Lab Activity 2.2
Responding to Changes in Salinity

  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


Some marine organisms such as fishes, reptiles seabirds, and marine mammals are osmoregulators. They are able to maintain an internal salt concentration that is less salty than seawater. Most marine organisms such as invertebrates are osmoconformers. They are unable to regulate their salt content and are more severly effected by changes in the salinity of their environment. In this experiment we will observe the effects of increased salinity on living Daphnia, waterfleas, which normally live in freshwater. Waterfleas are osmoconforming crustaceans and their internal salt content closely matches that of the environment around them. To determine their responses to changes in salinity we will use the animal's heart rate as a measure of its overall condition. By comparing its heart rate at various salinities we will be able to determine the effect of increasing salinity on a waterflea's condition.

Top  Instruction

Study the information, photographs, and graphs in the experiment that follows. Be sure to complete the observations and formulate answers to the questions you're asked.

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 4, pages 78 to 80
Marine Biology Coloring Book None
 

Observing Living Daphnia

Living Daphnia were observed with microscopes by placing the tiny crustacea in water filled depression slides. Each depression slide acted like a tiny aquarium that could be placed on the stage of a light microscope.

Experimental Set Up:

  1. We obtained a culture of the microcrustacea Daphnia and observed it under a dissecting microscope.

  2. We obtained a depression slide and coverslip. With a spoon we transferred a waterflea (Daphnia) to the depression in the slide and filled the depression with water from the culture. We placed the coverslip over the depression capturing the waterflea so that it couldn't swim around.

  3. We observed the waterflea at 35X magnification with a dissecting microscope to become familiar with its anatomy.
 

Observations:

  1. Observe the photograph of the waterflea. Notice its antennae and legs. Their movement establishes feeding currents and helps it respire.

  2. Observe the photograph of the waterflea. Note its heart which is located dorsally, just behind its head and eye.Describe the egg cells.

 

Observing Daphnia Heart Beats

A live Daphnia in a depression slide was examined at high magnification to watch and count its heart beats.

Experimental Set Up:

  1. We set up a compound microscope and focused on the waterflea's heart at 160X magnification.

  2. We removed the slide from the microscope being careful not to disturb the waterflea. We set it on the countertop and allowed it to remain at room temperature for 30 seconds.
 
Observations:

  1. Observe the photograph of the waterflea's heart.

  2. Note the outline of the heart which has been enhanced so you can get a good idea of how it looks.

 

Observing Daphnia in Freshwater

A live Daphnia in a depression slide was examined in freshwater to determine its heart rate.

Experimental Set Up:

  1. We carefully replaced the slide on the microscope, focused on the heart, and videotaped the heart beating. We did not let the waterflea remain on the microscope stage to long before starting the recording to prevent the lamp from heating it up above room temperature.

  2. We determined the heart rate of the waterflea in freshwater by counting the heart beats of the waterflea for 60 seconds and graphed the heart volume versus time.

Observations:

  1. Observe the graph of the waterflea's heart beat in freshwater.

  2. Determine the number of beats per minute.

 

Observing Daphnia in Seawater

A live Daphnia in a depression slide was covered with seawater and examined to determine its heart rate.

Experimental Set Up:

  1. We removed the slide from the microscope and carefully removed the coverslip. We removed the freshwater from the depression with an eyedropper and refilled the depression with seawater (salinity=33 ppt). We replaced the coverslip being careful not to squash the waterflea.
  2. We carefully replaced the slide on the microscope, focused on the heart, and videotaped the heart beating. We did not let the waterflea remain on the microscope stage to long before starting the recording to prevent the lamp from heating it up.
  3. We determined the heart rate of the waterflea in seawater. Count the heart beats of the waterflea for 60 seconds and graphed the heartbeats versus time.

Observations:

  1. Observe the graph of the waterflea's heart beat in seawater.

  2. Determine the number of beats per minute.

  3. How does the waterflea's heart rate in seawater compare to its heart rate in freshwater?

 

Observing Daphnia in Hypersaline Water

A live Daphnia in a depression slide was covered in hypersaline water and examined to determine its heart rate.

Experimental Set Up:

  1. We removed the slide from the microscope and carefully removed the coverslip. We removed the seawater from the depression with an eyedropper and refilled the depression with hypersaline water (salinity=66 ppt). We replaced the coverslip being careful not to squash the waterflea.
  2. We carefully replaced the slide on the microscope, focused on the heart, and videotaped the heart beating. We did not let the waterflea remain on the microscope stage to long before starting the recording to prevent the lamp from heating it up.
  3. We determined the heart rate of the waterflea in hypersaline water. Count the heart beats of the waterflea for 60 seconds and graphed the heart beat versus time.

Observations:

  1. Observe the graph of the waterflea's heart beat in hypersaline water.

  2. Determine the number of beats per minute.

  3. How does the waterflea's heart rate in hypersaline water compare to its heart rate in freshwater and in seawater?


Lab Activity 2.3 Asexual Reproduction