Download Unlike other marine mammals, the sea otter does not have a layer of

NAME ___________________________________________PER _________ DATE ____________
THE KELP FOREST COMMUNITY
MATERIALS: Colored pencils
BACKGROUND:
Unlike other marine mammals, the sea otter (Enhydra lutris) does not have a layer of blubber
(fat) to help keep it warm. If an otter's fur gets coated with oil or any other substance, the otter
can easily die from cold and exposure.
The sea otter is the largest member of the weasel
family. Southern sea otters typically reach about four feet
in length. Females average 45 pounds, while males
average 65 pounds. Alaskan or northern sea otters can
reach up to 100 pounds.
Sea otters are found in the shallow coastal waters of the
northern Pacific. Their historic range stretched from the
Kurile Islands of Japan, along the coast of Siberia and the Aleutian Chain and down the Alaska
and British Columbia coast to Baja California.
Sea otters are one of the only mammals other than primates known to use tools. Otters use
small rocks or other shellfish to pry prey from rocks and to hammer or pry open their food. They
can dive up to 180 feet when foraging for food. These intelligent animals live in shallow water
and prefer kelp forests, sometimes anchoring themselves in one place by wrapping strands of
kelp around their bodies while they rest.
Sea otters are a keystone species in the kelp forest
ecosystem, eating sea urchins, clams, snails, sea stars,
squid, octopuses and abalone. When present in healthy
numbers, they keep sea urchin populations in check.
When sea otters decline, however, urchin numbers
explode—as does their grazing pressure on bull kelp. The
urchins chew off the attachments keeping bull kelp in
place, causing them to die and float away. This decimates
kelp beds and sets off a chain reaction that depletes the
food supply for other marine animals and in turn causes
their decline.
Urchin Bed - Sea otters prey on sea
urchins, keeping their populations in
balance.
Recent data collected by both the Fish & Wildlife Service
and the U.S. Geological Survey show that the sea otter
population is declining.
The decline may be due to increased predation by killer whales. Killer whales normally don't eat
sea otters because they are too small. The whale's usual food source, Steller sea lions and harbor
seals, have declined drastically in recent years, however, causing the whales to shift to sea otters.
PROCEDURE:
a. Highlight in each population the largest value. This is the peak population size.
b. Calculate the percent by dividing the value given by the peak population size.
c. Graph each population as a percent. The graph is already set up for you. Use a different color
pencil for each population and make a legend.
YEAR
1972
1976
1977
1979
1980
1981
1982
1985
1986
1987
1988
1989
1990
1991
1992
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
POPULATION SIZE
SEA URCHINS
Pounds (millions)
1
0.5
1.5
1
0.5
0.5
0.5
2.5
10
24
31
27
18
16
12
8
6
6
5
3
3
5
4
6
2
1
Percent
SEA OTTERS
Number (x 1000)
75
30
28
26
24.5
24
22.5
6
Percent
-
-
-
Change in Population of Sea Otters
and Sea Urchins in California
80
60
40
20
0
1970
1980
1990
2000
Time (years)
Kelp Bed Canopy Loss in Ventura and
Los Angeles Counties
Population Size (acres)
Population Size
(percent remaining)
100
4000
3000
2000
1000
0
1905
1925
1945
1965
Time (years)
1985
2005
QUESTIONS :
1. What is a keystone species?
2. In the kelp forest, what is the keystone species? What does it eat?
3. What organism feeds primarily on kelp?
4. What is affecting the kelp population rate of growth?
5. What controls the size of the sea otter population?
6. Marine biologists are trying to farm (grow) kelp to increase the amount of kelp.
a. What would you expect to see happen to the sea urchin population? Why?
b. The sea otter population? Why?
7. Is the sea otter population increasing today? What’s affecting the sea otter population? Explain.
8. Why do you think there was a spike in the sea urchin population in the late 80s and early 90s?
9. Why do you suppose the population of sea urchins is declining even though their predators (sea
otters) are declining?
10. What recommendations would you make to help save the kelp forests in California?
11. Create a food chain for the kelp forest community. Be sure to use the following organisms: fish,
kelp, sea urchin, killer whale, and sea otter.