The impact of local and climate change drivers on the formation, dynamics, and potential recurrence of a massive fish-killing microalgal bloom in Patagonian fjord

• Published in: The Science of the total environment 2023-03, Vol.865, p.161288, Article 161288
• Main Authors: Díaz, Patricio A., Pérez-Santos, Iván, Basti, Leila, Garreaud, René, Pinilla, Elias, Barrera, Facundo, Tello, Alfredo, Schwerter, Camila, Arenas-Uribe, Sara, Soto-Riquelme, Camila, Navarro, Pilar, Díaz, Manuel, Álvarez, Gonzalo, Linford, Pamela M., Altamirano, Robinson, Mancilla-Gutiérrez, Guido, Rodríguez-Villegas, Camilo, Figueroa, Rosa I.
• Format: Article
• Language: English
• Subjects: Animals; aquaculture; autumn; Biogeochemistry; biomass; Brown tide; cell growth; Chile; Climate anomalies; Climate Change; environment; Estuaries; Harmful Algal Bloom; Heterosigma akashiwo; Microalgae; mortality; NW Chilean Patagonia; poisonous algae; public health; Salmon; Salmon mortality; solar radiation; Southern Annular Mode (SAM); species; tourism; traditional technology; Upwelling; Water
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.161288

Harmful algal blooms (HABs) in southern Chile are a serious threat to public health, tourism, artisanal fisheries, and aquaculture in this region. Ichthyotoxic HAB species have recently become a major annual threat to the Chilean salmon farming industry, due to their severe economic impacts. In early austral autumn 2021, an intense bloom of the raphidophyte Heterosigma akashiwo was detected in Comau Fjord, Chilean Patagonia, resulting in a high mortality of farmed salmon (nearly 6000 tons of biomass) within 15 days. H. akashiwo cells were first detected at the head of the fjord on March 16, 2021 (up to 478 cells mL−1). On March 31, the cell density at the surface had reached a maximum of 2 × 105 cells mL−1, with intense brown spots visible on the water surface. Strong and persistent high-pressure anomalies over the southern tip of South America, consistent with the positive phase of the Southern Annular Mode (SAM), resulted in extremely dry conditions, high solar radiation, and strong southerly winds. A coupling of these features with the high water retention times inside the fjord can explain the spatial-temporal dynamics of this bloom event. Other factors, such as the internal local physical uplift process (favored by the north-to-south orientation of the fjord), salt-fingering events, and the uplift of subantarctic deep-water renewal, likely resulted in the injection of nutrients into the euphotic layer, which in turn could have promoted cell growth and thus high microalgal cell densities, such as reached by the bloom. [Display omitted] •Climate change drivers and local hydrodynamics fostered a massive bloom of Heterosigma akashiwo in a Patagonian fjord.•Positive SAM phase promoted an increase in water temperature and upwelling.•Salt-fingering events also transport nutrients to the photic layer.•Hydrodynamic modelling shows that uplifts could promote the resuspension of microalgal benthic stages.