Detection of toxins and harmful algal bloom cells in shellfish hatcheries and efforts toward removal

As the start of the supply chain for the aquaculture industry, hatcheries are a crucial component in the success of oyster and northern quahog (hard clam) aquaculture on the East Coast of the US. Intermittent failures in hatchery production slow industry growth and reduce profits. To begin investigations into the possible role of algal toxins in hatchery production failure, post-treatment hatchery water from one research and four commercial hatcheries in lower Chesapeake Bay, USA, was sampled for (1) toxin presence and (2) harmful algal bloom (HAB) cell enumeration. Overall, seven toxin classes, likely produced by six different HAB species, were detected in post-treatment hatchery water, despite a lack of visually identifiable HAB cells within the facility. Toxins detected include pectenotoxin-2, goniodomin A, karlotoxin-1 and karlotoxin-3, okadaic acid and dinophysistoxin-1, azaspiracid-1 and azaspiracid-2, brevetoxin-2, and microcystin-LR. In a second, more targeted study, two batches of source water were followed and sampled at each step of a water-treatment process in the VIMS Aquaculture Genetics and Breeding Technology Center research hatchery in Gloucester Point, Virginia, USA. Two treatment steps showed particular promise for decreasing the concentrations of the three toxins detected in the source water, 24-h circulation through sand filters and activated charcoal filtration. Toxin concentrations of pectenotoxin-2, 3.53 ± 0.56 pg mL⁻¹, okadaic acid, 6.14 ± 0.69 pg mL⁻¹, and dinophysistoxin-1, 1.88 ± 0.0 pg mL⁻¹, were low in the source water. The sand filtration step decreased these concentrations by 49–62%. Activated charcoal filtration subsequently brought the concentrations down to <0.5 pg mL⁻¹, successfully removing another 87–99% of toxins from incoming water. With toxin breakthrough now documented in commercial hatchery facilities during non-bloom conditions, future studies are needed to investigate breakthrough and water-treatment options during more-intense bloom conditions, as well as the potential interactions of algal toxins with other stressors in a potentially multifactorial etiology underlying hatchery production failures.