Laminaria

Laminaria is a genus of brown kelp with 31 species found naturally in the cold waters of the north Atlantic and northern Pacific. It has long, tough blades and can grow quite large, giving it common names like devil’s apron (for its shape) or sea colander (when the blades have holes). Some species are simply called tangle. These seaweeds create shelter for fish and many invertebrates.

The life cycle of Laminaria involves two very different stages. The large, visible plant—made up of a holdfast, a stipe, and blades—is the sporophyte phase. This alternates with a microscopic gametophyte phase. Male and female zoospores are produced separately at meiosis, then grow into male and female gametophytes. The female egg matures inside the oogonium until sperm fertilizes it. Unlike Fucus, this cycle is heteromorphic.

Two species have been reclassified: *Laminaria japonica* is now considered a synonym of *Saccharina japonica*, and *Laminaria saccharina* is now *Saccharina latissima*.

Laminaria first reached China from Hokkaido, Japan in the late 1920s. It was then cultivated on a much larger industrial scale. The rocky, cold shores of Dalian on the northern Yellow Sea provided excellent growing conditions. In 1949, the harvest yielded 40.3 metric tons of dry weight. That same year, China began commercial farming, boosting dry-weight production to 6,200 metric tons. China still farms Laminaria on a large scale, though production has declined since the 1980s due to new mariculture technology. Laminaria needs cold water and can only survive above 36° N latitude.

Farming typically uses the floating raft method: young sporophytes are attached to submerged ropes, which are then tied to floating rafts.

In the wild, Laminaria grows in colder ocean waters, especially arctic regions, and prefers rocky shores where it can attach. Its height provides shelter that the open ocean lacks. Invertebrates live among the algae; sea snails and others feed on the blades, while sea urchins feed on the holdfasts, which can kill the plant. Red sea urchins on the North American Pacific Coast can devastate Laminaria if sea otters do not keep them in check. When Laminaria washes up on beaches, species like *Coelopa pilipes* feed and lay eggs on it.

The sporophyte can reach 7 meters (23 feet)—large for algae but smaller than giant kelps like *Macrocystis* and *Nereocystis*, which grow to 40–50 meters (130–160 feet). The gametophyte is only a few millimeters long. Unlike the simple gametophyte, the sporophyte has several tissue types, including sieve-like elements that move photoassimilates, similar to mesophyll cells in higher plants.

Laminaria has several uses. In medicine, a dried, compressed stick made from the seaweed can be used to slowly dilate the cervix for inducing labor, surgical procedures, or placing an intrauterine device. It is also a source of iodine, which supports thyroid health.

As food, Laminaria has been eaten since ancient times. The blade is typically boiled in broth or water, or dried. Most commercial cultivation, however, goes toward producing algin, iodine, and mannitol for industrial uses. In South Korea, it is made into a sweetmeat called laminaria jelly. Elsewhere, it is used in fresh salads or canned for preservation and sale. China is the largest producer and consumer.

For energy, algae are being studied as a biofuel source. Laminaria is one of five macroalgae genera that together account for 76% of farmed macroalgae tonnage. However, it is less desirable for burning because its ash content is 33%, compared to wood’s 2%. Algae also have high water content, requiring much energy to dry. Anaerobic digestion is the most promising method for extracting energy from Laminaria, though cost per kilowatt-hour remains a barrier.

Laminaria and other brown algae can absorb heavy metals, making them a focus of research for removing such metals from wastewater.