Acoustic emissions by marine algae during photosynthesis

Coastal underwater soundscapes typically contain signals from soniferous, biological processes. Identifying the sources that contribute to oftentimes acoustically complex soundscapes would facilitate a noninvasive, remote, and volumetrically integrative method to survey underwater ecological state, as has been demonstrated on land. To date the lack of knowledge on these sources has posed a challenge for extracting meaningful ecological information from underwater biological soundscape recordings. We have observed that photosynthesis by macroalgae is an acoustically active process, driven by oxygen bubbles separating from the algal surface and ringing at the Minnaert frequency. The resultant soundscapes correlate with benthic macroalgal cover across ecological gradients on shallow Hawaiian reefs during periods of daylight. Bubble size, production rate, and sound exposure level follow the concentration of dissolved oxygen, which in turn rises and falls with the availability of photosynthetically active radi...