Effect of ultrasonic algae control devices on non-target organisms: a review

Abstract

There is an increasing interest in using ultrasonication in controlling algal (cyanobacterial) blooms and biofouling, a physical method with presumably no adverse effects on non-target organisms, such as fish and zooplankton. At the beginning the use of ultrasound (US) to control algae and biofouling has focused on high-power US causing cavitation; however, due to the potential damage to non-target organisms including marine mammals and human divers, high-power US causing cavitation are not used anymore for algae control in natural environment. Current ultrasonic algae control devices use low-power and thus control algae and biofouling by utilising resonance frequencies and the sound pressure caused by a sound wave propagating through a water column. There are only few studies existing on the effect of US on non-target organisms with incomplete information on wavelengths and intensities of US devices. However, we can conclude that non-cavitation US devices used to control algae and reduce biofouling had no adverse health effects on studied fish species with no feeding and behaviour changes noticed. Caution should be taken when installingUS devices in marine locations since they may interfere with communication between sea mammals or may cause adverse effects on fish from subfamily Alosinae, the only known fish able to detect US. The studies dealing with non-cavitation US used to control algae and biofouling on non-target zooplankton have conflicting results from high mortality to no evident effects. Therefore, caution should be taken when using US for counteract algal growth in ponds or lakes, especially in terms of zooplankton and natural balance maintenance.