For years, sea urchins were overlooked marine creatures, often dubbed “sea porcupines” in foreign countries. Their peculiar appearance, with moveable spines and tubular feet reminiscent of starfish, kept people at a distance. However, it was only when the demand for sea urchins in international markets surpassed that of traditional seafood like lobster that their unique value became apparent, and then sea urchin farming was discovered.
The sought-after delicacy is the roe, also known as gonads or locally referred to as “alige,” which is cherished for its sweet, tangy, and exquisite flavor. In Tokyo’s wholesale markets, sea urchin gonads fetch prices ranging from US $58 to $160 per kilogram. Japan stands as the largest consumer of sea urchin gonads, followed closely by France and Korea.
The surge in the demand for sea urchins, coupled with their potential for a favorable economic return, led to uncontrolled and indiscriminate harvesting, threatening their population. This prompted marine experts from the Marine Science Institute (MSI) at the University of the Philippines Diliman to develop a sea urchin grow-out culture technology. This approach not only helps in conserving and sustaining sea urchin populations but also opens up lucrative business opportunities for both small and large fishery operators.
Understanding Sea Urchins
Before venturing into sea urchin farming, it’s essential to have a solid understanding of these marine creatures. In the Philippines, the most common sea urchin species is the Tripneustes grantilla, known locally as “swaki,” “santol-santolan,” “maritangtang,” or “kuden-kuden,” and commonly found in the Ilocos and Bicol regions. These sea urchins have purplish-brown bodies with numerous short white and orange spines. They reside on the sea floor and primarily feed on sargassum, a brown seaweed.
Sea urchins go through two distinct phases in their life cycle: the planktonic larval stage, which lasts 5-8 weeks, and the benthic adult stage, where they reach sexual maturity at 7-8 months after fertilization. Interestingly, it’s challenging to differentiate between male and female sea urchins based on their external appearance. The distinction is made by examining the color and texture of the gonads, the edible part of the sea urchin that contains sex cells and gametes. Each urchin has five strips of gonads between the rows of its tube feet. Female gonads are orange and contain granular eggs, while male gonads are yellow with cream-yellow sperms. Sea urchins spawn or release eggs throughout their two to three-year lifespan.
The Grow-Out Procedure
To embark on sea urchin farming, the first step is to conduct an initial survey in the prospective grow-out site to ensure the availability of sea urchin brood stock.
The construction of cages for sea urchin farming involves using durable, locally available materials such as PVC pipe frames covered with green polyethylene screens or nets. These cages are secured to the seafloor by tying the four corners of the net to bamboo stakes. The cage should be elevated at least one foot above the seafloor, with the top approximately 0.5 meters below the sea surface during low tide.
When sourcing sea urchin seed stock from a considerable distance, it’s crucial to follow proper transport procedures. Live sea urchins should be kept in Styrofoam iceboxes containing seawater during transport, similar to aquarium aerators. Each Styrofoam box can accommodate around 500-600 urchins. It is recommended to transport the seed stock early in the morning when the temperature is lower. Sea urchins should not be abruptly transferred from transport containers to sea cages, as sudden changes in water conditions can stress the urchins and lead to mortality.
The ideal number of sea urchins per cage should not exceed 500 to prevent overcrowding, which can result in competition among the urchins. Even when regularly supplied with sargassum, overcrowded cages can lead to non-uniform growth and smaller gonads.
Proper care and maintenance extend not only to the sea urchins but also to their source of food, sargassum. Indiscriminate stripping of sargassum can deplete algal beds over time. A better approach is to selectively harvest the plant’s secondary branches using a sharp knife or sickle, leaving the roots and the primary axis intact for future regeneration.
Sea urchins should be fed with sargassum once or twice a week, ensuring enough sargassum is available in the cage to support maximum feeding rates, rapid growth, and the development of large gonads.
One advantage of rearing sea urchins is that they do not require constant monitoring. Monitoring becomes necessary only if you want to periodically assess the growth performance of the sea urchins.
In a grow-out trial conducted to determine the survival rate of sea urchins, experts found that 85% of the population successfully survived. This high survival rate is attributed to the fact that sea urchins are relatively resistant to parasitic diseases.
A notable characteristic of sea urchins is their rapid growth, which tapers off as they get larger. As a result, thinning out the population becomes necessary. It is recommended to build additional cages to reduce stocking density, especially in the last month before harvesting, when the sea urchins are in their “fattening phase.” During this stage, it’s essential to maintain an ideal number of 200 individuals per square meter, providing them with high food rations.
Harvesting Sea Urchins
The best time to harvest sea urchins is when they reach a diameter of 7-8 cm. To maximize yield, it’s advisable to harvest sea urchins before they spawn, as those close to spawning have large, firm gonads. To determine if the urchins have large gonads, shuck about 10-20 of them. If the gonads are filled with nutritive cells or ripe sperms or eggs, it’s an indicator that the urchins are close to spawning. However, if more than half of the samples have thin and watery gonads, it suggests that the urchins have already spawned. In such cases, it’s recommended to wait another 2-3 weeks before harvesting.
Sea urchin farming can be a profitable venture if done with care and attention to detail. By understanding the biology and behavior of sea urchins and following the proper procedures for farming, you can not only contribute to the conservation of this species but also tap into a growing market demand for this delicacy, potentially reaping significant economic benefits.
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