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Ocean Research


August 2014 Issue

Manta Rays Take 80 Percent of Food From Palmyra Atoll Lagoons
Douglas McCauley and his colleagues at the University of California, Santa Barbara’s Department of Ecology, Evolution and Marine Biology, have studied the ecology of manta rays in the Palmyra Atoll, surrounded by more than 15,000 acres of coral reefs. The researchers’ findings appear in Marine Biology.

Using a novel combination of research tools, the scientists examined how the manta rays use lagoons, what particular habitat microfeatures are important, and what drivers make the fish come and go from Palmyra’s lagoons. The big question was why manta rays congregate in this particular habitat. It turns out it was at least partially because of the food.

The researchers used stable isotope analysis, a chemical assay of a tissue biopsy that provides an integrative view of what the animal ate in previous months. They matched the chemical signature of the mantas to that of zooplankton collected in the lagoons, verifying that this habitat serves as an important feeding ground.

“Using mathematical modeling we determined that many of the manta rays we encountered took around 80 percent of their energy from lagoon plankton,” McCauley said. “This discovery that lagoons can contribute such an important amount of food and energy to manta rays highlights the need to motivate management interventions in lagoons.”

Simpler Marine Life Forms Can Survive Higher Temps
The simpler a marine life form is built, the better it is suited for survival during climate change, scientists at the Alfred Wegener Institute at the Helmholtz Centre for Polar and Marine Research discovered in a new study published in Global Change Biology. While unicellular bacteria and archaea are able to live even in hot, oxygen-deficient water, marine inhabitants with a more complex structure, such as animals and plants, reach their growth limits at a water temperature of 41°C.

The researchers have been investigating the processes that result in animals having a certain temperature threshold up to which they can develop and reproduce. The scientists found that the reason for this is their cardiovascular system. Beyond the temperature threshold, the transport capacity of this system is no longer sufficient; the animal can then only survive for a short time.

The scientists evaluated more than 1,000 studies on the adaptability of marine life forms. Starting with simple archaea lacking a nucleus, bacteria and unicellular algae right through to animals and plants, they found the species in each case with the highest temperature tolerance within their group and determined their complexity. They found that the simpler the structure, the more heat-tolerant the species.

But the adaptation limit of an organism is not only dependent on its upper temperature threshold, but also on its ability to cope with small amounts of oxygen. While many of the bacteria and archaea can survive at low oxygen concentrations or even without oxygen, most animals and plants require a higher minimum concentration. The new research provides evidence that the body size of an organism plays a decisive role concerning adaptation limits.

The next question is the role the complexity of species plays for tolerance and adaptation to ocean acidification.

Australia’s RV Investigator Gets TRIAXUS Towed ROV
MacArtney (Esbjerg, Denmark) has supplied a TRIAXUS towed ROV to the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia’s national science agency. The TRIAXUS will be utilized on Australia’s Marine National Facility RV Investigator, which is currently undergoing the final stages of construction.

The TRIAXUS will be used in a range of oceanographic research activities. It has a CTD, laser optical plankton counter, transmissometer, fluorescence and PAR sensors. These instruments make the TRIAXUS well-suited for the many aspects of plankton research. In addition, utilizing the CTD, the TRIAXUS is also intended to be used in investigations of frontal features, air-sea interactions and much more.

Beyond TRIAXUS, the Investigator will feature a broad range of scientific systems and equipment to support scientists in oceanography, climatology, fisheries, marine ecosystem, environmental and geoscientific research. The Investigator will contribute to Australia’s ocean research capacity and deliver an opportunity for participation in research programs at a global scale.

First European Ship to Sail Great Lakes Possibly Found
Steven Libert, president of the Great Lakes Exploration Group, announced he has located what is believed to be the remains of Le Griffon, the first European ship to have sailed the upper Great Lakes. The 45-ton barque carrying seven cannons was built by the legendary French explorer René-Robert Cavelier, Sieur de La Salle, who was attempting to establish a Northwest Passage through Canada. La Salle wanted to provide a faster way to connect France with its trading partners in the Far East, and Le Griffon was to be a vital link in the route between Niagara and Illinois.

On its maiden voyage the ship sailed through unchartered waters across Lake Erie, Lake Huron and Lake Michigan. On its return trip, Le Griffon and her crew of six disappeared. Libert has spent the last 30 years researching historical records and conducting exploratory dives in upper Lake Michigan. On a dive last summer, Libert and his group discovered an area with a large hand-hewn wood timber protruding from the bottom. It is thought to be the vessel’s bowsprit, and carbon-dating tests are promising, but not conclusive. To confirm the exact identity of the vessel requires locating more items from the site, but with much of the ship entombed in the lake bottom, some high-tech equipment is needed. Key artifacts to find would be one or more of the seven cannons.

To effectively search the football-field-size area, Libert has acquired JW Fishers (East Taunton, Massachusetts) PT-1 pinpointing magnetometer.

To protect the scientific and historic value of this incredible find, a partnership has been established with the state of Michigan and the Republic of France. Work is continuing as weather permits.


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