How ocean acidification works hand-in-hand with warming and other global change stressors to promote toxic Pseudo-nitzschia harmful algal blooms along the West Coast

Toxic harmful algal blooms are an increasing problem globally, and the West Coast of the U.S. is no exception. In particular, massive neurotoxic blooms of the domoic acid-producing diatom Pseudo-nitzschia have recently appeared that are larger, more frequent, longer lasting, and much more toxic than any that have been historically recorded. In recent years, these blooms have caused extensive damage to our Dungeness crab fishery, and they pose an increasing threat to other shellfish and finfish industries. It has become clear that this unprecedented intensification of toxic domoic acid events is very likely linked to ocean environmental change. For instance, research in my laboratory has shown that ocean acidification can benefit the growth and increase the toxicity of many harmful algal bloom species, including Pseudo-nitzschia. At present day atmospheric CO2 concentrations, obtaining enough dissolved CO2from the water to support growth can be a problem for Pseudo-nitzschia, which can thus be “carbon dioxide-limited”, and so it may actually directly benefit from higher CO2 levels. There is a definite potential for future CO2 fertilization of more frequent and more intense toxic algal blooms. However, we are now realizing that to understand and predict how ocean acidification will influence harmful algal blooms, we also need to consider a number of other interacting global change impacts. These other direct and indirect human disturbances include sea surface warming, losses of dissolved oxygen, stratification of the surface ocean, and modification of natural nutrient cycles by urban and agricultural pollution. For instance, in addition to ocean acidification, we have also shown that ocean warming strongly promotes domoic acid production by Pseudo-nitzschia. I will discuss the complex network of interactions between ocean acidification and these many other global change multiple stressors that my lab group is currently working to understand, in order to help predict and perhaps mitigate the tremendously damaging toxic algal blooms that increasingly threaten our coastal fisheries and marine food webs.

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