How does zooplankton affect marine life?

There's this fast-swimming zooplankton (a small organism) that lives in groups. And it is tiny, growing to about 6 cm. But lying at the base of the food web in the Southern Ocean, the krill is what links the ecosystem together. Its population is on the decline, and this can have an unimaginable impact on marine life in the long run. How?

A new study published recently says krill population in its Antarctic habitat is likely to decline about 30% this century due to both natural climate variability and human activity-induced climate change. The study also adds that it will be difficult to "tell the difference between natural and human-caused effects on krill until late in the 21st century". This is worrisome due to two reasons. One is that unless we know how exactly human activity affects krill population, it may be difficult to initiate relevant steps to improve the situation. Two, it is said that "natural climate variability can obscure human-driven trends". Neither augurs well for the krill population.

As mentioned, krill are tiny creatures. But they are one of the most abundant too. For several sea creatures including penguins, seals, fish, and whales - in the ocean surrounding Antarctica, krill are the main food. Not just that. Many sea animals feed on the creatures that consume krill, which is why the krill has an important role to play in the aquatic food chain, especially in the Southern Ocean. If the krill population keeps coming down, it could affect several other creatures, causing a severe imbalance in the food chain. Krill are adapted to surviving harsh winters. But one wonders how well they can adapt to climate change.

Did you know?

The largest animal on Earth, the blue whale feeds almost exclusively on krill. Apparently, it needs to eat a few tonnes of these tiny crustaceans every day!

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What is hydrophone?

Just as a microphone collects sound in the air, a hydrophone detects acoustic signals under the water. Most hydrophones are based on a special property of certain ceramics that produces a small electrical current when subjected to changes in underwater pressure. When submerged in the ocean, a ceramic hydrophone produces small-voltage signals over a wide range of frequencies as it is exposed to underwater sounds emanating from any direction.

By amplifying and recording these electrical signals, hydrophones measure ocean sounds with great precision. While a single hydrophone can record sounds from any direction, several hydrophones simultaneously positioned in an array, often thousands of miles apart, result in signals that can be manipulated to “listen” with greater sensitivity than a single device. Omni-directional and hemi-directional hydrophones pick up sound from a particular direction and can be used to track fish movements.

In addition to NOAA's National Marine Sanctuaries, NOAA’s Pacific Marine Environmental Laboratory (PMEL) also frequently uses hydrophones. PMEL acquires long-term data sets of the global ocean acoustics environment to identify and assess acoustic impacts from both human activities and natural processes, such as underwater volcanoes, earthquakes, and icequakes on the marine environment.

Credit : Ocean Service

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Do turtles talk?

Yes, they do, says research. Since turtles don't have vocal cords, it was thought that they did not communicate through sounds. However, scientists have found that turtles communicate at such low frequency that sounds like "clicks, clucks and hoots" can be heard only through a hydrophone. What's surprising is that they talk when they are still inside their eggs just before hatching.

One of the most common sounds which a turtle may produce is the hissing sound. Turtles hiss by quickly expelling air from their lungs. They do this by tucking their heads into their shells.

A turtle in a new environment will hiss a lot as it is not used to its environment. Once the turtle gets used to its environment, you can expect it to hiss less. Snappers) hiss when approached.

They do this because they are stressed and feel threatened. Hissing coupled with heavy breathing produces a menacing sound. A threatened snapping turtle will attack when approached or provoked. Their bites are very powerful and are capable of crushing human bones.

When a turtle hisses, it’s best to leave it alone.

Credit : All Turtles

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Where are parrotfish found?

Parrotfish are bright-coloured fish found in and around coral reefs. They have fused teeth resembling a parrot beak which they use to scrape algae and seaweeds from the surface of corals and rocks, thereby helping the reefs stay healthy. They grind up the calcium carbonate reef material and excrete it as fine white sand.

Parrot fishes range to a length of about 1.2 metres (4 feet) and weight of about 20 kilograms (45 pounds), or occasionally larger. They are variable in colour, the male of a species often differing considerably from the female, and the young may differ from the adult. Parrot fishes are protogynous hermaphrodites; that is, they first function as females and later transform into males.

Parrot fishes are edible but are not, as a group, of great economic importance. The surf, or rivulated, parrot fish (Callyodon fasciatus) is an Indo-Pacific representative of the family; it grows to 46 centimetres (18 inches) or more, and the male is green and orange or red, the female blue and yellow. Atlantic species include the rainbow parrot fish, which grows to about 90 centimetres and is bright orange and green with a blue beak, and the queen parrot fish (Scarus vetula), which grows to about 50 centimetres and is blue with green, red, and orange if male but reddish or purplish with a white stripe if female.

Credit : Britannica

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What kind of tusks do walruses have?

Walruses, often found lying on the ice in the Arctic Circle, are massive marine mammals. Their distinctive features are their long, white tusks. The tusks are actually their upper canine teeth that grow all through their lives. Both males and females have tusks which they use to break through ice and haul their huge bodies out of frigid waters.

Both sexes possess long tusks (the upper canine teeth) that project downward from the mouth. In the male they can grow to about a metre in length and 5.4 kg (12 pounds) in weight. The tusks function mainly in mating display and in defense against other walrus. They are not used to dig food from the ocean floor. The walrus feeds at depths of less than 80 metres (260 feet), usually at 10–50 metres (30–160 feet). Rooting along the ocean floor with its snout, it identifies prey with its whiskers. The walrus’s diet consists largely of clams and mussels but occasionally includes fish and even small seals.

The walrus is valued by both the Inuit and commercial hunters for blubber, hide, and ivory tusks. Its numbers have been reduced by commercial operations. Walrus are now protected from sealers but are still subject to subsistence hunting by aboriginals. Like seals, the walrus is a pinniped. It is the sole living member of the family Odobenidae.

Credit : Britannica

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