Harmful Algal Bloom Dynamics in Patagonian Fjord Ecosystems

Patagonian fjords represent a unique marine environment where steep bathymetry, deep sills and large freshwater inputs combine to create strongly stratified water columns. Changes in regional climate patterns, including shifts in precipitation, wind regimes and ocean–atmosphere modes such as El Niño–Southern Oscillation and the Southern Annular Mode, drive variability in freshwater discharge, solar radiation and vertical mixing. These hydroclimatic fluctuations influence nutrient availability, enabling episodic upwelling of nutrient‐rich Pacific waters into the inner basins. In turn, these processes modulate the timing, duration and intensity of harmful algal blooms (HABs) dominated by species such as Alexandrium, Pseudochattonella and Heterosigma. Blooms have serious ecological and economic consequences, including massive salmon mortality and toxin accumulation in shellfish, with cascading impacts on coastal communities. Research now emphasises the interplay between large‐scale climate anomalies and local drivers—sill geometry, wind‐driven circulation and salinity gradients—in governing bloom dynamics. Improved understanding of these controls offers pathways for more effective monitoring, forecasting and management in a region that serves as a sentinel for climate‐driven change in high‐latitude coastal systems.

Research from Nature Portfolio

Analyses of the extreme 2016 bloom of Pseudochattonella cf. verruculosa have revealed how concurrent El Niño warming and a positive Southern Annular Mode phase led to anomalously low freshwater input, elevated solar irradiance and weakened stratification. These conditions allowed saline, nutrient‐rich waters to intrude past fjord sills, triggering one of the largest recorded fish kills in western Patagonia. Detailed time‐series of atmospheric, hydrological and oceanographic data demonstrate that subtle shifts in temperature and mixing can precipitate bloom initiation and persistence, underscoring the sensitivity of fjord ecosystems to remote climatic forcings.

Harmful Algal Bloom Dynamics in Patagonian Fjord Ecosystems publication trend

The graph below shows the total number of articles in harmful algal bloom dynamics in patagonian fjord ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Hydrographic stratification: vertical layering of water masses by density contrasts, which limits or promotes nutrient exchange between layers.

Upwelling: the process by which deeper, nutrient‐rich waters are brought to the surface, typically driven by wind patterns or topographical features.

Fjord sill: a submerged ridge at the mouth of a fjord that regulates the exchange of water and thus controls circulation and flushing times.

Ichthyotoxicity: the capacity of certain algal blooms to produce compounds that damage fish gill tissues, causing high mortality in aquaculture and wild stocks.

El Niño–Southern Oscillation (ENSO): a periodic climate phenomenon in the tropical Pacific that alters sea surface temperatures and atmospheric circulation, impacting weather and marine systems globally.

Southern Annular Mode (SAM): the leading mode of atmospheric variability in the Southern Hemisphere, influencing westerly wind strength and precipitation over high latitudes.

References

1. Toxic Algal Bloom Recurrence in the Era of Global Change: Lessons from the Chilean Patagonian Fjords. Microorganisms (2023).
2. Hydroclimatic conditions trigger record harmful algal bloom in western Patagonia (summer 2016). Scientific Reports (2018).
3. Seasonal hydrography and surface outflow in a fjord with a deep sill: the Reloncaví fjord, Chile. Ocean Science (2016).
4. Controversies in social-ecological systems: lessons from a major red tide crisis on Chiloe Island, Chile. Ecology and Society (2018).
5. Salinity-Growth Response and Ichthyotoxic Potency of the Chilean Pseudochattonella verruculosa. Frontiers in Marine Science (2019).