My Science School

Seven different species of sea (or marine) turtles grace our ocean waters, from the shallow seagrass beds of the Indian Ocean, to the colorful reefs of the Coral Triangle and the sandy beaches of the Eastern Pacific. While these highly migratory species periodically come ashore to either bask or nest, sea turtles spend the bulk of their lives in the ocean. WWF's work on sea turtles focuses on five of those species: green, hawksbill, loggerhead, leatherback, and olive ridley.

Over the last 200 years, human activities have tipped the scales against the survival of these ancient mariners. Slaughtered for their eggs, meat, skin, and shells, sea turtles suffer from poaching and over-exploitation. They also face habitat destruction and accidental capture—known as bycatch—in fishing gear. Climate change has an impact on turtle nesting sites; it alters sand temperatures, which then affects the sex of hatchlings. Nearly all species of sea turtle are now classified as endangered, with three of the seven existing species being critically endangered.

WWF is committed to stopping the decline of sea turtles and works for the recovery of the species. We work to secure environments in which both turtles and the people that depend upon them can survive.

Credit : World Wildlife Fund

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Octopus is a soft-bodied, eight-limbed molluscs of the order Octopoda. It lives in all the world's oceans. It has a bulbous head, eight arms with suction cups on the bottom and three hearts. The colour of its blood is blue because of the copper-based protein called hemocyanin in the blood.

 It squirts an ink-like liquid to deter predators. This will temporarily blind and confuse a potential attacker, giving him the time to swim away.

It can squeeze into (or out of) tight spaces in search of food and shelter. It diet includes clams, shrimps, lobsters, fish, and even sharks.

Females usually lay 200,000 to 400.000 eggs. They guard the eggs even without eating. Once the eggs hatch, the female octopus dies and so does male octopus within a few months.

Octopuses live in oceans all over the world. Most are pelagic, meaning they live near the water's surface in shells, reefs and crevices. Some species live on the floor of the ocean, making their homes out of caves. Octopuses tend to be solitary, though they do interact with other octopuses at times. Some species of octopuses hunt at night, while others only hunt at dusk and dawn. 

When scared, octopuses will shoot a dark liquid, sometimes called ink, at the thing that scared them. This will temporarily blind and confuse a potential attacker, giving the octopus time to swim away. The ink can also dull the attacker’s smelling and tasting abilities, according to the Smithsonian article.  

Octopuses can also change color to hide and match their surroundings. They can turn blue, gray, pink, brown or green. The mimic octopus can also flex its body to resemble more dangerous animals, such as eels and lionfish, according to the World Animal Foundation.

If an octopus does get caught — no problem. They can lose arms and regrow them, according to National Geographic. 

Octopuses are fast swimmers but they prefer to slowly crawl along the sea bottom. To swim, octopuses suck water into their bodies and shoot it out a tube called a siphon, according to the World Animal Foundation. This lets the octopus blast off, away from attackers. 

Picture Credit : Google

Can you believe that there are sharks that can live for over 400 years? Greenland sharks have the longest known lifespan of all vertebrates on Earth. Scientists estimated the age of a Greenland shark to be about 400 years in 2016. It is said that they do not even reach sexual maturity until they are about 150 years old.

Greenland sharks are rarely encountered by humans. They are thought to prefer colder, deeper environments but may be found anywhere between the sea surface and depths of 2,200 meters (about 7,200 feet). Greenland sharks are slow-moving, typically swimming at rates of less than 3 km (about 1.9 miles) per hour. They are carnivorous, and their diet is often made up of several different types of fishes, including smaller sharks, eels, flounders, and sculpins. Crustaceans, seabirds, and carrion—as well as terrestrial mammals (such as horses and reindeer) that likely fell through the ice—have been found in stomach analyses of the species. Greenland sharks are not considered dangerous to humans, in part because they live in regions where people do not typically swim; the only known report of a possible attack by a Greenland shark on a person dates to 1859.

Greenland sharks are considered to be a near-threatened species by the International Union for Conservation of Nature. The species was valued for its liver oil; about 114 litres (30 gallons) of liver oil can be obtained from a large specimen (see also fish oil). (Although the flesh of the Greenland shark may be eaten, it is toxic unless properly cleaned and dried or repeatedly boiled prior to consumption.) Greenland sharks were fished commercially from the 19th century until 1960. Norway persecuted Greenland sharks during the 1970s, because they were considered to be a nuisance that threatened other fisheries. In the early 1900s as many as 30,000 Greenland sharks were caught a year. In the present day the annual take is far smaller; small-scale subsistence fisheries in the Arctic harvest fewer than 100 individuals annually, and roughly 1,200 are caught accidentally in fishing trawls.

Credit : Britannica 

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The world has woken up to the threats posed by plastic-especially the single-use ones - to the environment and marine life in particular. In the recent decades, scientists have also come to recognise the dangers of microplastics, which are extremely small pieces of plastic debris resulting from the breakdown of plastic products. Now, they have sounded alarm over another tiny, yet hazardous plastic items called nurdles. Depending on their density, nurdles can either float to the surface of the water or sink below the surface. In either case, they are a threat to animals and birds.

What are nurdles?

Nurdles are lentil-sized plastic pellets used as raw material for most of today's plastic products. Made of plastics including polyethylene, polypropylene, polyvinyl chloride, and polystyrene, the pellets are transported to factories around the globe where they are melted down and used to I create plastic bags, kitchenware, bottles, and more. Through leaks, spills, and other storage or transportation errors, nurdles end up in the environment, eventually making their way to the ocean. When the X-Press Pearl container ship caught fire and sank in the Indian Ocean in May 2021. 87 containers full of lentil-sized plastic pellets aboard were accidentally spilled into the ocean.

Since the disaster, nurdles have been washing up in their billions along hundreds of miles of Sri Lanka's coastline, according to reports.

Why nurdles are a concern

According to The Guardian, 250,000 tonnes of the pellets end up in oceans each year. Because of their size and colour, nurdles look a lot like fish eggs, which makes them particularly appealing to seabirds, and other marine animals. Accidental ingestion of nurdles can cause ulcerations, starvation and eventually deaths in marine animals. Further, nurdles absorb toxins and harmful chemicals like persistent organic pollutants (POP) found in the air, and water. POP come from pesticides, toxins and other harmful chemicals. After nurdles absorb these toxic chemicals, they are eaten by fish and get passed on in the food chain. The toxin may eventually end up on our plates.

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Squids and octopuses are cephalopods, members that fall under the molluscan class Cephalopoda. But these aquatic invertebrates do not have shells. Their blood is blue due to the presence of copper in it, and they also have three hearts each. But octopuses and squids differ in their physical characteristics, habitat, and behaviour.

An octopus has a round head, while a squid's head is triangular in shape. Octopuses do not have any bone in their body, while squids possess a stiff structure known as a pen that acts as a flexible backbone. Octopuses do not have fins, while squids have two on their heads. Both have eight arms, but squids have two specialized tentacles in addition which are used to catch prey.

While octopuses live in the ocean floor, squids live in the open sea at various depths depending on the species. Octopuses feed on crustaceans on the sea bottom, while squids feed on shrimps and fishes. Usually, squids are larger than octopuses.

Picture Credit : Google