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Climate change shrinks marine life richness near equator
Read more on - Polity | Economy | Schemes | S&T | Environment
- The story: While Cuba’s marine life has suffered from overfishing and pollution, there is mounting evidence that the warming of waters due to climate change may be taking a large toll as well. Research published recently finds that the total number of open-water species declined by about half in the 40 years up to 2010 in tropical marine zones worldwide. During that time, sea surface temperatures in the tropics rose nearly 0.2 degree Celsius.
- What happens: During some summers, as the Caribbean water temperatures climb, the luminous coral colonies of gold, green and blue that ring the island nation of Cuba give way to patches of skeletal white. The technicolor streaks of darting tropical fish flash less frequently. The rasping sounds of lobsters go quiet. Climate change is already impacting marine species diversity distribution, with changes being more dramatic in the Northern Hemisphere where waters have warmed faster. While numerous factors like overfishing have impacted tropical species, the study published in the Proceedings of the National Academy of Sciences found a strong correlation between species decline and rising temperature. Fish species diversity tended to either plateau or decline at or above 20C (68 Fahrenheit), the researchers found.
- Blink of an eye: Past studies have shown that ocean warming is driving some species to migrate to cooler waters, the new study attempts to gauge that impact more broadly -- analyzing data on 48,661 marine species including fish, mollusks, birds and corals since 1955. The number of species attached to the seafloor -- including corals and sponges -- remained somewhat stable in the tropics between the 1970s and 2010, according to the study. Some were also found beyond the tropics, suggesting they had expanded their ranges. In other words, scientists say, species that can move are moving. From a geological time perspective, this is the blink of an eye.
- No options: For fixed species like corals, moving is not an option. One of the big questions is ‘Will coral reefs as ecosystems and corals as species be able to move north or south enough fast enough to adjust to a changing climate?’" Having fleets of fish and other swimmers shift rapidly to more temperate waters could devastate the coral ecosystems they leave behind -- along with any fishing and tourism industries that rely on them. Such changes can have a really huge impact on some of the most vulnerable human communities around the planet.
- A return to earlier: For Cuba, such an impact could unravel the island nation’s efforts to manage its underwater gardens although its corals have been less stressed by coastal development and pollution than corals elsewhere. They are considered more resilient to ocean warming. It's impressive to return to an area that experienced significant bleaching the year before, but looks perfectly healthy a year later. Cuba opened its first coral reef nursery four years ago to research which species coped best with warming and eventually to repopulate depleted reefs. The country is also restoring coastal mangroves, which serve as fish nurseries and shelter.
- Knowledge centre:
- Corals - Corals are invertebrate animals belonging to a large group of colourful and fascinating animals called Cnidaria. Other animals in this group seen in rock pools or on the beach include jelly fish and sea anemones. Although Cnidarians exhibit a wide variety of colours, shapes and sizes, they all share the same distinguishing characteristics; a simple stomach with a single mouth opening surrounded by stinging tentacles. Each individual coral animal is called a polyp, and most live in groups of hundreds to thousands of genetically identical polyps that form a ‘colony’. The colony is formed by a process called budding, which is where the original polyp literally grows copies of itself.
- Coral types and food - Coral are generally classified as either “hard coral” or “soft coral”. There are around 800 known species of hard coral, also known as the ‘reef building’ corals. Soft corals, which include seas fans, sea feathers and sea whips, don’t have the rock-like calcareous skeleton like the others, instead they grow wood-like cores for support and fleshy rinds for protection. While most of a corals diet is obtained from zooxanthellae, they can also ‘fish’ for food too. During feeding a coral polyp will extend its tentacles out from its body and wave them in the water current where they encounter small fish, plankton or other food particles. The surface of each tentacle has thousands of stinging cells called cnidoblasts, and when small prey floats or swims past, the tentacles fire these stinging cells, stunning or killing the prey before passing it to the mouth.
- Coral reefs - Hard corals extract abundant calcium from surrounding seawater and use this to create a hardened structure for protection and growth. Coral reefs are therefore created by millions of tiny polyps forming large carbonate structures, and are the basis of a framework and home for hundreds of thousands, if not millions, of other species. Coral reefs are the largest living structure on the planet, and the only living structure to be visible from space. Such coral reefs have evolved on earth over the past 200 to 300 million years, and over this evolutionary history, perhaps the most unique feature of corals is the highly evolved form of symbiosis. Coral polyps have developed this relationship with tiny single-celled plants, known as zooxanthellae. Inside the tissues of each coral polyp live these microscopic, single-celled algae, sharing space, gas exchange and nutrients to survive.
- Coral bleaching - Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. A warming planet means a warming ocean, and a change in water temperature—as little as 2 degrees Fahrenheit—can cause coral to drive out algae. Coral may bleach for other reasons, like extremely low tides, pollution, or too much sunlight.
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