Home Ocean Facts What is seaweed? What is seaweed? Seaweed is chock-full of vitamins, minerals, and fiber, and can be tasty. But almost all varieties have found their place, one way or another, into the human diet. Originally, seaweeds intended for human consumption were collected along the seashore or picked in the sea.
Those that were eaten fresh were harvested locally and consumed in short order. As seaweeds can be dried and, in that form, kept for a long time and transported easily, they were recognized early on as a valuable foodstuff and became a trading commodity.
Over time, the demand for seaweeds, for a multiplicity of purposes, grew so great that for many centuries they have been actively cultivated, especially in the Far East. The life history of algae is complicated, and this is what really differentiates them from plants. In fact, macroalgae can pass through life stages so distinct that, in the past, they have been mistaken for separate species.
Seaweed reproduction can involve either exclusively sexual or asexual phases, while some species display an alternation of generations that involves both in succession.
In the former, the seaweed produces gametes egg and sperm cells with a single set of chromosomes and, in the latter, spores containing two sets of chromosomes.
Some species can also reproduce asexually by fragmentation—that is, the blades shed small pieces that develop into completely independent organisms.
The the red alga Porphyra , used for making Japanese nori, has a highly complex life cycle. Asexual reproduction allows for fast propagation of the species but carries with it an inherent danger of limited genetic variation. Sexual reproduction ensures better genetic variation, but it leaves the species that depend on this method of reproduction with an enormous match-making problem, as the egg and sperm cells need to find each other in water that is often turbulent.
Some species solve the match-making problem by equipping the reproductive cells with light-sensitive eyespots or with flagella so that they can swim. Others make use of chemical substances, known as pheromones or sex attractants. These are secreted and released by egg cells and serve to attract the sperm.
Some species for example, the large seaweed masses in the Sargasso Sea secrete enormous quantities of slime, which ensures that the egg and sperm cells stick close to each other and do not go astray.
A newly discovered species of red seaweed is now named Porphyra migitae. The red alga Porphyra has an especially complicated life cycle, with a fascinating aspect that merits further discussion because of the interesting history associated with its discovery.
It relates directly to the cultivation of Porphyra for the production of nori, which is especially widely used in Japanese cuisine—most familiarly, as for the wrapping for maki rolls See the recipe in the caption for the nori roll image below. The blades used in nori production grow while the seaweed is in the generation that reproduces sexually, although the organism itself can actually develop asexually from spores.
The blades produce egg cells and sperm cells. The egg cells remain on the blades, where they are fertilized by the sperm cells. The fertilized eggs can then form a new type of spores, which are released. These spores germinate into a calcium-boring filament stage that can grow in the shells of dead bivalves, such as oysters and clams, in the process developing spots that give the organism a pinkish sheen.
Until the s it was thought that this sexual stage was actually an entirely separate species of alga, given the name Conchocelis rosea. Without an understanding of the true life cycle, it was not possible to grow Porphyra effectively in aquaculture.
No one knew where the spores for the fully grown Porphyra originated. This was the main reason for the recurring problems experienced by the Japanese seaweed fishers in their attempts to cultivate Porphyra in a predictable manner. It was an English alga researcher, Dr. Kathleen Mary Drew-Baker, who discovered the secret of the sexual segment of the Porphyra life cycle.
Drew-Baker was unaware of the difficulties of the seaweed fishers. Instead, she was preoccupied with shedding light on the mystery of why the species of laver Porphyra umbilicalis that grew around the coast of England seemed to disappear during the summer, reappearing again only toward the end of autumn. She tried without success to germinate spores that she had collected.
They would even grow on an eggshell. A few months later, the resulting small, roseate sprouts produced their own spores that, in turn, could germinate and develop into the well-known large purple laver.
Drew-Baker published her results in Shortly thereafter the Japanese phycologist Sokichi Segawa repeated her experiments using local varieties of Porphyra and found that they behaved in the same way as the English species. The mystery was solved and the results were quickly put to use in Japan. Drew-Baker died at a relatively young age in , apparently unaware that her curiosity and seminal research had laid the foundations for the development of the most valuable aquaculture industry in the world.
As in green plants, photosynthesis enables seaweeds to convert sunlight into chemical energy, which is then bound by the formation of the sugar glucose. The photosynthetic process uses up carbon dioxide, which is thereby removed from the water. In addition, phosphorous, a variety of minerals, and especially nitrogen are required.
Oxygen is formed as a by-product, dissolved in the water, and then released into the atmosphere. This by-product is of fundamental importance for those organisms that must, like humans, have oxygen to be able to breathe. Photosynthesis can even, to a certain extent, be carried out when seaweeds are exposed to air and partially dehydrated. They now run Maine Coast Sea Vegetables, a company which has its own building and 20 employees who transform the locally harvested seaweeds into more than 20 different products.
The raw material for this business is delivered by about 60 seaweed harvesters who work along the coasts of Maine and Nova Scotia, where algae are found in abundance. Shep trains the harvesters himself. It is of utmost importance to him that they understand the principles of collecting the different types of marine algae sustainably so that they do the least harm to the environment. Maine Coast Sea Vegetables processes about 50 tons of dried seaweeds annually, of which about 60 percent is the dulse for which the company is especially famous.
Eating dulse is an old tradition in Maine, brought to its shores by settlers from Wales, Ireland, and Scotland. They are also edible and can be used to make kelp lasagne! Another example of a delicious seaweed is nori, also known as laver. This is the familiar dark green wrapper used to make sushi, but you may be surprised to learn that nori is actually a red alga—the green colour is a result of it being dried and toasted.
Finally, why are algae—and seaweed—so important? Another is that they are an essential component of aquatic food webs, providing a source of nutrients for invertebrates and fish—freshwater and marine. They are also an important food source for humans e. In fact, there are too many reasons to list in this blog post, but you can click here to learn more!
You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email. These include seaweeds and algae.
Although commonly interchanged, these two may be similar in some ways but have various major differences. These are chlorophyll-containing organisms commonly found in aquatic environments such as marine bodies, sea, and even freshwater bodies. They are the most primitive organisms on earth with fossils dating back to three billion years.
They mainly include prokaryotic, eukaryotes and eukaryotic organisms. They could be macroscopic or microscopic and can either have a unicellular or multi-cellular cell structure. Although there is no specific estimation on the number of algae in the entire world, there exist , collected species.
These are plant-like organisms that attach themselves to rocks and other hard substances in an aquatic environment. They belong to the algae family. They have been useful to humankind mainly for food, industrial products, medicinal uses, and even fertilizers. Seaweeds belong to three different groups with more than 10, species namely, brown algae, green algae, and red algae. While green algae are common in freshwater and terrestrial situations, red and brown algae are common in marine environments.
While algae are chlorophyll-containing organisms commonly found in aquatic environments such as marine bodies, sea, and even freshwater bodies, seaweed are plant-like organisms that attach themselves to rocks and other hard substances in an aquatic environment.
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