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

Abstract

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 supplied 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 provided from water flowing through the open interstices between eggs, and larger eggs provide larger channels and thus less resistance to flow. Both types occur intertidally, where they are periodically exposed to air. Exposure to air can have a greater effect on oxygen supply via interstices than on supply via gel. Oxygen diffusing in interstices drained of water provides increased 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 matrix can reduce salinity change from desiccation while enhancing oxygen supply, whereas draining of interstices, though necessary for oxygen supply, may increase risk of desiccation.