Climate change may be weeding out the bacteria that form the
base of the ocean's food chain, selecting certain strains for survival,
according to a new study.
In climate change, as in everything, there are winners and
losers. As atmospheric carbon dioxide levels and temperature rise globally,
scientists increasingly want to know which organisms will thrive and which will
perish in the environment of tomorrow.
The answer to this question for nitrogen-fixing
cyanobacteria (bacteria that obtain energy through photosynthesis, or
"blue-green algae") turns out to have implications for every living
thing in the ocean. Nitrogen-fixing is when certain special organisms like
cyanobacteria convert inert – and therefore unusable – nitrogen gas from the
air into a reactive form that the majority of other living beings need to
survive. Without nitrogen fixers, life in the ocean could not survive for long.
"Our findings show that CO2 has the potential to
control the biodiversity of these keystone organisms in ocean biology, and our
fossil fuel emissions are probably responsible for changing the types of
nitrogen fixers that are growing in the ocean," said David Hutchins,
professor of marine environmental biology at the USC Dornsife College of
Letters, Arts and Sciences and lead author of an article about this research
that appeared inNature Geoscience on June 30.
"This may have all kinds of ramifications for changes
in ocean food chains and productivity, even potentially for resources we
harvest from the ocean such as fisheries production," Hutchins said.
How the study was
Hutchins and his team studied two major groups of
nitrogen-fixing cyanobacteria: Trichodesmium, which forms large floating
colonies big enough to see with the naked eye and makes vast "blooms"
in the open ocean, and Crocosphaera, which is also very abundant but is a
single-celled, microscopic organism.
Previous research showed that these two types of
cyanobacteria should be some of the biggest "winners" of climate
change, thriving in high CO2 levels and warmer oceans. However, those previous
studies only examined one or two strains of the organisms.
That's where USC's unique resource comes into play – the
university is home to a massive culture library of strains and species of the
organisms assembled by USC Associate Professor Eric Webb.
Using the culture library, the team was able to show that
some strains grow better at CO2 levels not seen since the start of the
Industrial Revolution, while others will thrive in the future
"It's not that climate change will wipe out all
nitrogen fixers; we've shown that there's redundancy in nature's system.
Rather, increasing atmospheric carbon dioxide changes specifically which
nitrogen fixers are likely to thrive," Hutchins said. "And we're not
entirely certain how that will change the ocean of tomorrow."