Sometimes, being a small fish in a big pond really does have its advantages. Especially when the big pond we are referring to is the ocean. The big blue is home to some awesome small sea creatures and different types of small fish, however, the smaller ones can be very very difficult to find. The world seems a lot bigger when you are only 4 mm small!
What is the Smallest Animal in the Ocean?
The ocean is not only home to the biggest animal in the world, the Blue Whale, but also home to some of the smallest animals in the world. Many scuba divers do not notice many of these tiny, mini sea creatures when diving.
Many of smallest animals in the world’s oceans are viruses & bacteria, making them all but invisible to the naked eye. But once you get beyond the microscopic level you’ll find that some of the smallest sea creatures are quite adorable!
They may be small, but don’t let that fool you, these animals are just as important to the ocean and its ecosystem. In no particular order, below we have put together our top 10 list of smallest animals in the ocean. From marine viruses to the super cool Irukandji jellyfish.
1. Marine Viruses
Let’s start small – like, microscopic small. Marine viruses exist similar as they do on land, with the smallest measuring just 40 nanometers (nm) in size. What the heck is a nanometre right?! In today’s society, you probably associate nano as a SIM card for an iPhone for example, to put this into perspective for you a nanometre is one billionth of a meter! The biggest marine viruses can grow up to 400 nm in diameter and are yet still invisible to the human eye without using an intensified microscope.
Marine viruses come in all sorts of sizes and with destructive capabilities; there are literally millions of different types of them! The existence of marine viruses was actually discovered through epifluorescence and electron microscopy of ecological water samples, following metagenomics sampling of uncultured viral samples. Cool eh!?
2. Marine Bacteria
Just like the marine viruses, marine bacteria exist just as on dry land, the ocean is home to infinite marine bacteria. The marine bacteria are the second smallest organisms found in the sea. Although bigger than the marine viruses, many of these bacteria are still very small in size, with some measuring only 1,000 nm in length. Although they may seem a lot larger than the marine viruses, these organisms still remain invisible to the naked human eye.
Studies of marine bacteria are becoming a quickly growing field within ocean research. In fact, did you know that in just one milliliter of seawater, you can find up to a million living microscopic organisms. Small but mighty, these bacteria play critical roles in the ocean’s environment. Yay for bacteria!
The sea is home to some of the planets smallest plant organisms. Many of these are single-celled green algae specimens. Around five times larger than the marine bacteria, they measure from 5,000 nm (5 micrometers). These teeny tiny algae tend to become prey for the larger, yet still small, marine creatures.
Algae really do vary when it comes down to size; ranging from the tiny microscopic mircomonas species to the gigantic kelps that are known to tower the ocean seabed by growing up to 60 meters (200 feet) tall. As well as their ecological roles played both by producing oxygen and providing food for most aquatic life, algae are also a source of crude oil which is used in some foods and numerous pharmaceutical and industrial products used by humans. Due to the popularity of the scrummy kelp and the oil it produces, giant kelp forests have now been granted an endangered status.
4. Dwarf Lantern Shark
Yes, that’s right, a shark made our top 10 smallest animals found in the ocean! The dwarf lantern shark is possibly the smallest known shark in the world, and quite clearly the cutest! The largest specimen ever to be recorded measured only 7.8 inches (20 cm) in length. That’s tiny! These small sea animals are found around the upper continental slops off of Venezuela and Colombia and swim at a depth of about 283 – 439 meters (928 – 1,440 ft).
The lantern shark can be identified by its teeny size even at maturity, by its long flattened head, it’s a mid-dorsal line and also by the black ventral markings. This awesome small fish is actually capable of producing light from an extraordinary array of photophores. Although the dwarf lantern shark isn’t targeted by commercial fisheries, its species could become threatened as a cause from by-catch. The impact of human activity on the dwarf lantern shark population is currently unknown.
5. Sexy Shrimp
Swit Swoo!! I know what you’re thinking, not your type of sexy? Think again! There is a reason the Thor Amboinensis is commonly known as the sexy shrimp, and that is down to its unusual body movements. They get this flamboyant nickname from the way they sway their abdomen back and forth with an exotic like flair. The sexy shrimp can grow up to about 1-¼ inches but are usually smaller. Most often found within the reefs of the Indo-Pacific, the sexy shrimp is generally found hiding amongst the tentacles of an anemone.
These flirtatious fellas are very popular amongst the macro photographers and they may be small, but the sexy shrimp also boasts a vibrant orange colored body which is decorated with white polka dot.
6. Juvenile Frogfish
Frogfish tend to be a favorite for divers to look for underwater and attract a lot of attention, especially to the underwater photographers. Their popularity is clear amongst the variety of small ocean fish, due to them being very well camouflaged and being able to adapt to their surroundings makes it difficult to spot them. Ranging in all kinds of sizes and different colors, these small saltwater fish are so ugly, it makes them cute!
Adult frogfish are known to grow from anything from an inch up to almost 22 inches. However, it is the baby frogfish that have made a spot on our smallest critter list. Dependent on the type, some juvenile frogfish can be smaller than an inch long in size, or even grow to just a few millimeters!! Cutest overload, we know. The small size makes it extremely difficult to find these little guys, but believe us; the search is truly worth it!
For the non-divers, the idea of a slug-like bottom dweller may seem a little boring or uninteresting, but they would be mistaken!! For us divers, the picture is painted very differently. Nudibranchs are little wonders of the ocean that many experienced scuba divers love to see. While these small colorful critters can grow up to about 12 inches (30 cm) long with the smallest being less than ¼-inch long (4 mm).
Ranging in extraordinary colors and striking forms, nudibranchs tend to give off a small and helpless vibe, but studies show them to be quite the contrary. Over 3,000 different species of these small creatures have been discovered to date with more being found and identified worldwide every single day.
8. Pygmy Seahorse
Another favorite amongst scuba divers and number eight on our list is the beautiful pygmy seahorse. This small saltwater fish spends their whole adult life living on soft corals and beautifully colored sea fans and are found in warm tropical waters. Growing to the average size of a fingernail they tend not to grow any bigger than an inch (2.4 cm) long. Juvenile pygmy seahorses are usually so tiny (a few millimeters in size), that they are basically invisible to the diver’s eye, especially as they are almost perfectly camouflaged to their surroundings.
Pygmy seahorses are not only the smallest of all seahorses but are one of the most popular subjects for the marco photographers. These little critters are extremely hard to see, but if you are lucky enough to be able to find them and get a picture, please be aware that they do not actually have eyelids and are therefore very sensitive to light!
9. Octopus Wolfi
The Octopus wolfi is the world’s smallest known octopus. And boy is it adorable! Found most commonly in the shallow waters of the western Pacific Ocean, they are a delight for divers to spot! The octopus wolfi is characterized by a pattern formed by papillate fringes around the edges of its suckers. It makes our list for measuring around 2.5 cm (1 inch) in length and normally weighs less than 1g (0.04 oz).
10. Irukandji Jellyfish
Remember the cute little guy Squishy, that Dory found in the film Finding Nemo? For those of you who haven’t seen the film (watch it, it’s great!), Dory finds a teeny tiny jellyfish and names it “Squishy”, blinded by its cutest, she touches it and gets a nasty sting! We have all been fooled by this kind of way before, but when it comes to the Irukandji jellyfish don’t be like Dory and let this cute little thing deceive you.
The Irukandji jellyfish is a deadly venomous type of box jellyfish. Growing to an adult size of only about 1 cm long; they not only hold the claim to being one of the smallest jellyfish in the world, but also the most venomous jellyfish in the world. Like most venomous animals in the world, they can be found in Australia. The Irukandji jellyfish are able to fire their stingers into their victim, and unlike most jellyfish, its stingers are found in the bell as well as its tentacle.