Rising Temperatures, Growing Threat: The Link Between Climate Change and Harmful Algal Blooms

By Vivek Saini 

As climate change intensifies, the proliferation of Harmful Algal Blooms (HABs) poses a significant threat to marine and freshwater ecosystems worldwide. Fuelled by a complex interplay of climatic and environmental factors, these blooms, ranging from microscopic organisms to larger seaweeds, wreak havoc on aquatic environments and pose dire consequences for coastal communities. 

While algae typically form the foundation of food webs, specific conditions trigger the uncontrolled growth of HABs, producing toxins that endanger marine life, from fish to mammals and birds. Infrequent yet severe human illnesses can result from exposure to these toxins. Beyond their toxic effects, HABs disrupt aquatic ecosystems through oxygen consumption, clogging fish gills, and smothering corals and vegetation. Termed harmful algal blooms collectively, these events affect coastal and Great Lakes states in the United States, posing a national concern. The economic impact on communities dependent on fishing and tourism underscores the urgency to understand and mitigate the climatic and non-climatic drivers behind HABs.

What are Harmful Algal Blooms (HABs) 

Harmful algal blooms, commonly known as HABs, manifest when colonies of algae, ranging from microscopic single-celled organisms to larger seaweeds, undergo unchecked growth in marine and freshwater environments. While algae typically form the foundation of food webs, certain conditions can trigger their uncontrolled proliferation. In some instances, these blooms produce toxins threatening the well-being of various marine life, including fish, mammals, and birds. Human illnesses resulting from HABs are infrequent but can be severe and even fatal.

The consequences of harmful algal blooms extend beyond toxicity. Some algae, though non-toxic, consume oxygen in water as they decay, leading to adverse effects on aquatic life. Others create issues such as clogging the gills of fish and invertebrates or smothering corals and submerged aquatic vegetation. The collective events caused by these occurrences are aptly termed harmful algal blooms, or HABs. These blooms impact every coastal and Great Lakes state in the United States, posing a national concern. The repercussions are not only felt in terms of public health and the well-being of marine ecosystems but also resonate economically, especially in coastal communities relying on fishing and tourism.

As climate change progresses and nutrient pollution increases, there is a growing concern that harmful algal blooms may become more frequent and emerge in locations. They were not previously affected. We must deepen our understanding of the mechanisms behind their formation, the conditions that trigger them, and their geographical prevalence. This knowledge is crucial to implementing practical strategies aimed at minimizing the harmful effects of HABs on both ecosystems and the communities that depend on them for their livelihoods.

A Dual Threat to Coastal Ecosystems and Communities

The socioeconomic impacts of harmful algal blooms (HABs) on fishing communities on the U.S. West Coast are significant. The 2015 domoic acid HAB event caused fishery closures and economic hardship, disproportionately impacting fishing workers. Fishers were less likely to recover financially from the event. This highlights the dual threat that HABs pose to coastal ecosystems and communities.

On one hand, HABs can devastate marine ecosystems. They can disrupt food webs, kill fish and marine mammals, and harm habitats. This can have cascading effects throughout the ecosystem. On the other hand, HABs can also have severe social and economic impacts on coastal communities. Fishery closures can lead to job losses, income reductions, and social disruption. Fishing communities often rely on healthy fisheries for their livelihoods and cultural identity.

The 2015 domoic acid HAB event is a stark example of the dual threat that HABs pose to coastal ecosystems and communities. It is crucial to consider both the ecological and socioeconomic impacts of HABs when developing management strategies.

Climatic factors affecting the growth of HABs

The impact of climate change on aquatic ecosystems is profound, particularly evident in coastal waters undergoing progressive warming, acidification, and deoxygenation that are expected to escalate throughout this century. Simultaneously, there is a widely acknowledged scientific consensus indicating an increase in the public health, recreation, tourism, fishery, aquaculture, and ecosystem impacts stemming from harmful algal blooms (HABs) over the past several decades.

HABs, marked by range expansion and heightened frequency in coastal areas since the 1980s, result from a combination of climatic and non-climatic factors, including:

1. Temperature Increase in Water:

Cyanobacteria, responsible for HABs, thrive in warm, sluggish water and are typically prevalent in warmer water temperatures. Consequently, the ongoing rise in water temperature due to climate change is anticipated to amplify the scale and duration of cyanoHABs. Warmer water conditions benefit cyanoHABs in various ways, such as their faster growth compared to other algae in warmer temperatures, efficient migration up and down the water column, and the absorption of sunlight that releases heat, further enhancing their advantages.

2. Salinity Changes:

Climate change predictions indicate potential reductions in freshwater runoff in certain regions due to drought and increased evaporation. These factors may elevate salinity in inland waters, impacting irrigation, harming crops, contaminating drinking water, and facilitating the intrusion of salt-tolerant and marine algae into inland lakes. In some U.S. regions, salt-tolerant algal HABs, known as ‘golden algae,’ have recurrently expanded into lagoons, causing fish fatalities in freshwater lakes since 2000. Additionally, increased runoff from intense rainfall can raise freshwater flows to coastal areas, preventing the mixing of oxygen-rich surface water with deeper layers and creating low-oxygen zones harmful to oxygen-dependent species.

3. Elevated CO2 Levels:

Algae, including cyanoHABs, rely on carbon dioxide for survival. Higher carbon dioxide levels in the air and water can lead to the rapid growth of algae. CyanoHABs, in particular, can float to the water’s surface, utilizing the increased carbon dioxide. Elevated carbon dioxide levels also raise water acidity, influencing competition among algal species and impacting organisms that graze on algae, collectively enhancing the competitive advantage of HAB species.

4. Rainfall Changes and Nutrient Loadings:

Climate change affects rainfall patterns, intensifying both rainfall and drought durations. Increased rainfall results in higher nutrient runoff into water bodies, fueling HABs, as observed in Lake Erie in 2011 and 2015. Extended drought periods allow water bodies to retain nutrients, favoring HAB species that thrive under elevated nutrient conditions. Furthermore, extreme rainfall events and subsequent freshwater flows may flush substantial nutrient loads, freshwater HABs, and associated toxins into estuaries and marine areas, heightening the risk of HAB development or exacerbation.

5. Sea Level Rise:

Scientists predict a one-meter rise in sea level by 2100, expanding shallow, stable coastal waters and providing more favorable conditions for HABs.

6. Coastal Upwelling:

Climate change is expected to alter the timing and intensity of coastal upwelling, where wind pushes warm surface water offshore, allowing nutrient-rich deep waters to rise. This may result in excess nutrients delivered by upwelling, potentially leading to more algal blooms, including HABs, especially when combined with increased nutrient pollution runoff from the land, particularly along the West Coast of the United States.

The negative repercussions of harmful algal blooms extend across various sectors, impacting food security, tourism, the local economy, and human health. As these blooms continue to escalate, there is a pressing need for comprehensive strategies to address both the climatic and non-climatic drivers contributing to their proliferation, safeguarding aquatic ecosystems and the socio-economic well-being of communities reliant on these resources.

References:

1. http://oceanservice.noaa.gov/hazards/hypoxia/
2. https://oceanservice.noaa.gov/hazards/hab/
3. https://www.sciencedirect.com/science/article/pii/S1568988320300792
4. https://www.sciencedirect.com/science/article/pii/S1568988319302045
5. https://www.epa.gov/habs/climate-change-and-freshwater-harmful-algal-blooms
6. Image source: https://www.pexels.com/photo/coastline-with-algal-bloom-water-5006877/

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