What is Plankton? The Real Monsters of the Ocean

icefish larva picture, what is plankton
Icefish larva, part of the plankton photo by: Wikimedia Commons

What is plankton? The Real Monsters of the Ocean

Night on the coral reef

As darkness slowly creeps over the coral reef, the night dwellers begin to appear. Coral relies upon its symbiotic algae to feed themselves during the day, but after dark the coral polyps unfold their sticky tentacles. These tentacles grab food (plankton) floating by in the water.

Black tip reef sharks, which have been snoozing lazily on the sandy bottom during the day, become violent predators. They travel in packs with some sharks flushing out and eating prey from the fish cowering in their reef lairs. Other sharks catch whatever the flushing sharks missed.

A chambered nautilus, the less sexy cousin of octopus and squid, slowly ascends from 2,000 feet deep to 300 feet deep, its shell’s chambers acting like a submarine’s ballast.


Then the real stars of the night show up, barely visible to the naked eye. The longest vertical migration takes place every night. Plankton rise from depths of 1,500 feet to feed near the surface.

I was lucky to see some of these other-worldly creatures on a Blackwater dive called “Pelagic Magic,” through Jack’s Diving Locker in Kailua-Kona on the Big Island of Hawaii. Divers hold onto ropes under the boat and like a seat back entertainment center on an airplane seat, each diver gets their own individual show. The highlight of my dive was seeing a squid flush red, catch a meal and dart to the surface, all in a blink of any eye.

Types of plankton

Plankton are the real monsters of the ocean, as the myriad of shapes and colors is outstanding. The larval form of many animals, like a crab or sea urchin, look nothing like the adults.

Much of the plankton is translucent because in the depths of the ocean they virtually disappear. Other plankton are bright red, which at the surface are obvious, but at depth they are barely visible. This is because red is the first color to be lost under the water. The further down you descend in the ocean, the less colors you see.

Phytoplankton vs. Zooplankton

There are two main types of plankton, the phytoplankton vs. zooplankton. “Phyto” means plant in Greek, and “Zoo” means animal (think of what lives at a zoo!). So the phytoplankton are the plants of the ocean, while the zooplankton are the animals of the ocean. Phytoplankton are very important because they make up the base of the food web, and they are responsible for one out of every two breaths you take! Just like how animals on land eat plants (do you eat your veggies?), the zooplankton depend on the phytoplankton for food. And plenty of larger animals-fish, whale sharks, manta rays, baleen whales-depend on plankton for as their food.

Did you know krill (part of the plankton) are the most abundant animal on Earth?