Lesson 2: Build Your Own
Ocean Food Web!
Materials
1. String cut into pieces. There should
be ~5 pieces of string per student.
Each piece should be about 5-10 feet
long.
2. Marine species cards (provided)
3. PowerPoint file and PDF showing
examples of roles played by different
organisms in a food web (provided)
4. Pictures demonstrating the difference
between a food chain and a food web
(provided)
5. Safety pins (optional)
Focus Question
What are the roles played by plants,
animals, and other organisms in marine food
webs off the California coast?
Grade Levels
6-8
Number of Participants
All students (no minimum or maximum)
Objectives
Upon completion of this lesson plan,
students should be able to:
1. Discuss different roles that animals,
plants, and other organisms play in
ocean food webs.
2. Understand the difference between a
food chain and a food web.
3. Describe how changes in the
abundance of one species can affect
other species in a food web.
Background Information for Educators
One way of classifying different
organisms that live in an ecosystem is
based on what they eat. Organisms that
generate their own energy through
photosynthesis are referred to as primary
producers. In marine ecosystems,
examples of primary producers include
plants (e.g., seagrasses, mangroves),
multicellular algae (e.g., kelp and other
seaweeds), single-celled algae (e.g.,
diatoms), and photosynthetic bacteria (e.g.,
blue-green algae or cyanobacteria). Some
marine ecosystems also include organisms
that produce energy through chemical
reactions in a process known as
chemosynthesis. Chemosynthetic
organisms are another type of primary
producer.
Primary producers are eaten by
organisms known as primary consumers.
Primary consumers can either be herbivores
(e.g., plant eaters) or planktivores (e.g.,
plankton eaters). In coastal ecosystems off
California, examples of herbivores include
sea urchins and kelp crabs, which both
consume kelp.
Photosynthetic plankton, or
phytoplankton, are eaten by a large variety
of organisms in pelagic (open-water)
ecosystems. Larger-sized plankton that eat
Science Content Standards for California
Public Schools
Grade 6: Ecology
5a. Students know energy entering
ecosystems as sunlight is transferred
by producers into chemical energy
through photosynthesis and then
from organism to organism through
food webs.
5b. Students know matter is transferred
over time from one organism to
others in the food web and between
organisms and the physical
environment.
5c. Students know populations of
organisms can be categorized by the
functions they serve in an ecosystem.
5d. Students know different kinds of
organisms may play similar
ecological roles in similar biomes.
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phytoplankton are collectively referred to as
zooplankton. Different species of
zooplankton may prefer to eat either large
phytoplankton, such as diatoms, or small
phytoplankton, such as cyanobacteria. To
give you a sense of the size of these
phytoplankton, about 7 of the larger diatoms
could fit on the head of a pin, whereas 750
small cyanobacteria could be crammed onto
the same pinhead.
Copepods and krill are both planktonic
crustaceans that prefer large-sized
phytoplankton. In contrast, small
phytoplankton may be eaten by ciliates,
which are a type of protist (a single-celled
eukaryotic organism). Some phytoplankton
are also eaten by animals that live on the sea
floor, such as mussels.
Primary consumers are eaten by
secondary consumers. Many small fishes
found in marine ecosystems, such as sardine,
anchovy, and lanternfish, are secondary
consumers. In benthic (or sea floor)
ecosystems, sea stars are an example of a
secondary consumer. Other types of
secondary consumers found in pelagic
ecosystems include squid, jellyfish, and
some species of whales. In pelagic
ecosystems, some secondary consumers may
occasionally eat both phytoplankton and
zooplankton. This is an example of
omnivory. Since sardine and jellyfish
mainly consume zooplankton, but
occasionally eat diatoms, they can be
considered omnivorous species.
Tertiary consumers that eat secondary
consumers are also common in ocean
ecosystems. Sometimes it is ambiguous
whether a species is a tertiary or quaternary
consumer in a marine ecosystem because a
food chain can include many steps where
one planktonic organism is eaten by another
planktonic organism. For simplicity, in this
lesson plan we use the term carnivore to
refer to all organisms at the level of tertiary
consumption or above. Examples of marine
carnivores include fishes, sharks, seabirds,
seals, sea lions, dolphins, and some whales.
Nutrients are recycled in ecosystems by
organisms that act as decomposers.
Bacteria are the most important type of
decomposers in marine ecosystems.
Bacteria consume organic matter that is
released into the water column by both live
and dead phytoplankton. Organic matter,
dead organisms, and feces that are not
consumed by bacteria will eventually sink
out of the water column and reach the sea
floor. On the sea floor, this organic matter
will be consumed by a variety of
scavengers. Many types of shrimp are
scavengers. Some marine scavengers are
referred to as detritivores, because they
feed upon detritus (decaying organic matter)
found on the seafloor. Sea cucumbers are an
example of a detritivore.
A food web is a schematic that shows
how energy and nutrients flow between
different organisms in an ecosystem. Food
webs are more complicated than a food
chain, where energy and nutrients flow in a
simplified, linear pathway between primary
producers, primary consumers, and
secondary consumers. In a food web,
animals may eat many types of prey items or
may change their preferred type of food as
they grow from juveniles to adults.
Although they are more complicated, food
webs provide a more realistic depiction of
how marine ecosystems function. This
lesson plan includes diagrams depicting
marine food chains and food webs to help
you explain this difference to your students.
Changes that affect one species can
spread throughout an ecosystem through
food webs. For example, an increase in
nutrients can cause phytoplankton to
reproduce rapidly, resulting in an increase in
their abundance. The phytoplankton will
provide additional food for zooplankton,
such as copepods and krill. This can cause
these types of zooplankton to become more
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abundant. In turn, the number of fish that
eat zooplankton may increase. When
changes in an ecosystem spread from
primary producers upward through a food
web, this is called bottom-up control.
In contrast, top-down control occurs
when the abundance of a carnivore changes
affecting the species that are eaten by the
carnivore. For example, sea otters were
hunted nearly to extinction by the beginning
of the 20th century. The reduced number of
sea otters caused an increase in the
abundance of sea urchins, which are eaten
by otters. The sea urchins preyed heavily on
kelp, causing the destruction of kelp forests
throughout much of the West Coast of North
America.
The marine ecosystem off California is
sometimes referred to as a wasp-waist
ecosystem. In wasp-waist ecosystems, there
are a large number of species of primary
producers and carnivores, but only a few
species of secondary consumers. The
important secondary consumers in this
ecosystem are small fishes, such as sardine
and anchovy. Since there are few other
secondary consumers, changes in the
abundance of sardine and anchovy can have
a large effect on both the organisms that
they eat and their predators.
Today humans play a major role in
marine food webs, since they catch many
organisms for their own consumption. This
is why several types of fishermen are
included as members of the marine food
web that students will construct.
top-down control, and wasp-waist
ecosystems.
Activity Summary
In this lesson plan, students will
construct an ocean food web that can
comprise up to 35 species that live in pelagic
and benthic environments off California.
Each student will be assigned a role of a
different species. These roles are described
on the marine species cards included as part
of this lesson plan. These cards list the
major components of each species’ diet.
Students will be given ~5 strings each and
will be instructed to find the students
playing the roles of the species that their
organism eats. Once a student finds these
other species, they are given the other end of
the student’s string to hold. In this way, the
students construct a representation of the
marine food web off the coast of California.
Once the food web has been constructed,
the teacher will pose a number of questions
about what happens if a particular organism
increases or decreases in abundance. When
an organism increases in abundance, the
student playing this organism will raise
his/her hand. A decrease in abundance is
indicated by a student sitting down at a desk
or on the floor. When an organism increases
in abundance, its prey will become less
abundant and its predators will become more
abundant. Students playing the role of prey
should sit down to indicate their reduced
abundance, while students playing predators
should raise their hands. A chain reaction of
students sitting or raising their hands will
propagate throughout much of the food web,
demonstrating the interconnection between
organisms in an ecosystem.
To help students master new vocabulary
and develop critical thinking skills, this
lesson plan also contains a few supplemental
activities. Step 2 under Lesson Plan Steps
describes several (optional) vocabulary
learning activities. Step 7 under Lesson
Key Words
Primary producer, primary and
secondary consumers, herbivore, carnivore,
omnivore, scavenger, decomposer, plankton,
photosynthesis, food chain, food web,
ecosystem
For advanced classes or older grade
levels, educators may also want to introduce
the following concepts: bottom-up control,
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Plan Steps includes a homework assignment
designed to encourage students to think
critically about the role of humans in marine
ecosystems and about the impacts of fishing
and climate change on ocean food webs.
whether each image is a primary
producer, primary consumer,
secondary consumer, carnivore,
scavenger, or decomposer.
3.) Images could be placed in various
stations throughout the classroom.
Students can be broken into groups
that travel to each station, where
students would discuss the role
played by each organism in the food
web.
Step 3: Once students have mastered the
new vocabulary, the teacher should provide
a brief overview of food webs and how they
differ from food chains. A PowerPoint file
visually demonstrating these differences is
provided. A PDF file of these diagrams is
also included for instructors who do not
have access to PowerPoint software.
Step 4: Students line up to select their
species card from a pile and take ~5 pieces
of string. 35 roles are available for students
to play when building their food web. For
smaller-sized classes, some organisms in the
food web can be left out. For larger classes,
some students can double up and play the
same role in the food web.
After choosing their species cards,
students stand in a circle where they read off
the name of their species and tell the class
what their species eats. After reading their
cards, students may want to pin their card to
their shirt to make it easier for other students
to recognize what organism they are
playing.
Step 5: Students then use their pieces of
string to self assemble the food web.
Students whose organism eats less than 5
species will not use all their pieces of string.
Step 6: The teacher describes several
scenarios where one organism increases or
decreases in abundance. If an organism
increases in abundance, the student playing
this organism raises their hand. A decrease
in abundance is symbolized by a student
sitting down. If an organism increases in
Preparation
The teacher will need to print out the
species cards provided at the end of the
lesson plan that will be given to each
student. To make it easier to see the species
that each student is playing, it may be useful
to either have students pin the species cards
to their clothing or have a string attached to
the cards, so that students can wear their
card like a necklace. To increase the
durability of the species card, they could be
(optionally) laminated.
A teacher should cut approximately 5
pieces of string per student. Each piece of
string should be ~5-10 feet so that the food
web does not become too tangled.
Lesson Plan Steps
Step 1: Introduce students to new
vocabulary words related to the different
roles that species play in food webs.
Step 2: To help students learn this
vocabulary, 12 images of plants, animals,
and fungi that play different roles in
terrestrial (or land) food webs are included
in this lesson plan. These terrestrial
organisms will likely be more familiar to
students than sea creatures. This should
allow students to focus more on learning the
new vocabulary, instead of learning about
what each organism eats. These images can
be used in one of three ways to help students
master their vocabulary:
1.) The images can be projected
overhead and the teacher can lead a
class discussion about the role that
each organism plays in a food web.
2.) Students can be divided into teams
and play a jeopardy-style game
where they are quizzed about
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abundance, its prey will become less
abundant, which is indicated by the students
who play prey species sitting down.
Predators of the more abundant species will
also increase in abundance. Students
playing predators should raise their hand.
This chain of reactions will then affect the
prey’s prey and the predator’s predators. At
the end of each scenario, the majority of
students will be either raising their hands or
sitting down to indicate how their abundance
has changed.
Here is a partial list of scenarios that the
class should try acting out. Additional
scenarios can also be devised by the teacher.
1.) What happens if an increase in ocean
nutrients causes there to be more
diatoms?
2.) What happens if hunters kill almost
all of the sea otters?
3.) What happens if ocean temperatures
become too cold for sardine causing
them to decrease in abundance?
4.) What happens if ocean temperatures
become too warm for anchovy
causing them to decrease in
abundance?
5.) What happens if sardines decrease in
abundance, while anchovy increases
in abundance?
The latter three scenarios reflect
historical changes in the ocean ecosystems
of California, where during different
decades conditions have either been
favorable for anchovy or sardine. Future
lesson plans in this unit will discuss
historical cycles in the abundance of these
two fishes. Acting out these scenarios will
help preview this subject matter.
Step 7: As a homework assignment,
students should write answers to the
following questions:
1.) Describe what role your organism
played in the marine food web.
2.) Why are humans important to
include in the marine food web?
3.) In the 1930s, the largest fishery in
California was for sardine.
However, during the following
decades, sardine became much rarer
due to changes in ocean temperature
and because too many sardine were
caught by fishermen. At the same
time that sardine became less
abundant, anchovy, another species
of small fish, increased in
abundance. Based on the activity
that you did in class today, how do
you think these changes in sardine
and anchovy will affect other
organisms in the ocean food web?
Questions?
Contact Rebecca Asch
Ph.D. student, Biological Oceanography
Scripps Institution of Oceanography
rgasch@ucsd.edu
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Marine Species Cards Marine Species Card 1 of 35 Pacific Sardine •  Secondary consumer •  Eats copepods, ciliates, and some diatoms •  Lives in open-­‐water habitats •  Bonus fact: John Steinbeck (a famous writer from California) has wri@en a book about the fishery for sardine. The Dtle of this book is Cannery Row. Marine Species Card 2 of 35 Anchovy •  Secondary consumer •  Eats copepods •  Lives in open-­‐water habitats that are close to the coast •  Bonus fact: The fishery for anchovy off South America was once the largest in the world. At that Dme, fishermen caught nearly 12 million tons of anchovy each year. •  Secondary consumer Lanternfish •  Eats copepods and krill •  Lives in the deep ocean, but comes to the surface at night to feed •  Bonus fact: Lanternfish have special cells that produce light. This is why they are named “lanternfish.” Marine Species Card 3 of 35 Marine Species Card 4 of 35 Diatom chain Diatom •  Diatoms are a type of microscopic algae. •  Primary producer •  Makes its own food through photosynthesis •  Bonus fact: A diatom is made of a single cell, but many diatoms can join together to form long chains. These chains look a li@le like a necklace. Marine Species Card 5 of 35 Copepod •  Copepods are a type of plankton. •  Primary Consumer •  Eats diatoms and ciliates •  Bonus fact: Copepods are the most abundant animals on Earth. This is a picture of marine bacteria giving off fluorescent light. The photo was taken under a microscope. Marine Species Card 6 of 35 Bacteria •  Herbivore •  Decomposers •  Mainly eat dying diatoms and blue-­‐green algae •  Bacteria live in all habitats in the ocean. •  Bonus fact: Did you know that there are a million bacteria in every drop of seawater? Marine Species Card 7 of 35 Blue-­‐green Algae •  Primary producer •  Make their own food through photosynthesis •  Live in the upper part of the ocean so that they have enough light for photosynthesis •  Bonus fact: Despite their name, blue-­‐green algae are actually a type of bacteria. Marine Species Card 8 of 35 Ciliate •  These are a very small type of plankton that belong to a group of organisms called “proDsts.” •  Primary Consumer •  Eats blue-­‐green algae •  Bonus quesDon: Can you spot the algae that the ciliate ate in the picture above? Marine Species Card 9 of 35 Yellowfin Tuna •  Carnivore •  Eats sardine, anchovy, lanternfish, and squid •  Lives in open-­‐water habitats •  Bonus fact: Tunas can migrate long distances. Some types of tuna swim across the whole AtlanDc Ocean between Europe and the United States. Marine Species Card 10 of 35 Brown Pelican •  Carnivore •  Eats anchovy and sardine •  Feeds in areas near the coast •  Bonus fact: Brown pelicans were once an endangered species, but they have now recovered. Marine Species Card 11 of 35 Risso’s Dolphin •  Carnivore •  Eats anchovy, sardine, and squid •  Bonus fact: The Navy has trained dolphins to help detect underwater mines. Marine Species Card 12 of 35 Blue Whale •  Secondary consumer •  Eats krill •  Bonus fact: The blue whale is the largest animal that has ever lived on Earth. It is bigger than the dinosaurs. Marine Species Card 13 of 35 This cormorant is diving to catch its food. Cormorant •  Carnivore •  Eats sardine and anchovy •  Feeds in areas near the coast •  Bonus fact: Fishermen in Japan and China have trained cormorants to help them catch fish. These fishermen have been pracDcing this tradiDon for 1,300 years. Marine Species Card 14 of 35 Mussel •  Primary Consumer •  Eats diatoms and blue-­‐
green algae •  Mussels live a@ached to the sea floor in shallow waters. •  Bonus fact: Mussels help keep the ocean clean by filtering water. Marine Species Card 15 of 35 Sea Star •  Secondary consumer •  Eats mussels •  Lives on the sea floor •  Bonus fact: Sea stars can regrow legs that are lost through injuries. Marine Species Card 16 of 35 Kelp •  Primary producer •  Makes its own food through photosynthesis •  Lives a@ached to the sea floor in coastal areas •  Bonus fact: Kelp can grow up to 2 feet each day. •  Primary Consumer •  Lives on the sea floor Sea Urchin •  Eats kelp •  Bonus fact: The eggs of sea urchins can be made into a type of sushi called uni. Marine Species Card 17 of 35 Marine Species Card 18 of 35 Sea OGer •  Secondary consumer •  Eats sea urchins, mussels, and crabs •  Lives near the coast •  Bonus fact: A sea o@er’s fur is so thick that it has one million hairs on each inch of its body. Marine Species Card 19 of 35 Orca •  Carnivore •  Different groups of orcas eat different things. Some eat fish, while other eat marine mammals. •  This par>cular orca belongs to a group that eats sea o?ers. •  Bonus fact: Each group of orcas has a disDnct dialect, or language, that they use to communicate. Marine Species Card 20 of 35 Sea Cucumber •  Scavenger •  Eats decaying ma?er on the sea floor. Much of this decaying ma?er used to be plankton, such as diatoms or blue-­‐green algae. •  Bonus fact: When threatened by a predator, sea cucumbers eject their internal organs. This is a decoy that distracts the predator and gives the sea cucumber a chance to escape. Marine Species Card 21 of 35 Garibaldi •  Carnivore •  Eats mussels and crabs •  Lives in kelp forests •  Bonus fact: Garibaldi is the official state fish of California. Marine Species Card 22 of 35 California sheephead •  Carnivore •  Eats urchins, mussels, crabs, shrimp, and sea stars •  Lives in kelp forests •  Bonus fact: All sheephead start off life as females, but then change into males as they grow. Molt shed by a kelp crab Marine Species Card 23 of 35 Kelp Crab •  Primary Consumer •  Eats kelp •  Lives in kelp forests •  Bonus fact: As crabs grow, they get too big for their shells, or carapace. A new carapace grows underneath the old one, which is shed by the crab. This process is called “molDng.” Marine Species Card 24 of 35 Leopard Shark •  Carnivore •  Eats crabs, shrimp, and fish, such as anchovy, rockfish, garibaldi and young California halibut •  Lives on the sea floor in coastal areas •  Bonus fact: Unlike other fish, sharks do not have bones in their body. Instead, carDlage is used to support their body. California halibut can camouflage well with sand on the sea floor. Marine Species Card 25 of 35 California halibut •  Carnivore •  Eats squid and fish, such as garibaldi, rockfish, and anchovy •  Lives on the sea floor in coastal areas •  Bonus fact: As halibut grow into adults, one of their eyes moves across its head, so that both eyes are on the same side of its head. Marine Species Card 26 of 35 Rockfish •  Carnivore •  Eats shrimp, crabs, squid, and fish (anchovy, sardine, and lanternfish) •  Lives in shallow and deep water near the sea floor •  Bonus fact: Some rockfishes can live to be 200 years old. Marine Species Card 27 of 35 Moon Jellyfish •  Secondary consumer •  Eats copepods, ciliates, and diatoms •  Lives in open-­‐water habitats •  Bonus fact: Jellyfish are very hardy organisms that can live almost anywhere in the ocean. They occur in tropical areas and cold regions. They live in very salty water and in ocean waters with li@le salt. A swarm of krill Marine Species Card 28 of 35 Feathery Gills Krill •  Primary Consumer •  Eats diatoms •  Lives in open-­‐water habitats •  Bonus fact: You can tell krill apart from shrimp because krill have their gills on the outside of their body. Gills are a feathery organ that help krill breathe. Marine Species Card 29 of 35 Market Squid •  Secondary consumer •  Eats copepods and krill •  Lives in open-­‐water habitats •  Bonus fact: The largest fishery in California catches market squid. Marine Species Card 30 of 35 Shrimp •  Scavenger •  Eats decaying ma?er on the sea floor. Much of this decaying ma?er used to be plankton, such as diatoms or blue-­‐green algae. •  Lives on the sea floor •  Bonus fact: While shrimp are delicious, many of the ways of catching them can destroy marine habitats. Marine Species Card 31 of 35 White Shark •  Carnivore •  Eats dolphins, anchovy, sardine, lanternfish, and squid •  Seals and sea lions are other items in the diet of these sharks. •  Bonus fact: You are more likely to be struck by lightning than to be killed by a shark. Marine Species Card 32 of 35 Fishermen Using a Purse Seine Net •  Carnivore •  A purse seine net is used to entrap large schools of fish by circling them with the net. •  Catches squid, sardine, anchovy, and tuna Marine Species Card 33 of 35 Fishermen Using Long Lines •  Carnivore •  Long lines can have thousands of hooks for catching fishes •  Catches yellowfin tuna, dolphins, and white sharks •  SomeDmes species that the fishermen do not want to catch get hooked on long lines. These include dolphins and sharks. Marine Species Card 34 of 35 Urchin Diver •  Carnivore •  Catches sea urchins •  Bonus fact: Many of the sea urchins are shipped over to Japan where they are made into sushi. Marine Species Card 35 of 35 Fishermen with a Trawl Net •  Carnivore •  Trawl nets are dragged along the ocean bo@om to catch fish. •  Catches rockfish and California halibut •  Trawl nets can also uproot other animals that live on the sea floor. Pictures for Learning Vocabulary Related to the Roles of Organisms in Food Webs Vocabulary Picture 1 of 12 Vocabulary Picture 2 of 12 Vocabulary Picture 3 of 12 Vocabulary Picture 4 of 12 Vocabulary Picture 5 of 12 Vocabulary Picture 6 of 12 Vocabulary Picture 7 of 12 Vocabulary Picture 8 of 12 Mold Vocabulary Picture 9 of 12 Vocabulary Picture 10 of 12 Vocabulary Picture 11 of 12 Vocabulary Picture 12 of 12 Differences between Food Chains and Food Webs Secondary consumer Primary producer Energy & nutrients Primary consumer Energy & nutrients Food Chain (Open-­‐Water Habitats) Fish Zooplankton Phytoplankton (single-­‐
celled algae that photosynthesizes) Food Chain vs. Food Web 1 of 3 Food Chain (Sea Floor Habitat) Sea oEer Kelp Sea urchins Food Chain vs. Food Web 2 of 3 Secondary consumer Energy & nutrients Primary consumer Energy & nutrients Primary producer Food Web for
the Northern
California
Current
Field et al. (2006)
Food Chain vs. Food Web 3 of 3