Category Sea/Ocean

What makes an aquarium equipped?

Only a few fish can adapt to life in the restricted space of a tank, but even these will die if they are not given the right surroundings.

The aquarium must be carefully prepared. On the bottom there should be a mixture of sand and pebbles to give a realistic look. Underwater plants are useful because they help to keep the water pure by absorbing waste products and providing oxygen. The water must be neither too cold nor too warm and it must not contain any harmful substances. It should cover to the aquarium is often used, to reduce evaporation and prevent the fish from jumping out.


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How to look after goldfish?

Goldfish make extremely popular pets. They are not difficult to look after providing you follow a few simple rules.

The first serious threat to a goldfish is when it is taken home from the pet shop. It should be swimming around in quite a lot of water and you should not take it in one of those small plastic bags. If you must use a plastic bag take the goldfish out of it as soon as possible or it may suffocate.

A second danger to goldfish is the tank it swims in. Tap-water contains chlorine which is poisonous to goldfish. This water is also too cold and might kill the pet.

A third danger is feeding which is all too often wrong for goldfish. These fish do not require much food, but what they do eat must be carefully chosen. Never give goldfish breadcrumbs: use the special food sold in shops but be careful to give it only in small quantities. Occasionally you can give goldfish a small amount of finely minced raw meat or the crushed yolks of hard-boiled eggs.

The larger the tank the happier the fish will be. The ideal tank is the aquarium but a large bowl will serve. Do not forget that even a goldfish can become bored and pine away living alone, so you should give it a companion, either male or female. Goldfish were originally natives of eastern Asia but were later introduced into China, Japan, Europe and the United States. They have been known to live for twenty-five years in captivity, but the average life span is usually much shorter.


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How sea-fishing carried out?

Fishing is one of the oldest activities known to man. Early man who lived on houses erected on poles above the water of lakes, soon learned how to catch the silent creatures that swam around underneath the surrounding waters. The fishing methods of those primitive peoples did not differ much from the lines, nets and hooks of today.

The implements used in fishing can be quite complicated, such as the lobster pots that are sunk, laden with bait, to the sea-bed and the nets which are rigged up by groups of people working together. When these nets are dragged along the water they are known as trawls.

Other types of nets are placed in the water to form a ring which is then gradually closed round the fish and lifted out of the water. This method is known as purse seining. In other netting systems fishermen simply block the fish’s means of escape and force them to swim into a special area where they are caught.


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What happens when the ocean becomes acidic?

Did you know the oceans absorb 30% of the CO2 emitted on Earth? At the outset, this might seem like a good thing because it means less carbon dioxide in the air and therefore reduction in global warming. But in the past decades, scientists have realised this comes at the cost of changing the ocean’s chemistry.

When carbon dioxide dissolves in seawater, it forms carbonic acid. When emission increases, a lot of CO2 dissolves in the ocean. Incidentally, the rise in CO2 emission is primarily attributed to human activities. The more the CO2, the more acidic the water gets. Subsequently, the pH level of water goes down. (pH is a measure of how acidic or basic water is.) This process is known as ocean acidification. Ocean acidification has the potential to damage the ocean chemistry. Even a small change in the acidity of seawater can have harmful effects on marine life, impacting chemical communication, reproduction, and growth.

Impact on shelled creatures

Ocean acidification affects ocean species in varying degrees. Creatures such as mussels, clams, urchins, starfish and corals are the worst affected. They make their shells and skeletons by combining calcium and carbonate from seawater. As acidification changes the chemistry of the ocean, these organisms struggle to build their shells and skeletons. Even if they are able to build skeletons in more acidic water, they may have to expend more energy which might otherwise be needed for activities such as reproduction. Further, scientists have found that ocean acidification causes shells of some species to dissolve and slows moulting in crabs and lobsters.

Acidification may also limit coral growth by corroding its skeletons. When reef-building corals are affected, a host of marine life that call the reef their home will also be affected.

Impact on fish

A small change in pH can make a huge difference to survival. In humans, a drop in blood pH level of just 0.2-0.3 can cause seizures, coma, and even death. Similarly, fishes are sensitive to pH. If their blood pH drops, they will have to burn extra energy to get rid of the excess acid in their blood through their gills, kidneys and intestines. This will reduce their ability to carry out other tasks such as hunting, escaping predators and reproducing.

Studies have shown that acidification changes the way sounds get transmitted through the water, making the underwater environment noisier.


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What is special about salmon?

Salmon comprises many species of fish. They are unique in that they live both in freshwater and salt water, and for this characteristic they are called “anadromous” Let’s find out more about how this happens.

Found in the Atlantic and Pacific oceans, salmon begin their life in freshwater. For the first few months (sometimes even a few years, depending on the species). The salmon live in freshwater, usually a river. And then they move to the ocean. Again, after living there for a while, when it’s time for them to spawn (lay eggs), they head back as adults to the same river they were born in. Soon after spawning, adults from some species die, and some repeat the cycle. These journeys are said to cover hundreds of miles in a salmon’s lifetime. According to research, salmon have an acute sense of smell, which is what helps them back to their birth place, though much time passes in between. Some have said it’s the Earth’s magnetic field that guides them.

But what’s more fascinating is how their bodies adapt to two different habitats.

Usually fish can die if they switch between salt and freshwater – when salt water fish get into freshwater. Their cells can burst and when freshwater fish enter salt water, their cells can shrivel. However, a complex adaptation mechanism involving body fluids comes into play to help the salmon survive. It happens at the intertidal zone (such as a seashore) before the young salmon enters the ocean. It gets used to the salty water by gradually drinking a lot of it, expelling excess salt and very little urine. These work in reverse when the adult returns to its freshwater home – it hardly drinks freshwater and has no need to expel salt. A study from 2015 made a revelation about another factor that helps the young salmon – light. Increased light during spring increased the production of a special enzyme which “stimulates the fish to prepare itself before it wanders out into salt water’.


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What is group of barracudas called?

A group of barracudas is called a battery. Barracudas are ferocious, opportunistic predators, relying on surprise and short bursts of speed, up to 43 km/h, to overtake their prey.

Barracuda are snake-like in appearance, with prominent, sharp-edged, fang-like teeth, much like piranha, all of different sizes, set in sockets of their large jaws. They have large, pointed heads with an underbite in many species. Their gill covers have no spines and are covered with small scales. Their two dorsal fins are widely separated, with the anterior fin having five spines, and the posterior fin having one spine and 9 soft rays. The posterior dorsal fin is similar in size to the anal fin and is situated above it. The lateral line is prominent and extends straight from head to tail. The spinous dorsal fin is placed above the pelvic fins and is normally retracted in a groove. The caudal fin is moderately forked with its posterior edged double-curved and is set at the end of a stout peduncle. The pectoral fins are placed low on the sides. Its swim bladder is large. Speedy and dynamic, they are slim, with small scales. Barracudas also have two well-separated dorsal fins, a protruding lower jaw, and a large mouth with many large, sharp teeth.


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Why don’t sharks just swim up to whales and start eating them?

Sharks do sometimes prey on whales, but adult whales are massive beasts that can and will kill sharks if they come too close. Calves are sometimes attacked, lone mothers with a calf are preyed upon, but whales often live in pods that defend one another. Even peaceful filter-feeder whales still pack a punch with their tails, whales are social and will defend one another and their sonar (okay, okay, echolocation) gives them immense advantage over sharks.

Fish are deaf or nearly deaf. The shark doesn’t even know the whale has a lock on it and is coming down, hard. The shark will smell the whale but by the time it can see the whale coming it will be too late. The whale can accurately locate the shark from kilometers away and act accordingly.


Credit : Quora

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What are the threats to seagrasses?

Like all seat creatures, seagrasses are destroyed by cyclones, over-grazing, fungal and other attacks. Seagrasses some times dry out in the inter-tidal areas. Have you seen them washed ashore? In estuaries, too much of freshwater and suit accumulation destroy seagrass beds.

The biggest seagrass enemy is human activity. We pollute the seawater when we use chemical pesticides and fertilizers and the water runs into seagrass beds on the coast. These chemicals support the growth of algae that block sunlight reaching seagrass. Sediments choke the leaves and sea dredging damages seagrass meadows. Boat anchors and large marine debris can kill sections of seagrass meadows.

Overfishing is bad too. Without fish, the sea-urchin population explodes. Sea urchins eat up seagrass. When large carnivorous fish like sharks are removed predators that eat invertebrates become more abundant. These in turn wipe out small pollinating creatures that the seagrass needs. An increase in herbivorous fish also kills off the seagrasses. You know of the food-chain, right?

Cyclones and tsunamis affect seagrasses. It takes time for left-over seagrasses to regenerate the meadow or for the seed-bank present in the sediment to give rise to new shoots.

Another big threat comes from global warming. When sea temperatures rise, marine heatwaves are created. These occur suddenly, spiking seawater temperature. Examples are the “record-breaking ‘Ningaloo Nino’ (2011) off Western Australia, the long-lasting ‘Blob’ (2013-2016) in the northeast Pacific ad El Nino-related extreme warming in 2016 that affected most of the Indo-Pacific. The number of marine heatwaves has increased around the world, and coral refs, seaweed beds and seagrass meadows are at maximum risk from marine heatwaves.

Biologists tell us that seagrasses bury carbon sediments faster than tropical forests do. When a tree dies, the carbon gets released into the atmosphere. in seagrass meadows, carbon gets stored in seabeds and even if the seagrass dies, carbon stays trapped inside the sediment. Destruction of the ocean food-chain, reducing ocean productivity. Even if protected areas are created for seagrasses, they will survive only if the seawater is clear.


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What is the role of seagrass in the marine ecosystem?

Where are they found?

Seagrasses are found is seas surrounding all continents except Antarctica. If you are lucky, you can spot them along the coast in clear, shallow waters. The water has to be clear so that sunlight can get through and help the photosynthesis. Some seagrass species grow in the space between the highest tide line and lowest tide line (inter-tidal zone). This is the area where you can see the seabed when the low tide retreats. Here seagrass grows close to mangrove belts and survives exposure to heat and dryness, thanks to the high humidity. Other species of sea grass (tape grass) are always found submerged in  water in the sub-tidal zone. The eelgrass occurs in estuarine areas. When conditions are suitable, sea grass form dense underwater ‘meadows’-some of which are large enough to be seen from space.


Sea grasses have roots, stems and leaves and produce flowers and fruits. They are closely related to land plants, and probably evolved from land living angiosperms (flowering plants) millions of years ago. The closest relatives to seagrass on land are grasses, palms and lilies.

How many seagrass species are known?

There are 72 different species of seagrasses in the world, belonging to four families. This is not much, but then “It is a huge challenge to evolve the capability to tolerate salt water and live in a submerged environment,” said Frederick Short a marine biologist from the University of New Hampshire and director of Seagrass Net, a global seagrass monitoring network.

The warm waters of the Indo-Pacific region have the highest number (14) of seagrass species in the world. This is because seagrass “evolved first in this part of the world, “Seagrass in this region have had a longer time to diversity and have had suitable growing conditions.

India being in the Indo-Pacific region, has 14 seagrass species. The Gulf of Mannar and Palk Strait house all the 14 species found in India, while the Lakshadweep and Andaman and Nicobar Islands have 8 and 9 species respectively.

How do they ‘breathe?

Land plants have small pores on their leaves called stomata, through which they can take in carbon dioxide from the air and release oxygen. Seagrasses do not have stomata. Instead, they have a thin cuticle layer which allows gases and nutrients to seep directly into the leaves from the surrounding water.

How do they reproduce?

The seagrass produces male and female flowers. The pinkish-green male seagrass flowers produce big pollen, up to 5mm long. Make flowers release pollen covered in a sticky, slimy substance into the surrounding water and the water-currents carry them over to the female flowers. Females have stigmas shaped like tentacles and are supported by coiled stalks. When male flowers release their pollen at night, the female flowers open their petals to ‘catch’ the drifting male flowers.

Their stalk straightens, and then coils and sinks down to the bottom.

Some seagrasses take the help of tiny marine invertebrates like amphipods (tiny shrimp-like creatures) and polychaetes (marine worms) for pollination. The seeds that result float and find suitable seabeds to grow new meadows.

In another method to sustain their species, seagrasses use their massive rhizomes-modified underground stems like ginger and turmeric. These rhizomes spread in the seabed and put out new roots and shoots. This way, a single plant can colonise a large area of seabed, and live on for thousands of years.

How are seagrasses helpful?

Dense seagrass growth traps flowing sediment and nutrients, and creates a world where life can thrive. Their leafy roof supports a wide grow on them: small marine invertebrates, which in turn attract sea anemones and fish; mega herbivores like green sea turtles and dugongs.


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What do sea pens do?

True to their names, sea pens resemble old-time quill writing pens. These colonial marine cnidarians (a large group of aquatic invertebrate animals) belong to the order Pennatulacea. Although the group is named for its supposed resemblance to antique quill pens, not all sea pen species live up to the comparison. Colours range from dark orange to yellow to white.

These underwater animals are actually a type of octocoral (soft coral), named for the eight stinging tentacles that they use to capture plankton (tiny floating plants and animals) to feed themselves. In fact, a single sea pen is both an individual and a colony. The basic unit of a sea pen, like all other corals, is a polyp, which consists of a sac-like body cavity enclosed by a mouth and surrounded by a ring of tentacles. The larva usually settles down in sand, mud, rubble or, sometimes, solid rock and this becomes the primary ployp. It buds into daughter polyps, and the sea pen grows. It is supported on a stem-like structure. While the larvae of some species settle close to their parents, others are carried great distances by ocean currents.

Some polyps feed by using nematocysts (a specialized cell in the tentacles of a jellyfish, corals and sea anemones, containing a barbed or venomous coiled thread that can be projected in self-defence or to capture prey) to catch plankton; some force polyps reproduce; and some force water in and out of canals that ventilate the colony.

Sea pens inhabit shallow and deep waters from the polar seas to the tropics. Some sea pens use a bulb inflated with water to anchor them to the sea floor. All have hard, internal skeletons, and at least some of them can glow in the dark.

Although many species live in shallow water, others have been found as deep as 20,013 feet (6,100 metres) below the surface. One species of Umbellula has been discovered living in cold, dark waters near Antarctica. It grows to about 10 feet (3 metres) long with a big, flat head of polyps at its end, the tentacles picking food out of the water as the head is pushed along by the current. Most sea pens, however, grow to between 2 inches and 6 feet, 7 inches (5 cm to 2 metres) in height.


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