Toribio Ramon A. Hechanova III, Jonathan H. Quiogue, Janvin Jessel A. Cariscal (March 2009)
Philippine Science High School Western Visayas Campus – Department of Science and Technology (DOST-PSHS WVC), Brgy. Bito-on, Jaro, Iloilo City 5000, Philippines
ABSTRACT
Ocean enrichment is one proposed solution to the global problem of high levels of atmospheric carbon dioxide. In the Philippines, there is a plan to dump 500 tons of urea in Sulu Sea. Marine scientists are concerned about the ecological risks posed by urea enrichment and recommended the assessment of its environmental costs.
Urea may affect the reproductive ability of marine broadcast spawners. To investigate the effect of urea on the fertilization and early embryonic development of marine organisms, this study used Tripneustes gratilla L., a well-established model organism for gamete research. The effect of urea on the egg viability of Tripneustes gratilla L. up to 48 hours of exposure (phase 1) and on early egg cell cleavage after momentary exposure (phase 2) was determined. In phase 1, eggs were exposed to 0, 26.1, 51.8 and 100.8mg/L urea and fresh sperm were added to the eggs after 0-, 24- and 48-hour exposure. Egg viability was determined in terms of % fertilization 30 minutes post-insemination. In phase 2, eggs were momentarily exposed to 0, 25.0, 50.0 and 100.0mg/L urea concentrations. The % of egg cells that attained two-cell stage 90 minutes post-insemination was determined.
In phase 1, at 0- and 48-hour exposure periods, the mean % fertilization of the egg cells exposed to urea concentrations was significantly lower than that of unexposed egg cells. At 24-hour exposure period, the mean % fertilization of egg cells exposed to 100.8mg/L urea concentration is significantly lower than in the other concentrations. In phase 2, mean % of two-cell stage embryo was significantly lower for egg cells exposed to urea than that for unexposed egg cells. (One-way ANOVA & post-hoc analysis, a=.05).
Therefore, exposure to urea lowers the percent fertilization of the egg and inhibits the attainment of two-cell stage in the embryo of the sea urchin Tripneustes gratilla L. These may also be true to other marine organisms such as fishes because sea urchins provide a good picture of the important events of fertilization even for vertebrates.