We know as sea urchins more than 1,000 species of animals that are characterized by having their bodies covered with thorns. All these species form the class Echinoidea, a group of animals closely related to stars, cucumbers and sea lilies, as well as brittle stars. Together they form the phylum Echinodermata, which means “spiny skin” because of its ornate skeleton.
As occurs in many echinoderms, sea urchins have a very powerful chewing apparatus. Around its mouth you can see 5 teeth that are used for chewing and scraping, but what exactly do sea urchins eat? Are they carnivores or herbivores? We tell you about it in this article about feeding sea urchins.
Are sea urchins carnivorous?
The best known relatives of sea urchins are stars. These, as we explained in the article on What do starfish eat, are voracious predators. Due to this and the terrifying appearance of its toothed mouth, there is a belief that sea urchins are carnivorous. The reality is that, although there are some carnivorous species, most are omnivorous
Most sea urchins base their diet on algae, although they supplement their diet with small live or dead animals that they are on their way. But what exactly do sea urchins eat? Let's see it.
Types of sea urchin feeding
The feeding of sea urchins depends on each species, its geographical location and, above all, the food available. Most sea urchins are opportunistic and consume the most abundant food in the ecosystem: algae. When these are not very numerous, they often consume other types of food, and can have a fairly varied diet.
What sea urchins eat also depends on the presence of predators. They often come out to forage at night, when their predators do not usually appear. Also, to avoid being too exposed, they do not stray too far from their shelter (cracks in rocks, corals, etc.). For this reason, they only consume what is close to where they rest during the day.
However, the above is not true for all species. Therefore, depending on their diet, sea urchins are usually classified into three types:
- Omnivorous sea urchins
- Herbivorous sea urchins
- Carnivorous sea urchins
What do omnivorous sea urchins eat?
Omnivorous sea urchins are the most common and numerous. They often have a favorite food and consume it in large quantities when it is abundant near their shelter. For most omnivorous sea urchins, this preferred food is leafy brown algae However, when these are scarce, they do not move much for fear of being preyed upon. This is when they have a more varied diet, which may include:
- Red Algae
- Green algae
- Diatome
- Cirrípedes
- Polychaetes
- Sponges
- Tunicates
- Bryozoa
These are some species of omnivorous sea urchins:
- Crowned Sea Urchin (Centrostephanus coronatus)
- Green hedgehog (A rbacia dufresnii)
- Long-spined sea urchin (Diadema savignyi)
- Black sea urchin (Arbacia lixula)
What do herbivorous sea urchins eat?
Very few sea urchins are considered herbivores. Typically, they are specialized in consuming a single type of algae, which can account for up to 90% of their diet. This is the case of the purple sea urchin (Strongylocentrotus purpuratus), which feeds mainly on geniculate coralline algae. They may also consume fleshy brown and red algae when they are abundant.
Another herbivorous sea urchin is the pink flower urchin (Toxopneustes roseus), whose diet is based on rhodoliths, that is, non-geniculate coralline algae. It's pink because its body is covered in rhodoliths, allowing it to camouflage itself while feeding. In addition to coralline algae, this sea urchin eats green algae and diatoms in small quantities. It very rarely eats bryozoans.
What do carnivorous sea urchins eat?
Carnivorous sea urchins are those that base their diet on the consumption of other animals. There are very few species and they feed mainly on sessile invertebrate animals, that is, they live fixed to a substrate. Like herbivores, carnivorous sea urchins often specialize in consuming a single type of food.
An example of a carnivorous hedgehog is the slate pencil hedgehog (Eucidaris tribuloides), specialized in consuming sponges, although it can eat other organisms in small numbers. Some carnivorous sea urchins are so adept that they can consume mobile animals such as clams and even other sea urchins. This is what sea urchins of the species Arbacia spatuligera eat, and they can even practice cannibalism when other foods are not very abundant.
Now that you know the different types of feeding of sea urchins, don't miss this other article in which we talk about all the Characteristics of the sea urchin.
