Meeting Abstract

P2.82  Wednesday, Jan. 5  Effects of Light Exposure on pH Gradients Inside Invertebrate Egg Masses PODOLSKY, R.D.; College of Charleston, Grice Marine Lab podolskyr@cofc.edu

Several groups of marine invertebrates reproduce by depositing clutches of fertilized eggs. The metabolic activity of such dense concentrations of embryos can alter the environmental conditions (e.g., the balance of respiratory gases) under which development takes place. In addition, photosynthetic microorganisms that populate the mass can also change the balance of respiratory gases. An important environmental parameter, pH, is known to be lowered by an increase in CO₂ concentration, which has been implicated in physiological challenges to development including the deposition of calcium carbonate in the larval shell. To understand the role of metazoan embryos and microorganisms in altering pH levels internal to egg masses, I measured pH along radial transects of the balloon-shaped egg masses of the bubble snail Melanochlamys diomedea. Prior to measurements, the masses had been kept under either light or dark conditions in order to allow the concentrations of gases inside the mass to reach steady state. pH was measured along transects radially through the center of the mass using a needle microelectrode while maintaining the light or dark treatment under which the mass had been held. pH dropped consistently in all masses from ambient (8.0) to a minimum of around 6.8 pH units within a few mm of the egg mass surface. Contrary to expectations, gradients were no steeper in dark- than in light-adapted masses, where the latter were expected to benefit from CO₂ uptake by photosynthetic symbionts. This result contrasts with earlier findings that O₂ availability to embryos is significantly enhanced by symbionts in the presence of light. This difference in the effect of light may be a consequence of differences in the solubility of the two molecules or to an unidentified capacity to buffer pH change inside egg masses.