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Human CO2 Emissions to Drive Key Ocean Bacteria Haywire, Generate Dead Zones, Wreck Nitrogen Web
2
September, 2015
Trichodesmium. It’s
the bacteria that’s solely responsible for the fixation of nearly
50 percent of nitrogen in the world’s oceans.
A very important role for this microscopic critter. For without
nitrogen fixation — or the process by which environmental nitrogen
is converted to forms usable by organisms — most of life on Earth
would not exist.
Now,
a new study produced
by USC and the Massachusetts-based Woods Hole Oceanographic
Institution (WHOI),
has found that human carbon emissions are set to drive this essential
organism haywire. Forcing evolutionary changes in which the bacteria
is unable to regulate its growth. Thus generating population
explosions and die-offs that will be very disruptive to the fragile
web of life in the world’s oceans.
Trichodesmium
— A Mostly Helpful Bacteria Essential to Ocean Life
Trichodesmium
is a form of cyanobacteria. It resides in the near surface zone
composing the top 200 meters of the water column. Possessing gas
vacuoles, the bacteria is able to float and sink through the water
column in order to access the nutrients it needs for growth —
nitrogen, iron, and phosphorus. A widespread bacteria, it is often
found in warm (20 to 34 C), nutrient-poor waters in the Red Sea, the
Indian Ocean, the North and South Atlantic, the Caribbean, near
Australia, and in the Northeastern Pacific.
Trichodesmium
congregates in blooms which are generally a straw-like color. For
centuries, this coloration has generated its common name — sea
straw. However, in higher concentrations it can turn waters red. The
Red Sea, for example, owes its name to this prolific little bacteria.
Trichodesmium blooms generate a strata that support mutualistic
communities of sea creatures
including bacteria, diatoms, dinoflagellates, protozoa,
andcopepods.
These small organisms, in turn, are fed on by a variety of fish —
notably herring and sardines.
But
Trichodesmium’s chief role in supporting ocean health is through
making nitrogen in the air and water available to living organisms.
It does this by turning environmental nitrogen into ammonia as part
of its cellular metabolism. This ammonia can then be used for growth
by a wide variety of creatures on up the food chain. Trichodesmium is
an amazing producer of this biologically available nitrogen —
perhaps generating as much as 50 percent of organic nitrogen in the
world’s oceans (70 to 80 million metric tons) each year.
Human
Fossil Fuel Burning is Projected to Drive Trichodesmium Haywire
But
now a new study by
USC and WHOI shows
that atmospheric CO2 concentrations projected to be reached by the
end of the 21st Century in the range of 750 ppm CO2 could force
Trichodesmium’s nitrogen fixation rate into overdrive and lock it
there indefinitely.
(Rate
of nitrogen fixation in Trichodesmium at 380 ppm CO2 [black and red],
at 750 ppm CO2 [pink, yellow and light blue], and when CO2 levels are
returned to 380 ppm after five years of exposure to 750 ppm levels
[dark blue]. Image source: Nature.)
The
study subjected Trichodesmium to atmospheric CO2 concentrations (750
ppm) projected under a somewhat moderate rate of continued fossil
fuel burning scenario by 2100 for five years. After this five year
period of exposure, Trichodesmium nitrogen fixation rates nearly
doubled (see above graphic). But, even worse, after the Trichodesmium
bacteria were returned to the more normal ocean and atmospheric
conditions under 380 ppm CO2, the rate of nitrogen fixation remained
elevated.
In
essence, researchers found that Trichodesmium evolved to fix nitrogen
more rapidly under higher ocean acidity and atmospheric CO2 states at
750 ppm levels. But when atmospheric levels returned to 380 ppm and
when oceans became less acidic, Trichodesmium’s rate of nitrogen
fixation remained locked in high gear. For an organism like
Trichodesmium to get stuck in a broken rate of higher metabolism and
growth is practically unheard of in evolutionary biology. Organisms
typically evolve as a response to environmental stresses. Once those
triggers are removed, organisms will typically revert to a near match
of previous states. Strangely, this was not the case with
Trichodesmium.
David
Hutchins, professor at the USC Dornsife College of Letters, Arts and
Sciences and author of the new study described
this alteration to Trichodesium as ‘unprecedented’ stating
that:
“Losing the ability to regulate your growth rate is not a healthy thing. The last thing you want is to be stuck with these high growth rates when there aren’t enough nutrients to go around. It’s a losing strategy in the struggle to survive.”
Uncontrolled
Blooms, Population Crashes, Biotoxin Production, Dead Zones
Nitrogen
is a key component of cellar growth. So Trichodesmium nearly doubling
its rate of nitrogen fixation means that the bacteria’s rate of
production will greatly increase as atmospheric CO2 levels and ocean
acidification continue to rise. Under heightened CO2, the bacteria
essentially loses its ability to restrain its population.
(Large
algae/bacterial blooms like this red tide off La Jolla, San Diego are
causing the expansion of hypoxic and anoxic dead zones throughout the
world’s oceans. A new study has found that one of the ocean’s key
microbes goes into growth overdrive as atmospheric and ocean CO2
concentrations rise — which would greatly enhance an already
dangerous rate of dead zone expansion in the world ocean system.
Image source: Commons.)
As
a result, researchers warn that Trichodesmium blooms may run out of
control under heightening levels of CO2. Such out of control blooms
would rapidly remove scarcer nutrients like phosphorous and iron from
the water column. Once these resources are exhausted, Trichodesmium
would begin to die off en-masse.
As with other large scale bacterial
die-offs in the ocean, the decaying dead cellular bodies of
Trichodesmium would then rob the nearby waters of oxygen — greatly
enhancing an already much amplified rate of anoxic dead zone
formation. And
we know that anoxic waters can rapidly become home to other, far more
dangerous, forms of bacterial life.
In addition, large concentrations of Trichodesmium are known to
produce biotoxins deadly to copepods, fish, and oysters. Humans are
also rarely impacted suffering from an often fatal toxicity response
called clupeotoxism when the Trichodesmium produced toxins biomagnify
in fish that humans eat. Sadly, more large Trichodesium blooms will
enhance opportunities for clupeotoxism to appear in human beings.
Exacerbating
this problem of heightened Trichodesmium blooms and potential related
dead zone formation is the fact that ocean waters are expected to
become more stratified as human-forced warming continues. As a
result, more of the nutrients that Trichodesmium relies upon will be
forced into a thinner layer near the surface — thus heightening the
process of bloom, die-off, and dead zone formation.
Final
impacts to ocean health come in the form of either widely available
nitrogen, (during Trichodesmium bloom periods) which would tend to
enhance the proliferation of other microbial life, or regions of
nitrogen desertification (during Trichodesmium die-offs). It’s a
kind of ocean nitrogen whip-lash that can be very harmful to the
health of life in the seas. One that could easily ripple over to land
life as well.
No
Return to Normal
But
perhaps the most shocking finding of the new research was that
alterations in Trichodesmium’s rate of growth and nitrogen fixation
may well be permanent after the stress of high CO2 and ocean
acidification are removed. Hinting that impacts to ocean health from
a rapid CO2 spike would be long-lasting and irreparable over anything
but very long time-scales. Yet more evidence that the best thing to
do is to avoid a major CO2 spike altogether by cutting human carbon
emissions to zero as swiftly as possible.
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Hat
Tip to Colorado Bob
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