Mario Sengco, a postdoctoral investigator in the WHOI biology department, knows a lot about clay. As a biologist, that may seem extraneous to his work with harmful algal blooms (HABs), but it turns out that clay is the key ingredient in a recipe that the Koreans, Chinese, and Japanese have been using for a decade to manage and control red tide.

Sengco, who came to the MIT/WHOI Joint Program in Applied Ocean Science and Engineering to work with Don Anderson, one of the world’s leading experts on HABs, successfully defended his Ph.D. thesis in August 2001. Sengco had just begun his graduate work when Anderson learned about the use of clay as a HABs mitigation tool by Asian colleagues in the mid-90s and Sengco was intrigued by the concept.

Clay, mixed with seawater, is sprayed into the water column, where the clay particles bind with harmful algae organisms and then sink to the bottom. In mesocosm experiments, the aggregate mixture is collected and removed from the site and transported back to the laboratory for analysis.

In laboratory experiments designed to mimic field conditions, results showed that clay can remove 80–90 percent of the toxins in 2-hour treatments. "While this knocks the remaining population down to lower levels," explains Sengco, "we wonder, from a practical perspective, is 80–90 percent removal enough? Do we re-treat to get even lower levels?"

Clay used in the experiments is native to the U.S., and different clays have been identified for their success at removing cells from each toxic algae tested. These include Alexandrium tamarense (the cause of Paralytic Shellfish Poisoning or PSP in the Northeast), Karenia brevis (a red tide that routinely effects Florida waters), Aureococcus anophageffrens (a brown tide organism), and Pfiesteria piscicida (the dinoflagellate associated with fish kills). Interestingly, the use of clay does not remove co-occurring species at the same efficiency with which the algal cells and certain algal toxins are removed.

Sengco says the use of clay to mitigate HABs is used routinely in Asia, primarily for aquaculture operations, which supply approximately 30 percent of the region’s fish. In the U.S., the concept has yet to catch on, due in large part to environmental concerns such as water quality. Such concerns are being looked at now, by the Anderson lab at WHOI and their collaborators at Mote Marine Laboratory, the U.S. Environmental Protection Agency laboratory in Gulf Breeze, Florida, and Dalhousie University. Much of the work has been funded by the ECOHAB project (Ecology of HABs), with support from NOAA, EPA, NSF, and Sea Grant.

Sengo knew even as an undergraduate at Southampton College that he wanted to work with HABs, yet his passion outside of his work is music: he is both a singer and a pianist. Currently, he is compiling a repertoire of early sacred music to be performed with a chorale group in local churches.

—Tracey Crago, WHOI Sea Grant