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| Enlarge ImageWHOI biologist Heidi Sosik uses a new robotic instrument to study the tiny plantlike cells that create the food for virtually all ocean life. "If we want the tools to look at these organisms," she says, "we have to invent and make them ourselves. You can’t buy them anywhere." (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution) |
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| Enlarge ImageTo gather information about coastal ecosystems, WHOI biologist Heidi Sosik traditionally went out in boats, took single water samples, and preserved them to identify phytoplankton cells later in her lab. It was a painstaking process and only provided data about about one place at one time in the coastal ocean. Her new instrument, Imaging FlowCytobot, continously sends images to shore, so she can observe microscopic organisms in real time in their changing environment. (Photo courtesy of Heidi Sosik, WHOI) |
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Related Multimedia |
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Images of diatoms captured by the Imaging FlowCytobot
Diatoms are microscopic, photosynthetic cells in coastal ocean surface waters whose populations increase (bloom) in fall and winter. They serve as critical food for other ocean life. Images of several kinds of diatoms were captured and identified with a new robotic underwater instrument, the Imaging FlowCytobot. (All images courtesy of Heidi Sosik, WHOI) |
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Heidi Sosik studies marine phytoplankton—the community of microscopic
plants that essentially make all the food for all the ocean. Like an
anthropologist documenting an undiscovered society, Sosik wants to
learn everything she can about the living things in her community—their
seasonal activities, nomadic habits, and nutrition. She is also part
engineer, building and tinkering with gadgets that promise to bring the
microscopic world of phytoplankton into focus.
Sosik is the first scientist to receive a joint fellowship from two
WHOI Ocean Institutes, the Coastal Ocean Institute and the Ocean Life
Institute. This summer and fall, she and colleagues are testing a new
instrument, the Imaging FlowCytobot, at the WHOI Martha’s Vineyard
Coastal Observatory (MVCO).
Very few people are aware that the majority of the world’s plants live in the ocean. Why are they so important?
Phytoplankton are like the grass and trees of the ocean. They’re just
as important to the planet as land plants, but basically
invisible—unless you go looking for them with tools and technologies
such as the ones I use. It’s easy to forget that they’re there, but it
would be a disaster for us if we forgot, and thus neglected to take
care of the ocean—a huge portion of the planet.
The water over the continental shelf harbors an entire ecosystem.
Phytoplankton are plant-like cells that feed larger plankton organisms
and the offspring of larger animals. And this begins a web of
interactions from plankton to the fish, whales, and birds that feed on
them.
What we’re after is a better understanding of what factors in the
environment determine where and when different kinds of phytoplankton
grow and bloom.
What are some of those ecologically important factors?
Phytoplankton are photosynthetic, so they need sunlight to make organic
matter. And they need nutrients, essentially fertilizer. All the
compounds that you read on the side of your breakfast cereal box—iron,
vitamins, and nitrogen—phytoplankton need those things, too.
Typically, nutrients are concentrated in the deep waters of the ocean.
But a variety of ocean circulation patterns causes water masses to well
up from deeper regions. These processes bring deep waters, along with
nutrients, into the shelf region at different times of the year. It’s
an absolutely natural fertilization process that’s critical for the
ecosystem.
The ecosystem also recycles: Phytoplankton are eaten by other organisms
that produce waste that contains nutrients, and those become available
again for the phytoplankton—much as manure fertilizes a garden.
Some areas of the coastal ocean have been exposed to too many
nutrients—which run off from septic systems, lawns, and agriculture, or
which are deposited in rain because we put nitrogen into the air. This
overnutrition causes the problem of eutrophication, in which rampant
algal growth depletes oxygen levels in the water.
What has prevented you from obtaining a clear picture of this dynamic ecosystem?
Answers have eluded us because we had to go out in boats, take single
water samples, look at them through the microscope, and meticulously
identify each cell—and then you have just one sample. The show-stopper
was not having continuous observations of ongoing changes.
What’s really exciting about our new technology is that we can now
watch and record the community changing along with the environment, at
the same time, in a natural system. There’s still a big puzzle to tease
out, because many factors contribute to the changes we see. Now, we can
get this fabulous information we need to solve the puzzle.
How do these instruments work?
For many years, my lab group has collaborated
closely with Rob Olson’s
group at WHOI to develop a submersible instrument we call the
FlowCytobot to count and identify tiny phytoplankton in the water. It’s
a laser-based system that “sees” single cells—on the basis of red light
that the chlorophyll in phytoplankton emits when it’s exposed to blue
or green light.
FlowCytobot has been operating almost continuously
at
the Martha’s Vineyard Coastal Observatory since 2003, and it works
great. But we discovered toward the end of 2003 that we had a big
problem.
Phytoplankton are diverse, from species too small to see with
microscopes to others visible to the eye. We designed the FlowCytobot
specifically to look at the smallest phytoplankton out there. But the
mixture of plankton species changes during the year. By fall, the
ecosystem is dominated by phytoplankton called diatoms, many of which
were too big for our instrument to measure.
These population changes are as dramatic as succession on land, where
over decades marsh changes to grassland and then to forest. In plankton
communities, such dramatic succession happens every year over a few
months. It’s critical that we understand what causes these shifts,
because if something changes so that the winter diatom blooms don’t
occur, for example, that could have serious implications for the rest
of the ecosystem.
So could you adjust FlowCytobot to also identify diatoms?
It turns out that it’s not possible to make one instrument that does a
good job measuring both the smallest and largest phytoplankton. For
diatoms, we needed a way to count cells in larger volumes of water and
to take pictures through a microscope, along with the red fluorescence
measurements.
We were experimenting with this dual ability in the lab, and colleagues
would ask when we were going to build it into a submersible instrument.
But it requires so much power, and generates so much data, we at first
didn’t think we could put it under water. The idea that you could have
an autonomous underwater microscope, and actually run it
continuously—we just laughed. But after our experience working at MVCO,
it occurred to us that it wasn’t that farfetched. We had had success
with the first FlowCytobot, and we knew we had power available. Within
a year, we came around to realizing we could do this.
So now there are two instruments, and they work together. The original
FlowCytobot counts and measures fluorescence of small cells; then the
Imaging FlowCytobot does the same thing for large diatoms, and also
takes microscope photographs for identification.
How did you solve the power and data problems?
There’s no doubt in my mind that we wouldn’t have gone down the path of
building the imager if we didn’t have the Martha’s Vineyard Coastal
Observatory. We can plug our instrument into its seafloor node, which
is cabled to shore. The cables provide essentially unlimited,
continuous power- and data-transmission capabilities.
FlowCytobot and Imaging FlowCytobot at MVCO will let us look at the
entire community from the smallest cells to the largest. If everything
works—and we’re crossing our fingers!— we should get data that capture
this dramatic shift from the late-summer, small-cell “field of grasses”
to this bloom of large organisms in the fall—the “trees.” It will be
really interesting to see how that shapes up.
Over the next 10 to 20 years, we envision employing instruments for
continuous, long-term monitoring of plankton, nutrients, and
oceanographic conditions at a network of several coastal observatories
spanning the U.S. East Coast. Then, scientists from many oceanographic
disciplines—biology, physical oceanography, and chemistry— can begin to
piece together the bigger picture, over time and space. We’ll be able
to see the effects of climate change on the ecosystem, for example, or
how changes in one region affect other coastal areas.
We’ve been surprised at how difficult it has been to get federal
funding for instrument-development work, but support from the WHOI
Coastal Ocean Institute and the WHOI Access to the Sea program is
helping us install our instruments at MVCO this summer. We think that a
successful proof-of-concept deployment will make us poised to be
competitive to solicit future funding from national agencies.
What sorts of applications might this research have?
We are very interested in the basic question of what regulates
phytoplankton communities. For example, the timing and occurrence of
the winter plankton blooms are very important for other species that
rely on them as a food source—fish and invertebrates. If the bloom
fails one winter, then you may get low survival of fish. We’re all
hopeful that, down the road, the kind of basic information we are
collecting will allow us to do a better job of managing fisheries and
other coastal resources.
First, we need to have a better understanding of the ecosystem’s
natural variations. Only then will we be able to be smarter about how
to manage human activities in the coastal ocean.
— Kate Madin
Posted: September 9, 2005 [top] |
