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 supplyof oxygen in water. When embryos are embedded in a gelatinousmatrix, oxygen is supplied by diffusion through the gel, andthicker masses require more gel per embryo. When an adherentmass of eggs lacks a gel matrix, oxygen can be provided fromwater flowing through the open interstices between eggs, andlarger eggs provide larger channels and thus less resistanceto flow. Both types occur intertidally, where they are periodicallyexposed to air. Exposure to air can have a greater effect onoxygen supply via interstices than on supply via gel. Oxygendiffusing in interstices drained of water provides increasedrates of supply to masses of adherent eggs. In contrast, diffusionthrough gel is similar for masses in air and water. Effectsof emersion on desiccation also differ for the two types ofegg masses. Additional gel matrix can reduce salinity changefrom desiccation while enhancing oxygen supply, whereas drainingof interstices, though necessary for oxygen supply, may increaserisk of desiccation.