MODIFIED SEAWATER

3/11/1998

There are four cations needed for normal development in the sea urchin: SODIUM, POTASSIUM, CALCIUM and MAGNESIUM. Use the following formulas to illustrate the need for each of these ions.

All measurements are in grams per liter of artificial seawater. Start with 750 ml of distilled water and add components in the order shown, top to bottom. After all of the salts have been added and dissolved, bring the total volume to one liter (mix until uniform).

	NORMAL	(-) SODIUM	(-) POTASSIUM	(-) CALCIUM	(-) MAGNESIUM
Sodium Chloride	25	59 grams of Choline Chloride*	25	25	27.7
Potassium Chloride	0.7	0.7	0	0.7	0.7
Calcium Chloride * 2H2O	1.4	1.4	1.4	0	1.4
Magnesium Chloride * 6 H2O	4.7	4.7	4.7	4.7	0
Magnesium Sulfate * 7 H2O	6.3	6.3	6.3	6.3	0
Sodium Bicarbonate	0.2	0.2 grams of Potassium Bicarboonate	0.2	0.2	0.2

*Choline Chloride can be purchased from the Sigma Chemical Company cat# C1879.

The pH of normal seawater is between pH 8.0 and 8.3

Removing anions can be more difficult, but…..

Zero Sulfate - substitute an additional 5.2 grams of magnesium chloride * 6H2O for the magnesium sulfate * 7H2O

Zero Bicarbonate - Boil and cool (covered) a little over one liter of distilled water (removes the CO2 from the water). Mix up the seawater you want without the sodium bicarbonate. Keep stirring to a minimum and use a well stoppered glass bottle. This seawater will not last (covered, a few hours), as it picks up CO2 from the air very quickly.

Zero Chloride - The most common substitute for chloride is nitrate. This is not perfect, but can be tried. Most nitrates support rapid oxidation (gunpowder). Use care to insure the jar does not go missing, hmm. The formula becomes:

36.4 grams of sodium nitrate
1.0 grams of potassium nitrate
1.6 grams of calcium nitrate OR 2.2 grams of calcium nitrate * 4H2O
4.3 grams of magnesium nitrate * 2H2O OR 5.9 grams of magnesium nitrate * 6H2O
6.3 grams of magnesium sulfate * 7H2O
0.2 grams of sodium bicarbonate

QUESTIONS

What happens to fertilization in each of the variations of seawater? Is sperm behavior affected?. Does the egg fertilize? Is a fertilization membrane raised? Does it look normal?
What happens to development in each of the variations of seawater? Look for timing, morphological and behavioral changes.
Can the embryo be "rescued" by putting it back into normal seawater? Is there a time limit to rescuing?
Contrast the effects on sea urchins with what happens in human physiology [library research] when an ion is missing.
BEYOND BEYOND - what happens when heavy metals, such as iron, zinc or copper are missing or are present in too high of a concentration? Normal seawater from the ocean has iron, zinc and copper (as do some commercial "Instant Ocean" formulas), but the above "normal" formulas do not. How do you remove heavy metals from seawater? [library research, see chelators] Here is a link to ALL of the components in sea water.

S.U.E. - CONTENTS