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Lab Activity 9.2
Beachrock Microhabitats
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Directions
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Study
the instructional material below. Be sure to click on each of the photographs
for an enlarged view in a separate window. The
larger version is necessary to complete the assignment.
It opens in a separate window which can be resized by grabbing the bottom
right corner and dragging it. It
can also be moved by
grabbing the top heading bar and dragging it.
Be sure to close the extra window by using the X in IBM, or the close box
in MAC when you are finished using them. |
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Introduction
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Marine
biologists have found rocky shores convenient sites to study the interactions
between organisms and their environment. Rocky intertidal organisms live
in an environment that has both terrestrial and marine aspects. They have
unique adaptations that allow them to survive in this in between world.
Each species lives within a specific range of microhabitats that provide
for its needs. In this lab you will study a subtropical, rocky, intertidal
reef located in the Northern Gulf of California. Your studies will include
an examination of the basic biotic and abiotic characteristics of this environment.
You will consider the effects of habitat heterogeneity on the distribution
of the benthic flora and fauna. In this particular lab activity you will
study the biota associated with limestone, beachrock microhabitats. |
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Instruction
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Study
the information and photographs in the exercises that follow. Click the
link and use the Checklist of
the Biota of Beachrock Microhabitats to record and keep track of the
species you find in each of the beachrock microhabitats described below.
Copy the checklist into your notebook or print the checklist and add it
to your notebook. Check off the species you find in each microhabitat as
you study the biota. Use the checklist to answer the study questions. Be
sure to write the answers to the study questions in your notebook.
Be sure
to write about what you are learning in the lab section of your notebook.
You will be expected to answer questions about the lab activity during
the lab self test and lab quiz. It helps to have your text and coloring
books open beside you for support.
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Supporting
Information |
Refer
to the Assigned Readings Below: |
Marine
Biology Textbook |
Chapter
11, pages 236 to 244 |
Marine
Biology Coloring Book |
Plate
3 to 6 |
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Upper
Beachrock
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Observations:
The beachrock lying
close to the sandy beach is located at tidal heights between +1
and +2 feet. This beachrock is inhabited by a different association
of organisms from that located lower in the intertidal. The upper
beachrock is at greater risk of drying completely during spring
tides and experiences greater temperature changes than the lower
beachrock.
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Lower
Beachrock
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Observations:
The beachrock lying
close to the low tide line is located at tidal heights between -1
and +1 feet. This beachrock is inhabited by a different association
of organisms from that located higher in the intertidal. The lower
intertidal beachrock is exposed to the air for short periods of
time during spring tides only.
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Beachrock
Surfaces
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Observations:
The surfaces of the
beachrock are inhabited by a variety of seaweeds and invertebrate
animals. In general the amount of living material associated with
these surfaces increases seaward and is greatest below the 0 tidal
level. The numbers of species (diversity) also increases in a seaward
direction.
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Study Questions:
- Develop a species
list of seaweeds found on beachrock surfaces.
- What generalizations
can you make about the types of seaweeds found on beachrock?
- How many species
are there?
- Does one general
type predominate?
Click
to observe seaweeds
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Study Questions:
- Develop a species
list of invertebrates found on beachrock surfaces.
- What generalizations
can you make about the types of invertebrates found on beachrock?
- How many species
are there?
- Does one general
type predominate?
Click
to observe invertebrates
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Study Questions:
- Develop a species
list of molluscs found on beachrock surfaces.
- What generalizations
can you make about the types of molluscs found on beachrock?
- How many species
are there?
- Does one general
type predominate?
Click
to observe molluscs
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Beachrock
Crevices
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Observations:
Crevices in the beachrock
provide added protection from environmental hazards including temperature
extremes, drying, and predation. The shade inside beachrock cracks
creates a microhabitat that is cool and moist. The tight spaces
make it difficult for predaceous animals to manipulate or remove
prey.
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Study Questions:
- Develop a species
list of organisms found in beachrock crevices.
- What generalizations
can you make about the types of organisms found in beachrock crevices?
- How many species
are there?
- Does one general
type predominate?
Click
to observe organisms
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Beachrock
Overhangs
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Observations:
Beachrock overhangs
are produced by erosive activities that undercut the rock platform
leaving suspended visors of rock. The lack of sunlight under the
visors makes it difficult for seaweeds to survive. This makes it
easier for sessile animals to establish themselves by reducing competition
for a space to anchor to the rock and grow.
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Study Questions:
- Develop a species
list of organisms found under beachrock overhangs.
- What generalizations
can you make about the types of organisms found under beachrock
overhangs?
- How many species
are there?
- Does one general
type predominate?
Click
to observe organisms
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Beachrock
Slabs
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Observations:
Beachrock slabs are
produced by erosive activities that completely undercut the visors
of rock so that they colapse onto the rock platform. The slabs can
be moved by large waves but since they are flat they resist being
overturned. The lack of sunlight under the slabs makes it impossible
for seaweeds to survive. This makes it easier for sessile animals
to establish themselves by reducing competition for a space to anchor
to the rock and grow.
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Study Questions:
- Develop a species
list of organisms found under beachrock slabs.
- What generalizations
can you make about the types of organisms found under beachrock
slabs?
- How many species
are there?
- Does one general
type predominate?
Click
to observe organisms
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Inside
Beachrock
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Observations:
The beachrock is
soft and held together by calcium carbonate cement. As such it is
subject to chemical and biological weathering. Rain falling on beachrock
at low tide will dissolve the calcium carbonate enough to form tiny
pits in its surface. These pits can be occupied by the larvae of
boring species which can, to varying degrees, enlarge the cavities
by mechanical abrasion and by the secretion of minute amounts of
acid that will further dissolve the carbonate cement. Many boring
species occupy the same cavities throughout their lives enlarging
them until they die. Borings left after the deaths of the borers
may then be used as homes by non-boring species. The beachrock is
riddled with bored cavities and these small spaces are another microhabitat.
Inside the cavities conditions are cramped, dark, cool and wet.
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Study Questions:
- Develop a species
list of organisms found inside beachrock.
- What generalizations
can you make about the types of organisms found inside beachrock?
- How many species
are there?
- Does one general
type predominate?
Click
to observe organisms
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