Field application and validity of a red-tide acoustic sensing system (RASS) for monitoring and alerting of harmful algal blooms (HABs) in fish cage farm

Abstract

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 July 26th to 6th August 2018, the dinoflagellate Cochlodinium polykrikoides was the most abundant HAB species across all locations. A standard curve between the relative received acoustic intensity (dB) as measured by RASS and cell densities of HAB species was constructed (R2 = 0.846) and was successfully applied to quantify the HAB cell density. The dB values noticeably increased from 25th July 2018 and decreased from 1st August. The dB values corresponding to warning level of HABs (≥ 100 cells · mL-1) were not measured after 5th August. The highest 22 dB was recorded on 29th July, which corresponded to 2,782 cells mL-1. To evaluate the efficacy and accuracy of the RASS, a significant correlation (R2 = 0.997) between HAB cell abundance and backscattered acoustic signals was conf