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.
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.
Analysis
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 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