OCEAN MICROCOSM: Researchers mimicked ocean conditions in four liter "microcosms" to determine how rising temperatures might affect the marine food chain.
Image: © A. Anton
-
What a Plant Knows
How does a Venus flytrap know when to snap shut? Can it actually feel an insect’s tiny, spindly legs? And how do cherry blossoms know when to bloom? Can they...
Read More »
This June, the world's oceans reached 17 degrees Celsius, their highest average temperature since record keeping for these data began in the 19th century. And a new experiment suggests that those balmier waters might mean big changes for the marine food chain.
Marine ecologist Mary O'Connor of the National Center for Ecological Analysis and Synthesis at the University of California, Santa Barbara, and colleagues at the University of North Carolina at Chapel Hill set up five four-liter "microcosms" of seawater filled with microorganisms from the Bogue Sound estuary on the North Carolina coast. Over the course of eight days last spring, the scientists then exposed the microcosms to varying degrees of warming and nutrient levels to mimic storm flow into an estuary.
Theoretically, increased nutrients and warmth should fuel the growth of tiny drifting plants known as phytoplankton—as evidenced by seasonal dead zones that form at the mouths of many rivers worldwide when the tiny plants bloom, die and, while decaying, suck up all the available oxygen in the seawater. But the researchers found that increasing temperatures, although initially enhancing the growth of phytoplankton, also allowed increased grazing by zooplankton (microscopic animals) and bacteria, according to the results published today in PLoS Biology.
"As temperature rises, the zooplankton start to grow faster than the phytoplankton," O'Connor explains. "The zooplankton are more abundant and faster-growing, and are able to eat all the phytoplankton in warmer water. This creates a bottleneck in the food chain that could have large implications for the ocean's food web."
Not only does that mean that there are fewer phytoplankton around to suck up carbon dioxide, but it could also mean less food for other grazers. But it does not necessarily mean that the zooplankton will gorge themselves to death; other research has shown that food webs with more animals (consumers) than plants (producers) is sustainable for at least five years. And higher on the food chain it is zooplankton, such as krill, that are feasted on by marine life ranging from fish to whales.
Boosting the number of zooplankton, however, means the overall mass of ocean life declines: the tiny animals metabolically burn 90 percent of the phytoplankton they consume, incorporating only 10 percent. All told, with a 6-degree Celsius rise in water temperature, total biomass in the warmest microcosm shrank by 50 percent, O'Connor reports.
This effect only holds, however, in areas that are rich in nutrients. In the experimental microcosms where the nutrients nitrogen and phosphorus were kept low, those limits defined the relative abundance of plants and animals. And other factors—ocean acidity or salinity—could also play large roles. "The ultimate effect of temperature on zooplankton and consumers higher in the food chain will depend on other ocean conditions that affect resource availability," O'Connor says.
That could mean that nutrient-rich waters in places like the Arctic Ocean will begin to see this food chain shift as the seas continue to warm—and a consequent rise in the number of fish. "Our experiments and current theory suggest that warming in nutrient-rich areas should increase [the number of] fish," O'Connor says. "I think we can figure out how and where climate change may lead to greater fish productivity and where it might reduce fish productivity."
But even in the Arctic, there is typically a nutrient limit, says phytoplankton ecologist Michael Behrenfeld of Oregon State University. "It's a very interesting idea," he says. But an increase in fish harvests "might be a bridge too far with this. There are other factors that need to be considered."
For example, his own satellite-imagery research on the phytoplankton in the North Atlantic reveals that bloom starts in wintertime as a result of deep, nutrient-rich water welling up to the surface. Warming is diminishing that upwelling and therefore the availability of nutrients. "We see a decrease in blooms," Behrenfeld says. "How much can we use [four-liter] microcosms to extrapolate to natural systems, especially natural systems at longer timescales?"
Nevertheless, the experiment provides a glimpse of how the marine food chain might be transformed by climate change. "Worldwide, ocean waters are warming and will continue to warm by several degrees," O'Connor says. "By understanding the effects of temperature in these ideal conditions, we can begin to apply this model to natural systems."
See what we're tweeting about
12 Comments
Add CommentQuote 'Not only does that mean that there are fewer phytoplankton around to suck up carbon dioxide,'
Reply | Report Abuse | Link to thisIs that should be suck up OXYGEN instead of CARBON DIOXIDE?
Quote : 'Not only does that mean that there are fewer phytoplankton around to suck up carbon dioxide,'
Reply | Report Abuse | Link to thisIs that should to be 'suck up oxygen' instead of 'suck up carbon dioxide'?
Phytoplankton are plants and use carbon dioxide as a nutrient. Zooplankton are animals. They use oxygen and release carbon dioxide.
Reply | Report Abuse | Link to thisQuote 'Theoretically, increased nutrients and warmth should fuel the growth of tiny drifting plants known as phytoplankton—as evidenced by seasonal dead zones that form at the mouths of many rivers worldwide when the tiny plants bloom, die and, while decaying, suck up all the available oxygen in the seawater.'
Reply | Report Abuse | Link to thisImply: phytoplankton suck up all the available oxygen in seawater.
Then quote'The zooplankton are more abundant and faster-growing, and are able to eat all the phytoplankton in warmer water'.
That means: zooplankton are able to eat all phytoplankton. Consquently, phytoplankton population will decrease.
So it should to be: 'Not only does that mean that there are fewer phytoplankton around to suck up oxygen...' because we can only know from context that 'mass phytoplankton suck oxygen'.
Although it is common sense that plant release oxygen, no words previous indicate phytoplankton release more quantity of oxygen than carbon dioxide they consume. And they do have words saying 'phytoplankton suck oxygen'.
Just as a point of clarification, the phytoplankton produce oxygen. It is consumed upon their death by other microorganisms feasting on their dead bodies as part of the process of decay. So rhodinsthinker has it right.
Reply | Report Abuse | Link to this"Quote 'Theoretically, increased nutrients and warmth should fuel the growth of tiny drifting plants known as phytoplanktonas evidenced by seasonal dead zones that form at the mouths of many rivers worldwide when the tiny plants bloom, die and, while decaying, suck up all the available oxygen in the seawater.'
Reply | Report Abuse | Link to thisImply: phytoplankton suck up all the available oxygen in seawater."
No, when plants die, the metabolic processes that are produced in decay consume oxygen. The phytoplankton are dead, they are not consuming anything, the bacteria eating the dead phytoplankton are very much alive, and are consuming oxygen. See here: http://en.wikipedia.org/wiki/Bacterial_decay#Plant_decomposition
Especially the last line.
"The chemical aspects of plant decomposition always involve the release of carbon dioxide."
"Quote 'Theoretically, increased nutrients and warmth should fuel the growth of tiny drifting plants known as phytoplankton—as evidenced by seasonal dead zones that form at the mouths of many rivers worldwide when the tiny plants bloom, die and, while decaying, suck up all the available oxygen in the seawater.'
Reply | Report Abuse | Link to thisImply: phytoplankton suck up all the available oxygen in seawater."
No, when plants die, the metabolic processes that are produced in decay consume oxygen. The phytoplankton are dead, they are not consuming anything, the bacteria eating the dead phytoplankton are very much alive, and are consuming oxygen. See here: http://en.wikipedia.org/wiki/Bacterial_decay#Plant_decomposition
Especially the last line.
"The chemical aspects of plant decomposition always involve the release of carbon dioxide."
George_utk please read this:
Reply | Report Abuse | Link to thishttp://en.wikipedia.org/wiki/Bacterial_decay#Plant_decomposition
And pay special attention to the last line:
"The chemical aspects of plant decomposition always involve the release of carbon dioxide."
The phytoplankton, which are basically plants, are *DEAD* they are not consuming anything, the bacteria consuming the dead phytoplankton are very much alive and are releasing the carbon dioxide.
Sorry about the triple reply. Bad redirect there.
Reply | Report Abuse | Link to thisThanks for your explanation, MariaPR, and it's ok for multi-reply since it is the problem of slow update of website.
Reply | Report Abuse | Link to thisI understood DEAD phytoplankton's decaying release carbon dioxide. Phytoplankton produce oxygen when alive, but if we see the whole life cycle of it and its total contribution, can we say the total oxygen it produce is less than the carbon dioxide it realse when decaying? If not, why seasonal dead zones in sea appear?
Trees, for example, they produce oxygen in daytime and also release carbon dioxide in nigntime and after dead. But I believe that they produce more oxygen than carbon dioxide in natual conditions, including their decaying time, otherwise no reason for us to need trees. And we will never have dead zones in land because of too many trees, right? So if phytoplankton is the reason of dead zones, why can we say it suck up carbon dioxde?
Quote 'as evidenced by seasonal dead zones that form at the mouths of many rivers worldwide when the tiny plants bloom, die and, while decaying, suck up all the available oxygen in the seawater.' From this paragraph exclusively, one conclusion is got: dead zones form because of decaying plants. So the existenc of phytoplankton as a species donot contribute oxygen in sea. Right?
Reply | Report Abuse | Link to thisI think you might be looking the wrong way (I know that this is quite an old topic but i want to set clarify something).
Reply | Report Abuse | Link to thisPhytoplankton are primarily autotrophic (jst like plants and trees), they utilise carbon dioxide and sunlight to produce oxygen and energy. The consequence of there being fewer trees (through deforestation for example) is that less carbon dioxide is taken up by trees(resulting in less oxygen being produced, ceteris paribus). Now back to this journal, as the zooplankton diminish plankton populations, less carbon dioxide is utilised in photosynthesis.
Hence the statement "there are fewer phytoplankton around to suck up carbon dioxide" is right. Hope this helps.