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Ocean Research


January 2014 Issue

Great White Shark Genes Similar to Humans
A new study by scientists from Nova Southeastern University's (NSU) Save Our Seas Shark Research Centre and Cornell University undertook the first large-scale exploration of the great white shark's genetic repertoire. The researchers compared the transcriptome (i.e., the set of RNA sequences expressed by the organism's genes) from the white shark heart to the transcriptomes from the best studied fish research model (the zebrafish) and humans to look for similarities and significant differences that might explain the distinctiveness of the white shark.

Surprisingly, the researchers found that the proportion of white shark gene products associated with metabolism had fewer differences from humans than zebrafish (a bony fish).

The researchers were also surprised to find that other aspects of the white shark heart transcriptome, including molecular functions as well as the cellular locations of these functions, also showed greater similarity to humans than zebrafish.

One possibility for the apparent greater similarity between white sharks and humans in the proportion of gene products associated with metabolism might be due partly to the fact that the white shark has a higher metabolism because it is not a true cold-bodied fish like bony fishes.

The transcriptome also revealed a much lower abundance than found in other vertebrates of a DNA sequence that occurs in repeated triplet form. In human genes that contain such repeated triplet sequences, an aberrant increase in their number has been linked to a variety of neurological disorders.

It's not known whether sharks are immune to neurological genetic diseases, but the fact that these DNA patterns occur in such low abundance in white shark genes may indicate a reduced chance of similar such disorders.

MBARI Maps Campeche to Study Comet Crash
About 65 million years ago, an asteroid or comet crashed into a shallow sea near what is now the Yucatán Peninsula of Mexico. The resulting firestorm and global dust cloud caused the extinction of many land plants and large animals, including most of the dinosaurs. Monterey Bay Aquarium Research Institute (MBARI) researchers have found evidence that remnants from this devastating impact are exposed along the Campeche Escarpment, an immense underwater cliff in the southern Gulf of Mexico.

The ancient meteorite impact created a crater more than 160 kilometers across. This crater is almost invisible today, buried under hundreds of meters of debris and almost a kilometer of marine sediments. Although fallout from the impact has been found in rocks around the world, little research has been done on the rocks close to the impact site, in part because they are so deeply buried. All existing samples of impact deposits close to the crater have come from deep boreholes drilled on the Yucatán Peninsula.

In March 2013, an international team of researchers led by MBARI's Charlie Paull created the first detailed map of the Campeche Escarpment. The team used multibeam sonars on the RV Falkor, operated by the Schmidt Ocean Institute. The resulting maps have recently been incorporated in Google Maps (maps.google.com) and Google Earth (earth.google.com) for viewing by researchers and the general public.

Sedimentary rock layers exposed on the face of the Campeche Escarpment provide a sequential record of the events that have occurred over millions of years. Based on the new maps, Paull believes that rocks formed before, during and after the impact are all exposed along different parts of this underwater cliff. The newly created maps of the Campeche Escarpment could open a new chapter in research about one of the largest extinction events in Earth's history.

First Drill Core Recovered From Pacific Ocean Lower Crust
Jonathan Snow from the University of Houston and Kathryn Gillis from the University of Victoria in Canada led a team of 30 researchers from around the world on a $10 million expedition that recovered the first-ever drill core from the lower crust of the Pacific Ocean.

Traveling aboard the Integrated Ocean Drilling Program Expedition 345 to the Hess Deep in the Pacific Ocean, they recovered core sections of lower crustal rocks, called gabbros, that formed more than two miles beneath the seafloor. A large rift valley in the eastern equatorial Pacific, the Hess Deep is like an onion sliced and pulled apart, revealing its deeper layers.

The two-month expedition, aboard the drilling vessel JOIDES Resolution, confirmed for the first time the widespread existence of layered gabbros in the lower crust. By studying thin slices of the gabbros under polarizing microscopes, the scientists identified substantial amounts of the mineral orthopyroxene, a magnesium silicate that was thought to be absent from the lower crust. The fourth phase of ocean drilling was approved in late November by the National Science Board.

Seahorse Heads Perfect for Capturing Prey
Seahorses are slow, docile creatures, but their heads are perfectly shaped to sneak up and quickly snatch prey, according to marine scientists from The University of Texas at Austin.

The prey, in this case, are copepods. Copepods are extremely small crustaceans that are a critical component of the marine food web.

Copepods escape predators when they detect waves produced in advance of an attack, and they can jolt away at speeds of more than 500 body lengths per second.

In calm conditions, seahorses catch their intended prey 90 percent of the time.

This study looked at the dwarf seahorse, Hippocampus zosterae, which is native to the Bahamas and the U.S. To observe the seahorses and the copepods in action, researchers used high-speed digital 3D holography techniques, which revealed that the seahorse's head is shaped to minimize the disturbance of water in front of its mouth before it strikes. Just above and in front of the seahorse's nostrils is a kind of 'no wake zone,' and the seahorse angles its head precisely in relation to its prey so that no fluid disturbance reaches it. Other small fish with blunter heads, such as the three-spined stickleback, have no such advantage.


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