Acoustic characteristics and spatiotemporal distribution of photosynthesis-related sounds in seagrass beds of Li'an Port, Hainan Province, China

The biological component of the ocean soundscape has traditionally been attributed to sounds produced by aquatic animals, with much less known about those generated by plants. In this study, we investigated the acoustic signals produced by seagrass and its epiphytic algae during photosynthesis in a seagrass bed at Li'an Port, Hainan Province, China. Photosynthetic bubbles formed monopole sound sources, and we employed passive acoustic monitoring (PAM) technology at two sites to capture associated acoustic signals. Single pulses were detected and extracted using a neural network. Acoustic signal rates rose during non-photosynthetic periods, coinciding with wave breaking, human activities, or biological disturbances. We then manually checked the signals and removed the pulses from these interference processes throughout the 19-day recording period to specifically focus on analyzing the photosynthesis signals. The acoustic characteristics, including sound pressure level (SPL), duration, peak frequency, and −3 dB bandwidth were analyzed to assess differences between the sites. Photosynthesis-related acoustic signal rates peaked in the afternoon, and its average signal rate showed a roughly parallel trend to that of dissolved oxygen (DO) and temperature. These findings suggest that PAM of photosynthetic bubbles revealed another biological component of the overall ocean soundscape. This approach may advance research on quantifying primary productivity in aquatic systems and promises to serve as a valuable tool for rapid, direct assessment of ecosystem health with capacity for long-term continuous monitoring.