Category Science

How sharks pretending to be dead?

Lemon sharks are rendered harmless when flipped on their backs. These top predators of the sea go limp after about 15 seconds and will play dead long enough for scientists to conduct experiments on them!

The Central American cichlid only pretends to be dead in order to lure unsuspecting prey. It has intricate markings that make it look like a decaying fish. When scavengers come near, the cichlid instantly comes to life and eats the clean-up crew. In Lake Malawi, East Africa, Livingstone’s cichlid sinks to the bottom of lake and lies motionless on its side. Its skin is also blotchy like a carcass!

 

Picture Credit : Google

What are the effects of Hypoxia?

  • While fish and mobile invertebrates such as shrimp and crabs migrate out of hypoxic areas, slow-moving, bottom-dwelling creatures such as clams and oysters die after extended exposure.
  • It has also been found that fish that flee the potential suffocation may quickly become unconscious and die.
  • It was found in a study that low oxygen levels recorded along the Gulf Coast of North America led to reproductive problems in fish involving decreased size of organs, low egg counts and lack of spawning.
  • Alteration in marine ecosystem also has socio-economic impact on humans. It affects people whose livelihood depends on fishing.

 

Picture Credit : Google

How Dead Zone formed?

Dead ones generally occur near areas where heavy agricultural and industrial activity spill nutrients into the water. The excess nutrients, especially nitrogen and phosphorous, cause the rapid growth of microscopic algae called phytoplanktons. This phenomenon is called the nutrients, grow, die and sink to the bottom, where they are decomposed by bacteria. The bacteria inhale the dissolved oxygen in the water as they decompose the phytoplankton. This leads to the depletion of oxygen available to other marine life.

If the phytoplanktons are cyanobacteria, the problem is further intensified they are not consumed by zooplankton and fish. Hence they accumulate in water, leading to the expansion of dead zones. The bacterial degradation of their biomass consumes more oxygen in the water.

While nutrients run-off has been known for decades, researchers say that climate change is making the lack of oxygen worse. As more carbon dioxide is released enhancing the greenhouse effect much of the heat is absorbed by the oceans. In turn, this warmer water can hold less oxygen.

Stratification

The other worrying factor is the possible hindrance to replenishment of oxygen. This happens when the water is warmer than usual. Oxygen in the air and the surface usually gets dissolved in the water below by tides and winds. This helps restore the gas consumed by bacteria. When the temperature of the water is high, less dense water flowing into the ocean from rivers sits on top of salty dense water. This process is called stratification. A barrier is formed between the separated masses of water, hampering the replenishment process.

 

Picture Credit : Google

What are Dead Zones?

Dead zones are low oxygen areas in the world’s oceans and lakes. A combination of physical, chemical and biological factors creates dead zones, with nutrient pollution being the major culprit. These nutrients come from the run-off of chemical fertilizers and wastewater.

Hypoxic zones can occur naturally, but scientists are concerned about the areas created or enhanced by human activity.  Excess nutrients that run off land or are piped as wastewater into rivers and coasts can stimulate an overgrowth of algae, which then sinks and decomposes in the water. The decomposition process consumes oxygen and depletes the supply available to healthy marine life.

Dead zones occur in many areas of the country, particularly along the East Coast, the Gulf of Mexico, and the Great Lakes, but there is no part of the country or the world that is immune. The second largest dead zone in the world is located in the U.S., in the northern Gulf of Mexico.

 

Picture Credit : Google

Are our oceans going breathless?

Dissolved oxygen in water is essential for the survival of fish and other aquatic organisms. Levels that are too high or too low can harm aquatic life and affect water quality. There are regions in oceans across the globe where the concentration of dissolved oxygen can be so low that marine animals can suffocate and die, and as a result, these regions are often called dead zones. A new study by the conservation group the International Union for the Conservation of Nature (IUCN) has revealed that the number of dead zones has quadrupled in the last half-century – from only 45 in the 1960s to as many as 700.

Citing climate change and increase in nutrient pollution as the causes, the IUCN has warned that many species of fish, including sharks, tuna and marlin are at particular risk. These fishes are sensitive to low levels of the life-giving gas due to their large size and energy demands.

The report on ocean oxygen loss concluded that deoxygenation is already altering the balance of marine life to the detriment of species across the food chain. The biomes that supports about a fifth of the world’s current fish catch are formed by ocean currents usually bring oxygen-poor water to coastlines. So, these areas are especially vulnerable to even tiny variations in oxygen levels, it said.

On currently trends, oceans are expected to lose 3-4% of their oxygen globally by 2100. Most of that loss is predicated to be in the upper 1,000 mt – the richest part of the ocean for biodiversity.

 

Picture Credit : Google

WHAT IS THE PAYLOAD BAY?

The payload bay is where the Shuttle’s cargo is kept during flight. It measures 18.3m by 4.6m (60ft by 15ft), which is large enough to hold two small buses end to end. The two large bay doors can be opened when the Shuttle reaches low-Earth orbit, allowing the cargo to he lifted into space.

Payload is the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight. Depending on the nature of the flight or mission, the payload of a vehicle may include cargo, passengers, flight crew, munitions, scientific instruments or experiments, or other equipment. Extra fuel, when optionally carried, is also considered part of the payload. In a commercial context (i.e., an airline or airfreight carrier), payload may refer only to revenue-generating cargo or paying passengers.

For a rocket, the payload can be a satellite, space probe, or spacecraft carrying humans, animals, or cargo. For a ballistic missile, the payload is one or more warheads and related systems; their total weight is referred to as the throw-weight.

The fraction of payload to the total liftoff weight of the air or spacecraft is known as the “payload fraction”. When the weight of the payload and fuel are considered together, it is known as the “useful load fraction”. In spacecraft, “mass fraction” is normally used, which is the ratio of payload to everything else, including the rocket structure.

There is a natural trade-off between the payload and the range of an aircraft. A payload range diagram (also known as the “elbow chart”) illustrates the trade-off. The top horizontal line represents the maximum payload. It is limited structurally by maximum zero-fuel weight (MZFW) of the aircraft. Maximum payload is the difference between maximum zero-fuel weight and operational empty weight (OEW). Moving left-to-right along the line shows the constant maximum payload as the range increases. More fuel needs to be added for more range.

The vertical line represents the range at which the combined weight of the aircraft, maximum payload and needed fuel reaches the maximum take-off weight (MTOW) of the aircraft. If the range is increased beyond that point, payload has to be sacrificed for fuel.

The maximum take-off weight is limited by a combination of the maximum net power of the engines and the lift/drag ratio of the wings. The diagonal line after the range-at-maximum-payload point shows how reducing the payload allows increasing the fuel (and range) when taking off with the maximum take-off weight.

The second kink in the curve represents the point at which the maximum fuel capacity is reached. Flying further than that point means that the payload has to be reduced further, for an even lesser increase in range. The absolute range is thus the range at which an aircraft can fly with maximum possible fuel without carrying any payload.

Picture Credit : Google