American Oceans

What Eats Seaweed?

Seaweed plays a significant role in marine ecosystems, providing food and shelter for a wide range of organisms.

sargassum seaweed

In an interconnected web of life, many creatures feed on this underwater vegetation, relying on it as a primary food source, while others enjoy it as part of a varied diet.

Some of the most common seaweed-eating animals include crustaceans such as crabs, shrimp and lobsters, as well as starfish, sea urchins and betta fish.

Other marine life that consume seaweed consists of turtles, eels, pufferfish, sea lions, penguins, and even certain bird species like the albatross. As part of the food chain, these organisms aid in maintaining a balanced ecosystem and contribute to the overall health of our oceans.

It is important to note that while some animals solely rely on seaweed as their primary sustenance, others may only turn to it when their preferred food sources are scarce.

This highlights the versatility and adaptability of these creatures in their ever-changing habitats and reinforces the vital role seaweed plays in supporting a diverse range of marine life.

Marine Organisms That Eat Seaweed

Seaweed, a vital part of marine ecosystems, serves as a primary food source for various marine organisms.

Turtle eating seaweed

In this section, we will discuss different types of marine organisms that consume seaweed as a part of their diet.

Herbivorous Fish

Some fish species are herbivores, primarily feeding on seaweed and other marine plants.

Examples include the pufferfish and betta fish, which are known to graze on seaweed for their nutritional needs. Additionally, some larger fish, such as sea turtles and some dolphins, also consume seaweed.

Sea Urchins

Sea urchins are another group of marine organisms that feed on seaweed. They use their sharp teeth and intricate mouthparts to scrape seaweed off rocks and consume it.

Purple and red sea urchins eat a piece of kelp

Sea urchins play a crucial role in maintaining the balance of marine plant life by controlling the growth of seaweed populations.

Crabs and Lobsters

Crabs and lobsters are omnivorous crustaceans that include seaweed in their diet. Both animal and plant matter make up their meals, with seaweed being a common food source.

These crustaceans use their powerful claws to grab and tear pieces of seaweed to consume, and they contribute to a balanced marine food web involving seaweed, crustaceans, and fish.

Terrestrial Animals Feeding on Seaweed

While seaweed is a popular food source for marine creatures, there are also terrestrial animals that rely on it for sustenance.

Some of these animals live in coastal environments and regularly interact with the ocean. In this section, we will discuss two groups of terrestrial animals that feed on seaweed: birds and mammals.


Several bird species are known to consume seaweed, particularly those living in coastal regions.

snipe sandpipers

One such bird is the dusky moorhen, which forages on aquatic plants, including different types of seaweed. Other birds that incorporate seaweed into their diet include gulls, ducks, and some shorebirds.

Seaweed provides these birds with essential nutrients and minerals that support their overall health.

For shorebirds, feeding on seaweed can also create opportunities to find other food sources, such as small invertebrates that live within the seaweed.


In addition to birds, some mammal species also consume seaweed. One example is the North Ronaldsay sheep found in Orkney, Scotland.

Sheep herds that have adapted to eat kelp in the Western Fjords of Iceland

Living in a coastal environment, these sheep have adapted to a diet consisting primarily of seaweed, which supplies them with the necessary nutrients for survival.

Another mammal known to eat seaweed is the marine iguana of the Galapagos Islands. Although considered a reptile, its feeding behavior is similar to that of some terrestrial mammals.

These unique iguanas graze on seaweed in the intertidal zone, supplementing their diet with other aquatic plants they can find.

It’s important to note that the availability of seaweed as a food source for terrestrial animals may be limited, with some species only relying on it when other food sources are scarce.

Nonetheless, seaweed plays a crucial role in the diets of certain bird and mammal species that have adapted to living near the sea.

Microorganisms and Decomposers

Seaweeds and other marine vegetation not only serve as a primary food source for larger animals, but they also play a crucial role in the context of microorganisms and decomposers.

These tiny organisms contribute significantly to the breakdown of organic matter, recycling nutrients, and maintaining the stability of marine ecosystems.


Marine bacteria are often the first decomposers to break down dead seaweed and other plant material in the ocean.

set of seaweed on stone tropical fungi or algae

They take advantage of the numerous organic compounds present in the seaweed, breaking them down into simpler forms that can be reused by other organisms in the ecosystem.

One example of bacteria that consume seaweed is the Cytophaga. This type of bacteria possesses enzymes that can decompose the complex carbohydrates found in seaweed, such as alginates and fucoidans.

As these bacteria break down the organic matter, they release nutrients like nitrogen and phosphorus back into the marine environment, which can be utilized by other primary producers such as phytoplankton.


Like bacteria, marine fungi also play an essential role in the decomposition of seaweed.

Fungi possess specific enzymes that enable them to break down the cellulose and other complex compounds found in the cell walls of seaweeds. T

he breakdown of cellulose releases sugars and other nutrients that can be absorbed and utilized by the fungi for their own growth and reproduction, as well as supporting other marine organisms through the food web.

Some examples of marine fungi that decompose seaweed include species from the genera Aspergillus, Penicillium, and Lulworthia.

Their combined effort in decomposing seaweed materials contributes to a healthy and balanced marine ecosystem by recycling valuable nutrients and maintaining overall biodiversity.

Human Consumption and Uses

Culinary Applications

Seaweed is a highly versatile ingredient used in various cuisines, particularly in Asian cultures such as Japan, Korea, and China.

woman eating dry seaweed

Consumption of seaweed, or kaiso, in Japan once accounted for more than 10% of the national diet, with an average seaweed intake of 3.5 kg per household in 1973 (Indergaard 1983). In culinary applications, seaweed can be found in dishes such as sushi, soups, and salads.

Furthermore, it is an important source of nutrients, including amino acids, vitamins, and minerals.

Industrial and Pharmaceutical Uses

Seaweed has a wide range of uses beyond human consumption. Industrially, it can be employed in the production of biofuels, due to its high biomass and quick growth rate.

Additionally, seaweed extracts, such as alginates, agar, and carrageenan, are extensively utilized in the food, cosmetics, and pharmaceutical industries as stabilizers, thickeners, and emulsifiers.

In the pharmaceutical world, seaweed-derived compounds have displayed promising potential for the development of new drugs.

These compounds possess various therapeutic properties, including antioxidant, antimicrobial, and anti-inflammatory activities, which could lead to novel treatments for several diseases and conditions.

Agriculture is another area where seaweed plays a significant role, as it has traditionally been used as an animal feed supplement, particularly in coastal regions of Scotland and Northern England.

Recently, research has shown that incorporating seaweed into livestock diets can potentially reduce methane emissions from cattle, illustrating seaweed’s potential environmental benefits as well.

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