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 4 / 13 PLOS ONE Photosynthetic oxygen bubble stream sounds from aquatic macrophytes pondweed plant in an aquarium (Photo 2), and that sound was similar to Exemplar 3 below in most ways, including range of peak frequencies. At locations other than Gull Lake, in the presence of macrophytes, we encountered sounds that were qualitatively similar to the sago pondweed POBS, strongly suggesting a shared origin. However, we did not investigate these other sounds further. Gas samples from a bubble stream collected from a plant in the lake, and from the aquar- ium plant, were found to contain c. 100% oxygen, as expected from plant tissues during sunlit conditions. We therefore interpreted the focal sounds as photosynthetic oxygen bubble sounds, for which we suggest the acronym POBS. Photosynthetic bubble stream sounds and corixid stridulations dominated our record- ings, accounting for over 90% of the sounds we recorded. Three sound-producing species of corixids were present at Gull Lake (Cenocorixa dakotensis, Cenocorixa bifida, and Corisella tarsalis) and all were identifiable by their calls. Our identifications were confirmed in aquaria as well as in the field. Corixids were the most abundant aquatic insects in Gull Lake, but other potential sound makers (e.g., some dytiscid beetles) were also present in smaller numbers. Worldwide, more than 7000 aquatic insect species are thought to produce sounds [37], with sound producing taxa also listed by Aiken [29] and corixids with stridulator structures listed

by Hungerford [38]. Aidan Sheppard [unpublished data], in a 2018 study of aquatic hemipterans and beetles in the same location at Gull Lake, dip-netted 380 sound-producing corixids, 233 non-sound producing corixids and other hemipterans, and 27 aquatic beetles. Other aquatic invertebrates encountered frequently during our study included mayfly larvae (Ephemeroptera), midge Photo 1. Aerial (drone) view of Gull Lake shallows, with two researchers for scale. The fine dark reticulations are sections of sago pondweed plants, and a number of methane craters are visible as well. https://doi.org/10.1371/journal.pone.0317424.g001