Harmful Algal Blooms in a Changing World

Mark L. Wells, School of Marine Sciences, University of Maine

Harmful Algal Blooms (HABs) are a very small fraction of naturally occurring phytoplankton blooms globally that can have substantial impacts on human and ecosystem health. These blooms encompass toxic events, where phytoplankton produce toxins that accumulate in the food web, fish-killing events, where the simple presence of certain phytoplankton can lead to massive fish kills, and high-biomass events that lead to hypoxia and anoxia in coastal and shelf waters.  There are indications that HABs have been increasing in their frequency and distribution globally, and that these patterns appear to be consistent with climate change.  However, we lack the information needed to test this hypothesis. Although simple models can predict the control single parameters (e.g., nitrogen) have on HAB organisms, we lack the capacity to integrate multiple stressors and their synergistic interactions. Even less is known about direct competition through allelopathic and other algal species-to-species interactions. For example, the release of domoic acid by toxigenic diatoms increases their competitive success over non-toxic diatoms. Recent workshop findings illustrate how little is known about how projected changes in global environmental conditions will affect the relative success of HAB organisms. New research strategies are needed if we are to determine whether climate change is affecting the frequency and severity of HAB events. Answering this question is critically important because global populations will depend more on the coastal zone for food resources over the next century.