My Science School

Found in tropical and subtropical oceans worldwide, barracudas are muscular fish with streamlined, torpedo-shaped bodies. Undoubtedly, they have a fearsome appearance and ferocious behaviour. They are opportunistic predators that launch surprise attacks.

Barracudas are attracted to shiny objects, like the silvery fish they prey on. Humans that enter the water with glittering objects, such as watches and jewellery, may cause curious barracudas to investigate and mistake these objects for a food source.

Divers with shiny objects are reported to have been attacked by barracudas. As a precaution, divers are usually advised to remove shiny objects before entering the waters.

Barracudas feed on fish such as jacks, grunts, groupers, snappers, small tunas, mullets, killifishes, herrings, and anchovies by simply biting them in half. They kill and consume larger prey by tearing chunks of flesh.

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For centuries, travellers to South America have brought back some gruesome stories about fish with teeth that can strip the flesh of any animal foolish enough to try to cross the rivers that are their home. These stories were about piranhas, freshwater fish with razor-sharp teeth. In fact, the term piranha in a Brazilian language means ‘tooth fish’.

Most of the piranhas are sized between 12 and 35 centimeters. The red-bellied piranha is the largest among the lot and it grows to a size of half a meter!

Piranhas hunt in groups of more than a hundred members. Several groups can converge in a feeding frenzy if a large animal is attacked, although this is rare. Piranhas have excellent hearing capability. When a piranha locates the prey, signals are sent to the group acoustically. Everyone in the group rushes in to take a bite and then swims away to make way for the others.

The angler fish lives in one of the most uninhabitable habitats in the world- the lightless bottom of the sea. Living at depths of at least 2000m this species lives its life in the complete absence of sunlight. Some of them live in the sea floor while others live close to the sea floor.

The angler fish won’t impress you with good looks. For many species of angler fish, the males are much smaller than females. The females have a piece of dorsal spine that protrudes above their mouths like a fishing pole. In fact, they get their name because of this feature.

The tips of the spine have luminous flesh that attracts prey. Using a muscular skin flap, a deep-sea anglerfish can either hide or reveal its lighted lure. By pulsing the light and moving the lure back and forth, they successfully attract crustaceans, fishes, and other prey. Their bodies are flexible and mouths so big that they can swallow prey that is thrice their size.

Many of you might have spotted lion fish in aquariums. A fish with a unique appearance, it is an invasive predator. Its fins are venomous and are capable of producing painful, puncture wounds. A sting from a lionfish is extremely painful to humans and can cause nausea and breathing difficulties.

This fish is endemic to the South Pacific and Indian oceans. Lion fish corner their prey against reefs and rocks, then strike suddenly to swallow the prey as a whole. They have the unique ability to expand their stomachs to accommodate prey of larger sizes.

The best known lion fish species is perhaps the red lion fish with red-and-white zebra stripes. Their venom is dangerous and it has lightning-fast reflexes to capture prey, mainly fish and shrimp.

Lion fish threaten reef systems by preying on fish that clean the reef and keep it healthy.

The lion’s mane jellyfish is the world’s largest jellyfish. It is usually found in colder oceans like the Arctic, northern Atlantic, and northern Pacific Oceans. The lion’s mane jellyfish gets its name from its tentacles which resemble the mane of a lion. These tentacles grow up to a size of three metres and are packed with stinging cells. They are used to catch their favourite fish, smaller jellyfish and zooplankton.

It is interesting to watch a lion’s mane jellyfish catch its prey. At first, it delivers a sting loaded with neurotoxins and when the prey is immobilized, it is moved to its mouth using specialized tentacles called oral arms.

Scientific research has suggested that jellyfish actually thrive in areas that are affected by human activity. Overfishing, climate change and pollution have helped promote more jellyfish swarms by reducing their main predators and competitors and increasing their prey.

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The octopus is a unique animal. It is intelligent, and has a sharp vision and a devastating array of offensive organs for attacking the prey. It is a fast swimmer, too. These qualities make the octopus a supreme predator.

Octopuses vary a great deal in size; the smallest is about 5 cm long, while the largest species may grow to 5.4 metres in length and have an arm span of almost 9 metres! They inhabit various regions of the ocean, including coral reefs, open sea waters, and the seabed.

The body of an octopus is designed for hunting. Its skin cells have the ability to change colour with the help of which it camouflages near rocks and the coral reefs. Its tentacles have muscular discs that help it catch prey. The octopus usually ambushes its prey; when a suitable prey comes, it shoots out one of its eight long tentacles and traps it. It usually feeds on crabs, shrimps and lobsters though it can attack larger prey like sharks as well.

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The crown-of-thorns starfish is a large starfish that preys upon hard, or stony coral polyps. It is the world’s second largest starfish and grows up to the size of one meter. It has venomous thorn-like spines that cover its upper surface, resembling the biblical crown of thorns, and that is how it got its name.

The crown-of-thorns starfish is a well-known coral predator. It eats coral prey by extruding the stomach out from its body, covering the corals. An individual starfish can consume up to 6 square metres of living coral reef per year. Its spines are somewhat flexible; they are used for locomotion and for defence from potential predators.

The crown-of-thorns starfish are an important part of the ecosystem in normal numbers on healthy coral reefs. If more than 30 crown-of-thorns starfish are found in a hectare, it is called an outbreak. Outbreaks have been known to cause serious harm to coral reefs in some areas.

As its name suggests, the giant otter is huge. Its body grows to a length of up to 1.7 metres, which is the longest of all the otters on Earth.

Giant otters are also known as river wolves. They live in freshwater rivers and streams which are usually affected by seasonal flooding. Fish makes up the majority of their diet. They hunt either alone or in groups. A giant otter eats two to four kilograms of food per day. Fish are supplemented by crustaceans, snakes, and other river creatures.

Giant otters are well adapted for the aquatic way of life. They have webbed feet, water-repellent fur to keep them dry and warm, and nostrils and ears that close in the water. They swim by propelling themselves with their powerful tails and flexing their long bodies.

Giant otters are active during the day. They also have the reputation of being the noisiest of all the otters; scientists have documented distinct vocalizations that indicate alarm, aggression, and reassurance.

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Sea anemones are known for their beauty; with their spectacular white, green, blue or red patterns and circles of petal-like tentacles, sea anemones have the appearance of harmless underwater flowers. It is with this appearance that they manage to deceive a lot of marine creatures.

More than 1,000 sea anemone species are found throughout the world’s oceans at various depths in varying sizes- some are as small as half an inch, while others may grow up to a size of six feet! Warmer seas are home to the largest and most colourful sea anemones.

Sea anemones are close relatives of jellyfish and corals. They do not have a solid skeleton. Some species have adhesive-secreting structures and cover themselves with grains of sand, bits of shell, or other foreign objects. With their elastic bodies and venomous tentacles, they trap a range of marine creatures including small fish, shrimps and crabs.

Do you know what a siphonophore is? It is an animal made up of a colony of organisms working together. The Portuguese man-of-war is a colony of individual organisms called polyps. It is often mistaken for a jellyfish, but truth be told, it is a highly venomous open ocean predator. It typically feeds on small marine organisms, such as fish and plankton.

Each polyp that makes up a Portuguese man-of-war is intertwined with the others, has highly specialized functions and cannot survive without the others. The largest of the polyps is known as the float; it is a bag of secreted gas which keeps the colony afloat. There are also feeding polyps, which are small digestive bags, each with its own mouth.

Tentacle polyps are the ones that look like elongated threads below the float and are studded with stinging cells. They have numerous venomous microscopic nematocysts which deliver a painful sting powerful enough to kill fish. They use the sting against predators as well. Apart from these, there are reproductive individuals as well.

Sea otters inhabit the Pacific coast. These sleek, furry marine mammals have no insulating layer of fat like other animals that live in colder climates, but are kept warm by their fur and high metabolism.

Sea otters were hunted for their fur to the point of near extinction. In fact, sea otters have the densest fur of any mammal; the coat of a sea otter has over half a million hairs per 6.5 square centimeters! These animals are very clean as well; they wash themselves after eating and frequently clean their fur with paws.

The way sea otters eat is interesting; they use their stomach as a table. A sea otter eats in the water, lying on its back, with its food on its chest. Sea otters are the only otters to give birth in the water. Mother sea otters have the ability to nurture their young while floating on their backs.

Sea otters play an instrumental role in controlling sea urchin populations which would otherwise inflict extensive damage to kelp forest ecosystems (underwater forests).

The humpback whale is an enormous creature; it is as big as a school bus! It is known both for the howling sounds it makes and the amazing acrobatic abilities.

Humpbacks feed primarily in summer and live off their fat reserves during winter. They use many innovative methods for feeding. One such method is called bubble net feeding.

A group of whales will swim in a shrinking circle blowing bubbles below a school of prey. The shrinking ring of bubbles will encircle the school and confine it in an ever-smaller cylinder. This way, they can swallow thousands of fish in a single gulp.

Mother humpbacks swim close to their young ones, often touching one another with their flippers. Humpbacks roam all over the world and the place where they could be located depends on the time of the year.

The walrus has a unique look with a long tusk and a moustache. It is usually found in the Arctic Circle, basking along with its companions. Though it is extremely sociable and playful, a walrus can be really aggressive during the mating season.

The diet of a walrus usually consists of clams and mussels. It occasionally includes fish and even small seals. It roots along the ocean floor with its tusk and identifies its prey with its whiskers.

The walrus has an iconic tusk which it uses for a variety of reasons. It is used to haul its enormous body out of frigid waters, and to break breathing holes into ice from below. But it is not used to dig up food.

Walruses usually live in large groups numbering up to a hundred and above. They occupy the coasts and margins of ice shelves, where they periodically haul themselves onto beaches and ice floes to rest and bask.

Sea lions are relatives of seals and walruses. They can be distinguished by their external ear flaps, long fore-flippers, short, thick hair, and a big chest and belly. Their strong flippers and streamlined body make them well-adapted to the aquatic way of life.

California sea lions are known for their intelligence, playfulness, and noisy barking. Keeping their playfulness aside, they are skilled hunters - they can hunt continuously for up to 30 hours!

California sea lions are also known to cooperate with other predators like dolphins while hunting large schools of fish. They prey on a wide variety of seafood, mainly squid and fish, and sometimes clam. The fish and squid species they commonly eat include salmon, hake, Pacific whiting, anchovy, herring, rockfish, lamprey, dogfish, and market squid. Depending on how much food is available, they either eat alone or in groups.

California sea lions aren’t normally dangerous to humans, and attacks are uncommon, but they are large and unpredictable wild animals with sharp teeth; so it’s better to maintain a healthy distance!

The leopard seal is named after its black and grey spotted coat. It is also known as sea leopard. Its resemblance with leopards, however does not stop with the appearance. Like leopards, sea leopards too are fierce hunters.

Leopard seals are the most formidable hunters of all the seals. They are the only seals that feed on warm-blooded prey. They have powerful jaws and sharp teeth with which they devour their prey including small fish, squid and other seals. Leopard seals occupy Antarctic and sub-Antarctic waters, which give them an opportunity to prey on penguins as well.

The way a leopard seal hunts penguins is interesting. At first, it surveys the entire edges of the ice while remaining submerged. It then waits for the birds to enter the ocean and catches them while they are swimming. It grabs the penguin by its feet and shakes it vigorously until the bird is dead, a cruel death for the penguin indeed.