Corals are very unique marine invertebrates that are known for making reefs and living in large colonies. Stony corals, those that form reefs, develop a calcium carbonate-based skeleton. Soft corals can live in reef ecosystems, but they do not form a hard exoskeleton and may resemble marine vegetation. Looking at these organisms, it’s easy to mistake them for plants, and it’s even harder to imagine them feeding. So, what do corals eat?

We’re going to show you what different types of corals eat and how they manage to eat at all.

What Are Corals?

Before we look at what they eat and how they eat, let’s take some time to examine the nature of corals. Although they may look like plants or even minerals, corals are animals. Specifically, they belong to the Cnidaria Phylum and the Anthozoa subphylum of the Animalia kingdom.

These animals are usually individual polyps that live in large colonies together. Even if it seems like the organism is a single being, it’s usually not. Instead, individual polyps numbering in the thousands or beyond can form colonies together. Generally, two types of corals are recognized. Stony corals and soft corals are two broad types of these animals.

Stony corals, or hard corals, are known for developing a hard skeletons throughout their life cycles. These creatures build reefs, and they’re known for living in shallow water with access to a lot of sunlight. Stony corals’ hard skeletons protect them from predators.  

Soft corals can resemble marine plants, lacking the same skeleton made of calcium carbonate seen in hard corals. Instead, they rely on chemical compounds to drive off predators. You can spot them by counting the number of tentacles present on each of their polyps. Soft corals have eight tentacles.

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What Foods Do Corals Consume?

Coral
Corals eat dissolved organic matter, phytoplankton, and zooplankton.

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Corals eat zooplankton, bacterioplankton, dissolved organic matter, small crustaceans, phytoplankton, and nutrients resulting from the symbiotic relationship they have with dinoflagellates.

Not every type of coral consumes each type of food that is listed here. Instead, many differences exist between corals’ eating habits. Some of them rely more on dinoflagellate algae symbiosis for food and others feed directly on creatures that inhabit their environment by catching them.

A Complete List of What Corals Eat

Before we explore how corals gather and consume their foods, let’s take a closer look at their choice of meals. Here is a more thorough list of the foods that corals consume throughout their lifespans. Their preferred meals include:

  • Zooplankton
  • Phytoplankton
  • Detritus
  • Dissolved organic matter (DOM)
  • Small fish
  • Small crustaceans
  • Floating eggs
  • Bacterioplankton
  • Pseudoplankton
  • Invertebrate larvae
  • Byproducts of photosynthesis

As you can see, corals’ meals are just as diverse and unique as the animals themselves. Now, let’s explore how corals obtain their meals and eat them.

How Do Corals Find Food?

Animals That Don't Have a Brain - Coral
Coral uses its tentacles to catch its food.

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When you look at a coral polyp, it may seem just about impossible for them to actively obtain food. They seem to be completely anchored and incapable of obtaining food. They’re far from helpless, though. Sometimes, corals will simply use their tentacles to direct free-floating food into their mouths. Other times, it’s not as simple as moving food from one area to another.

Corals can actually capture prey. The tentacles of a polyp are riddled with nematocyst cells. When prey brushes against these cells, these cells activate, sending out a swift barb on a thread that punctures the prey and injects them with a type of poison. From there, the tentacles can sweep the prey into the mouth while the nematocysts reset for another attack.

The other way that corals obtain food is also interesting. As we’ve mentioned, many types of corals have symbiotic relationships with zooxanthellae, a type of dinoflagellate from the Symbiodinium genus. These organisms can conduct photosynthesis, giving the coral access to glucose, amino acids, and other byproducts that provide energy to the host coral. In return, the zooxanthellae obtain carbon dioxide and other wastes that they can utilize.  

To say that corals have interesting, unique methods of obtaining food is an understatement!

Are Corals Dangerous to Humans?

Corals have two ways that they can harm humans but eating them is not one of the methods. First off, stony coral can cut a person if they come into contact with it. These wounds require cleaning and care to prevent them from becoming infected.

The other way that corals can harm people is by stinging them. If a person gets too close to coral and rubs against it, they may feel a stinging sensation. Some types of coral are more dangerous than others, though. The more potent ones can sting humans and cause a painful rash from where the coral contacts the skin.

Coral isn’t harmless, but it’s not going to kill a human being unless they impale themselves on a large piece of coral.

What Do Pet Corals Eat?

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Pet corals can eat small bits of fish, krill, or shrimp.

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Caring for a pet coral requires understanding the foods that they can eat. For the most part, coral owners provide a wide variety of foods to their pets to find something they eat.

It’s not uncommon for corals to eat commercial pellets, flakes, and freeze-dried foods as pets. However, corals still form symbiotic relationships with zooxanthellae and rely on photosynthesis while they’re in the tank.

Also, pet corals can eat fresh foods like small bits of fish, shrimp, krill, or even squid. Using a wide variety of foods when feeding corals can lead to better outcomes and ensure the pet coral gets the required nutrition.

All told, corals are complex animals that can take a variety of shapes. Unfortunately, many species of coral are now endangered, largely to the impacts of human beings. Pollution, sedimentation, fishing, and climate change all have led to negative outcomes for corals throughout the world.

While corals may not seem all that important since they only cover a very small portion of the ocean floor, their reef habitats help support about a quarter of all marine animals.

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