Eucheuma denticulatumUpdate: 11/20/2014
Eucheuma denticulatum, a perennial red seaweed, is composed of rigid clumps of low-growing, cartilaginous thalli. These clumps can range in size depending on growing conditions, but are able to reach considerable size, up to 50 centimeters in length and weighing over 1 kilogram. The primary axis and regularly spaced branches are cylindrical, each bearing whorled spinose (spine-like) branchlets which sometimes develop into secondary lateral branches. This one species can be found in a variety of shades from brown to green to red, especially when cultivated. Eucheuma denticulatum is most commonly found growing on coarse sand to rocky substrates in the intertidal to shallow subtidal zone where it is exposed to strong currents and wave action. This algae has the unique ability of its branches to form secondary holdfasts to other plants as well as the substrate, forming thick carpet-like beds of seaweed where individual plants are hard to distinguish. This growth pattern coupled with the strength of the holdfasts enables Eucheuma denticulatum to withstand such strong water movement without being torn up or shredded. Quite the contrary, it seems to prefer such a harsh environment as it has never been recorded in calm or protected habitats. Cultivated Eucheuma denticulatum grows most rapidly in areas of strong tidal currents, higher salinity (away from estuaries), bright light, over bottoms of sand and coral and rock. It is a similar species to Kappaphycus alvarezii.
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Eucheuma denticulatum is native to the Indian Ocean, but since being discovered as a source of iota carrageenan, it has been spread elsewhere through cultivation. It can be found in the following countries: Philippines, Indonesia, Vietnam, Cambodia, India, Madagascar, Tanzania, Fiji, Kiribati, Tonga, and Vanuatu.
Eucheuma denticulatum has traditionally been a component of many island cuisines around the Indian ocean and continues to be used as such. However, the primary cause for cultivation of this seaweed is as the major source of the hydrocolloid known as iota carrageenan, which has unique properties that distinguish it from other carrageenans and make it a valuable asset in many applications from the food industry to cosmetic products. Iota carrageenan is also considered a phycocolloid, meaning a hydrocolloid that is derived from seaweed. In this case, that red seaweed is Eucheuma denticulatum. It is one of three carrageenans, the others being kappa and lambda. Some of the main advantages of using iota as a thickening or a gelling compound is that it yields more elastic or softer gels, as opposed to kappa, which is a source of more rigid or brittle gels. When constructing formulas using iota carrageenan, it is important to note that it reacts best with the presence of calcium such as with milk or cream. It is also important to note that gels made using iota have the ability to be frozen and then thawed before use. This makes it possible to make a base and to mold it and freeze it or keep it frozen and to take it out before service, thus prolonging the shelf life of the gel.
Eucheuma denticulatum was originally harvested from natural stocks growing in Indonesia and the Philippines. In the 1970s, cultivation began in both countries and this now supplies most of these species, with only small quantities being collected from the wild. Cultivation of Eucheuma denticulatum has spread to many other countries, most successfully in Tanzania, Vietnam and some of the Pacific Islands, such as Fiji and Kiribati. Cultivated in many areas, most notably Philippines, Indonesia, Malaysia, and Eastern Africa. Several cultivars are known but only a small number are successfully and widely cultivated. It is often planted in areas where Kappaphycus alvarezii grows poorly seasonally.
Common aspects of Eucheuma denticulatum farming include using short, thin lines or loops to secure multiple small "seedlings" spaced at regular intervals to a longer, thicker line. This longer line could be secured at either end to a stake, another line, a frame, or a raft. Maintenance involves visiting each farming area 2 to 3 times per week to remove epiphyte algae growing on the Eucheuma denticulatum, tightening of loose lines, and checking for ice-ice and other signs of damage to the crop. Harvesting occurs every 4 to 6 weeks, and depending on the method, can involve bringing in entire lines, or un-tying each piece of seaweed directly. Regardless of cultivation method, the seaweed must be tried to around 35% moisture content, which could be achieved by drying on mats or fronds on the shore, or on a dock, or hanging from drying lines, or using more advanced methods such as with a solar tunnel drier. A portion of each harvest (perhaps 10%) is retained to commence the next cycle.
The "off-bottom method" for cultivating Eucheuma denticulatum uses large stakes driven into the seabed in a rectangular shape. A thicker line runs between the "ends" of the rectangle. Between these ends, long (10 - 20 meter) thick lines are run, and the seedlings are secured to these long lines via "tie-ties". An off-bottom farm may become exposed to open air for short periods of time at certain low tides, although it remains submerged most of the time. An advantage of the off-bottom method is that it can be visited at slack and low tides without a boat, and it is often closer to the home of the farmer. Disadvantages include proximity to rainwater runoff, which can reduce growth or trigger ice-ice disease, susceptability to higher temperatures, and also these shallow water farms can be more vulnerable to grazers such as rabbitfish.
The "long-line method" can be used in deeper water, and requires the use of floats, which can be small buoys, but are often simply empty plastic water jugs or bottles with the caps still secured. Weighted blocks at either end anchor the line, floats are adjusted to provide the proper depth of the Eucheuma denticulatum seaweed just below the surface. These lines can be dozens of meters long. An advantage of this approach is that much greater farming areas can be exploited by a farming community. There are higher operational costs due to required use of boats, and more maintenance to periodically untangle the long lines.
The "raft method" of cultivation for Eucheuma denticulatum uses a material such as bamboo to construct on the order of 10-meter square rafts, which are in turn secured to the bottom by an anchor (often a concrete block). Rafts are more expensive to construct, but they offer the convenience of being towed in to shore for harvest and replacement with new seedlings. Then, the farmer can boat back with the replenished raft in tow to the float, and re-secure the raft. In general, the rafts are less susceptible to becoming entangled with each other than the long lines. A "basket method" has emerged in certain areas in the Philippines and Indonesia, which is similar to the raft method, but uses floating baskets. There is an additional cost for the baskets, and more substantial floats are required, but work effort is reduced by eliminating the tedious work associated with tie-ties each harvest.
Eucheuma denticulatum is an important crop that can be grown in rough, wave-tossed areas that are unsuitable for other, more delicate commercial seaweeds. Studies have also shown that this species can be useful as bioremediation for wastewater and nutrient saturated areas, especially around fish farms.