Photosynthetic oxygen bubble stream sounds from aquatic macrophytes, and their consequences for acoustic biodiversity inventories and acoustic communication in shallow freshwater settings

PLOS ONE | https://doi.org/10.1371/journal.pone.0317424 April 23, 2025 5 / 13 PLOS ONE Photosynthetic oxygen bubble stream sounds from aquatic macrophytes larvae (Diptera: Chironomidae), and scuds (Amphipoda: Gammarus lacustris), none of which are known or suspected to produce sounds. Fishes in the Gull Lake shallows comprised only emerald shiners (Notropis atherinoides) and brook stickleback (Culaea inconstans); both present in small numbers, but apparently not producing sound despite us closely following numerous fishes with the hydrophone. We did not record any sounds originating from fishes, animals other than corixids (includ- ing swimming and wading birds), or anthropogenic sounds such as boat motors. Boat motor sounds did not propagate into the shallow water even when boats were clearly visible, perhaps because of the dampening effect of the sand substrate, and the wide shallow zone of the lake. The POBS sounds produced by sago pondweed have not been described before, and we therefore undertake to characterise them here. The five recordings we chose as exemplars for the diversity of photosynthetic oxygen bubble stream sounds from sago pondweed are charac- terised as follows, with numerical data presented in Table 1. Exemplar 1 Recorded on July 22, 2023, the first sound (Fig 1) was captured in shallow (<20 cm) water. A bubble stream, visible from above, was the source of the sound produced. Mean syllable length was 221.64 ms, with peak frequencies ranging from 1.6 to 2.6 kHz. Duration and amplitude of

each syllable were consistent for the first four seconds before becoming more muted and less easily distinguished. Frequency also decreased during this period. Audibly, the sound is a peri- odic “quack quack quack” oscillation, slowing down during the second half of the recording. Photo 2. Bubble stream emanating from a bend at the base of a sago pondweed stem. Photographed in a five- gallon aquarium. https://doi.org/10.1371/journal.pone.0317424.g002