The ocean is absolutely packed with animals of all shapes and sizes. From the smallest plankton to the largest whale, the animals in the ocean show an amazing diversity in size, shape, and lifestyle. This diversity makes them so fascinating to study.
The animals in the ocean grow much, much bigger than those on land. Animals which live in the depth of the ocean tend to be much larger than those who live in shallower areas. This is known as deep sea gigantism. The most outstanding example of deep sea gigantism is the Colossal Squid although there are a number of other species who are very small in shallow areas but monstrously large in the deep ocean. Crustaceans and mollusks are the most likely to be found in a giant form. Considering how much of the ocean is yet to be explored, it wouldn’t be in the least surprising to find many more giant creatures inhabiting the deepest parts.
There are many reasons why animals in the ocean can grow to such enormous proportions, these include:
Availability of Food
The ocean is teeming with food. The lowest level of the food chain is phytoplankton, small plants that convert nutrients in the water and sunlight into energy. The next level up is the zooplankton, which gets its energy from the phytoplankton, and then in their turn is eaten by krill, fish, and other crustaceans. Big fish, whales, walruses, and seals eat the krill, fish and crustaceans. When there is as much food available as there is in the ocean, this allows animals to grow bigger and bigger with each generation.
If their habitat changes, big animals are affected more than smaller animals. If a big animal has to travel further to find food, this can mean that it needs to be bigger to store more energy in its body to help it last out these long searches.
Size is also an important evolutionary survival tool. The larger the animal, the less predators it has. So size is a defence tool.
Temperature could be another factor that promotes gigantic growth. Many of the larger species live at great depth, where the environment is dark and cold as no sunlight can penetrate so deep. Larger size gives a smaller surface area to volume ratio, helping the animal to conserve heat more effectively. A larger animal can also have a thicker layer of fat or blubber to help keep warm.
Animals on land cannot grow as big as animals in the sea because they need bigger and thicker bones to carry the weight but in the sea, the water’s buoyancy eliminates the need for big bones.
As you go deeper under the ocean, the pressure increases. So animals that live in the deepest parts of the ocean need to have bodies that can stand formidable pressure.
Here are some examples of the diversity of animals that can reach gigantic proportions:
The Blue Whale
The largest mammal on earth and possibly the largest mammal ever to live on earth is the Blue Whale. The Blue Whale belongs to rorqual family of whales, which also includes the humpback whale and the minke whale. The largest blue whale ever recorded was 33 metres long and they can weigh up to 150 tons. The blue whale only eats krill, which is a tiny shrimp-like creature but is abundant in the ocean. Blue whales can be seen in all the oceans from the both poles to the equator.
The Whale Shark
The largest fish in the ocean is the Whale Shark, averaging 9 metres long. The largest measured was 12.2 metres long but they are thought to get longer than that. It may be called a whale but it is classified as a shark which makes it a fish. This is another creature that only eats plankton. Whale sharks live all over the world and filter thousands of tons of water every hour. These fish can live to over 100 years old and don’t reach maturity until they are over 30.
The Colossal Squid
The Colossal Squid is the biggest ocean dweller with tentacles. This immense squid is very elusive and mysterious. They normally grow to about 14 metres but the largest measured was 18 metres long and weighed 900 kilograms.
Although the Colossal Squid is the largest invertebrate on Earth, little is known of them. The colossal squid has the most enormous eyes, measuring about 25 cm (11 inches) in diameter and are probably the biggest on any animal as well as a large beak, making them a fearsome predator. They can even take on sperm whales. They have a complex nervous system and advanced brain.
The Lion’s Mane Jellyfish
The biggest jellyfish is the Lion’s Mane Jellyfish found in the coastal waters around England. It has been known to grow up to two metres long and is equipped with a deadly sting.
The Japanese Spider Crab
The largest shelled animal in the ocean is the Japanese Spider Crab that can measure four metres from claw to claw and weigh up to 40 pounds. They are found in the Pacific Ocean off the Japanese coast. The crab itself isn’t very big, it just looks it because of its enormous claws. This edible crab eats absolutely anything, including the bodies of people who have drowned. This crab can reach 100 years of age.
The Giant Clam
The largest shelled mollusk is the Giant Clam. They can reach 1.2 metres long and weigh up to 500 pounds. Found around Southeast Asia and the Indian Ocean, they can live over 100 years unless they are taken for food or their shells. The amazing thing about the giant clam is that they live on the sugars and proteins that are produced by billions of tiny algae that live in their bodies. They also siphon in water to take in plankton.
There are two species of starfish competing for the title of longest and heaviest starfish, the Giant Sea Star, Pisaster giganteus, which is found off the Pacific Coast from British Columbia to California and has a span of 60 cm and weighs up to six kilograms and the Midgardia xandaros from the Gulf of New Mexico with a span of 1.38 metres.