Lab Activity 9.2
Beachrock Microhabitats

  Directions

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.

  Introduction


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.

Top  Instruction

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.

 
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
 

 

Upper Beachrock

 

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.

 

 

 

Lower Beachrock

 

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.

 

 

Beachrock Surfaces

 

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.

Study Questions:

  1. Develop a species list of seaweeds found on beachrock surfaces.
  2. What generalizations can you make about the types of seaweeds found on beachrock?
  3. How many species are there?
  4. Does one general type predominate?

Click to observe seaweeds

 

Study Questions:

  1. Develop a species list of invertebrates found on beachrock surfaces.
  2. What generalizations can you make about the types of invertebrates found on beachrock?
  3. How many species are there?
  4. Does one general type predominate?

Click to observe invertebrates

 

Study Questions:

  1. Develop a species list of molluscs found on beachrock surfaces.
  2. What generalizations can you make about the types of molluscs found on beachrock?
  3. How many species are there?
  4. Does one general type predominate?

Click to observe molluscs

 

 

 

 

 

Beachrock Crevices

 

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.

Study Questions:

  1. Develop a species list of organisms found in beachrock crevices.
  2. What generalizations can you make about the types of organisms found in beachrock crevices?
  3. How many species are there?
  4. Does one general type predominate?

Click to observe organisms

 

 

 

 

Beachrock Overhangs

 

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.

Study Questions:

  1. Develop a species list of organisms found under beachrock overhangs.
  2. What generalizations can you make about the types of organisms found under beachrock overhangs?
  3. How many species are there?
  4. Does one general type predominate?

Click to observe organisms

 

 

 

 

Beachrock Slabs

 

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.

Study Questions:

  1. Develop a species list of organisms found under beachrock slabs.
  2. What generalizations can you make about the types of organisms found under beachrock slabs?
  3. How many species are there?
  4. Does one general type predominate?

Click to observe organisms

 

 

 

 

Inside Beachrock

 

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.

Study Questions:

  1. Develop a species list of organisms found inside beachrock.
  2. What generalizations can you make about the types of organisms found inside beachrock?
  3. How many species are there?
  4. Does one general type predominate?

Click to observe organisms

 


Lesson 9
Lab Activity 9.1 Beachrock Seashore