Difference Between Algae and Seaweed (With Table)

Micro-organisms are available in large-scale diversity at the global level. It can combat the exceptional chemical and context background. Abundant of microorganisms are in primeval places in undersea ecosystems, by capturing the sun’s stamina through photosynthesis and with their performance in decomposition, dispensing of the minerals stored in organic tissue.

Autotrophic creatures are labeled as “Algae”. “Micro-organism” is the term used to be defined as the organisms that carry out photosynthesis. The cyano-bacteria are termed as algae. They vary in size from small (microscopic) to large groups (macrophytes).

Algae and seaweed are well-defined and contrasting relation of aquatic entities that are both photosynthetic. Both of them are eukaryotes that come under the kingdom of “Protista”. Their cell walls are incorporated with cellulose. By the process of diffusion, both of them excerpts nutrients from the water.

The difference between algae and seaweed is that algae are a giant, manifold category of photosynthetic eukaryotic plants, spanning from unicellular Micro-algae to Macro-algae. But, seaweed is defined as the macroalgae that are macroscopic in nature, multicellular in structure, and has marine habitation.

Algae are found eminently in water bodies, while seaweed grows in shallow marine waters, which is of 100 m depth. Moreover, both of them play a crucial role in ecosystems as primary and essential producers.

Comparison Table Between Algae and Seaweed

Parameters of ComparisonAlgaeSeaweed
DefinitionChlorophyll consisting of organisms present in
Aquatic habitats like the sea, marine water
and freshwater bodies
Similar to a plant structure that binds
oneself to other rigid and impenetrable
substances in Aquatic habitat.
Comprises ofAbout 3,20,500 breeds/speciesAbout 10000 breeds/species
Bestows asPrime producers in Aquatic food chainCrucial breeding ground for fisheries and
marine varieties.
Type of habitationIn sea, marine and freshwater habitationOnly in marine habitation
Type of plantEither heterotrophic or autotrophicCompletely Autotrophic
Found asFree-floating or beneath the waterBeneath the water
AppearancesEither Macroscopic or microscopicParticularly macroscopic
Type of micro-organismsBoth multi-cellular and unicellularSolely multi-cellular
Grows eminently inDeep and Shallow waterShallow marine waters (below 100m)
Example of speciesUnicellular ‘Micro-algae’ like Diatoms and
Chlorella to ‘Macro-algae’ like Large brown algae

What is Algae?

Algae are one of the most basic or paramount organisms of the world, comes under the kingdom of “Protista”. Algae are said to be both prokaryotic as well as eukaryotic organisms. Their structure can be defined as unicellular or multicellular. They can be macroscopic and microscopic in nature.

They can live in any aquatic environment, which can be freshwater, marine, and even in brackish water. All the Algae bodies are photosynthetic and autotrophic, with a few heterotrophs as well.

They conjointly produce an ample amount of energy by photosynthesis because of the presence of Chlorophyll in them. There are abundant species of their type in the world. Additionally, they produce a huge value of about 70% of the earth’s atmospheric oxygen. They have very simple cellular structures.

There are totally three divisions of algae are:

  1. Chlorophyta (commonly known as “Green Algae”)
  2. Rhodophyta (generally known as “Red Algae”)
  3. Phaeophyta ( frequently known as “Brown Algae”)

All of the above usually vary because of the amalgamation of photosynthetic pigments endowed in the plant bodies. The Green algae are a diversiform class of algae that has chlorophyll, xanthophylls, and beta-carotene.

Although, phycoerythrin is an important type of photosynthetic pigment present in Rhodophyta. On the other hand, the two key pigments found in Phaeophyta are chlorophyll and fucoxanthin.

What is Seaweed?

Seaweeds are the elementary plants that belong to the family of “Algae”. It is also called “Marine macroalgae”. They can survive only in Marine water (seawater).

It can be defined as an assertive class of plants with dissimilar properties. These are plant-like organisms that are adhered to rock or another solid substrate in sea-side areas. They reside with over 10,000 species, which is generally classified into three groups:

  1. Phylum Ochrophyta (Brown algae) – found in brown or green-yellow color  
  2. Phylum Rhodophyta (Red algae)
  3. Phylum Chlorophyta (Green algae)

Both brown and red algae are completely found in Marine water, while Green algae are found commonly in freshwaters such as lakes, and rivers and in terrestrial areas like walls, houses, tree barks, rocks, and in any damp places.

Humans use seaweeds in copious ways as they have ample amount of vitamins and nutrients like:

  1. Fertilizer
  2. Medicine
  3. Food (famous Carrageenan agar and other gelatinous products)
  4. Industrial products

The structure of seaweed is somewhat simple and insignificant. They use the diffusion process to extract nutrients from the water for the need of transportation.

Main Differences Between Algae and Seaweed

  1. Algae can be either autotrophic or heterotrophic in nature while Seaweed is only autotrophic in nature.
  2. Multi-cellular as well as unicellular micro-organisms are present in the Algae family, whereas Seaweed is found as completely multi-cellular organisms.
  3. Algae can survive in any type of water bodies while seaweed can only live in marine habitation.
  4. Algae generally produce 70% of the total amount of atmospheric oxygen in the world.
  5. While Seaweed can be edible, and used by humans in many ways while Algae supports by creating a higher rate of sun’s energy through photosynthesis.


Algae are a divergent class of aquatic organisms that are mostly photosynthetic, as microalgae or macroalgae. These can be unicellular or multicellular.

Generally, unicellular algae are present in both marine and freshwater, which is beneath the water or free-floating.

Contrarily, seaweed is termed as macroalgae, which is multicellular in structure and can survive in marine water. They are benthic and can grow in surface water.

Also, algae serve as premier producers in aquatic food chains, while seaweed offers the needed immediate dwelling place for fisheries and other marine creatures. The main difference between algae and seaweed depends on their size, environment, and the reason for their survival.


  1. https://www.ncbi.nlm.nih.gov/pmc/articles/pmc3053594/
  2. http://nopr.niscair.res.in/bitstream/123456789/26485/1/JSIR%2060%285%29%20378-382.pdf