Dynamics and Ecological Impacts of Harmful Algal Blooms

Harmful algal blooms (HABs) arise when particular microalgal species proliferate rapidly in aquatic systems under favourable conditions, notably elevated nutrient loads, thermal stratification and light availability. Physical drivers such as upwelling, circulation and water‐column stability interact with biological traits—motility, cyst formation and allelopathic interactions—to determine bloom onset, duration and collapse. Climate‐driven shifts in temperature, acidification and deoxygenation are altering bloom phenology and expanding the geographic range of toxin‐producing taxa. Toxins released by bloom events, including neurotoxins and hepatotoxins, can cascade through food webs, causing fish mortalities, shellfish contamination and wildlife poisoning, with knock‐on effects on fisheries, aquaculture and public health. At the ecosystem level, HABs modulate carbon and nutrient cycling by influencing sedimentary remineralisation, oxygen demand and microbial community succession. Socio‐economic impacts range from fishery closures and tourism losses to healthcare costs. A deeper understanding of bloom dynamics is essential for forecasting events, evaluating mitigation strategies and safeguarding ecosystem services in a changing climate.

Research from Nature Portfolio

Recent studies have shown that domoic acid, a potent neurotoxin, not only affects planktonic and benthic fauna but also restructures nitrogen cycling in coastal sediments. Under toxin exposure, the abundance of genes driving denitrification and anammox declines, deterministic assembly of microbial communities intensifies and nitrogen removal processes are inhibited. This highlights cascading effects on broader biogeochemical cycles.

Investigations into complex toxin–pollutant mixtures during a prymnesium bloom revealed that natural phycotoxins and anthropogenic organic micropollutants interact synergistically to heighten neurotoxicity. In vitro assays demonstrated that B-type prymnesins dominate mixture toxicity in aquatic organisms and human cell lines, while trace micropollutants contribute to subtle potentiation. Such findings underscore the need to consider combined stressors in toxicity risk assessments.

Dynamics and Ecological Impacts of Harmful Algal Blooms publication trend

The graph below shows the total number of articles in dynamics and ecological impacts of harmful algal blooms across all publications each year (not limited to Nature Index journals).

Technical terms

Eutrophication: Enrichment of water bodies with nutrients (nitrogen and phosphorus) that fuels excessive algal growth.

Denitrification: Microbial conversion of nitrate to nitrogen gas, a key nitrogen‐removal process in sediments.

Anammox: Anaerobic oxidation of ammonium with nitrite to produce nitrogen gas, supporting sediment nitrogen loss.

Micropollutants: Trace organic chemicals from anthropogenic sources that can interact with natural toxins and organisms.

Phycotoxin: Bioactive compound synthesised by certain algae that can cause toxicity in animals and humans.

References

1. Phaeocystis: A Global Enigma. Annual Review of Marine Science (2023).
2. Marine toxin domoic acid alters nitrogen cycling in sediments. Nature Communications (2023).
3. Mixtures of organic micropollutants exacerbated in vitro neurotoxicity of prymnesins and contributed to aquatic toxicity during a toxic algal bloom. Nature Water (2024).
4. Marine harmful algal blooms (HABs) in the United States: History, current status and future trends. Harmful Algae (2021).
5. Climate Change and Harmful Algal Blooms: Insights and perspective. Harmful Algae (2019).