10 of the Smallest Ocean Animals

There are some pretty big creatures in the seven seas.

But what about the other end of the scale? There are some truly remarkable tiny critters at the other end of the spectrum. On this list, readers can learn about ten of the most interesting small ocean animals.

Krill

Size: 35mm

Location: Antarctic ocean

This term has almost become encompassing for various species. But broadly speaking, krill are a collection of small crustaceans. The word roughly translated means “fry” which is the word for a baby fish. However, they are not members of the fish family.

Perhaps the most interesting thing about krill is that they are so numerous. They form a large part of the diet of the aforementioned Blue Whale which as you may be aware is the largest animal to have ever lived.

Pea Crab

Size: 20mm

Location: Atlantic and Pacific coastlines

Pea crabs are tiny species of crab. They are very widespread.

Like most crab species they have pincers, although there are no occurrences of this causing danger to humans.

Karenia Brevis

Size: At their smallest they are 20mm

Location: Gulf of Mexico

This tiny single-celled organism has a big legacy. It is the organism that causes the infamous Florida Red Tides. While it isn’t directly an issue to human beings rapid blooms can wreak havoc on marine ecosystems making this little organism a big problem. They are clever organisms that use their twin flagella in order to propel themselves and can travel great distances.

Irukandji Jellyfish

Size: 10mm

Location: Australia

These might be considered giants compared to some of the creatures on this list, but they are still pretty small measuring in at roughly half a centimeter. They’re small but they pack a punch. They have a potent toxin that can be fatal in rare cases, perhaps a surprise given its tiny size, but even if it does not kill you directly, it can lead to Irukandji syndrome. One of the effects of this is that it creates a feeling of certain doom and triggers anxiety attacks and nausea. All of which can be pretty bad if you are in the sea. There is thought to be a wealth of unattributed deaths that might have been caused by this tiny creature.

Brine Shrimp

Size: 15mm

Location: Worldwide in saltwater and marshes

You may know brine shrimp by their commercial name as they are sold in their dormant form and dubbed sea monkeys. They do hold the distinction of being one of only a few animals that have the ability to survive without a metabolism. Or the sum of all the chemical processes in an organism.

Mysida or Mysis shrimp

Size: 5mm

Location: freshwater lakes in North America

While slightly bigger than some of the creatures on this list (they start at about half a centimeter) they still sit proudly on the list. Their diet consists of another creature on this list as they are often fed brine shrimp. For fans of “Sea Monkeys,” this might make Mysis shrimp enemy number one.

Copepods

Size: 1mm

Location: Worldwide in saltwater

Again, these are a favorite of the reef-keeping community. Often a colony of these tiny creatures will develop independently in a reef setup. They are vast and tiny. They are a major food source and are grazed on by everything from clownfish to the wonderfully vibrant Mandarin Goby. They are also the main food source for seahorses who need an almost constant supply of tiny critters to survive. Some dwell on the ocean floor and on rocks. Others swim in the currents.

Chlamydophrys

Size: At their smallest they are 12 μm (micrometers)

Location: Worldwide

These tiny aquatic organisms are so small they are hard to distinguish from one another. It is a eukaryotic species and feeds on organic matter.

Algae

Size: At their smallest they are 0.5 μm (micrometers)

Location: Worldwide

Algae may be considered by some to be a plant. Interestingly algae are responsible for the majority of the earth’s oxygen-rich atmosphere. Far more than trees (which are often attributed the moniker of oxygen kings due to their photosynthesis.) The truth is that algae are not truly a plant or an animal. It is difficult to classify at all. However, there are a vast array of types and it survives and thrives in freshwater and saltwater alike.

Plankton

Size: At their smallest they are 0.2 μm (micrometers)

Location: Worldwide (in fresh and saltwater)

This is a diverse range of creatures. And believe it or not, they live in the air as well. They are unable to move and instead rely on the current of the water (or air) to provide them with movement. They consist of bacteria, algae, and protozoa. Their unusual and interesting appearance makes them interesting to study.

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