Ocean Science Archives

Ocean’s Color Affects Hurricane Paths

A change in the color of ocean waters could have a drastic effect on the prevalence of hurricanes, new research indicates. In a simulation of such a change in one region of the North Pacific, the study finds that hurricane formation decreases by 70 percent. That would be a big drop for a region that accounts for more than half the world’s reported hurricane-force winds.

It turns out that the formation of typhoons — as hurricanes are known in the region — is heavily mediatedby the presenceof chlorophyll, a green pigment that helps the tiny single-celled organisms known as phytoplankton convert sunlight into food for the rest of the marine ecosystem. Chlorophyll contributes to the ocean’s color.

“We think of the oceans as blue, but the oceans aren’t really blue, they’re actually a sort of greenish color,” said Anand Gnanadesikan, a researcher with the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey. “The fact that [the oceans] are not blue has a [direct] impacton the distribution of tropical cyclones.”

In the study, to be published in an upcoming issue of Geophysical Research Letters, a journal of the American Geophysical Union, Gnanadesikan’s team describes how a drop in chlorophyll concentration, and the corresponding reduction in ocean color, could cause a decrease in the formation of hurricanes in the color-depleted zone. Although the study looks at the effects of a simulated drop in the phytoplankton population (and therefore in the ocean’s green tint), recently-published research argued that global phytoplankton populations have been steadily declining over the last century.

Gnanadesikan compared hurricane formation rates in a computer model under two scenarios. For the first, he modeled real conditions using chlorophyll concentrations in the North Pacific observed by satellites. He then compared that to a scenario where the chlorophyll concentration in parts ofthe North Pacific Subtropical Gyre — a large, clockwise-circulation pattern encompassing most of the North Pacific — was set to zero.

In the latter scenario, the absence of chlorophyll in the subtropical gyre affected hurricane formation by modifying air circulation and heat distribution patterns both within and beyond the gyre. In fact, along the equator, those new patterns outside the gyre led to an increase in hurricane formation of about 20 percent. Yet, this rise was more than made up for by the 70 percent decrease in storms further north, over and near the gyre. The model showed that more hurricanes would hit the Philippines and Vietnam, but fewer would make landfall in South China and Japan.

In the no-chlorophyll scenario, sunlight is able to penetrate deeper into the ocean, leaving the surface water cooler. The drop in the surface temperature in the model affects hurricane formation in three main ways: cold water provides less energy; air circulation patterns change, leading to more dry air aloft which makes it hard for hurricanes to grow.The changes in air circulation trigger strong winds aloft, which tend to prevent thunderstorms from developing the necessary superstructure that allows them to grow into hurricanes.

A decrease in hurricanes in the North Pacific is just one example of how changing chlorophyll concentrations can have far-reaching, previously unconsidered, effects. The specific outcomes over different patches of the ocean will vary based on local currents and ocean conditions, said Gnanadesikan.

A complete absence of chlorophyll in parts of the ocean would be a drastic change, Gnanadesikanadmits. Yet, its potential impact is still important to consider, he maintains. The northern Pacific gyre that he studied isalready the “biological desert of the ocean,” he said. So the surprise, then, is that “even in this region that is apparently clear, biologically-mediated heating is important.”

This research was primarily supported by NOAA, with additional support from the National Aeronautics and Space Administration.

Authors:

A. Gnanadesikan, G. A. Vecchi, W. G. Anderson, R. Hallberg: Geophysical Fluid Dynamic Laboratory, National Oceanic and Atmospheric Administration, Princeton, New Jersey, USA

Ocean Dwelling Salps – Nature’s Near-Perfect Little Engine Just Got Better

What if trains, planes, and automobiles all were powered simply by the air through which they move? Moreover, what if their exhaust and byproducts helped the environment?

Well, such an energy-efficient, self-propelling mechanism already exists in nature. The salp, a smallish, barrel-shaped organism that resembles a kind of streamlined jellyfish, gets everything it needs from the ocean waters to feed and propel itself. And, scientists believe its waste material may actually help remove carbon dioxide (CO2) from the upper ocean and the atmosphere.

Now, researchers at the Woods Hole Oceanographic Institution (WHOI) and MIT report that the half-inch to 5-inch-long creatures are even more efficient than had been believed.  Reporting in the current issue of the Proceedings of the National Academy of Sciences, they have found that the ocean-dwelling salps are capable of capturing and eating extremely small organisms as well as larger ones, rendering them even hardier—and perhaps more plentiful—than had been thought.

"We had long thought that salps were about the most efficient filter feeders in the ocean,” said Laurence P. Madin, WHOI Director of Research and one of the investigators. “But these results extend their impact down to the smallest available size fraction, showing they consume particles spanning four orders of magnitude in size. This is like eating everything from a mouse to a horse."

Salps capture food particles, mostly phytoplankton, with an internal mucous filter net. Until now, it was thought that thier menu was limited to particles only as large as or larger than the 1.5-micron-wide holes in the mesh.

But a mathematical model suggested salps somehow might be capturing food particles smaller than that, said Kelly R. Sutherland, who wrote the paper as part of her PhD thesis at the MIT/WHOI Joint Program for graduate students. In the laboratory at WHOI, Sutherland and her colleagues offered salps food particles of three sizes: smaller, around the same size as, and larger than the mesh openings.

“We found that more small particles were captured than expected,” said Sutherland, now a postdoctoral researcher at Caltech.  “When exposed to ocean-like particle concentrations, 80 percent of the particles that were captured were the smallest particles offered in the experiment."

This finding is important for a number of reasons.  First, it helps explain how salp--which can exist either singly or in “chains” that may contain a hundred or more--are able to survive in the open ocean, their usual habitat, where the supply of larger food particles is low.  Madin, who served as Sutherland’s advisor at WHOI, adds: “Their ability to filter the smallest particles may allow them to survive where other grazers can't.”

Second, and perhaps most significantly, it enhances the importance of the salps’ role in carbon cycling. As they eat small, as well as large, particles, “they consume the entire 'microbial loop' and pack it into large, dense fecal pellets,” Madin says.

The larger and denser the carbon-containing pellets, the sooner they sink to the ocean bottom. “This removes carbon from the surface waters,” says Sutherland, “and brings it to a depth where you won’t see it again for years to centuries.”

And the more carbon that sinks to the bottom, the more space there is for the upper ocean to accommodate carbon, hence limiting the amount that rises into the atmosphere as CO2, explains co-author Roman Stocker of MIT’s Department of Civil and Environmental Engineering .

“The most important aspect of this work is the very effective shortcut that salps introduce in the process of particle aggregation,” Stocker says. “Typically, aggregation of particles proceeds slowly, by steps, from tiny particles coagulating into slightly larger ones, and so forth.

“Now, the efficient foraging of salps on particles as small as a fraction of a micrometer introduces a substantial shortcut in this process, since digestion and excretion package these tiny particles into much larger particles, which thus sink a lot faster.”

This process starts with the mesh made of fine mucus fibers inside the salp’s hollow body. Salps, which can live for weeks or months, swim and eat in rhythmic pulses, each of which draws seawater in through an opening at the front end of the animal. The mesh captures the food particles, then rolls into a strand and goes into the gut, where it is digested.

It had been reasoned that the lower limit of particles captured by a salp was dictated by the size of the openings in the mesh (1.5 microns) In other words, particles smaller than the openings were expected to pass through the mesh.  But the new results show that it can capture particles as small as 0.5  microns and smaller, because the particles stick to the mesh material itself in a process called direct interception, Sutherland says.

"Up to now it was assumed that very small cells or particles were eaten mainly by other microscopic consumers, like protozoans, or by a few specialized metazoan grazers like appendicularians,” said Madin. “This paper indicates that salps can eat much smaller organisms, like bacteria and the smallest phytoplankton, organisms that are numerous and widely distributed in the ocean."

As much as they are impressed with the practical implications involving carbon exchange, the scientists are captivated by the unique, almost magical performance of this natural undersea engine.

The work--funded by the National Science Foundation and the WHOI Ocean Life Institute--“does imply that salps are more efficient vacuum cleaners than we thought,” says Stocker. “Their amazing performance relies on a feat of bioengineering--the production of a nanometer-scale mucus net--the biomechanics of which still remain a mystery, adding to the fascination for and the interest in these animals.”
www.whoi.edu

Rare Coral Discovered in Pacific Ocean

By OurAmazingPlanet.com Staff

What could be the world's rarest coral has been discovered in the remote North Pacific Ocean.

The Pacific elkhorn coral (Acropora rotumana) — with branches like an elk's antlers — was found during an underwater survey of the Arno atoll in the Marshall Islands.

Corals are tiny creatures that live in skeleton-covered colonies, creating the illusion that a coral community is one single organism. This newfound coral colony may be the first time this species has been spotted in more than 100 years, according to researchers at the Centre of Excellence for Coral Reef Studies (CoECRS) in Queensland, Australia.

"When I first saw it, I was absolutely stunned," said research team leader Zoe Richards of CoECRS.

The huge coral colonies were 16 feet (5 meters) across and nearly 7 feet (2 m) high and "were like nothing I'd seen before in the Pacific Ocean," Richards said.

The coral colony looks like the critically endangered elkhorn coral (Acropora palmata) of the Atlantic Ocean, but genetic analysis has shown that the Atlantic and Pacific varieties are different species.

The Pacific elkhorn is of the Acropora genus, the dominant genus of reef-building corals, the researchers said, so learning how the Pacific version lives will provide clues about these exotic marine creatures and will help determine their conservation status.

"So far I have only found this new population of coral to occur along a small stretch of reef at a single atoll in the Marshalls group," Richards said. "It grows in relatively shallow water along the exposed reef front and, so far, fewer than 200 colonies are known from that small area."

The Pacific elkhorn coral colonies are the largest of all the Acropora colonies observed at Arno Atoll, indicating that these are relatively old, Richards said.

The Pacific elkhorn coral colony was a rare find, but it may not be an entirely new species. Corals fitting the description of the Pacific elkhorn were first described in 1898 near Fiji in the South Pacific, but scientists don't have enough genetic information from this earlier find to say if the corals are a match, Richards said.

The Atlantic relative, A. palmata is regarded by most marine researchers as the outstanding symbol of the plight of Caribbean corals. It is rated as critically endangered after vanishing from most of its Caribbean reef habitat in recent decades.

"When Zoe showed me pictures of the Pacific elkhorn, I was shocked," said coral geneticist David Miller of CoECRS and James Cook University, also in Queensland. "The colonies look just like the critically endangered Caribbean species A. palmata, one of the most distinctive of all corals. The fact that these colonies might represent a species that has not been seen for over a hundred years (A. rotumana) says something about how much we know about the remote reefs of the North Pacific," Miller said.

The newfound coral colony is detailed in the June 2 edition of the journal Systematics and Biodiversity.

After the Oil Spill: New Research Sheds Light on Coral Susceptibility to Environmental Stress

Much attention has been paid to the fate of wildlife living on and above the Gulf of Mexico's surface. Now, a new research study published in the June 2010 print issue of the FASEB Journal looks toward the seafloor to explain coral susceptibility to disease outbreaks when they encounter environmental stress and to set the stage for understanding exactly what type of undersea environment is necessary to promote coral health and growth after the oil spill cleanup

In addition, this research also opens doors for the development of new tools that can assess the health of corals, which is important when trying to establish manmade reefs or to save ones that already exist.

"We hope this study will highlight the need to maintain favorable environmental conditions on reefs to maximize the functioning of coral immune mechanisms and avert outbreaks of coral disease and bleaching," said Caroline Palmer, one of the researchers involved in the work who is from the Australian Research Council Centre of Excellence for Coral Reef Studies and School of Marine and Tropical Biology at James Cook University in Queensland, Australia. "Otherwise, declining environmental conditions associated with extractive activities, deteriorating water quality and a changing climate will threaten the long term persistence of corals and coral reefs, which support millions of lives worldwide through fisheries, tourism, and coastal protection amongst other functions."

Palmer and colleagues sampled several coral species from the Great Barrier Reef to determine whether a suite of cellular and biochemical mechanisms of immunity were active. Using histological techniques they documented the presence and area of melanin-containing granular cells and the activity of specific enzymes as measures of oxidative damage and repair. Then the scientists investigated the relationship between coral immunity and disease and susceptibility to by analyzing the data on the activity of innate immunity in conjunction with published data on coral species' susceptibilities to oxidative bleaching and disease. Results suggest that different coral species invest different amounts of resources in immunity and defense, which may explain differences in the susceptibility to negative environmental impacts.

"You don't have to be a marine biologist to know that the Gulf oil spill is an environmental disaster of the first order. Stuff leaching from the ocean floor is the worst environmental challenge a coral reef can face," said Gerald Weissmann, M.D., Editor-in-Chief of the FASEB Journal. "But with luck, and with marine biology to explain how coral reefs survive, we can begin to get the Gulf ecosystems back on track sooner rather than later."

According to the National Oceanic and Atmospheric Administration, "Corals that are spawning at the time of an oil spill can be damaged because the eggs and sperm, which are released into the water at very precise times, remain at shallow water depths for various times before they settle. Thus, in addition to compromising water quality, oil pollution can disrupt the long-term viability and reproductive success of corals, rendering them more vulnerable to other types of disturbances. In western Australia and the Flower Garden Banks of the northern Gulf of Mexico, spawning occurs in late summer or fall."

Source: Sciencedaily.com
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Federation of American Societies for Experimental Biology,

Journal Reference:

Caroline V. Palmer, John C. Bythell, and Bette L. Willis. Levels of immunity parameters underpin bleaching and disease susceptibility of reef corals. The FASEB Journal, 2010; 24 (6): 1935 DOI: 10.1096/fj.09-152447

Federation of American Societies for Experimental Biology (2010, June 1). After the oil spill: New research sheds light on coral susceptibility to environmental stress. ScienceDaily. Retrieved July 26, 2010, from http://www.sciencedaily.com­ /releases/2010/06/100601101548.htm