Here and Gone ■ 383last century. Overall, phytoplankton appeared
to have declined by about 1 percent of the global
average each year.
One percent sounds like a small number, but
that amount every year just since 1950 translates
into a staggering total phytoplankton decrease
of 50 percent in the world’s oceans.The Precious 1 Percent
A 50 percent loss in the main producer in any
ecosystem is a worrisome number, but especially
with respect to phytoplankton. Phytoplankton
support fisheries, produce half the oxygen we
breathe, and take in carbon dioxide from the
atmosphere, which helps offset the greenhouse
effect and global warming.
An ocean with less phytoplankton will func-
tion differently because ecosystems depend on
energy capture, the trapping and storing of solar
energy by the producers at the base of the ecosys-
tem’s energy pyramid. Herbivores, carnivores,
and detritivores all depend indirectly on energy
capture. If an ecosystem has an abundance of
producers, it can often support more consumers
at higher trophic levels. In a tropical forest, for
example, an abundance of plants capture energy
from the sun, and the forest teems with life. On
the flip side, relatively little energy is captured in
an environment with few producers. In tundra or
desert regions, for example, less food is available,
and fewer animals can live there. These significant
differences have prompted ecologists to categorize
large areas of Earth’s surface into distinct regions,
called biomes, that are defined by their unique
climatic and ecological features (Figure 21.8).
Assessing the overall amount of energy
captured by producers is important in deter-
mining how an ecosystem works, because energyIn a first-of-its-kind analysis, Boyce, together
with his adviser Boris Worm and the oceanogra-
pher Marlon Lewis, combined two types of chlo-
rophyll measurements. The first type, dating all
the way back to 1899, were recorded with noth-
ing more than a rope and a disk.
In 1865, the pope asked priest and astronomer
Pietro Angelo Secchi to measure the clarity of
water in the Mediterranean Sea for the purposes
of the papal navy. Secchi designed one of the
simplest measurement devices ever used: a dinner
plate–sized disk painted with black and white
stripes attached to a rope. The disk is lowered
into water until the white stripes disappear (as
they become obscured by chlorophyll from phyto-
plankton), and the depth at that point is recorded
(Figure 21.7; see also the chapter-opening photo).
Chlorophyll concentrations derived from Secchi
disk measurements have been corroborated by
satellite data, so scientists know they are reliable.
In addition to gathering Secchi disk data, scien-
tists at sea use lab tools to directly measure the
quantity of chlorophyll in the water (as opposed to
observing its color and relating that to chlorophyll
concentration). Boyce found hundreds of thou-
sands of these direct chlorophyll measurements
online in open-source databases. “There’s been a
huge increase in the amount of publicly available
oceanographic data out there,” says Boyce.
But to use the data, Boyce first had to separate
the wheat from the chaff. “With any big data-
base, there are bound to be measurements that
are entered incorrectly, for whatever reason,”
says Boyce. He, Worm, and Lewis ruled out
measurements that were inappropriate for their
study, such as those taken where the ocean floor
was less than 25 meters deep, because changes
of water transparency in those cases could be
caused by sediment or runoff from landmasses
nearby rather than by phytoplankton.
The team analyzed each data set separately—
Secchi disk measurements and direct chlorophyll
measurements—and then together. To combine
the two, they converted all the Secchi measure-
ments into the same units as those used for direct
chlorophyll concentrations. In total, the blended
data set included 445,237 chlorophyll measure-
ments collected between 1899 and 2008.
What they found made them pause. With
those two different methods of analysis, they
identified a significant decline in phytoplankton
levels—a whopping 60–80 percent—in Earth’s
oceans where data were available during the
Figure 21.7
Secchi disks indirectly measure
chlorophyll concentrations
The Secchi disk is lowered into water
until its white stripes become obscured
by the chlorophyll in phytoplankton.