A dragnet for toxic algae?

Harmful algal blooms (HABs) are among the most dire ocean-related human health risks. They occur when single-celled algae in the ocean accumulate, often due to interactions between their swimming behavior and the movement and structure of the water column. Often referred to as "red tides," these vast, swirling patches can produce toxins that can cause a range of human health problems, including neurological disorders, respiratory infections, and paralysis.

Given that these blooms pose a direct threat to humans-and to marine life-Dan Ward of Massachusetts-based Ward Aquafarms has been on the lookout for HABs at his shellfish farming sites on Cape Cod. In particular, he's relying on a WHOI-developed solution for real-time detection of HABs in real time in his shellfish beds.

Ward initially contacted WHOI biologist Mike Brosnahan in 2016 after an algal bloom of a species called Pseudo-nitzschia was detected in waters near his shellfish beds. This particular species can cause Amnesic Shellfish Poisoning (ASP) leading to permanent short-term memory loss. Brosnahan had been experimenting with a compact submersible camera system, the Imaging FlowCytobot (IFCB), to detect algal bloom species in the water. The instrument, which WHOI scientists Heidi Sosik and Rob Olsen originally developed for spying on phytoplankton populations, is roughly the size of a scuba tank and easily hangs off a dock or any structure in the water where monitoring is needed.

An Imaging FlowCytobot (IFCB) is pulled up from a shellfish bed at Ward Aquafarms in Falmouth, Massachusetts. The instrument takes up to 12 photos of plankton cells per second, and uses specialized algorithms to identify harmful algal species that produce toxins. (Photo by Daniel Hentz, © Woods Hole Oceanographic Institution)

"The sensor produces hundreds of thousands of images a day, allowing us to detect harmful species that produce toxins or kill farmed animals," says Brosnahan. "And it can stay in the water for many months with basically zero maintenance."

Inside, the IFCB's camera takes photos of individual phytoplankton cells at a rate of up to 12 per second. Image recognition algorithms identify and count the species.

"We can alert shellfish farmers to the presence of these harmful organisms and give them the opportunity to mitigate whatever damage might come from these blooms," Brosnahan says.

At one of Ward's farming sites on the Cape, the submerged camera system sends alerts when critical thresholds are reached for particular species. Ward then turns off the incoming water flow to his nursery, switches the system into recirculating mode to keep toxic water out, and turns on an air system to keep oxygen levels sufficient for the shellfish as he and his crew wait out the bloom.

"Once the threat is gone, we just turn the water back on and we're back in business," Ward says.

Ward isn't the only shellfish farmer who stands to benefit from the solution. Brosnahan and colleagues have begun deploying a region-scale network of IFCBs and other sensors called the HAB Observing Network-New England (HABON-NE). Observations are fed to a central web portal, the WHOI HAB Hub, which presents HAB data within interactive maps and plots for farmers, resource managers, and other stakeholders.

Monitoring data from the HAB Observing Network-New England (HABON-NE) are presented in interactive maps and plots. Shellfish farmers, resource managers, and others can access the information from a central web portal, the WHOI HAB Hub.

The science team aims to grow the network over coming years so it spans from Rhode Island to the Canadian border, demonstrating a functional system prototype that may soon serve the entire U.S. coast.

"IFCB monitoring can make a huge difference for individual farmers," says Brosnahan. "We are working to make the information they provide more accessible so that others can take advantage of it, too."