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Investigation
2
A Close Look at Monterey Bay National Marine
Sanctuary
Activity Learning Objectives
Standards Geography Standard 1 Science Standard Develop understanding of populations and ecosystems |
Activity:
Conducting A Transect Along the Seafloor:
NOAA's Monterey Bay National Marine Sanctuary
Guiding
Question What if you were to conduct a horizontal transect in Monterey Bay
National Marine Sanctuary, based upon the habitat types along your
transect, what species would you expect to find? (See
Background.) Materials Monterey Bay Sanctuary Bathymetric
Chart, one for each group Metric ruler Graph paper with x- and y-axis Access to the Internet
(optional) Discussion The information for this activity may
be substituted with that from another
sanctuary. For example, the Florida Keys
National Marine Sanctuary website has
information about the coral reef habitat.
Check out http://www.fknms.nos.noaa.gov. MBNMS contains one of the world's most
geologically diverse and complex seafloors and
continental margins. The MBNMS is located on a
plate boundary which separates the North American
Plate from the Pacific Plate, and is marked by the
San Andreas fault system. This is an active
tectonic region with common occurrences of
earthquakes, submarine landslides, flood discharges
and coastal erosion. It is also a region of
extensive natural and economic resources. Coastal
topography varies greatly, encompassing steep
bluffs with flat-topped terraces and pocket beaches
to the north; large sandy beaches bordered by cliff
and large dune fields mid-sanctuary; and
predominately steep, rocky cliffs to the south.
Low-to high-relief mountain ranges and broad,
flat-floored valleys are prevalent farther inland.
(From Geology section of MBNMS Site
Characterization at website: http://montereybay.nos.noaa.gov/sitechar/geol2.html#2b) Procedure: Give each student a copy of the MBNMS
Chart. Discuss with your students the
different features on the map (contour
lines reveal different seafloor features
such as the continental shelf, canyons,
seamounts, and banks). Discuss how
geologists create these maps. (See below.)
What are some ways scientists might use
these maps? (Map data allows us to get a
picture of the seafloor & its
habitats. This tells us a lot about what
plants and animals live there). Explain to students that scientists
conduct transect studies as one way to
characterize the geological, physical, and
biological characteristics of an
ecosystem. Tell students that they are
going to plan a research cruise in the
Monterey Bay Sanctuary using an underwater
submersible. Please see "Meet DeepWorker" background
information. Have students select a horizontal transect
on their maps that they would be interested in studying.
How do you determine the length and depth of a transect?
The transect should be a straight line from one point on
the map to another. Using a ruler, have each student draw
a straight line on their map to indicate the location of
the transect. To help illustrate the underwater
topography along a transect, have students
make profile charts. On a separate piece
of paper, have them create a "T" table:
one column for distance from the starting
point of their transect (Point A) and one
for depth of the seafloor. Then have them
collect data at every centimeter along
their transect using the scale 1cm = 1 km.
For example, measuring one centimeter on
the ruler from Point A (which is equal to
one kilometer from the starting point of
their transect), the contour line
indicates depth is 25 meters. At two
centimeters (or two kilometers from Point
A), the depth is 30 meters. (See following
example). Once students have collected data along
their transects and created data tables,
have them create profile charts to show
the underwater topography. If computer
graphing capabilities are not available,
hand out graph paper and have students
title and label their graphs: distance
(km) along the bottom or X axis, and depth
increments (m) along the side or Y axis.
Students can refer to their data tables
for ranges of values. Have students use their data tables to
plot the points on their profile charts,
then draw a profile by connecting the
points on the chart. Give each student a copy of the
Benthic Habitat Types handout. Have
them determine what kinds of sediments
they would find along their transects and
indicate these on their maps. Encourage
students to ask questions about their
findings; for instance, "Where did these
sediments come from?," "How did they get
here?," "Why are they distributed as they
are in different zones?" Students may not
have answers to these questions, but
asking them is an essential part of doing
science and is the first step in
scientific inquiry. For more information,
refer to the book "Natural History of
Monterey Bay National Marine
Sanctuary." Give each student a copy of the
Animal Species handout. Based on
the sediments found along their transects,
what species would they expect to find?
What is their reasoning to support these
expectations? One of the fishes inhabiting
NOAA's Monterey Bay National
Marine Sanctuary is the center of
study for an Expeditions
investigation. Rockfish
(Sebastes spp.) congregate
in particular habitats in MBNMS.
A related species, the Redfish
(Sebastes fasciatus)
inhabit similar areas in NOAA's
Stellwagen Banks National Marine
Sanctuary. By comparing the day
and night habits of these two
fish, scientists hope to find
relationships between them which
might prove useful when making
decisions to best protect their
populations. If you have access to the Internet,
have students refer to the Sustainable
Seas Expeditions website (http://www.sustainableseas.noaa.gov
and http://www.nationalgeographic.com/seas)
to follow the research being conducted in
Monterey Bay National Marine Sanctuary.
What species are the Sustainable Seas
Expeditions researchers finding? How do
these findings compare with the
predictions made by students? Have students write a detailed
description of their findings. If they
were able to follow the Sustainable Seas
Expeditions research project on the web,
have them draw conclusions about their
predictions and the actual findings. In Most of our knowledge about seafloor
topography comes from soundings: sending
sound waves into the water and measuring
the time it takes for them to bounce off
the ocean floor and return. From these
soundings, scientists can create a map of
the seafloor. The device used to send sound waves is
called an echo sounder, or sonar. Towed
behind a ship, it bounces about 120 narrow
beams of sound, also called "pings," off
the seafloor several times per second.
Another instrument collects the sound that
echoes back. The ship passes back and
forth over a given area, much the way you
mow a lawn, sending these many beams of
sound as it goes. A computer on board the
boat calculates the depth based on the
time it takes for the echo of the beam to
return to the surface. Sound travels
through the ocean at an average speed of
1,460 meters (4,800 feet) per second.
(Sound travels about five times faster
through water than it does through air.)
To calculate the depth, divide the total
amount of time it takes for a ping to hit
the bottom and bounce back by two. (You
divide by two because the total includes
the trip down and back.) Then multiply
that figure by 1,460. For instance, if it
takes two seconds for sound to return to
the ship, the water must be 1,460 meters
deep. At the same time, the sonar gathers
information about the composition of the
ocean floor by measuring the strength of
the returning signal. For example, mud absorbs sound,
therefore a muted echo indicates a muddy
bottom. A strong echo indicates a rocky
bottom. Scientists supplement these sonar
images with videos, still photographs, and
samples. For more information on seafloor
mapping, see: http://sustainableseas.noaa.gov/missions/channel2/background/sonar.html a PDF version of these images can be found in the fullcurr.pdf
document (2.7mb)
As a result of extensive studies of the seafloor
in Monterey Bay National Marine Sanctuary, much is
known about its topography and sediment types.
Sediment type is one of many factors that define
the kinds of algae and animals living in a
particular area. By knowing these sediment types,
and the habitats preferred by different species,
scientists can predict what organisms they might
find in an area. Using underwater submersibles and
other scientific equipment, scientists can compare
their predictions with actual findings.
Transect in Monterey Bay
National
Marine Sanctuary
Discuss with students the relationships
among the organisms, their physical
surroundings, and their geographical
location. What physical conditions does
each organism favor? Does the organism's
predators and prey favor the same
conditions? What kinds of patterns can be
seen among organisms, physical conditions,
and their geographical location?
Monterey Bay Sanctuary Bathymetric Chart
Common
Name: Cold seep
clams
Prey: demersal
fish, crustaceans,
mollusks, echinoderms,
worms, also scavenges on
carcasses
Prey: small
fish, zooplankton
(especially copepods),
amphipods, mysids,
shrimps, worms
Prey:
Eats small crustaceans,
algae, and sometimes
worms and molluscs.
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Last modified on: Jan 15,
2000