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Detecting Filamentous Cyanobacteria Blooms in the Baltic Sea
Using Turner Designs Model 10-AU Fluorometer
About The Finnish Institute of Marine Research
The Finnish Institute of Marine Research (FIMR, http://www.fimr.fi/en.html)
is a government-funded institution under the Ministry of Transport
and Communications. FIMR is a multidisciplinary research institution
carrying out basic research and providing services in the fields
of physical, chemical and biological oceanography. The activities
are mainly focused on the Baltic Sea. FIMR employs approximately
120 people, about half of them are directly involved in research
activities.
Harmful cyanobacteria blooms in the Baltic Sea
The Baltic Sea, in the northern Europe, is surrounded by 9 countries
and approximately 85 million people live in its catchment area.
Ecologically the Baltic, which is the second biggest brackish water
basin in the world, is unique. Since the last ice-age this basin
has succession from lake to brackish sea, nowadays the salinity
varies from 20 PSU in southern basin to near zero values in the
Bothnian Bay in north. The low salinity, together with ice winters,
largely affects the distribution of aquatic flora and fauna in the
Baltic. Seasonality, with varying colors, in the open sea phytoplankton
community can be perceived even by casual observer. Spring bloom
with brownish colored diatoms and dinoflagellates is followed by
clear water season in mid-summer. Towards the end of summer some
locations suffer from frequent cyanobacterial blooms, with turquoise
or green to yellow colors. In calm and warm days in June-August,
one can observe kilometer-wide pea soup-like surface accumulations
of filamentous cyanobacteria. These summer blooms of nitrogen-fixing
filamentous cyanobacteria, with main species Nodularia spumigena,
Aphanizomenon sp, and Anabaena spp., counteract the reduction of
anthropogenic nitrogen load, have possible toxic effects for the
other components of the ecosystem and thereby may lower the value
of fisheries, and affect the recreational use of coastal area. The
intensity of these blooms is related to low inorganic N:P ratio,
high temperature of surface waters, and low wind mixing.
Photo 1: Aimar Rakko from University of Tartu taking sample of filamentous
cyanobacteria in a traditional way
To find out the triggering factors for these blooms and to analyze
their environmental consequences, and thereby support science based
management of the Baltic Sea, phytoplankton dynamics must be studied
with the relevant spatial and temporal resolution. For this task,
in FIMR the traditional methods for phytoplankton studies have been
supplemented with automated detection systems placed on ships of
opportunity, and with satellite data. In the Baltic Sea, the Alg@line
system (www.balticseaportal.fi),
coordinated by FIMR, for the detection of phytoplankton biomass
by fluorescence has been running for ten years. Alg@line utilizes
merchant ships and ships of Finnish coastal guard. Currently 9 vessels
have flow-through fluorometers and thermosalinographs operating,
providing approximately 1.5-2 million observation per year.
Phycobilin fluorescence as a tool for cyanobacteria detection
Chlorophyll in vivo fluorescence is, however, not optimal for the
detection of cyanobacteria as for these species fluorescence at
the wavelengths specific for chlorophyll is very weak. Instead,
these species contain phycobilin pigments that have their own specific
wavelengths for excitation and fluorescence emission. Our previous
studies with pure phytoplankton cultures and experimental work in
field has provided important background for cyanobacterial detection
by fluorescence. We have noted that bloom forming filamentous species
in the Baltic are the main source of phycocyanin related optical
signals. Picocyanobacteria (i.e. cells <2#956;m), not forming
the blooms, together with some eucaryotic species, is the main source
of phycoerythrin signals. Studies with cultures provide us also
information on the environmental control of the variability in cellular
phycobilin content. That is extremely significant information when
analyzing the field data.
Already 20 - 30 years ago it was suggested that phycobilin fluorescence
could be used to estimate cyanobacterial distribution - and since
that we have made some attempts in the Baltic Sea as well. Now,
our aim in Alg@line is to start operational detection of phycocyanin
in Baltic by summer 2005. During EU-funded project FERRYBOX (http://www.ferrybox.org)
we have conducted vigorous laboratory tests with Turner 10-AU fluorometer
with phycocyanin kit (excitation 620 nm, emission 650 nm), and we
have verified that the sensitivity and linear range are suitable
for detection of natural concentrations of filamentous cyanobacteria.
As well we have noted the high specificity of instrument; the effects
of light scattering and overlapping fluorescence from dissolved
matter and other pigments are negligible. Phycocyanin fluorescence
readings are further normalized to known concentrations of commercially
available C-phycocyanin in buffer, as the actual in vitro phycobilin
concentration measurements are hard to perform from discrete water
samples.
Figure 1: Excitation - emission matrix for colored dissolved organic
matter (CDOM), and for cultured green algae with high chlorophyll
a fluorescence and filamentous cyanobacteria with high phycocyanin
fluorescence.
Steps towards operational use of phycocyanin fluorescence
In pre-operational testing phase in summer 2004, we used phycocyanin
fluorometer during cruises of RV Aranda. It was operated in flow-through
mode together with two fluorometers for chlorophyll detection (AU-10
and Cyclops-7), and flow-through spectrofluorometer. Discrete samples
were taken from water flow to determine pigment concentrations,
count phytoplankton cells and to measure the light absorption by
phytoplankton. More data is needed, but our objective is to obtain
estimates on the variability in cyanobacterial biomass and pigment
specific fluorescence intensities for calibration purposes of phycocyanin
fluorometer.
Photo 2: Pasi Ylöstalo and a set of Turner fluorometers in RV Aranda
As an example of data collected thus far, the grid recorded in July
26.-27. 2004 in the Gulf of Finland, Baltic Sea, shows clearly the
location of cyanobacterial bloom batches, with high phycocyanin
fluorescence, in the middle cruise grid. The locations of these
high phycocyanin areas are identical to visual observations of bloom
areas. Clearly, phycocyanin and chlorophyll fluorescence were not
directly related. Obviously, chlorophyll measured by in vivo fluorescence
mainly reflects the eucaryotic part of the phytoplankton community
while phycocyanin reflects only filamentous cyanobacteria in our
study area.
Figure 2: Spatial variability of Chlorophyll a concentration, phycocyanin
fluorescence and their ratio as estimated by two Turner AU-10 fluorometers
during a bloom of filamentous cyanobacteria, July 26 - 27, 2004
in the Gulf of Finland, Baltic Sea.
Next steps in our phycocyanin fluorescence research includes evaluation
of Cyclops 7 phycocyanin fluorometer, and installation of one phycocyanin
fluorometer for operational use in 2005. Then the seasonal phycocyanin
profiles across the Baltic Sea will be used in evaluation of bloom
development, to assist selection of sampling sites for dedicated
cyanobacterial research, in validation of ecosystem models, and
in validation of ocean color data for cyanobacterial distribution.
Study group
Other scientist directly involved in phycocyanin related studies
in FIMR are Pasi Ylöstalo (instrument testing, phytoplankton physiology),
Seppo Kaitala (satellite images, Ferrybox systems), Mika Raateoja
(Alg@line coordinator, phytoplankton physiology).
Additional Information:
Jukka Seppälä
Finnish Institute of Marine Research
P.O. Box 33, FIN-00931
Helsinki, Finland
jukka.seppala@fimr.fi
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