Bloom Forming Cyanobacteria

A Novel Surveillance Method for Bloom Forming Cyanobacteria

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Overview:

Cyanobacteria have increasingly gained attention from a broad array of professionals (public health officials, water quality managers) and the public (watershed associations, citizen scientists) in light of the biotoxins (cyanotoxins) they produce and the potential ecological, economic and public health risks they impose. It has been suggested that an increase in water temperature and nutrients may be responsible for the increased occurrence of cyanobacteria blooms. (1-3) The regulatory community has responded with programs ranging from public awareness to descriptive and/or numerical limits. All efforts include a monitoring component which includes the observation and evaluation of cyanobacterial blooms. (4) As such, there has been increasing demand for new methods to assess the presence and abundance of cyanobacterial populations.

The existing monitoring tool box consists of a suite of physical, chemical and biological parameters. Of the three types of parameters, the integrative nature of a biological parameter can provide useful insight into the intrinsically dynamic systems that harbor cyanobacteria. The biological parameters, as a continuum of analysis, include visual, pigment, genetic and toxin analysis. (5-9) The analyses provide differing yet complimentary information, all with unique requirements for sample handling/transport, laboratory resources, and costs, and most importantly timeliness for reporting and data quality. For example, the visual evaluation of turbidity using a Secchi disk provides on-site results and is easily accomplished with trained volunteers, yet does not discriminate the source of the turbidity. The enumeration of cyanobacterial cells with light microscopy can vary significantly (Bray-Curtis Index =60%) (10), requires a trained analyst with results typically available within 3-5 days. The testing for toxin producing synthetase genes using quantitative polymerase chain reaction (qPCR) amplification and quantification of cyanotoxins using enzyme-linked immunosorbent assay (ELISA) techniques both provide high quality  information yet require intensive laboratory resources and trained personnel, with results typically available within 3-5 days.

Phytoplankton contain a variety of photosynthetic pigments that are used for capturing sunlight for photosynthesis. Chlorophyll a (Chl-a), which is present in all plants, is commonly used to estimate the biomass of freshwater phytoplankton. Unique among the freshwater cyanobacteria is the accessory photosynthetic pigment phycocyanin (PC). Pigment analysis using advanced fluorometric equipment and techniques can be used for the in-vivo quantification of both Chl-a and PC to represent the cyanobacterial population. (11-15)

Cyanobacteria possess other unique characteristics that provide them competitive advantages over other phytoplankton. One striking characteristic is the presence of gas vesicles which provide buoyancy in the water column (i.e. they can float). Certain cyanobacteria can regulate relative buoyancy through the process of photosynthesis/respiration and the resultant production/consumption of carbohydrates, which act as ballast. (16, 17) They can exhibit varying amplitudes of migration that coincide with the level of incident light. Thus they can exhibit tremendous spatial variability, being found as distinct stratified layers in the water column, accumulations just below the water surface or at the surface as a bloom. The cyanobacteria that are typically found in surface blooms include Microcystis spp., Anabaena spp., Aphanizomenon spp., Oscillatoria spp., Woronichinia spp. (18) The genera are known to produce the cyanotoxins that pose human health risks.

The purpose of this study was to evaluate bloom forming cyanobacteria using a novel method and monitoring device that would provide samples for fluorometric analysis. The monitoring system could be used to evaluate important changes in the cyanobacterial population that could signal the onset of a bloom. It is anticipated that samples obtained using this method can be also used for visual and toxin analysis to provide a comprehensive profile for use by resource managers.

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