Two designs of marine egg masses and their divergent consequences for oxygen supply and desiccation in air

Two common types of egg masses rely on differing routes of supply of oxygen in water. When embryos are embedded in a gelatinous matrix, oxygen is supp lied by diffusion through the gel, and thicker masses require more gel per embryo. When an adherent mass of eggs lacks a gel matrix, oxygen can be pro vided from water flowing through the open interstices between eggs, and lar ger eggs provide larger channels and thus less resistance to dow, Both type s occur intertidally, where they are periodically exposed to air. Exposure to air can have a greater effect on oxygen supply via interstices than on s upply via gel. Oxygen diffusing in interstices drained of water provides in creased rates of supply to masses of adherent eggs. In contrast, diffusion through gel is similar for masses in air and water. Effects of emersion on desiccation also differ for the two types of egg masses. Additional gel mat rix can reduce salinity change from desiccation while enhancing oxygen supp ly, whereas draining of interstices, though necessary for oxygen supply, ma y increase risk of desiccation.