Global Harmful Algal Blooms

Overall objective: To achieve a better understanding of BHAB and to provide tools to manage and mitigate the impacts of these events on human health and the environment.


Left: In Tuamotu atolls (French Polynesia), coral extraction represents one of the major human disturbances responsible for coral reef destruction, thus leading to enhanced ciguatera risk. © Institut Louis Malardé (Tahiti, French Polynesia).

Right: The benthic harmful dinoflagellate, Ostreopsis cf. ovata. Scanning Electron Micrograph of a culture isolated from the Gulf of Naples (Mediterranean Sea). Laura Escalera, Stazione Zoologica Anton Dohrn, Naples (Italy).




Rationale. The CRP on “HABs in Benthic Systems” was the last CRP launched by GEOHAB, in 2010 (GEOHAB 2012), created because of more frequent events and geographic expansion of benthic microalgae (BHABs). Tropical regions have been traditionally threatened by CFP associated with blooms of the toxic benthic dinoflagellate Gambierdiscus. It is assumed that ciguatoxins (CTX) produced by Gambierdiscus are bioaccumulated in reef fishes. CTXs are responsible for the most common algal toxin-related illnesses, globally affecting the greatest number of victims and often with significant long-term health effects (see for instance the recent review by Friedman et al. 2017). Recently, Gambierdiscus has also been documented in new areas, in subtropical and temperate latitudes (e.g., Fraga et al. 2011; Nishimura et al. 2014). Blooms of another benthic and toxic dinoflagellate, Ostreopsis, have become more frequent and intense, especially in temperate waters (e.g., Rhodes 2011; Selina et al. 2014). Ostreopsis produces palytoxins (PLTX) and analogues (ostreocins and ovatoxins) that have been related to fatal seafood intoxications in the tropics (Randall 2005). In temperate areas, while such impacts have not been reported yet, some outbreaks have been associated with massive benthic faunal damage and respiratory irritation in humans exposed to aerosols in the area affected by Ostreopsis proliferation (Vila et al. 2016 and references therein). Global warming can be a main factor of the biogeographic extension of benthic HAB species (e.g., Tester et al. 2010), but other anthropogenic disturbances may also be involved. Examples include coral reef destruction (Lehane and Lewis 2000) and increasing plastic pollution, which may constitute an efficient dispersal mechanism for benthic species (e.g., Masó et al. 2003, Zettler et al. 2013). 

The objectives identified in the BHAB CRP (GEOHAB 2012) were intensively addressed by the international community and significant progress was achieved in a relatively short time, as reviewed in Berdalet et al. (2017a) and Berdalet and Tester (in press). Still, the objectives and questions formulated in GEOHAB (2012) are valid, constitute a main research focus in the affected areas and will benefit from international cooperation and coordination. For these reasons, the BHAB CRP will be continued in GlobalHAB as a GlobalHAB theme. 

Furthermore, recognition of the global importance and impact of CFP is reflected by the adoption by the IOC, in coordination with the World Health Organization (WHO), the Food and Agriculture Organization (FAO) and the International Atomic Energy Agency (IAEA) of a “Global Ciguatera Strategy” in 2015 and by the initiatives launched by other agencies, including the U.S. NOAA and specific laboratories. These initiatives are aimed at capacity building (such as the training events held in Tahiti, Dominican Republic and Nantes in 2015 and 2016), development of official toxin detection and quantitation methods (e.g., development of the fluorescent RBA method for CTX detection, Hardison et al. 2016), and documenting the actual human and economic impacts of CFP. GlobalHAB will work in coordination with the mentioned agencies to implement the “Global Ciguatera Strategy”. 

Although Gambierdiscus and Ostreopsis are the most important BHAB genera and most research has been focused on these taxa, GEOHAB (2012) also noted the need to clarify the toxic potential of other organisms, including certain dinoflagellates (Coolia spp., Prorocentrum lima), diatoms (Nitzschia navis-varingica, Amphora coffeaformis) and cyanobacteria (Hydrocoleum glutinosum, Phormidium laysanense, Spirulina weissi, Oscillatoria cf. bonnemaisonii, Anabaena sp., and Trichodesmium erythraeum). Recent observations from French Polynesia have also highlighted similar potential health risks linked to consumption of the gastropod Tectus niloticus (Gatti et al., 2015). A new ecotoxicological phenomenon, ciguatera shellfish poisoning (CSP) to describe CTXs in shellfish has been proposed, and it is recommended that cyanobacteria should be monitored concurrently with other toxic microalgae in order to manage tropical seafood poisonings effectively.


Specific objectives 

  • Improve knowledge of the ecology, physiology, toxicity and toxin transfer mechanisms through marine food webs, to determine fundamental parameters for modeling BHAB dynamics. 
  • Standardize sampling methods for organisms and toxins. 
  • Develop official methods for toxin detection and quantification, and fast screening in fish and other seafood. 
  • Determine the impacts of BHABs on marine organisms and ecosystems. 
  • Investigate the impacts of climate change and anthropogenically driven changes on BHAB dynamics. 
  • Determine the epidemiology of CFP in cooperation with health agencies and monitoring agencies (see also Theme 10. Health). 
  • Estimate the global and local socio-economic costs of CFP (see also Theme 11. Economy). 
  • Facilitate data sharing among research groups for modeling studies, to ascertain the trends on BHAB events, to design management and prevention strategies, etc. 
  • Clarify the uncertainties regarding the toxicity of other benthic genera, especially cyanobacteria. 
  • Coordinate with the IPHAB Task Team to implement the multi-agency IOC-IAEA-FAO- WHO “Global Ciguatera Strategy” (hab.ioc-unesco. org/).


Example tasks 

  • Inter-comparison and teaching workshop on the methods to detect CTX activity (e.g., fluorescent RBA, radioactive methods, etc.). 
  • A modeling workshop centered on BHAB dynamics. 
  • An Open Science Meeting on BHABs, as a continuation of the 1st OSM on BHABs, organized by GEOHAB in June 2010, in Honolulu. 
  • A 2nd International Conference on Ostreopsis Development (ICOD-2), as a follow-on to the 1st conference, held in Villefranche in 2011, with a special issue of a journal as a deliverable. 
  • Specific sessions at ICHA meetings, for example, in Nantes (France), 2018, and in Los Cabos (Mexico), 2020. 
  • Coordination of GlobalHAB with IOC regional groups (FANSA, WESTPAC) in areas affected or potentially affected by CFP. 
  • Engage appropriate health and fishery professionals through existing channels and regional meetings of FAO and WHO to better understand needs and abilities to implement tools related to management of CFP, as identified also in Theme 10. Health.



  • Develop cost-effective methods to detect CTX and toxic Gambierdiscus species. 
  • Determine the potential risk of PLTX-like toxins in seafood-borne poisoning in the Mediterranean Sea. 
  • Clarify the natural and anthropogenic factors favoring BHABs. 

    - Define alert conditions for BHAB events to prevent exposure to CTX (Gambierdiscus) or irritative compounds-containing        aerosols (Ostreopsis)

    - Guidelines for habitat preservation in order to prevent BHAB outbreaks.

    - Coordination to implement the multiagency IOC-IAEA-FAO-WHO “Global Ciguatera Strategy”.



The complete list of references can be found here.

User Location