Harmful algal blooms (HABs) are a major environmental problem in all 50 US states and nearly every country around the world. Best known as “red tide,” HAB events are capable of imposing severe impacts on human health, aquatic life, and ecosystems. Because environmental impacts to aquatic ecosystems can be as large and significant as those associated with chemical contamination, HABs should be included routinely as a contaminant of potential concern when monitoring and assessing the impact of anthropogenic activities on aquatic ecosystems. The economic impact in the US alone is considerable. According to Hoagland and Scatasta (2006), the cost of coastal HAB events is at least $82 million/y with the majority of the impact on the public health and commercial fisheries sectors. The National Centers for Coastal Ocean Science believes the costs are far greater due, in part, to the lack of information about individual events, unquantified economic effects of environmental impacts, and sociocultural impacts such as loss of cultural practices and values, increased reliance on social services, decreased recreational opportunities, and shifts in livelihoods. The ecological impact can be devastating. HAB events are capable of generating natural toxins that can cause large-scale mortalities of fish, turtles, birds, and aquatic mammals (e.g., dolphins, manatees, and whales) (Landsberg 2002). HAB events are triggered by sudden increases in populations of diatoms, dinoflagellates, and cyanobacteria (i.e., blue-green algae); their adverse effects can be direct (i.e., poisoning via the production of neurotoxins [e.g., cyanotoxins], asphyxiation via disruption of gill tissues, or asphyxiation from O2 depletion in the water column), or indirect (i.e., ingestion of food contaminated with algal toxins, loss of top predators) (Hallegraeff 1993). Terrestrial animals such as dogs and cattle, as well as humans, can also be affected by drinking water or eating food containing algal toxins, and the aesthetic impacts can be immense (Jacobs 2013). HABs are global phenomena that are not restricted to any specific geographic regions. They are increasing in frequency, intensity, and duration in freshwater, transitional (e.g., estuarine), and marine environments (Pavagadhi and Balasubramanian 2013; Quiblier et al. 2013; Wetz and Yoskowitz 2013). For example, an unusually large, long-lasting HAB in 2015 shut down shellfish fisheries along the west coast of North America (http://phys.org/news/2015-06-massive-algal-bloom.html). There is no single environmental condition that triggers a HAB event. In some cases, HABs appear to be caused by increased anthropogenic loadings (e.g., the release or accumulation of excessive nutrients, iron, and other essential elements) into fresh and coastal waters; in other cases, HABs result from natural factors including coastal upwelling, El Niño events, and inputs of wind-borne, iron-rich dust from the Sahara and other desert areas (Moore et al. 2008). Co-occurrence of HAB events with increasing surface water temperatures, ocean acidification, and changes to upwelling, precipitation, and evaporation patterns suggests that global climate change also may be a contributing factor (Dale et al. 2006; Moore et al. 2008; Jarvie et al. 2012). My personal experience with HABs, aside from exercising caution in eating coastal shellfish, includes a coastal marine pulp mill in Alaska (United States) associated with extensive fish mortalities, and a coal mine in Alberta (Canada) linked to the deaths of a dog and 2 cows that drank the water from a tailings pond. In both cases, regulators and the public assumed that the primary culprit was one or more chemical contaminants in the effluent. A great deal of time and effort was spent investigating these “usual culprits” before any thought was given to the possibility of HABs. The fish, dog, and cows all died from HAB neurotoxins. The coal mine now monitors for the presence and abundance of potentially harmful algae, as do other mines in the region; however, this is not yet common practice for anthropogenic discharges to aquatic ecosystems. It should be. To date, ecotoxicologists, aquatic ecologists, and other professionals involved in contaminant monitoring and assessment rarely consider the possibility of a biological condition as the cause of environmental damages or poisoning of wildlife or livestock. HABs are not typically listed as contaminants (or stressors) of potential concern in ecological or human health risk assessments. Chemicals are the usual suspects, for example, in agricultural run-off, effluent discharges, sediments, and storm water. We should no longer view the environment narrowly and need to adopt a wider view that includes serious consideration of biological contamination. HABs, in particular, need to be considered routinely in ecological and human health risk assessments involving the aquatic environment. More research is needed to better understand how and why HABs occur and to identify the relationships between physical and chemical conditions and biological interactions. There is evidence, for example, that selective feeding by zooplankton on nontoxic algae may be a mechanism facilitating the formation of certain HAB events (Scotti et al. 2015). The effects of HABs on aquatic ecosystem function and services should be included in assessments of coastal and freshwater environmental management planning, with emphasis on reducing their occurrence, intensity, and ecological impacts. There is ample evidence indicating that HABs are becoming a significant global environmental problem. The time has come to afford this biological phenomena its due consideration as a globally persistent and increasingly problematic contaminant of potential concern. Peter M Chapman Senior Editor Integrated Environmental Assessment and Management North Vancouver, British Columbia, Canada

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