Old Theory of Phytoplankton Growth Overturned, Raise Concerns for Ocean Productivity

A new study concludes that an old, fundamental and widely accepted theory of how and why phytoplankton bloom in the oceans is incorrect.

The findings challenge more than 50 years of conventional wisdom about the growth of phytoplankton, which are the ultimate basis for almost all ocean life and major fisheries. And they also raise concerns that global warming, rather than stimulating ocean productivity, may actually curtail it in some places.
This analysis was published in the journal Ecology by Michael Behrenfeld, a professor of botany at Oregon State University, and one of the world's leading experts in the use of remote sensing technology to examine ocean productivity. The study was supported by NASA.
The new research concludes that a theory first developed in 1953 called the "critical depth hypothesis" offers an incomplete and inaccurate explanation for summer phytoplankton blooms that have been observed since the 1800s in the North Atlantic Ocean. These blooms provide the basis for one of the world's most productive fisheries.
"The old theory made common sense and seemed to explain what people were seeing," Behrenfeld said.
"It was based on the best science and data that were available at the time, most of which was obtained during the calmer seasons of late spring and early summer," he said. "But now we have satellite remote sensing technology that provides us with a much more comprehensive view of the oceans on literally a daily basis. And those data strongly contradict the critical depth hypothesis."
That hypothesis, commonly found in oceanographic textbooks, stated that phytoplankton bloom in temperate oceans in the spring because of improving light conditions -- longer and brighter days -- and warming of the surface layer. Warm water is less dense than cold water, so springtime warming creates a surface layer that essentially "floats" on top of the cold water below, slows wind-driven mixing and holds the phytoplankton in the sunlit upper layer more of the time, letting them grow faster.
There's a problem: a nine-year analysis of satellite records of chlorophyll and carbon data indicate that this long-held hypothesis is not true. The rate of phytoplankton accumulation actually begins to surge during the middle of winter, the coldest, darkest time of year.
The fundamental flaw of the previous theory, Behrenfeld said, is that it didn't adequately account for seasonal changes in the activity of the zooplankton -- very tiny marine animals -- in particular their feeding rate on the phytoplankton.
"To understand phytoplankton abundance, we've been paying way too much attention to phytoplankton growth and way too little attention to loss rates, particularly consumption by zooplankton," Behrenfeld said. "When zooplankton are abundant and can find food, they eat phytoplankton almost as fast as it grows."
The new theory that Behrenfeld has developed, called the "dilution-recoupling hypothesis," suggests that the spring bloom depends on processes occurring earlier in the fall and winter. As winter storms become more frequent and intense, the biologically-rich surface layer mixes with cold, almost clear and lifeless water from deeper levels. This dilutes the concentration of phytoplankton and zooplankton, making it more difficult for the zooplankton to find the phytoplankton and eat them -- so more phytoplankton survive and populations begin to increase during the dark, cold days of winter.
In the spring, storms subside and the phytoplankton and zooplankton are no longer regularly diluted. Zooplankton find their prey more easily as the concentration of phytoplankton rises. So even though the phytoplankton get more light and their growth rate increases, the voracious feeding of the zooplankton keeps them largely in-check, and the overall rise in phytoplankton occurs at roughly the same rate from winter to late spring. Eventually in mid-summer, the phytoplankton run out of nutrients and the now abundant zooplankton easily overtake them, and the bloom ends with a rapid crash.
"What the satellite data appear to be telling us is that the physical mixing of water has as much or more to do with the success of the bloom as does the rate of phytoplankton photosynthesis," Behrenfeld said. "Big blooms appear to require deeper wintertime mixing."
That's a concern, he said, because with further global warming, many ocean regions are expected to become warmer and more stratified. In places where this process is operating -- which includes the North Atlantic, western North Pacific, and Southern Ocean around Antarctica -- that could lead to lower phytoplankton growth and less overall ocean productivity, less life in the oceans. These forces also affect carbon balances in the oceans, and an accurate understanding of them is needed for use in global climate models.
Worth noting, Behrenfeld said, is that some of these regions with large seasonal phytoplankton blooms are among the world's most dynamic fisheries.
The critical depth hypothesis would suggest that a warmer climate would increase ocean productivity. Behrenfeld's new hypothesis suggests the opposite.
Behrenfeld said that oceans are very complex, water mixing and currents can be affected by various forces, and more research and observation will be needed to fully understand potential future impacts. However, some oceanographers will need to go back to the drawing board.
"With the satellite record of net population growth rates in the North Atlantic, we can now dismiss the critical depth hypothesis as a valid explanation for bloom initiation," he wrote in the report.
Behrenfeld et al. Abandoning Sverdrup's Critical Depth Hypothesis on phytoplankton blooms. Ecology, 2010; 91 (4)

The Ocean's Prey Problem

The food source upon which commercial and recreational fish, marine mammals and seabirds depend to survive is being steadily exhausted, according to a new report by Oceana, "Hungry Oceans: What Happens When the Prey Is Gone?" These so-called "prey fish" are the foundation of many marine animals' diets, and have been depleted to dangerously low levels due primarily to overfishing and climate change. "We have caught all the big fish and now we are going after their food," says Oceana marine scientist Margot L. Stiles. "Until recently it has been widely believed that prey fish are impossible to overexploit because their populations grow so quickly. We are now proving that untrue as the demands of commercial fisheries and aquaculture outpace the ocean's ability to provide food for us and itself." The future of both commercial and recreational fisheries is threatened by the loss of prey fish, especially those that are currently rebuilding from depletion. Hungry Oceans identifies bluefin tuna, striped bass, Pacific salmon and Pacific halibut as key species dependent on prey fish. Marine mammals and seabirds also depend on access to prey fish for their daily survival and for their young, including blue whales, humpback whales, penguins and terns. Hungry Oceans proposes, among other conservation measures, a moratorium on new fisheries targeting prey species, catch limits for existing fisheries and giving top priority to ocean predators. "Fisheries managers simply take prey for granted despite their critical role in the ecosystem," says Stiles. "We need to act responsibly when taking prey from natural predators, with our eyes open to the consequences for the ocean and for our own supply of seafood." Reporting by Jessica Rae Patton

Genes From Tiny Algae Shed Light On Big Role Managing Carbon In World's Oceans

Scientists from two-dozen research organizations led by the U.S. Department of Energy (DOE) Joint Genome Institute (JGI) and the Monterey Bay Aquarium Research Institute (MBARI) have decoded genomes of two algal strains, highlighting the genes enabling them to capture carbon and maintain its delicate balance in the oceans. These findings, from a team led by Alexandra Z. Worden of MBARI and published in the April 10 edition of the journal Science, will illuminate cellular processes related to algae-derived biofuels being pursued by DOE scientists.

The study sampled two geographically diverse isolates of the photosynthetic algal genus Micromonas—one from the South Pacific, the other from the English Channel. The analysis identified approximately 10,000 genes in each, compressed into genomes totaling about 22 million nucleotides. "Yet, surprisingly, they are far more diverse than we originally thought," said Worden. "These two picoeukaryotes, often considered to be the same species, only share about 90 percent of their genes."
To put this in perspective, humans and some primates have about 98 percent genes in common. Worden said that the algae's divergent gene complement may cause them to access and respond to the environment differently. "This also means that as the environment changes, these different populations will be subject to different effects, and we don't know whether they will respond in a similar fashion." She said that their apparently broad physiological range (exemplified by their expansive geographical range) may result in increased resilience as compared to closely related species, enabling them to survive environmental change better than organisms with a narrower geographic range. Testing the hypotheses developed through cataloging their respective inventory of genes, Worden said, will go a long way towards understanding their biology and ecology.
Algae were blazing the pathway of photosynthesis long before plants colonized land—so the results bear significantly on terrestrial plant research as well.
"Genome sequencing of Micromonas and the subsequent comparative analysis with other algae previously sequenced by DOE JGI and Genoscope [France], have proven immensely powerful for elucidating the basic 'toolkit' of genes integral not only to the effective carbon cycling capabilities of green algae, but to those they have in common with land plants," said Eddy Rubin, DOE JGI Director.
Tiny Micromonas, less than two microns in diameter, or roughly a 50th of the width of a human hair, are one of the few globally distributed marine algal species, thriving throughout the world's oceans from the tropics to the poles. They capture CO2, sunlight, water, and nutrients and produce carbohydrates and oxygen. Their productivity—which provides food resources within marine food webs—as well as their knack for capturing carbon, and influencing the carbon flux that may have bearing on climate change, make these algae keen target of study.
"Micromonas is a representative of a well-sampled group of green algae with the largest number of sequenced genomes. With these four genomes in hand--two Micromonas and two Ostreococcus--we can observe patterns of genome organization as well as the diversity between different organisms in this group," said JGI's Igor Grigoriev, one of the senior authors of the paper.
Embedded in the genetic code are clues about how photosynthesis transformed from a barren orb into the earth we know today.
"The Micromonas genomes encapsulate features that now appear to have been common to the ancestral algae that initiated the billion-year trajectory that led to the 'greening'—the rise of land plants—of the planet," said Worden. As highlighted in the Science article, comparing the strains to each other and in turn to the other characterized algal and plant genomes, will help to illustrate the dynamic nature of evolutionary processes and provide a springboard for unraveling the functional aspects of these and other phytoplankton populations.
Motility is another distinguishing aspect of the ecology of Micromonas. In the relatively viscous saltwater of the ocean, the flagellated Micromonas could give Michael Phelps a run for his money. Unlike other algae genera sequenced to date, these swift swimmers can cut through the water column at a rate of 50 body lengths per second, and are phototactic, meaning that they can swim towards the sunlight from which they derive their energy.
In previous studies, Worden and her colleagues showed that picoeukaryotes such as Micromonas comprised, on average, only a quarter of the picophytoplankton cells in a Pacific Ocean sampling, but were responsible for three-quarters of the net carbon production. They were also shown to be subject to heavy grazing pressure; their lack of a cell wall may make them more digestible as prey. In this case carbon may be efficiently sequestered by the "biological pump," the suite of processes that enable the algae to capture atmospheric carbon and transport it from the ocean surface zones to the depths below.
This research serves as a complement to field studies seeking to confirm emerging key players in global carbon fixation. "By understanding which genes a specific strain employs under certain conditions, we gain a view into the factors that influence the success of one group over another," Worden said. "We may then be able to develop models that could more effectively predict a range of possible future scenarios, that will result from current climate change." Micromonas may well serve as a bellwether for current and future ocean conditions, helping to guide appropriate decision making, which given the prevailing CO2 trends, is urgently needed.
The genome sequencing of Micromonas was conducted under the auspices of the DOE JGI Community Sequencing Program (CSP), supported by the DOE Office of Science.
Journal reference:
Worden et al. Green Evolution and Dynamic Adaptations Revealed by Genomes of the Marine Picoeukaryotes Micromonas. Science, 2009; 324 (5924): 268-272 DOI: 10.1126/science.1167222

Climate Gas Could Disrupt Food Chain

Levels of a climate cooling gas will change as carbon dioxide increases, affecting food webs along the way, said Dr Michael Steinke at a Science Media Centre press briefing December 10।

Microbes in the ocean produce the gas dimethyl sulphide, or DMS. It causes clouds to form above the sea, which reflect the sun's rays away from the earth. Research suggests that plankton produce more DMS when they get hot so that clouds will cool them down. "Our work on the effect of carbon dioxide on DMS levels showed some interesting results" said Dr Steinke, from the University of Essex. "DMS production is likely to change in the future."
DMS is responsible for the "seaside smell". Dr Steinke discovered that plankton may use DMS when looking for prey like the way bees are attracted to fragrant flowers. "The role of DMS in climate change has been studied for years. Its role in marine ecology was unknown and this is what we are investigating."
Marine animals including seals and birds use DMS to find food and navigate. "DMS plays an important role in oceanic food webs" said Dr Steinke. "If DMS levels change, many marine animals could find it more difficult to search for their prey." This could have an effect on the food we eat.
Current discussions include using DMS in the "eco-engineering" of climate. Its cloud forming ability could be used to reduce global warming. However, Dr Steinke's results show it may not be simple. "We have found that the production of DMS is much more complex than we thought and there will be plenty more surprises to come."
Adapted from materials provided by Society for General Microbiology.

Oceans could absorb far more CO2

The ocean's plankton can suck up far more airborne carbon dioxide (CO2) than previously realised, although the marine ecosystem may suffer damage if this happens, a new study into global warming says।

The sea has soaked up nearly half of the CO2 that has been emitted by fossil fuels since the start of the Industrial Revolution.
The gas dissolves into surface waters and is then transported around the oceans.
But a key role is played by plant micro-organisms called phytoplankton, which take in the dissolved gas at the ocean's sunlit surface as part of the process of photosynthesis.
This plankton dies and eventually sinks to the ocean floor, thus storing the carbon for potentially millions of years.
One of the big questions is how much more of CO2 the sea can absorb.
If, like a saturated sponge, the oceans cannot take up any more, atmospheric concentrations of CO2, the principal greenhouse gas, would sharply rise and stoke global warming।

Acidification
Another concern is that rising levels of dissolved CO2 also causes acidification of seawater.
Wildlife such as coral, which secretes a skeletal structure, are known to be affected by acidification but the impact on other marine species is largely unknown.
In an innovative experiment reported in the journal Nature, researchers closed off part of Raune fjord in southern Norway to see how plankton reacted to different levels of CO2.
They used nine large enclosed tanks of seawater that were exposed to CO2 concentrations likely to prevail over the next 150 years.
These three levels were today's concentrations of CO2; double that concentration, to simulate the air in 2100; and triple, replicating the air in 2150.
To feed the plankton, the researchers added nutrients to simulate food usually brought up by ocean currents and upwelling, and then monitored plankton levels over the next 24 days.
The investigators found that, the higher the CO2 level, the more the plankton bloomed.
The organisms were able to gobble up to 39 per cent more dissolved carbon compared with today, but did not need any additional nutrients to achieve this.
The findings "underscore the importance of biologically-driven feedbacks in the ocean to global change," the authors said, led by Ulf Riebesell of the Liebniz Institute of Marine Sciences in Germany.
'Geo-engineering'
However, the paper warns taking the carbon out of the air and placing it into the sea could cause problems.
Algal blooms could inflict oxygen depletion in some parts of the ocean while rising carbon levels may cause an imbalance in primary nutrients, with implications that could ripple across the marine food web.
Supporters of so-called geo-engineering - unconventional projects aimed at easing global warming - have been closely looking at plankton, seeing in it fantastic potential as a carbon sponge.
Their schemes entail sowing the sea with iron filings and other nutrients to encourage plankton growth and thus suck up more of the atmospheric CO2.
Mainstream scientists say such experiments are unjustified, given the uncertainty surrounding the environmental impact and the many knowledge gaps that persist about ocean topography and currents.

Why Is The Ocean Salty?

The saltiness of the sea comes from dissolved minerals, especially sodium, chlorine, sulfur, calcium, magnesium, and potassium, says Galen McKinley, a UW-Madison professor of atmospheric and oceanic sciences।

Today’s ocean salt has ancient origins. As the earth formed, gases spewing from its interior released salt ions that reached the ocean via rainfall or land runoff.
Now, the ocean’s salinity is basically constant. “Ions aren’t being removed or supplied in an appreciable amount,” McKinley says. “The removal and sources that do exist are so small and the reservoir is so large that those ions just stay in the water.” For example, she says, “Each year, runoff from the land adds only 0.00005 percent of total ocean salts.”
In lakes, relatively rapid turnover of water and its dissolved salts keeps the water fresh – a water droplet and its ions will stay in Lake Superior for about 200 years, compared to roughly 100 to 200 million years in the ocean. “Even if you did have any accumulation of an ion in a lake, it would be washed out quickly,” McKinley explains.
Ocean salts, however, have no place to go. “The ions that were put there long ago have managed to stick around,” McKinley says. “There is geologic evidence that the saltiness of the water has been the way that it is for at least a billion years.”
Note: This story has been adapted from material provided by University of Wisconsin-Madison.

Conservationists Say Plankton Growth Threatened By Ocean Acidity

A conservation group says the Pacific and Atlantic oceans are absorbing too much carbon from excessive greenhouse gas emissions. The organization wants California and other west coast states to use the federal Clean Water Act to protect the waters off their coasts. KPBS reporter Ed Joyce has details.The Center for Biological Diversity says acidification is changing the chemistry of the world's oceans. The group says the oceans are absorbing excess carbon dioxide produced by humans, which makes sea water more acidic.Brendan Cummings is the center's oceans program director. He says the acidity hurts the growth of plankton -- a key player in the ocean food chain.Cummings: Without phytoplankton in the abundant numbers we have now, marine life which relies upon it, which is the building block of the oceanic food webs, starts to decline.He says higher acidity could affect the growth of shellfish and remove food sources for several salmon species. Cummings says ocean waters should be listed as impaired under the federal Clean Water Act.He says if that happens, California and other states would be required to limit carbon dioxide pollution from entering ocean waters under their jurisdiction.Ed Joyce, KPBS News.

Deep Ocean's most turbulent areas has big impact on Climate

More than a mile beneath the Atlantic's surface, roughly halfway between New York and Portugal, seawater rushing through the narrow gullies of an underwater mountain range much as winds gust between a city's tall buildings is generating one of the most turbulent areas ever observed in the deep ocean।

In fact, the turbulence packs an energy wallop equal to about five million watts -- comparable to output from a small nuclear reactor, according to a landmark study led by Florida State University researcher Louis St. Laurent and described in the August 9 edition of the journal Nature.
The study -- an international collaboration of scientists from the United States and France -- documents for the first time the turbulent conditions in an undersea mountain range known as the Mid-Atlantic Ridge. It provides never-before-seen evidence that deep water turbulence swirling in the small passageways of such mountains is generating much of the mixing of warm and cold waters in the Atlantic Ocean.
Better understanding of the mechanisms of mixing is crucial, says St। Laurent, an assistant professor of physical oceanography at FSU and the study's co-principal investigator, because mixing produces the overall balance of water temperatures that helps control the strength of the Gulf Stream -- the strong, warm ocean current that starts in the Gulf of Mexico, flows along the U.S. east coast to Canada and on to Europe, and plays a crucial climate role.

"Oceanographers are working hard to understand how processes in the ocean help to keep the Earth's climate stable," St. Laurent said. "We are aware that the climate is warming, but we don't yet fully understand how the changes will affect society. Our work will result in better models for predicting how the ocean will affect the climate in the future and a better understanding of sea-level rise, weather patterns such as El Nino, and the impact of these events on fisheries."
St. Laurent compared the flow of seawater through underwater gullies in the Mid-Atlantic Ridge to the wind, so familiar to hikers, that blows through mountain passages on land.
"That wind creates a condition known as turbulence, which can blow the hat from your head," St। Laurent said. "In the ocean, turbulence is produced when water flows quickly though oceanic passages. The turbulence stirs the almost freezing-water near the bottom with warmer water that is closer to the surface much as you would mix cream into coffee by stirring it with a spoon.

"We know that the mixing of warm surface water with very cold deep water is one of several factors that influence the Earth's climate," he said. "The mixing we observed and measured for our study allows the warmth at the surface of the ocean to 'diffuse' deep into the sea. The overall balance between warm and cold water in the Atlantic helps control the strength of the Gulf Stream, which moves heat away from the Earth's equator toward regions that receive much less heating from the sun's rays."
St. Laurent's co-principal investigator and co-author was Andreas M. Thurnherr, a former postdoctoral researcher in the FSU oceanography department and now a scientist at Columbia University. The field study took place in August 2006 during a three-week expedition aboard a French research vessel to a location close to the Azores, volcanic islands 2,000 miles east of the U.S. and west of Europe that comprise an above-sea portion of the mostly submerged Mid-Atlantic Ridge.
To measure the energy generated by the extraordinarily intense turbulence more than a mile below the ocean's surface, St. Laurent and crew used a custom-made instrument called the "turbulence profiler," outfitted with special sensors.
"The turbulence profiler measured the output using 'watts,' the same unit of measurement as printed on light bulbs," St. Laurent said. "In the undersea mountain passage where we intentionally looked, we found turbulence levels as large as one-10th watt per cubic meter of seawater. This is a huge amount of energy when you add all the seawater in the passage, equal to around five million watts, which is comparable to output from a nuclear reactor."
Article: "Overflow Mixing of Lower Thermocline Water on the Crest of the Mid-Atlantic Ridge"

Note: This story has been adapted from a news release issued by Florida State University.

Warming-Induced Increases in Ocean Productivity

In setting the stage for their important new study, McGregor et al। (2007) say "coastal upwelling occurs along the eastern margins of major ocean basins and develops when predominantly along-shore winds force offshore Ekman transport of surface waters, which leads to the ascending (or upwelling) of cooler, nutrient-rich water." In addition, they note that these regions of coastal upwelling account for about 20% of the global fish catch while constituting less than 1% of the area covered by the world's oceans. Thus, in an attempt to better understand the nature of this productivity-enhancing phenomenon of great practical and economic significance, they studied its long-term history along the northwest coast of Africa - in the heart of the Cape Ghir upwelling system off the coast of Morocco - by analyzing two sediment cores having decadal-or-better resolution that extend from the late Holocene to the end of the 20th century, i.e., from 520 BC to AD 1998.

This work revealed an anomalous cooling of sea surface temperatures during the 20th century, which the four researchers say "is consistent with increased upwelling।" In addition, they note that the "upwelling-driven sea surface temperatures also vary out of phase [our italics] with millennial-scale changes in Northern Hemisphere temperature anomalies and show relatively warm conditions during the Little Ice Age and relatively cool conditions during the Medieval Warm Period।"

How does this happen? One potential scenario discussed by McGregor et al। starts with an impetus for warming that leads to near-surface air temperatures over land becoming warmer than those over the ocean. The greater warming over the land then "deepens the thermal low-pressure cell over land while a higher-pressure center develops over the slower-warming ocean waters." As this occurs, "winds blow clockwise around the high and anticlockwise around the continental low." With the coast representing the boundary between the two centers, the resulting wind is "oriented alongshore and southward (equator-ward), which thus drives the upwelling and negative sea surface temperature anomalies."

In addition to their observations of this phenomenon, McGregor et al। state that similar anti-phased thermal behavior - i.e., the cooling of coastal waters that leads to enhanced coastal upwelling during periods of hemispheric or global warming - has been observed in the Arabian Sea and along the Iberian margin, as well as in parts of the California Current and the Peru-Chile Current. Consequently, it would appear that by enhancing the upwelling of cooler nutrient-rich waters along the eastern margins of major ocean basins, global warming helps to significantly enhance global-ocean primary productivity, which leads in turn to an increase in global-ocean secondary productivity, as represented by the global fish catch.

Somewhat analogous findings were reported in the same issue of Science by Boyd et al. (2007), in their major review of iron enrichment experiments that were conducted between 1993 and 2005, which experiments have conclusively demonstrated, in their words, that "phytoplankton grow faster in warmer open-ocean waters, as predicted by algal physiological relationships." Hence, it can be appreciated that this conglomerate of results clearly suggests total ocean productivity should have benefited immensely from 20th-century global warming, and that it will likely continue to benefit from continued global warming, just as total terrestrial productivity has likewise benefited from the historical increases in both the atmosphere's temperature and its CO2 concentration (see the many pertinent items we have archived under Greening of the Earth in our Subject Index).All told, therefore, both on land and in the sea, things appear to be looking ever better for the biosphere in terms of earth's thermal environment and its atmospheric composition, in spite of the unrelenting din of denial of this profusely-documented fact that emanates unceasingly from the world's climate alarmists.

Plankton Species' Genome Analysis Yields Surprises Regarding Evolution And Global Photosynthesis

An international team of scientists led by Scripps Institution of Oceanography at UC San Diego and the Department of Energy's (DOE) Joint Genome Institute has peered into the genetic makeup of two species of phytoplankton, the tiny plants key in global photosynthesis and carbon cycling, and come away with surprising results about evolutionary engineering and new ideas about the role that a poorly understood chemical element may play in the world's oceans।

For several years, Scripps Oceanography's Brian Palenik and his collaborators, including scientists from France, Belgium and Germany, have been analyzing and annotating an organism called Ostreococcus. At one micron it is the smallest known phytoplankton and one of the smallest of all the eukaryotes, organisms with specialized internal cell structures that include plants and animals. A teaspoon of seawater taken off the Scripps Oceanography Pier typically contains more than 100,000 eukaryotic phytoplankton, which are found throughout the world's oceans. Phytoplankton are responsible for nearly half of the planet's photosynthesis.
Advances in genomics have allowed scientists to begin digging deeply into a long-standing biological puzzle concerning the mechanisms behind the divergent genomes of related photosynthetic phytoplankton species. The international team's work, published in the online edition of Proceedings of the National Academy of Sciences, is the first comparison of the genetic makeup of two closely related eukaryotic phytoplankton and the mechanisms that make them biologically similar and distinct.
"Through our research we've been trying to understand Ostreococcus' role in marine ecosystems," said Palenik, who indicated Ostreococcus cells contain nearly five times the DNA of comparably sized organisms such as cyanobacteria. "Genomics has taught us that you can learn much more when you can do a comparison.. The first genome is exciting but the second genome is even more exciting because you can suddenly compare organisms and see what each is doing differently and what they are doing the same."
The researchers' comparison of Ostreococcus lucimarinus (recently sequenced by the DOE's Joint Genome Institute) and Ostreococcus tauri yielded several surprising results, including the documentation of a "new" chromosome differing between the species. Another chromosome appeared somewhat different between the species and the researchers believe it may serve as a gene transfer "trash can" where foreign DNA is integrated. Yet another difference was the identification of a chromosome featuring the same-albeit rearranged-genes in the two species. The researchers hypothesize that this chromosome may be related to sexual functions because the rearrangements are enough to prevent sex between the species.
"These are pretty remarkable differences that we didn't expect," said Palenik, a professor in the Marine Biology Research Division at Scripps. "We would expect the DNA to change slowly and see a small number of differences between the two species as they slowly evolve... This is the case for much of the genome. From a future applied perspective, from our comparison we are learning the tricks nature has used to 'engineer' an extremely small eukaryotic cell. This may have future applications in bioengineering."
Another important finding described in the paper is the prominent role that the element selenium plays in Ostreococcus. Humans require selenium in small amounts and most people have roughly 25 selenium proteins. Tiny Ostreococcus organisms were shown to have up to 21 selenium proteins, an enormous number relative to their small genome and microscopic size.
Palenik believes this may be because selenium enzymes are some 10- to 50-times more efficient than similar enzymes that don't use selenium. Based on their size, such efficiency is important to help conserve resources such as nitrogen.
"We may need to think more about how selenium helps drive the health of the oceans," said Palenik. "It's a nutrient element that we don't understand very well and now we have evidence of a group of organisms that clearly use it intensively. We may need to think about how this is affecting primary production in the oceans."
Future research by Palenik and his colleagues will involve a third Ostreococcus organism, which will lead to further comparisons and evolutionary evaluations.
"Genomic comparisons are exciting because they allow us not to just document the diversity of the ocean but to start to understand the processes behind that diversity and see all of the changes in the evolution of two species," said Palenik.
Coauthors of the paper include Chris Dupont, Vera Tai, Sheila Podell and Terry Gaasterlandof Scripps; Jane Grimwood and Jeremy Schmutz of Stanford University School of Medicine; Andrea Aerts, Asaf Salamov, Nicholas Putnam, Kemin Zhou, Robert Otillar, Gregory Werner, Inna Dubchak, Daniel Rokhsar and Igor V. Grigoriev of the DOE's Joint Genome Institute; Pierre Rouze, Stephane Rombauts, Steven Robbens and Yves Van de Peer of Ghent University; Richard Jorgensen, Carolyn Napoli and Karla Gendler of the University of Arizona at Tucson; Evelyne Derelle, Gwenael Piganeau, Séverine Jancek and Hervé Moreau of the Université Pierre et Marie Curie Paris 6; Sabeeha Merchant of the University of California, Los Angeles; Olivier Vallon of the Université Paris 6; Andrea Manuell of The Scripps Research Institute; Martin Lohr Johannes of Gutenberg-Universität; Gregory Pazour of the University of Massachusetts Medical School; Marc Heijde, Kamel Jabbari and Chris Bowler of the Centre National de la Recherche Scientifique; Qinghu Ren and Ian Paulsen of The Institute for Genomic Research; and Chuck Delwiche of the University of Maryland at College Park.
The research was supported by the DOE, the European network "Marine Genomics Europe" and performed under the auspices of the DOE's Office of Science, Biological and Environmental Research Program, the University of California, Lawrence Livermore National Laboratory, Lawrence Berkeley National Laboratory, Los Alamos National Laboratory and Stanford University.
Note: This story has been adapted from a news release issued by Scripps Institution of Oceanography - UC San Diego.

Global warming will reduce ocean productivity, marine life

Global warming will reduce ocean productivity, marine lifeDecember 07, 2006 - CORVALLIS, Ore. — A 10-year, satellite-based analysis has shown for the first time that primary biological productivity in the oceans–the growth of phytoplankton that forms the basis for the rest of the marine food chain–is tightly linked to climate change, and would be reduced by global warming. The study, published this week in the journal Nature by researchers from Oregon State University and five other institutions, found that on a global scale, a warmer climate could cause a rapid, overall reduction in marine life."This clearly showed that overall ocean productivity decreases when the climate warms," said lead author Michael Behrenfeld, an OSU professor of botany and expert on remote sensing of marine biology."There is significant regional variability, with some areas showing enhanced production and some area losses," Behrenfeld said. "But on a global basis there is an inverse relationship – increased temperatures cause decreased marine phytoplankton production."This climate response can be traced to increased stratification in the oceans, the study showed. When the ocean surface warms, it essentially becomes "lighter" than the cold, dense water below, which is loaded with nutrients. This process effectively separates phytoplankton in the surface layer–which need light for photosynthesis–from the nutrients below them, which they also need for growth.The satellite data used in the study were from NASA's SeaWiFS satellite, or Sea-viewing Wide-Field-of-view Sensor. Since its launch in 1997, SeaWiFS has measured changes in the color of the ocean–as more and more phytoplankton are added, the color shifts from blue toward green. By studying these color changes from space, scientists can calculate how much phytoplankton pigment is in the water, relate this to photosynthetic rate, and correlate these changes to simultaneous changes in climate.The first climate-driven change in ocean production measured in this study occurred between 1997 and 1999, when the oceans were recovering from one of the strongest El Nino events on record. With the end of the El Nino, global climate began to cool and there was a surge in ocean phytoplankton productivity that peaked in late 1999.The second climate event was a long-term warming trend that started in 2000 and continues today. Over this period, the ocean sea surface became overall warmer and more stratified, and phytoplankton productivity went down almost in lockstep at a rate of about 190 million tons of carbon a year. On a regional scale, the decreases in production often exceeded 30 percent.Despite their microscopic size, ocean phytoplankton are responsible for about half of the photosynthesis on Earth, a process that removes carbon dioxide from the atmosphere and converts it into organic carbon to fuel nearly every ocean ecosystem.Compared to terrestrial land plants, however, phytoplankton use a very small amount of biomass to convert large amounts of carbon, because they are eaten by predators about as quickly as they grow. The entire global phytoplankton biomass is consumed every two to six days, in contrast to land plants that might have turnover rates of a year to hundreds of years."This very fast turnover, along with the fact that phytoplankton are limited to just a thin veneer of the ocean surface where there is enough sunlight to sustain photosynthesis, makes them very responsive to changes in climate," Behrenfeld said. "This was why we could relate productivity changes to climate variability in only a 10-year record. Such connections would be much harder to detect from space for terrestrial plant biomass."Results of the study may provide important insight into how ocean biology might respond to sustained global warming, the researchers said. "A common prediction among global climate models is that warming will cause ocean production to decrease at mid-latitudes and low latitudes, due to intensified stratification," Behrenfeld said, "This is precisely the response we observed."Climate models also predict long term global warming will cause enhanced phytoplankton production near the poles, because of longer growing seasons, and shifts in the organisms dominating different ecosystems across the globe. These predictions have not yet been confirmed by satellite ocean measurements, and detection of them may require a longer record or advances in satellite technology.Climate not only influences ocean biology, but ocean biology influences climate."Rising levels of carbon dioxide in the atmosphere are a key part of global warming," Behrenfeld said. "This study shows that as the climate warms, phytoplankton production goes down, but this also means that carbon dioxide uptake by ocean plants will decrease. That would allow carbon dioxide to accumulate more rapidly in the atmosphere, making the problem worse."Better understanding this "feedback mechanism" which compounds global warming is a top priority for study, the researchers say.Oregon State University