in the ocean

Microorganisms Living things, such as plants and animals, are known as organisms.. Phytoplankton and zooplankton As we learned, plankton are the tiny floating organisms in the ocean.. Th

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In the ocean / Sabrina Crewe ; consultant, Anne K Camper.

p cm (Under the microscope)

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Illustrations by Stefan Chabluk

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Acknowledgments

We would like to thank the following for permission to reproduce photographs: H.M.S Challenger Library:

p 29; Dennis Kunkel Microscopy, Inc.: pp 8, 24, 25 both; MicroAngela: pp 4, 16, 20, 22 left, 23; NOAA: pp 10 both, 11, 14, 19, 22 right, 26 (1), (3), (4), and (5), 27 top left, top right, middle right, and bottom; Science Photo Library: pp 9 (Steve Gschmeissner), 12 (Sinclair Stammers), 13 (Claire Ting), 17 both (Steve Gschmeissner),

18 (Volker Steger and Christian Bardele), 21 (Dante Fenolio), 26 (2) (Science Source); Shutterstock Images:

pp 5 (Emin Kuliyev), 6 (Pinosub), 15 (Armin Rose), 27 middle left (Vittorio Bruno).

Explore These Web Sites 31

Some words are bold the first time they appear

in the text These words are explained in the glossary at the back of this book.

Invisible

Oceans

The oceans that cover

most of Earth are vast,

with towering waves

and dark depths Huge

whales, enormous

octopuses, and plants

as tall as buildings live

in this watery world But

there is another, invisible

world in the oceans

Microorganisms

Living things, such as

plants and animals, are

known as organisms

Organisms that are too

small to see with the

human eye are called

microorganisms

Many microorganisms

that live in the ocean

are known as plankton

The word plankton

means drifting, and that’s

what plankton do They

float and drift with the

movement of the water

Micro-Monster

The Lucifer is a very small kind

of shrimp that is among the plankton floating in the ocean

The word lucifer means

light-bearing or bright, and the Lucifer shrimp can glow in the dark! The Lucifer has eyes sticking out

on stalks, which give it a better view of its surroundings

Some plankton are marine animals or animal-like

creatures Others are more like plants They may be tiny, but these organisms are important for all living things

We’ll find out why, and discover many other things, as

we take a look at the ocean under the microscope

Micro-Scientist

A microbiologist is

a scientist who studies microorganisms A marine microbiologist focuses

on microscopic life-forms in the ocean

Micro-Fact

Near the surface

of the ocean, every

drop of ocean water

contains thousands

of plankton

The Ocean Web

To understand the microscopic world of the ocean, we have to learn a little about how all living things in the ocean work together They depend on each other for food and survival Microorganisms are an important part of this network

Phytoplankton and zooplankton

As we learned, plankton are the tiny floating organisms

in the ocean Those that are similar to plants are called

phytoplankton Animals or animal-like plankton are

So what’s the difference? All

livings things need energy,

and that energy comes from

food Zooplankton eat other

living things to get their

food Phytoplankton make

their own food through

photosynthesis Using the

Sun’s energy, they combine

water and carbon dioxide

(a mix of carbon and oxygen)

to produce carbohydrates.

Webs and chains

The Sun’s energy is the starting point

for almost all food Phytoplankton use

it to make their own food and grow

Zooplankton eat phytoplankton Small

fish and crustaceans survive by

eating zooplankton Bigger fish and

other large marine animals prey

on these smaller ones

This passing of energy

from one organism to

another is known as a

food chain There are

many different food

chains, however, and

they often cross over

Together, many food

chains form a food web

Micro-Fact

Phyto- means plant, and zoo- refers to animals

So phytoplankton means drifting plant, and zooplankton means drifting animal

This diagram

of a marine food chain shows how energy produced by phytoplankton feeds zooplankton and bigger animals

Ocean Bacteria

Living things need nutrients to keep them healthy and help

them grow The nutrients in the ocean come from organisms that die and settle on the ocean floor There, they are broken

down by decomposers

Many decomposers are microorganisms, especially

bacteria Let’s find out more about bacteria and how they

play an important part in the ocean web

What are bacteria?

Bacteria are some of the smallest living things in the ocean and on land They

have only one cell, and

this cell does not have a

nucleus Bacteria multiply

by dividing themselves

An important job

Many kinds of bacteria live among the dead plant and animal matter in the ocean Most feed by absorbing nutrients from the dead organisms that they live on

Bacteria break down, or decompose, the matter they use for food This process releases substances into the water that become nutrients for phytoplankton The most phytoplankton are found in areas where the ocean is rich in nutrients These nutrients can also come from rivers that flow into the ocean

Many bacteria

are rod-shaped, like

these ones found in

the ocean They are

magnified here

more than

5,000 times.

How Small

Is Small?

Scientists say that a teaspoonful of seawater contains between 10 million and 100 million marine viruses They are so small that you would have to put more than 20 billion of them together before you could see them!

Viruses

One type of microbe

is smaller than a

bacterium, and that is a

virus Some are so tiny

that they are measured

in nanometers Viruses,

however, are not really

organisms A virus is a

package of chemicals

that can only multiply

inside a living cell, or

host Viruses invade

the cells of plants,

animals, and bacteria

In the ocean, viruses

infect bacteria living

9

Life in the Deep

In some parts, the ocean is more than 30,000 feet deep Not many organisms can live at those depths There is little or no sunlight So without the Sun’s energy, how can there be life?

at a hydrothermal vent get nutrients from bacteria that live in their tubes

This photo shows

a hydrothermal vent

deep in the ocean The

cloud comes from the hot

water gushing out The water

is full of minerals that

provide nourishment for

the microorganisms

living around

the vent

get their energy from the

minerals in the boiling

water gushing from the

vents They live on the

surface of the vents or on

larger creatures that also

flourish in this extreme

environment

Archaea

Many of the microbes that

live in the thermal vents

are archaea These are not

animals, plants, viruses, or

bacteria But, like bacteria,

they have one simple cell,

and they are very tiny Most

archaea are only 1 to 15

micrometers in size.

11

Micro-Fact

Scientists believe

that the microbes in

hydrothermal vents are

related to the earliest

So as you can imagine, the ocean depths are full of extremophiles!

As we learned, most bacteria absorb their food from other living things But there is an important type of bacteria

in the ocean that is different

Using photosynthesis

Like other bacteria, cyanobacteria

do not have a nucleus in their single cell But unlike other bacteria,

cyanobacteria make their own food They float on the surface of water and use sunlight to perform photosynthesis

Organisms that use energy from photosynthesis are called

phototrophs And because they

are phototrophs, or plant-like, cyanobacteria are part of the floating world we know as phytoplankton

Trichomes and coccoids

Cyanobacteria live together in large groups Some form filaments, or strands, in which long chains

of them are joined together

These cyanobacteria are called trichomes Others, known as coccoids, live together in a group inside a blob of jelly

Oscillatoria

is a trichome

cyanobacteria because

its cells form long strands

You can see the individual

cells that make up

the strands in

this photo.

Bubbles of oxygen

Whether they are in chains or blobs, cyanobacteria

often form mats over areas of the ocean As they

photosynthesize, cyanobacteria absorb carbon dioxide and release oxygen You can often see bubbles of oxygen rising from the mats

Prochlorococcus

The smallest known phototroph—only about

0.6 micrometers in size—is a cyanobacterium

called Prochlorococcus But it may also be the

most important There can be 100 million of these cyanobacteria in a quart of seawater Scientists believe they could perform as much photosynthesis

as all other phytoplankton put together

All About Algae

Most kinds of phytoplankton

in the oceans belong to

a large group of organisms

called algae Algae are

plant-like because they perform photosynthesis, but they are not actually plants

Marine algae produce the same green substance—chlorophyll— that plants do So, many species are green in color But some algae can be red, purple, brown,

or yellow because they contain other pigments (colors) besides chlorophyll These red and green algae are growing

on rocks in the Pacific Ocean

Micro-Fact

Most algae are

microscopic, but some

are very big Large algae

are what we know as

seaweed, and they

can be over 100

feet long

What are algae?

Algae don’t have stems,

roots, or leaves Algae

often live joined together

in long strands, but some

species float around by

themselves

Many algae have

just one cell, and they

reproduce simply by

dividing their cells Other

algae create new cells,

called spores, which they

release into the water to

make new algae

Algae and Earth’s Cycles

Algae and cyanobacteria are essential to Earth’s natural cycles The carbon cycle is the movement of carbon among air, water, and living things If there is too much carbon

in the air, Earth gets too warm But oceans remove a lot of carbon dioxide from the air by dissolving it in their waters Phytoplankton help because they take in carbon dioxide from the water during photosynthesis This allows the oceans to absorb more carbon dioxide from the air And because they only need the carbon, phytoplankton release the oxygen They provide the world with about half the oxygen that living things need to survive

When ocean water freezes into ice, algae of different colors can make icebergs stripy!

The most plentiful of all phytoplankton are diatoms Diatoms are enclosed in a cell wall that forms a hard casing These cases are made of silica, which is the same stuff that glass is made

of Diatoms come in all kinds of interesting shapes and often have beautiful patterns Whatever their shape, diatoms are symmetrical, which means that one half is the mirror image of the other

Micro-Fact

Some dinoflagellates glow in the dark You can see a flicker of blue light

in the ocean at night if

a group of these dinoflagellates isdisturbed

There are about 2,000 kinds

of dinoflagellates, and some

of them are phototrophs They

have little tails called flagellae,

which help them move

Dinoflagellates can reproduce very fast, creating a huge number of cells called

a bloom Some dinoflagellate blooms can poison other marine life These dinoflagellates are red in color, so their blooms are called “red tides.”

You can see the microscopic shields that form a ball around this coccolithophore.

which help them move

Dinoflagellates can reproduce very fast, creating a huge number of cells called

can poison other marine life These

shapes and range

in size from 5

micrometers to

2 millimeters

Do you remember zooplankton? They are the microscopic animals and animal-like creatures that float in the ocean There are thousands of species of tiny organisms that make up the zooplankton population They fall into three

main groups: microanimals, protozoa, and the larvae

of larger animals

Protozoa

Protozoa are

microorganisms

that are similar to

animals, but they are

simpler in structure

Protozoa often have

only one cell, and

many reproduce by

dividing themselves

But they can move

around in the water and

catch prey to eat Sometimes,

they catch and eat other protozoa

bigger than themselves!

Larvae

Some larger marine creatures are

microscopic when they are larvae

A larva is an animal in the stage

before it becomes an adult Marine

This amoeba

is a kind of protozoa It lives

in the seas off western Australia and eats diatoms

larvae may turn into worms, coral,

snails, or fish, but they start out as

zooplankton We’ll take a look at

some of these later

Microanimals

Animals are living things that have many cells,

can move themselves around, and feed on plants or

other animals With a microscope, you will find a world

of miniature animals on land and in the ocean We call them microanimals because they are too small to be

seen easily by the human eye

Microanimals in the ocean feed on other zooplankton and on phytoplankton Some of the most common

microanimals are crustaceans, which we’re going to

look at next

19

These zooplankton are microscopic crustaceans The one in the center

is the larva of

a bigger crustacean.

Not all crustaceans are microscopic The crustaceans

we picture when thinking about the ocean are bigger animals, such as lobsters and crabs Shrimp are crustaceans, too What these crustaceans have in common is a hard outside skeleton They also have bodies with separate segments, or jointed parts

Many microscopic crustaceans live below the ocean surface and come up

at night to feed on plankton Some live attached to other animals Others live in the sand on the ocean floor

Yet others create their own houses and float around

Copepods

Copepods are usually 1 or 2 millimeters in length Some species live on the ocean floor Others float on or near the surface as zooplankton—

Micro-Monster

The Pleuromamma is a

copepod with antennae

as long as its body The

antennae are covered in

small hairs that pick up

signals, such as smells or

movements This detection

system enables the

Pleuromamma to attack

prey with lightning speed

Crustaceans

A Phronima is an

amphipod that lives in

the middle and upper areas

of the ocean It makes its

home inside another tiny

animal called a salp The

Phronima will kill the salp,

hollow out its body,

and move in!

in fact there are usually more

copepods than any other

zooplankton

Amphipods

Amphipods, like

copepods, may live at

the top or bottom of

the ocean depending

on their species Most

of them have flat bodies,

and they all have three

pairs of tail legs that

they flick to move quickly

through the water

21

Micro-Fact

Some copepods are parasites, which means they live and feed on a host instead of swimming around to find food Parasitic copepods live on fish A large shark may have hundreds on its fins and gills and even

in its nose!