Field application and validity of a red-tide acoustic sensing system (RASS) for monitoring and alerting of harmful algal blooms (HABs) in Korean coastal waters

Globally, harmful algal blooms (HABs) caused by marine phytoplankton pose a significant threat to human health and result in enormous economic loss. Many strategies have been implemented for their detection, management, and control. One such instrument is the red-tide acoustic sensing system (RASS) which utilizes a backscattered acoustic signal to detect microalgal cells in the water column, proving to be a cheap and easy tool for the HABs detection. In the current study, five RASSs were deployed at fish farms located in HAB-occurring areas of South Korea during the summer of 2018, and their performance examined for the HABs detection. From 26 July to 6 August 2018, the dinoflagellate Cochlodinium polykrikoides was the most abundant HAB species across all locations. A standard curve between the relative received level (RRL) of acoustic intensity as measured by RASS and cell densities of HAB species was constructed ( R 2 = 0.846) and was successfully applied to quantify the HAB cell density. The RRL values noticeably increased from July 25, 2018 and decreased from August 1. The RRL values corresponding to warning level of HABs (≥ 100 cells mL −1 ) were not measured after August 5. The highest 22 RRL was recorded on July 29, which corresponded to 2,782 cells mL −1 . To evaluate the efficacy and accuracy of the RASS, a significant correlation ( R 2 = 0.997) between HAB cell abundance and backscattered acoustic signals was confirmed. Results from our study show that the RASS can produce accurate, real-time bloom data, providing significant advantages for the warning of HABs.