» A fragile ocean: Protecting the ocean from harmful algal blooms and disease outbreaks
11.06.2018 - Intergovernmental Oceanographic Commission

A fragile ocean: Protecting the ocean from harmful algal blooms and disease outbreaks

© Elisa Berdalet

In the last article of our series on women scientists’ perspectives on emerging ocean science issues, Dr. Elisa Berdalet addresses the issue of harmful algal blooms (HABs), more commonly known as red or green tides.

Let yourself dive into key ocean science issues through the eyes of women that have dedicated their lives to oceanography, and who shared their latest scientific findings at the 4th International Symposium on the Effects of Climate Change on the World’s Oceans, ECCWO (Washington D.C., USA, 4-8 June) – a gathering of leading ocean and climate researchers from more than 50 countries.

Our interviewees offer us a warning about just how much is at stake when it comes to the conservation and sustainable use of the ocean in a changing climate, but they also highlight how the scientific community can play a significant role in bridging the gap between knowledge and action.

Thanks to a growing body of science, exciting innovations and discoveries, we now have a greater understanding of our planet’s climate system – but how do we turn decision-relevant knowledge into concrete steps toward delivering the ocean we need for the future we want? We asked Dr. Elisa Berdalet (ICM-CSIC, Barcelona) to explain why this is crucial to decision-makers and society at large. She is Chair of the Scientific Steering Committee of the GlobalHAB Programme coordinated by UNESCO’s Intergovernmental Oceanographic Commission (IOC) and the Scientific Committee on Oceanic Research (SCOR).

How would you explain harmful algal blooms and their threats to a politician or your local councilor?

I will start by a comparison with a land scene. Imagine sheep or cows grazing few but highly poisonous flowers grown within the grass. Cattle could be dramatically intoxicated, and though they may survive, they would no longer be suitable for human consumption.

Similarly, in aquatic ecosystems in all latitudes, certain microalgae, cyanobacteria and seaweeds (all of them photosynthetic because they produce the oxygen we breath through photosynthesis) can proliferate in excess – they “bloom” – and cause harm to plants, animals or humans in different ways. We call these events "harmful algal blooms (HABs)". The excessive abundance of these photosynthetic organisms can alter the natural equilibrium in the aquatic ecosystem, disrupting aquatic fauna and food webs, killing fish, or contributing to low oxygen “dead-zones”.

What are the effects of HABs? First, they can change the color of water. We traditionally call them “red tides”, but in reality, HABs come in many colors: "brown tides" caused by Aureococcus and Aureoumbra, "green and golden tides" due to the proliferation of the seaweeds Ulva and Sargassum, and “blue-green” tides due to blooming cyanobacteria. There are even some highly toxic organisms such as the Dinophysis species, which cause harmful blooms without changing the color of the water.

While HABs mostly spoil tourism and recreational use of the ocean due to the water color and the bad odors, they may sometimes be very toxic and severely impact marine and human health. Consumption of contaminated seafood produce different health disorders defined in base of the dominant symptoms, namely, Paralytic (PSP), Diarrheic (DSP) or Amnesic (ASP) Shellfish Poisonings, and Ciguatera Shellfish Poisoning (CFP). Methodological progress and continuous investment in research and monitoring are fundamental to keep detecting new toxins and protect human and ecosystem health from the impacts of HABs.

Aquaculture sites in Cam Ranh Bay, Vietnam
Fin-fish, shellfish, crustaceans and macroalgae aquaculture has many benefits, including the production of nutritious high-protein food, reducing the pressure on natural resources and supporting sustainable economic development and employment. Aquaculture operations are threatened by phycotoxin contamination and mass mortalities of cultured animals caused by HABs. There is a need to monitor HAB species and their toxins in aquaculture sites in order to prevent seafood intoxication and economic loss.
Photo credit: Y. Fukuyo

What are the knowledge gaps on what we know of harmful algal blooms, if any?

Some HABs are part of natural processes, driven by seasonal rhythms of the aquatic ecosystems. We also know that certain human activities can foster HAB occurrence. Namely: nutrient pollution and eutrophication, intensive use of coastal zones that degrades ecosystems biodiversity, alteration of water circulation dynamics through artificial beaches and harbors construction, and dispersion of exogenous species through ships ballast waters or aquaculture operations. Reducing our human pressures on the ecosystems can decrease the risk of HABs occurrence. However, because HABs are natural phenomena, there is no realistic way to completely prevent them from happening.

In the last decades, multidisciplinary and coordinated scientific research at local and international levels (as conducted under the IOC/UNESCO and SCOR programmes GEOHAB and GlobalHAB) has allowed remarkable progresses in the understanding of both, natural processes and anthropogenic stressors underlying HAB dynamics. New knowledge enables prediction of the occurrence of certain HABs, a main tool to manage their negative impacts. However, global warming and climate change may affect the trends, frequency and abundance of HABs in a so far unknown way. In the meantime, monitoring harmful species and their toxins is the best way to prevent HABs impacts on human health and the ecosystems.

Do harmful algal blooms tend to happen in limited scope, or can they also affect multiple countries at once?

Some HABs have a very local geographic extension, affecting, for instance, small beaches. In other cases HABs may have big extensions covering more than one country. For instance, in the Baltic, cyanobacteria blooms can affect Norway, Sweden and Finland waters. Some blooms can extend all along the Pacific coast of America, from Alaska to California, and certain blooms can occur along the coasts of the Arabian Sea or in Asian waters affecting simultaneously different countries. All these events can usually be visualized by satellite.

The reason for this is the existence of water circulation patterns that operate simultaneously at big scale along the coasts: nature does not know about political borders. For instance, in the West coast of the Iberian Peninsula, some particular algal species are transported northwards from Portugal’s coastal waters to the Galician Rías in Spain where the presence of this species even at very low cell concentrations prevents shellfish extraction for several months due to the risk of diarrheic shellfish poisoning (DSP).

As mentioned, in addition to spatial scale, the impact of the HAB events depends on their periodicity or recurrence. Some HABs have an annual periodicity, but others could depend on processes with a high temporal scale (several years), such as the El Niño or La Niña Southern Oscillations. Understanding the exact link between these processes at planetary scale and HABs at local scale requires long-term data series and complex, multidisciplinary studies.

Satellite image of a bloom of phytoplankton off the coast of Oregon and Washington on July 26, 2014
Image courtesy of NASA Earth Observatory

Most people are used to seeing “green” or “red” tides, and they usually attract a lot curiosity. Is there a role for citizen science in studying or combatting this phenomenon?

Yes, indeed! Observing nature is one of the most pleasant activities. Nowadays, citizen collaboration is becoming a relevant and helpful tool to increase information about many natural scientific challenges, including HABs. People can be trained and provided with simple tools to contribute to monitoring HABs and prevent their impacts. There are already excellent experiences and new possibilities are offered with online communication through websites, combining images and data. For instance, in the US, the National Oceanic and Atmospheric Administration (NOAA) and the National Centers for Coastal Ocean Science (NCCOS) have developed efficient systems that include training activities for volunteers in coordination with scientists and stakeholders.

The Sitka Tribe of Alaska Environmental Research Laboratory (STAERL) staff instruct workshop participants on proper shellfish processing techniques for saxitoxin analysis.
Photo credit: NOAA, https://products.coastalscience.noaa.gov/hab/

The Seawatchers platform, coordinated by the Institute of Marine Sciences (ICM-CSIC) in Barcelona, is another great international forum that connects citizens and scientists to investigate the current state of our shared ocean. In the coming weeks, the Platform will launch a new challenge to detect the presence of the Ostreopsis, an algal species that produces upper track respiratory irritations in humans who bathe in temperate beaches, such as the Mediterranean, Brazil or Japan.

These initiatives are extremely positive. The platforms empower citizens and increase their ocean literacy. In addition, citizen science facilitates the establishment and maintaining of sentinel sites to observe natural and anthropogenic changes, and can serve as useful tools to support environmental and health policies.

Is there anything in particular that citizens can do in their everyday lives to help?

Of course! In our planet, everything is interconnected. We have one planet only, and the health of the ocean is fundamental for the planet’s and our own well-being. HABs are a natural phenomenon that can be facilitated by human-induced elements. Citizens must ask policy makers and authorities to avoid dumping sewage on the coasts, limit the use of the seashore areas, and work for the sustainable use of marine resources. At personal level, we can have a respectful attitude towards the ocean: we have a responsibility to keep beaches and waters clean, and to preserve the environment. Changes are occurring fast. If we are to fulfill our responsibility to leave a decent legacy to future generations, we need to change our minds and behavior now.


UNESCO’s Intergovernmental Oceanographic Commission (IOC) has co-organized the quadrennial International Symposium on the Effects of Climate Change on the World’s Oceans since 2008 in collaboration with the International Council for the Exploration of the Sea (ICES), the North Pacific Marine Science Organization (PICES), and the Food and Agricultural Organization of the United Nations (FAO).

Follow all about last week’s ECCWO on Twitter at @ECCWO!

For more information, please contact:

Salvatore Arico (s.arico(at)unesco.org)

Elisa Berdalet (berdalet(at)icm.csic.es)

Or visit:

ECCWO Symposium website

<- Back to: All news
Back to top