Identification of cyanobacteria overwintering cells and environmental conditions causing growth: application for preventative management.
Abstract
Harmful algal blooms (HABs) formed by freshwater cyanobacteria pose risks to human and ecological health globally. Some cyanobacteria form overwintering cells that remain in the sediment during non-ideal growth conditions and provide an inoculum for HABs during the growing season, perpetuating the cyanobacterial life cycle. Preventative management targeted at decreasing the viability of overwintering cells is an attractive strategy for limiting HAB formation and decreasing risks. However, this approach is novel, and information is needed for sampling, identification and enumeration of overwintering cells in sediments as well as methods for determining if overwintering cells have the potential to contribute to HAB formation. Peer reviewed literature related to these topics are available; yet these data need to be synthesized and placed into the context of management. Therefore, a strategic review was conducted to inform methods and data needs for this preventative strategy. To sample overwintering cells, corers or dredges are used to collect surficial (0-2 cm) sediment layers containing overwintering cells. Identification and enumeration of overwintering cells via light microscopy are aided by dilution, sieving, or density separation of cells from sediment. Incubation studies which simulate environmental conditions triggering akinete germination and cell growth provide evidence of overwintering cell viability. Critical environmental conditions are light (≥0.5 μmol m-2 s-1) and temperature (20-30°C) for triggering akinete germination and growth of quiescent vegetative Microcystis sp. cells, respectively. Limited information was available on the roles of mixing and dissolved oxygen as environmental conditions for germination and growth. Synthesized information can be used to identify potential areas of concern in which overwintering cells are contributing to HABs. Additionally, this information can be used to design incubation studies in which field collected sediments containing overwintering cells are placed in ideal environmental conditions for germination and growth and cyanobacteria transferring to the water column are measured over time. These data inform investigations of areas that are candidates for preventative management and measurements of overwintering cell responses to management.