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Title of Longituindal Study: The Effect of Sea Star Body Mass on Amonia Concentration in Seawater
Doug Foster, Cal State University, Northridge.
Question:
How does an increase in the combined body mass of sea stars (Patiria minata) affect the ammonia concentration in
an aquarium?
Standards:
7th Grade Life Science:
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept:
a. Students know cells function similarly in all living organisms
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
a. Select and use appropriate tools and technology (including calculators, comput ers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.
Experimental Design
Five sea stars (Patiria miniata, common name, “bat star”) were divided into three groups and placed into 3 separate aquariums, each containing 1 liter of seawater. The combined sea star body mass of was different for each aquarium. Patira minata (common name: bat star) is a sea star species native to Southern California, having a range extending from Sitka, Alaska, to Baja California.
The ammonia concentration of the water was measured at approximately 6 hour intervals, using
Independent variable
The independent variable was time.
Dependent variables
The dependent variable was the concentration of ammonia in the seawater.
Series
The series was the summed body mass of bat stars. The summed mass was different for each aquarium.
Controls:
An aquarium containing 1 liter of seawater only (no bat stars) served as the control. The temperature ranged from 22-23 degrees C (72-74 degrees F).
Materials:
1- Aquarium Pharmaceuticals International (API) Amonia NH3/NH4 Test Kit (Petco)
4 – Small plastic aquariums, brand Lee’s Critter Keepers; size: small (9.13” X 6” X 6.13”) (23.2 cm X
15.2 cm X 15.6) (Drs. Smith and
Foster)
1- Pocket Digital Balance, Brand: Centech 1000g Digital Scale (Harbor Freight)
4L- Filtered seawater- (Catalina Water from 7 Seas Tropical Fish Store in San Pedro, CA)
5- Bat Stars (Patiria miniata) collected intertidally off of the Palos Verdes Pennisula,CA
( Note: Most aquatic animals produce ammonia as a breakdown product of protein and nucleic
acid metabolism. The kit can be used to measure the ammonia production of other aquatic
invertebrates, fish, some amphibians and some reptiles (turtles).
Procedure
The mass of each bat star was measured prior to placing it into a plastic container filled with 1 liter of seawater. The bat stars were then distributed amongst 3 aquariums such that each aquarium contained a different sum total of body mass. One of the three aquariums contained one bat star, the remaining two aquariums each contained 2 bat stars. A fourth aquarium containing only 1 L of sea water served as a control. The ammonia concentration of all four aquariums was measured at approximately 6 hour intervals using the API test kit. The measurement involves comparing the color of a prepared solution to a color chart (colorimetric analysis). The steps were as follows:
1) Draw 5 ml of water from aquarium
2) Add 8 drops of Rea
gent # 1 (according to the instruction sheet, R1 contains sodium salicylate)
3) Add 8 drops of Reagent # 2 ( sodium hydroxide, sodium hyperchloride)
4) Shake for 5 seconds
5) Wait for 5 minutes
6) Compare the color of the fluid against the color key that comes with the kit.
Additional Notes
The animals were initially observed at approximately 1 hour intervals for signs of stress. When it became clear the ammonia levels were remaining low the observation frequency decreased.
A follow up trial was run with all 5 brittle stars placed in one aquarium. Ammonia levels were measured at approximately 2 hour intervals before and after feeding.
In addition to measuring ammonia, the bat stars were filmed using the application Frameograph using an iPod Touch G4.
Operational definitions: When the fluid color was between options, the higher value was used. Times were rounded to the nearest ½ hour.
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