GSO oceanographer studies
microscopic organisms in world’s oceans
You
can’t see them with the naked eye, but they’re all over the ocean: diatoms,
single-celled organisms that drift on currents.
These
microscopic creatures are key to the planet’s health.
They sit at the base of
the food chain, feeding everything from zooplankton to fish.
Through
photosynthesis diatoms also regulate the air people breathe, and they regulate
the global climate.
Yet
they remain a mystery to many scientists.
Tatiana
Rynearson, an oceanographer at the University of Rhode Island’s Graduate School
of Oceanography, and Kerry Whittaker, who received her doctorate from GSO in
2014, are contributing their knowledge about diatoms through a paper published by the Proceedings of the National Academy of Sciences.
Diatoms
are enormously diverse, with an estimated 200,000 species. The physical and
ecological processes that support this diversity are widely debated by
oceanographers, evolutionary biologists and microbial ecologists.
Whittaker
and Rynearson, who was Whittaker’s adviser at GSO, explored the diversity of
the diatom species, Thalassiosira rotula. To accomplish this, the
team collected cells of this one species from around the world.
They
reached out to researchers from 19 places across hemispheres and ocean basins,
from the coast of Germany and South Africa to Tasmania and Puget Sound in
Washington state. The researchers took seawater samples and sent them to GSO by
Federal Express five times during the year.
In
the lab, individual cells of Thalassiosira rotula were
isolated from the samples and cultured. These samples were then “genetically
fingerprinted’’ to examine if they were related—a technique often used by
forensic scientists.
The
team concluded that the species has a remarkable ability to travel throughout
the ocean, influencing “high genetic connectivity among global populations,”
say Rynearson and Whittaker.
On
land, geographic distance limits the genetic relationship between things. For
example, two trees located close together tend to be more genetically related
than two trees separated by a great distance.
Surprisingly,
the team’s data show that geographic distance might not limit relatedness or
“genetic connectivity” of diatoms, possibly due to the potential of diatoms to
disperse widely as they drift with the tides and currents.
Instead
of geographic distance being the primary regulator of relatedness between
diatom populations, the team found that environmental conditions play a much
stronger role.
For
example, diatom populations sampled from similar marine environments tended to
be more closely related than populations from different environments.
So
what is one of the environmental factors that was most important in explaining
the distribution of diversity within the species? The answer is temperature, a
factor that is changing rapidly in the ocean in response to climate change.
Understanding
genetic diversity and how it is regulated in these important diatoms has
implications for studies that try to predict how a changing environment will
influence the productivity of diatoms, say Rynearson and Whittaker.
“The
bottom line is that we now have a global-scale view of diversity in diatoms,
and it’s fundamentally different than what we see on land,’’ says Rynearson.
“The mechanism on land is distance but in the ocean—and for diatoms—it appears
to be the environment. In particular, it’s the temperature, and temperature
is changing rapidly in response to climate change.’’
“This
work provides a global snapshot of diversity that reveals the importance of
environmental conditions in driving the evolution of these ecologically
influential organisms,’’ says Whittaker. “In the context of a rapidly changing
ocean environment, this insight is important for predicting the impact of
climate change on primary producers in the ocean, particularly diatoms.”