Fig. 3. Continuous records of Periophthalmus modestus egg-chamber air P_O2 (black line) and the timing of the male's egg-chamber visits (indicated by impedance signals, grey spikes) in relation to the tidal cycle. Data acquisition began with the day of instrumentation and continued until egg hatching, initiated by the male on a rising tide (blue triangle). The beginning of day zero is set to the time when a burrow was covered by an incoming tide, following which egg hatching occurred. The initial high P_O2 reflects the opening of the egg chamber to air during instrumentation. (A) Record for a burrow regularly covered (blue bars) and uncovered by the tidal oscillation (red lines show the highest tide). (Note: No impedance data for day –3 due to a technical problem.) (B) Record for a burrow located sufficiently high on the mudflat to be continually exposed to air until day zero when the rising tide covered the burrow (blue bar) and hatching occurred (blue triangle).