Exploring the use of acoustics in monitoring harmful algal blooms in Alfacs Bay (a Mediterranean lagoon)

Abstract

Harmful algal blooms (HABs) are a special concern in Alfacs Bay, which is an area of high ecological importance and an active aquaculture site in the North-West Mediterranean. Because HAB events are recurrent in the area, much effort has been invested in studying the population dynamics of the species causing them. Between 2007 and 2011, multidisciplinary data have been collected using a variety of physical, optical and direct-sampling methods. Of particular interest here is an AquaDopp (Nortek) profiler that has collected 2 MHz backscattering data over 4 bloom periods. We investigate the connection between variations in water column backscatter and the biomass of the total phytoplankton community, and in particular with the late spring-early summer high biomass bloom of the ichthyotoxic dinoflagellate Karlodinium spp. Are the phytoplankton and the HAB species the source of the scattering, or is it related to activity at another trophic level or other environmental variables? Can these scattering events be used to remotely sense HAB blooms? What are the limitations of the approach?