Detecting Filamentous Cyanobacteria Blooms in the Baltic Sea

Parameters: Cyanobacteria

The Finnish Institute of Marine Research (FIMR) 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, 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 (10AU 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. 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. 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).

Photo 2: Pasi Ylöstalo and a set of Turner fluorometers in RV Aranda

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.

Author: Dr. Jukka Seppala Institution: Finnish Institute of Marine Research, Baltic Sea, Finland