Effect of yellow loess on clearance rate in seven species of benthic, filter-feeding invertebrates

Attempts have been made, especially in Asia, to displace harmful algal blooms (HABs) by spraying ‘china clay’ and ‘loess’ over affected coastal waters. The impact of this technique on benthic communities and processes is not known. We examined the effects of yellow loess on clearance rates of the benthic, filter‐feeding invertebrates, Crassostrea virginica (Gmelin 1791), C. gigas (Thunberg 1793), Mytilus edulis (Linnaeus 1758), M. trossulus (Gould 1850), Argopecten irradians (Lamarck 1819), and Crepidula fornicata (Linnaeus 1758). An Obelia species of hydroid was also studied and the percent time open was analysed. Depletion rates were measured using a range of loess concentrations suspended in culture with unicellular algae (Rhodomonas lens) in 0.45 μm filtered seawater. The effects of loess on clearance rates and behaviour were species‐specific. C. virginica was not impacted until clay concentrations reached 1.0 g L^?1, while A. irradians showed a significant decrease at 0.01 g L^?1. M. edulis showed a significant decrease in clearance rates at the 1 and 10 g L^?1 concentrations. For hydroids, the percent time open was significantly lower than the control at 0.01, 0.1, and 10 g L^?1. We clearly demonstrate that loess has a significant negative impact on filter‐feeding invertebrates. The use of clay as a strategy for mitigation of HABs should be approached with extreme caution. While the control of active blooms may eventually be possible, it may not necessarily be an environmentally advisable or responsible approach to dealing with HABs.