122Microlife
Some living things, such as elephants and oak trees, are difficult to miss
if you’re standing next to one, but others are much harder to see. There
are thousands of species of microscopic organism living in the air, on
land, and in water all around you, and on
your body, too!
LIVING WORLD
KRILL are tiny
crustaceans that eat
plankton. Large
marine animals,
including whales,
feed on the krill,
making them a vital
link in the food chain. ALGAE Most
phytoplankton is
made up of algae.
Many algae are made
up of just one cell, like
these diatoms.TAKE A LOOK: ALGAE
BLOOMING
Algal blooms are a
sign of nature out of
balance. The bloom
blocks sunlight, uses up
nutrients, and starves
or poisons other plants
and animals. GLOWING
Several algae are
bioluminescent: they
give out light when
they are disturbed.
This alga, Noctiluca,
can make the sea
glow an eerie green.WHAT’S IN THE WATER?
In addition to fish and other marine
creatures, our oceans, rivers, and lakes are
teeming with plankton—microscopic life
that drifts with the current. Plankton
includes tiny animals (zooplankton) and
plantlike life-forms (phytoplankton). Many
creatures eat plantkon, and in this way
whole aquatic ecosystems depend on it.Single-celled algae belong to
a group of organisms known
as protists. Like plants, these
algae make food from
sunlight, using a process
called photosynthesis
( p. 87).