386 ■ CHAPTER 21 Ecosystems
ECOLOGY
A loss of 500 million tons of phytoplankton
each year could potentially affect the ocean’s
NPP and ocean life. “Almost all biological life in
the ocean depends on phytoplankton. A reduc-
tion in the biomass of phytoplankton will result
in less secondary production in the oceans,” says
Boyce. That means fewer sharks, whales, fishes,
eels—you name it.
The team’s discovery was shocking, to say
the least. No one else had documented a global
decline in phytoplankton before. So, to be confi-
dent in their results, Boyce and Worm did several
more rounds of data analysis, checking again
and again to make sure they were using the right
numbers in ways that correctly represented what
was happening in the natural world. And over
and over, they came back with the same results:
global phytoplankton declined over the last
century. In 2010, they published that finding in
the peer-reviewed scientific journal Nature.Phyto-Fight
The scientific community reacted immediately.
Some researchers doubted Boyce’s conclusions;
others were outright incredulous. Paul Falkowski
at Rutgers University told a New York Times
reporter that he had not found the same trend in
a long-term analysis of the North Pacific (though
Boyce contends that their trends were very simi-
lar), and another team had actually seen an
increase in phytoplankton starting around 1978
in the central North Pacific. Falkowski called
Boyce’s paper “provocative” but said he would
“wait another several years” to see whether satel-
lite data would back up the finding.
Then, in 2011, three separate research teams
went so far as to publish formal critiques of the
work. One suggested that the declining trend was
an error resulting from the use of two different
types of measurements: Secchi disk readings and
direct chlorophyll measurements. A second team
echoed that idea, reanalyzed the data in a way that
showed an increase in phytoplankton, and then
bluntly concluded, “Our results indicate that much,
if not all, of the century-long decline reported by
[Boyce] is attributable to this [sampling bias] and
not to a global decrease in phytoplankton biomass.”
The third team noted that Boyce’s finding
conflicted with eight decades of data on phyto-
plankton biomass collected by a large project
called the Continuous Plankton Recorder (CPR)capture influences the amount of food available
to other organisms. The net primary productiv-
ity (NPP) of an ecosystem is the energy, acquired
through photosynthesis over a particular time
period, that is available for the growth and
reproduction of producers. NPP is the amount
of energy captured by photosynthetic organisms
minus the amount they expend on cellular respi-
ration and other maintenance processes. NPP is
typically determined by estimating the amount of
carbon captured during photosynthesis. This can
be done by measuring the amount of new biomass
produced by the photosynthetic organisms in a
given area during a specified period of time.
According to scientists’ estimates, the NPP
of all producers on Earth exceeds 100 billion
tons of carbon biomass per year. Roughly half
of this productivity comes from phytoplankton
in the ocean. Therefore, phytoplankton capture
approximately 50 billion tons of carbon per year.
So if Boyce’s calculations are right, a loss of 1
percent of that biomass is 500 million tons of
organic matter lost from the oceans each year.
That’s a lot of biomass to lose.
Net primary productivity relies on four things:
sunlight, water, temperature, and the availability
of nutrients. The most productive ecosystems on
land are tropical forests; the least productive are
deserts and tundra (including some mountain-
top communities). The most productive ecosys-
tems in water are estuaries—regions where rivers
empty into the sea—because nutrients drained off
the land stimulate the growth and reproduction
of phytoplankton and other producers, which in
turn nourish large populations of consumers.
The least productive aquatic biome is the deep
ocean, where sunlight does not penetrate.
Despite similarities between the NPP require-
ments on land and in the ocean, the global pattern
of NPP differs between the two. On land, the NPP
is highest at the equator and decreases toward the
poles. But in the ocean, the general pattern relates
not to latitude but to distance from shore: the
productivity of marine ecosystems is typically high
in ocean regions close to land and relatively low
in the open ocean (Figure 21.9). This is because
nutrients needed by aquatic photosynthetic organ-
isms are in better supply near land, thanks to
delivery from streams and rivers. Wetlands such
as swamps and marshes, which trap soil sediments
rich in nutrients and organic matter, can be so
productive that they match the productivity levels
of tropical forests.