Seaweeds are plants that grow in salt water.  They belong to a group of organisms called Algae. Algae are divided into macro-algae which are commonly known as seaweed, micro-algae which are sometimes known as phytoplankton, and maerl which are very small with a hard calcium crust and are unattached to rocks so they live on the sea bed. 


Macro-algae are large algae divided into brown, red and green groups and look similar to plants. They are slightly different to plants in a number of ways. They do not have roots like land plants but instead absorb nutrients across their entire surface from the surrounding water. Like land plants, they use sunlight to photosynthesise and produce carbohydrates and organic, bio-available nutrients. So that they stay relatively close to the surface and have access to daylight, algae attach themselves to rocks with fibrous strands called ‘holdfasts’ which attach to rocks (or even boats, ropes and piers) to keep them close enough to a light source to photosynthesise. They contain “blades” similar to leaves in plants. A collection of blades are called “fronds”. Some macro-algae have “air-bladders” which help them float to the surface to catch the sun. Other macro-algae have no “air-bladders” just a long flexible “stipe” for support, similar to a stem in plants. Nutrients are absorbed from the water by the entire structure of the algae, unlike in plants, which absorb nutrients from the soil through their roots. 


The fronds are more like the leaves which we would associate with land plants. It is these fronds that are harvested and used for food. If you are a food manufacturer, it is the fronds you will be using in your products. We are trying to encourage the sustainable harvest of seaweeds which would ensure that only the top part of the fronds are harvested. This would allow the plant to keep on growing and regenerate itself. Unfortunately, some industries destroy the plants and use all parts of the plant indiscriminately to obtain bio-active ingredients.


Micro-algae are much smaller organisms and can only be seen under a microscope. They are like floating plants and they are not attached to anything. There are two common types of micro-algae. Diatoms are one variety and they have oil within their bodies. This helps them to float. Dinoflagelletes are another variety of micro-algae which have “flagella”. The flagella help the dinoflagellates to swim. Certain varieties of dinoflagellates glow in the dark at night when disturbed. Micro-algae are often called “phytoplankton”, which are the main food source of massive whales such as basking sharks and blue whales. Like land plants, they are primary producers at the bottom of a number of food chains, sustaining a variety of organisms which we later feed on, such as fish and crab. 

For information on seaweeds on this site please use these links:

Atlantic Wakame,  Bladderwrack,  Carrageen,  Channelled Wrack,  Dillisk,  Egg Wrack,  Forest Kelp,  Gut Grass,  Kelp,  Nori,  Pepper Dillisk,  Sea Lettuce,  Sea Spaghetti,  Serrated Wrack,  Sugar Kelp,  Velvet Horn,

For more detailed information on seaweeds please visit:

The Seaweed Site