Dentification and prioritization of sites with overwintering cyanobacteria to inform preventative management of harmful algal blooms

Abstract

Cyanobacteria causing harmful algal blooms (HABs) can overwinter in sediments as quiescent cells (akinetes or vegetative colonies) and contribute to bloom resurgences. Targeting overwintering cells in sediments for preventative management may provide a viable approach to delay onset and mitigate blooms. However, there are limited resources for this novel strategy. Given the growing global impact of HABs, the ability to identify and prioritize sites that are influenced by overwintering cells will be a critical step for preventative management. Therefore, the overall objective of this study was to identify and illustrate relevant data to support identification and prioritization of sites that contain overwintering cells with the potential to form HABs. To achieve this, sediment samples were collected from three HAB-affected reservoirs (Marion Reservoir, KS; Fort Gibson Lake, OK, and Heyburn Lake, OK) as pertinent examples. Cyanobacteria enumeration and growth potential data from incubation studies were assembled for prioriti-zation. Overwintering cells were present in all HAB-affected reservoirs, with 85% of sites (n ¼ 13) containing overwin-tering cells in sediments and 54% of sites (n ¼ 13) with a planktonic growth potential producing problematic cell densities (. 100,000 cells ml􀀁1). On the basis of the weight of evidence, Marion Reservoir, followed by Fort Gibson, and last, Heyburn Lake, have the greatest potential for over-wintering cells to contribute to HABs. These data indicate that a monitoring approach should consider at least two lines of evidence: 1) presence and density of overwintering cyanobacteria and 2) growth potential as informed by laboratory incubation studies to predict growth risk and prioritize locations for preventative management.