viral mass mortality of cyanobacteria occurs in nature, rarely recorded

1. Remote Sensing of Virally Induced Mass Mortality of Cyanobacteria Stefan Simis, Steef Peters , Herman Gons • viral mass mortality of cyanobacteria • occurs in nature, rarely recorded • great ecological significance • accompanied by drastic optical changes • Aim • develop remote sensing tool to monitor cyanobacterial dynamics, identify events of mass lysis. • step 1: retrieving the light absorption by the cyanobacterial pigment phycocyanin to discriminate cyanobacteria from spectral reflectance

2. Remote Sensing of Virally Induced Mass Mortality of Cyanobacteria Stefan Simis, Steef Peters , Herman Gons

3. Phycocyanin in Lake IJsselmeer, The Netherlands Remote Sensing of Virally Induced Mass Mortality of Cyanobacteria Stefan Simis, Steef Peters , Herman Gons

4. Remote Sensing of Virally Induced Mass Mortality of Cyanobacteria Stefan Simis, Steef Peters , Herman Gons Abstract We develop a remote sensing tool to investigate drastic changes in cyanobacterial dynamics that can be attributed to viral activity in shallow, eutrophic lakes. Viruses can be major controlling agents in the growth of cyanobacterial populations. A disturbance in the balance between virus and host can lead to drastic losses of photosynthetic pigments. A remote sensing tool for the monitoring of cyanobacterial biomass can aid in the identification of these events in nature. The pigment phycocyanin (PC) is present in all cyanobacteria and few other species. All phytoplankton species possess chlorophyll a (Chl a). Absorption of light by PC can be detected by the 620 nm band of MERIS on ENVISAT. We have developed an algorithm to retrieve the light absorption by PC from reflectance spectra of turbid water bodies that are dominated by cyanobacteria. Future work is directed towards the optical characterization of virally induced mass lysis, to aid the understanding of viral control on cyanobacterial populations. Phycocyanin in Lake IJsselmeer (NL) Figure 1. PC algorithm used with MERIS image of Lake IJsselmeer, The Netherlands, Sept. 2002. PC in g/L. Phycocyanin retrieval A ratio of MERIS bands at 705 and 620 nm, was used with the Gordon model to retrieve PC from turbid water(1): The backscattering coefficient bb is retrieved from the MERIS band at 675 nm(2). CDOM and tripton absorption are neglected. To obtain the phycocyanin concentration, apc is divided by the specific absorption coefficient of PC, a*pc, which should be calibrated for the water body under observation. • References: • Simis, S.G.H, H.J. Gons, S.W.M. Peters, and H.L. Hoogveld. in prep. Parameterization and calibration of a phycocyanin retrieval algorithm for turbid water and MERIS. • Gons, H.J., M. Rijkeboer, and K.G. Ruddick. 2002. A Chlorophyll-Retrieval Algorithm for Satellite Imagery (Medium Resolution Imaging Spectrometer) of Inland and Coastal Waters. Journal of Plankton Research 24:947-951. Figure 3. Pigment ratio PC : Chl a and a*pc in a cyanobacteria-dominated lake. Figure 2. PC retrieval during field and laboratory studies including viral mass mortality of cyanobacterial populations. a*pc was measured for each sample. Results The correspondence between predicted and measured PC in both the field and the laboratory environment is good, when a*pc could be derived from optical measurements (R2=0.95, figure 2). Without information on a*pc, the error in the prediction of phycocyanin rises with fluctuating cellular pigment ratios (figure 3, 4) and plankton composition throughout the seasons (not shown). Using a fixed value for a*pc, calibrated for the Dutch Lake IJsselmeer when dominated by cyanobacteria, yields insights into the spatial distribution of cyanobacteria (figure 1). Conclusion For small lakes with a homogeneous species composition, PC can be predicted with a minimum set of required optical measurements. To improve the utility of the algorithm it is necessary to investigate the effects of cellular pigment composition and the occurrence of other pigments than Chl a and PC in the plankton community. Figure 4. Error in PC prediction when using a fixed value for a*pc. department of Netherlands Institute of Ecology (NIOO-KNAW), Centre for Limnology — Rijksstraatweg 6, P.O. Box 1299, 3600 BG MAARSSEN, The Netherlands E-mail: s.simis@nioo.knaw.nl — www.nioo.knaw.nl RoyalNetherlands Academy of Arts and Sciences Microbial Ecology