Monthly Archives: October 2010
Squids can hear and their primitive ears can help us better understand how human hearing works.
The ordinary squid, Loligo pealii, is well known as a kind of floating buffet. “Almost every type of marine organism feeds somehow off squid,” said biologist Aran Mooney from the Woods Hole Oceanographic Institution. Not just fish, but also many birds, seals, sea lions, dolphins, and whales depend heavily on squid.
|Researchers attaching electrodes to the sedated squid|
Yet, despite their importance in the food web, it is amazing how little we know about the squid – what senses they rely on to navigate, avoid danger, find food, and communicate with each other. Scientists know that fish and other vertebrates can hear, but it wasn’t clear whether the squid could even detect sound.
Finding this out isn’t exactly trivial; it’s not as if you can just play a tone and see if a squid raises a tentacle in response. The researchers had to develop techniques to learn if, and what, squid can hear. In a study published in The Journal of Experimental Biology, they confirmed that squid can indeed detect sound. Now, they have begun to investigate the rudimentary sensory organ to see what it can tell us about hearing in higher animals.
A primitive ‘ear’?
In humans ears the sound waves strike the eardrum and set it vibrating. An array of tiny bones in the middle ear amplifies the vibrations and sends them rippling through fluid in a spiralling tube called the cochlea. The cochlea is lined with hair cells. On one end, they have hair-like structures that project into the fluid in the cochlea; on the other end, the cells connect with nerve fibres outside of the cochlea. The vibrations generate movement of the fluid, which bends the hairs and triggers nerve impulses.
Squid have two organs called statocysts, which have similarities with cochleas. Located near the base of the brain, each statocyst is a hollow, fluid-filled sac lined with hair cells. On the outside of the sac, the hair cells are connected to nerves, which lead to the brain. “It’s like an inside-out tennis ball,” Mooney said, “hairy on the inside, smooth on the outside.”
Inside each sac is a tiny grain of calcium carbonate called a statolith. It enables the squid to sense its position in the water. Structurally, the statocyst “is analogous to our auditory system” and is likely an evolutionary step toward higher-order hearing organs, said Mooney.
Can you hear it now?
The scientists used a technique similar to hearing tests routinely conducted on newborns, who, like squid, can’t readily affirm that they’ve heard something. In those tests, electrodes are placed on the infants’ heads, and sounds are presented to them through earphones. The sounds stimulate electrical activity in nerves that is recorded by the electrodes.
It wasn’t easy to attach electrodes to a squid so the researchers developed a noninvasive method to anesthetise squid for up to five hours. The sedation enhances the potential for squid to become a valuable “lab rat” to help us learn more about human hearing.
The findings showed that statocysts respond to sounds, but only to relatively low frequencies, up to 500 Hertz; they do not detect the high frequency sounds that dolphins use to find prey. (Human hearing spans a range from about 20 Hz to 20,000 Hz.)
Mooney thinks the statocysts have a lot to teach us about how ears evolved. “Humans, fish, and animals use hair to detect sound and movement,” he said. “Their hair cell structures are similar to squid, but also different. There is probably a basic structure that evolved millions of years ago, but we have taken different evolutionary paths since.”
“By learning more about squid hearing and squid hair cells, we might learn what is important in human hearing,” he said.
“We need to learn more about the basic functioning of squid ears first, but down the road, squid ears and hair cells might be models for examining human hearing.”
Article taken from The Bangalore Mirror
Globally, millions of sharks are ruthlessly hunted for their fins. After catching the sharks and cutting their dorsal fins, the sharks are then tossed back into the sea to die a slow and painful death!!
Apart from the horror of this practice, the balance of sea life is seriously disturbed as sharks are high up the food chain and control the population of a large variety of smaller fish-life. India is one of the biggest killer of sharks!!
The barbarians are now at our gates because most other nations of the world have started restricting fishing practices that lead to killing of Sharks. The mighty Mobile Phone that has empowered the fisherman with easy access to shark fin buyers, has made India the centrepiece of the regional shark-finning industry. We should never ignore the compulsions of the poor fishermen of our country, but are we about to sell the health of our oceans for a few measly dollars? We say, NO! There are choices, without compromising the fishermen’s income, to save our ecosystem!
These are pictures of catch from a boat held by local authorities for illegally fishing in the waters of Lakshadweep. The boat responsible was doing IUU, Illegal, Unregulated and Unreported fishing. Lakshadweep’s territorial waters are an area only boats from Lakshadweep are permitted to fish.
Local fishermen use only the eco-friendly pole and line fishing techniques and target tuna and illegal fishing boats from Kerala and Tamil Nadu pose a great threat to the livelihood and ecology of Lakshadweep, and its an increasing threat these days.
Inner Space Speciation Project to the Celebes Sea. Credit: Russ Hopcroft
LONDON, England – There are more than one million different types of creatures living in the world’s oceans today, according to a newly-released, decade-long effort to record marine life species around the world.
The Census of Marine Life, which was an international effort began that in the year 2000 and was officially completed on Monday, featured more than 2,700 experts, from over 80 different countries and territories, representing 670 different institutions.
“We prevailed over early doubts that a Census was possible, as well as daunting extremes of nature,” Dr. Ian Poiner, chair of the Census Steering Committee, said in a statement. “This cooperative international 21st century voyage has systematically defined for the first time both the known and the vast unknown, unexplored ocean.”
The researchers completed more than 540 expeditions and spent roughly 9,000 days at sea in order to formulate the world’s first, comprehensive catalog of aquatic lifeforms. According to the Associated Press (AP), they successfully counted and validated a total of 201,206 different species, though the scientists who participated in the $650-plus million dollar project believe there are far more marine creatures out there yet to be officially recognized.
“All surface life depends on life inside and beneath the oceans. Sea life provides half of our oxygen and a lot of our food and regulates climate. We are all citizens of the sea. And while much remains unknown, including at least 750,000 undiscovered species and their roles, we are better acquainted now with our fellow travelers and their vast habitat on this globe,” said Poiner.
According to the Census findings, more than 16,000 new species have been discovered since the start of the cataloging effort in 2000, including 1,200 new species collected and described by participating scientists over the past 10 years and over 5,000 others that were collected during the Census but have yet to be described. In a press release, Census officials estimate that between 100 and 150 new fish species were encountered every year, and an estimated 5,000 others have yet to be discovered. They also estimate that there could be over one billion types of marine microbes in the world.
“The Census enlarged the known world,” said Myriam Sibuet, Vice-Chair of the Census Scientific Steering Committee. “Life astonished us everywhere we looked. In the deep sea we found luxuriant communities despite extreme conditions. The discoveries of new species and habitats both advanced science and inspired artists with their extraordinary beauty. Some newly discovered marine species have even entered popular culture, like the yeti crab painted on skateboards.”
Starting on Monday, over 300 key members of the Census are scheduled to participate in a three-day meeting at the Royal Institution of Great Britain, the Royal Society, and Natural History Museum in London to discuss and share their discoveries. A second Census will also be discussed during this week’s meeting, as well as during next fall’s World Conference on Marine Biodiversity in Scotland.
“The Census united scientists from more than 80 nations with different talents, equipment, and interests,” Paul Snelgrove, who led the assembly and report of the Census results, said in a statement on Monday. “It matched the immensity and complexity of ocean life with a human enterprise able to grasp it. The understanding and well-being of marine life may well depend on continued unity of international science.”
Congrats to our new batch of indian instructors passing out from Andaman Diving Academy’s Oct 2010 PADI IDC. All your hardwork has paid off. All the best to you guys and hope to see more and more new indian instructors!
From Left : Rob (IE Examiner), Ruben, Karan, Rico(Course Director), Beemraj,Poonam