SEAWEED AND ALGAE can be found all over the world. Like bacteria, algae were among the first forms of life on earth. Algae survive under the most severe circumstances, and many researchers believe we owe our existence to the development of algae billions of years ago. That is because algae practice photosynthesis (like trees and plants do), releasing oxygen into the atmosphere and enabling life as we know it. There are thousands of species of seaweed that can differ from one another like day and night. Some kinds grow very slowly and remain small; others create entire forests, so-called “kelp forests,” in the water. Most types of seaweed are edible, though their flavors vary widely. For example, sea lettuce (Ulva lactuca) is a tender green seaweed that is very accessible, while other kinds are much tougher and not as easy to eat. In Asia, seaweed has been a staple for years and is considered a delicacy. In the United States and Europe, the popularity of seaweed is steadily on the rise. Just a few years ago, not many people were looking for it in their local grocery stores. Nowadays, it’s everywhere, being sold in most grocery stores in some variety.
Algology, or phycology, is the scientific study of algae. Phyco (phukos in Greek) means “seaweed” and logy (logos) is defined as “knowledge” or “science.” Seaweed is the umbrella term for the entire group of macroalgae that live in salt water, brackish water, or freshwater. Algae can be divided into two groups: microalgae (unicellular organisms, like chlorella) and macroalgae (multicellular organisms, like seaweed).
We already know about tens of thousands of species of algae, and new species are being discovered constantly. From an evolutionary perspective, algae are very old. It’s estimated that multicellular seaweeds came into existence about 1.2 billion years ago. Unicellular algae have been around for even longer, about 2 billion years. Fossils of algae that date back 600 million years have been found. Seaweed species are usually categorized among the cryptogams (plants that do not produce flowers or seeds), like ferns. They resemble ferns in terms of their structure and reproduction, and are more elementary in that respect than flowers, trees, or agricultural crops.
In terms of their build, seaweeds do resemble plants, with a “root,” a stalk, and leaves. There are a few big differences, though. The root of seaweed, called the holdfast, isn’t used to absorb water and nutrition from the soil as with land plants, but rather to cling to rocks, shells, and other weeds. Not all seaweeds cling to a fixed object—some algae float in the water. Connected to the holdfast is a stalk that supports the leaves of the weed. Because seaweeds have a more elementary structure than terrestrial plants, which are at a more advanced degree of evolution, they are able to grow faster and produce more biomass than their terrestrial neighbors.
There are three groups: green algae, brown algae, and red algae. The color is determined by the composition and amount of pigment present in the algae, which differs by group. Pigments are chemical compounds that reflect light and are perceived as color. Photosynthetic pigment captures light for photosynthesis, and likewise differs by group. Algae that live in deeper waters require more pigment to absorb sunlight than algae growing just below the surface. Laminaria abyssalis, a relative of the oarweed, has been found at a depth of 360 feet (110 m). Red algae can live in the deepest water, as they are capable of absorbing energy from the sun at very deep levels. Some algae are able to live as deep as 820 feet (250 m) below sea level if the water is exceptionally clear; only 0.0005 percent of sunlight comes through at this depth. Aside from the above-mentioned groups of algae—the red, brown, and green algae—there is a fourth group: blue algae, also called blue-green algae. Blue algae aren’t actually algae but bacteria, specifically cyanobacteria. Most of these algae are poisonous. A tasty exception is spirulina.
Seaweed grows in every sea or ocean, from the warmer waters around the equator to the ice-cold areas around the poles. Algae need water, sufficient sunlight, nutrients, and sometimes an “anchor” to attach themselves to. Seaweed uses light energy from the sun (photons) to grow, and this happens with help from photosynthetic pigments. During photosynthesis, water and carbon dioxide (CO2) are converted into sugars with light energy derived from the sun. Oxygen (O2) is an important by-product of this process.
Because seaweeds need light, they usually grow near the water surface. Most seaweeds live at a depth of up to 16 feet (5 m) underwater. There is hardly sufficient light below that level. The majority of seaweed species grow near coastal areas and rocky seashores, but some species float freely in the ocean. There are species that always need to stay submerged because they’ll die once they dehydrate. Other species can survive without water for a while, during low tide, for example. Seaweeds can form sprawling forests in the water with plants that reach several feet long. These kelp forests form a world on their own: Fish and other sea creatures live in these underwater habitats, using the algae as protection from open water.
The life cycle and reproduction of seaweed species differ from those of regular plants. Different species of seaweed are distinguished by their cycles, though we don’t know the origin, growth, or development of many kinds. With kelp, a group of brown algae, the cycle starts when mature weeds develop spores. The spores develop into gametes, which are either male or female. When these gametes are fertile, the males produce sperm cells, the females produce egg cells, and they fuse into a “sporophyte” or “baby alga.” The cycle comes full circle when young algae grow into mature algae and start producing spores for future generations.
Then there’s vegetative reproduction, which occurs in some algae. It happens because of vegetative growth: when a piece of algae—a leaf, for example—tears off and fosters the growth of an entire new seaweed. This is comparable to replanting cuttings of plants that grow on land. In these cases, the seaweed grows thanks to nutrients in the water, crucially the elements phosphorus and nitrogen.
Green algae derive their name from their color. The Chlorophyta can be found as multicellular organisms or unicellular ones—of which there are 1,500 to 2,000 species! Green algae live in both salt water and freshwater, and the unicellular algae particularly prosper on the coast, just above the flood line. These algae prefer nutrient-rich waters: High concentrations of phosphate and nitrate (due to pollution) are good for them. Green algae contain the same photosynthetic pigments as land plants, chlorophyll a and chlorophyll b. A well-known green algae is the Ulva, or sea lettuce, which lives near the east and west coasts of the United States, among other waters.
Wakame
by Wild wier
Brown algae are almost exclusively saltwater species and are rarely found in freshwater. Most kinds live in the cold waters of the Northern Hemisphere. One of the largest algae of any type is a brown alga: the giant kelp (Macrocystis pyrifera), which can grow up to 200 feet (60 m) long and is found near southern Alaska. Another brown alga is the sargassum, which creates unique ecosystems in the tropical waters of the Sargasso Sea. In the North Sea, one finds mostly oarweed (Laminaria digitata) and devil’s apron (Saccharina latissima). Worldwide, there are an estimated 1,500 to 2,000 species of brown algae.
Red algae vary greatly in color: from soft pink to dark red, purple, and even a black-red. The color is determined by the amount of red pigment in the seaweed. These algae do have green pigment (chlorophyll), but they’re dominated by the red pigments (phycocyanin and phycoerythrin).
About 6,500 species of red algae are known. Most red algae can be found in salt water, but a few species are known to exist in freshwater. Because they absorb the blue light from the sunlight spectrum better than green or brown algae do, they’re better suited to deeper waters. One can also find red algae just below the surface. In general, red algae grow more slowly than species in the other two groups. They mostly live in warmer waters and can be found in abundance in Asia.
Red algae are most used for consumption. The seaweed in sushi, nori, is a red algae. It’s often thought that nori is green algae because of its color in food. However, nori turns that greenish-brown only as a result of drying and roasting during processing.
Seaweed fields, South Korea
by Nasa Landsat
