degree of protection. The fertilized egg, once met with the free-floating sperm released by males, develops into a free-swimming blastula embryo in as few as 12 hours. Initially a simple ball of cells, the blastula soon transforms into a cone-shaped echinopluteus larva. In most species, this larva has 12 elongated arms lined with bands of cilia that capture food particles and transport them to the mouth. In a few species, the blastula contains supplies of nutrient yolk and lacks arms, since it has no need to feed. Several months are needed for the larva to complete its development, which begins with the formation of the test plates around the mouth and anus. Soon, the larva sinks to the bottom.
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| Sea urchin larva, called "Pluteus". |
Why Culture Sea Urchins and what is its importance???
For human consumption, As a source of Income, Sea urchin have high demand both in local specialty restaurants and international market, It has lucrative market in Japan, France, Korea, China and other Western countries, Culture area serves as mini reproductive reserve.
I. Culture Technology
Cage Culture
A. Site Selection
The site should have a high water movement and tidal flushing with salinity range of 30-35 ppt. It should be sheltered from storms and bad weather. It should also be far from nearby freshwater sources such as river mouth. Sufficient water depth (at least 1- 1.5m deep at low tide.), They should also have abundant source of sea urchin food (Sargassum). Visible and easily accessible from the shore not situated along frequently used boat routes where bancas might run over the cages.
B. Cage Construction
The materials used are hard bamboo, steel bars or PVC pipes for frames covered with green polyethylene screen or net size 3/4 as enclosure. Cage dimension is 1.5m x 0.5m x 1.0m
C. Cage Installation
The constructed cages are installed on the sea floor by tying its four corners to bamboo or wooden stakes firmly driven to the sea floor. The cage should be elevated at least (1) foot above the seafloor and the top should be about 0.5 m below the seawater surface during low tide. The cage should be spaced a few feet apart to ensure sufficient water flow in the area. A marker (tall bamboo pole) should be erected to warn approaching boats of the presence of the cages.
D. Acquisition of Stocks
Sea urchin seed stocks can be gathered from the site if there is abundant supply of it. Juvenile sea urchin usually measures from 32-44 mm in equatorial diameter. Seed stocks can be gathered through simple picking. If the source of seed stock is far from the grow-out area, proper transporting procedure should be strictly followed. Live sea urchins while in transport should be kept in Styrofoam iceboxes (with aerators similar to aquariums) that contain seawater. About 500-600 urchins can be placed in one Styrofoam box. It is recommended to transport the seed stock early in the morning when the temperature is lower. Sea urchins, regardless of how they are transported, should not be abruptly transferred from the transport containers directly to the sea cages because sudden change in water conditions can further stress the urchins and may cause them to die.
Acclimatize first the seed stocks before stocking to the cages by floating the container in the seawater in the area for a few minutes and slowly pouring the seawater into the container until the stocks can already adopt with the environment in the area.
E. Stocking
The Initial stocking density of 500 pcs per cubic meter is recommended. Thinning of the stock is done as they grow by transferring the smaller ones to another cage usually a month before harvesting. Stocking should be timed to avoid the typhoon months at harvest time.
F. Feeding
Feeding is done once or thrice a week in “ad libitum” manner preferably with fresh Sargassum or aragan. There should be enough amount of sargassum left in the cage to ensure that urchins feed at maximum rates, grow faster, and consequently develop large gonads. When gathering sargassums for feeding, cut only the branches, and do not uproot the plant to ensure sustainability.
G. Maintenance
Maintenance includes regular monitoring of the stocks, cleaning and removing of decaying left over algae and other debris being entangled on the screen. Thinning is done to make sure that all of the stocks grow optimally. It is also necessary to guard the cages against poachers and vandals.
H. Harvesting
Sea urchins will be harvested once they reached 7-9 cm. Depending on market considerations. This will be sold live or the roe may also be processed and packed before selling. Sea urchin roe can be sold fresh, packed in brine or in the form of a paste.
