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Phytoplankton ecology

"Phytoplankton" is the collective name for a group of microscopic, aquatic photosynthetic organisms. Most phytoplankton are single-celled eukaryotes, and are invisible to the naked eye. They are, however, very abundant: one litre of seawater can hold several million phytoplankton cells.

Phyto bloom picture from ESA Scotland 070508
Aerial view of a plankton bloom, off the Scottish coast

At certain times of the year dense aggregations of phytoplankton, called "blooms", occur. These may make the sea surface appear red, green or brown.

Due to their high rates of biological activity, they are very important in sustaining life in the oceans. They can also influence climate at the global scale. Microscopic algae account for only 2% of the total global plant biomass, but  almost 50% of the annual global carbon fixation.

Here at Cefas we are discovering more about the diversity of these organisms, especially those species that are potentially toxic. We are also trying to understand how planktonic "primary production" will respond to future changes in the seas and oceans. This information is essential if we're to gain a better understanding of the quality of our oceans' and coastal seas' health, productivity and diversity.

Our investment in modern diagnostic tools enables us to:

  • measure the potential consequences of marine eutrophication
  • identify the species that form phytoplankton blooms and toxic events
  • better understand the relationship between functional groups and the marine food web, including commercially important fish stocks.

Collecting samples and data

Collecting a representative sample of phytoplankton is the first challenge. Each season has characteristic species assemblages; and there are differences in composition between nutrient-rich coastal waters and the deep ocean.

In the past, phytoplankton were mainly sampled by scientists at sea on research vessels or with the Continuous Plankton Recorder. The Recorder was designed to record the presence and abundance of herbivorous (plant-eating) zooplankton, as well as some of the larger phytoplankton species.

Now, we can detect the presence of phytoplankton from orbitting satellites above the Earth, or from unmanned sensors tethered at the sea surface. As a part of the UK's Clean Seas Environment Monitoring Programme, we have developed an autonomous monitoring system to provide a high-frequency temporal and spatial data set of physical, chemical and biological observations. These include phytoplankton biomass and species determination at selected sites around the coasts of England and Wales.

Integrating data from multiple sources, through projects like the Europan Marine Ecosystem Observatory (EMECO), is helping us to build a more coherent picture of the state of our seas.


Analysing tiny planktonic algae can be difficult: little is known about the diversity of some phytoplankton groups, particularly the most minute cells (those less than 5 microns, which are practically invisible even when using the best microscopes).

Corethron hystrix - flow cytometry
Corethron hystric (Hensen), isolated from the Irish
Sea (September 2009), analysed by flow cytometry

We are now able to: 

  • assess phytoplankton diversity in different water bodies
  • identify certain toxic species from their DNA signatures, using molecular biological techniques: denaturing gel electrophoresis (DGGE), ARISA and real-time quantitative PCR
  • classify phytoplankton from their size, shape and optical properties, using an high-speed analytical flow cytometry (which can classify up to 5,000 microalgal cells per minute).

The results of these techniques are essential for developing size-based food-web models to predict the yield of fish stocks; generic models to describe the role of phytoplankton in the carbon and nitrogen cycles of pelagic and benthic ecosystems; and mass-balance models to estimate biomass and food-web consumption of elements, in term of groups of species or individual species.

For more information about our work, please contact phytoplankton_ecology@cefas.co.uk

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Last Modified: 27 April 2014