Environmental Drivers Likely Deepening the Impacts of Harmful Algal Blooms

Some HABs produce toxins that are harmful to organisms, while others are nontoxic and deplete the water of oxygen as they decay. Aquatic organisms are vulnerable to HABs, which can clog the gills of marine animals and smother corals, for example; this leads to losses for aquaculture and fisheries industries through the loss of stock, harvest bans, and loss of market confidence. Fish and shellfish kills are dominant in many areas that depend on aquaculture, including East Asia, Southeast Asia, South America, Norway, Russia, the UK, and the US. 

Health issues can arise from HAB-contaminated drinking water, as well as water used for agriculture. Toxins in crops can accumulate to dangerous levels, making them unfit for consumption. Semi-arid regions with intensive agriculture and water bodies with high levels of nutrients are at higher risk. Field workers are also at risk of inhaling toxins when an overhead irrigation system is used. 

HABs could increase the complexity and cost of water treatments and may lead to plant shutdowns. Algae can accumulate in systems that pump in water from contaminated water bodies – including irrigation, desalination, and water treatment, and plant cooling systems – clogging pipes, reducing water flow, accelerating corrosion of infrastructure, and fouling membrane surfaces. The risk of neurotoxins and skin-irritating compounds in the remaining treated water threatens seawater desalination and water treatment plants. Desalination plants had to be shut down for several days in Israel in 2020 and the UAE in 2019. There are over 15,000 desalination plants in more than 150 countries, with around 50 percent in the Gulf region and West Asia; HABs greatly restrict the ability to desalinate water for drinking and industrial use, exacerbating the impact in water-scarce areas. HABs can also negatively impact power generation facilities, particularly those that use water for cooling. The shallow, slow-flowing, and high-temperature waters in cooling and settling ponds, combined with excessive nutrients in intake water or the use of chemicals, create the ideal circumstances for algae to bloom.

The tourism industry is also likely to be impacted. HABs can foul beaches, create unsightly and odorous water conditions, and lead to beach closures, deterring tourists and recreational users. Negative perceptions may linger even after water quality is restored. The 2018 red tide bloom in Florida (US) resulted in an estimated loss of USD 2.7 billion to tourism-related businesses. HABs can also reduce property values near affected water bodies due to diminished water quality, unsightly conditions, and loss of recreational opportunities.  
 

As a complex interplay of factors influences HABs, it is difficult to isolate the specific effects of climate change. Nevertheless, warmer waters and intensifying rainfall do influence HABs by altering key factors in their growth and distribution, like water temperature, salinity, and nutrient availability. Different species of HABs are also influenced by local and regional factors that may be water body and species-specific, making accurate forecasting challenging. 

Some generalizations can be made about the likely amplifying impact of climate change on HAB distribution and severity. With progressive warming, HABs are likely to migrate toward the poles, affecting new ecosystems. Warmer temperatures could also extend the growing season and intensify HABs in areas where temperatures are below those supporting maximal growth. However, temperatures in some areas may increase until they are too high to support HAB growth. Climate change-influenced increases in heavy rainfall could result in more nutrient runoff, promoting conditions favourable to HABs.

Climate change is likely to exacerbate HABs’ impacts across various sectors, ecosystems, and communities, especially in those near coastal and freshwater areas. Costs range from direct damages to indirect effects on industries, tourism and recreation, property values, increased burdens on public health systems and water treatment infrastructure, ecosystem services, and restoration efforts.  

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