Biology subjects

Sterner, R. W.

Publications and source records attributed to Sterner, R. W..

2 recordsLinked to original sources

bioRxiv2024

Spatio-temporal dynamics of cyanobacterium Dolichospermum lemmermannii populations in a bloom-prone region of Lake Superior

Cyanobacterial Harmful Algal Blooms (cHABs) are increasingly common in marine and freshwater environments, including the Laurentian Great Lakes (LGL). Lake Superior has seen two large-scale cyanobacterial blooms (2012 and 2018) along the Wisconsin shoreline west of the Apostle Islands, caused by the cyanobacterium Dolichospermum lemmermannii. The drivers of bloom formation in Lake Superior are not yet certain, with many factors known to trigger blooms elsewhere in the LGL being absent in Lake Superior. Furthermore, little is known about D. lemmermanniis spatial structure or phenology. Thus, we sought to track the seasonal population dynamics of D. lemmermannii to shed light on its growth, physiology, and abundance. In 2021, we used 16S rRNA amplicon and shotgun metagenomic sequencing to characterize spatiotemporal patterns of D. lemmermannii abundance and diversity along the bloom-prone Wisconsin shore of Lake Superior. In 2022, we performed net tows and direct colony counts in another localized area. No large-scale bloom event was observed during either year, though several smaller blooms were observed. D. lemmermannii abundances were low at nearly all sites and sampling times. Spikes in abundance occurred in July and September, particularly near Siskiwit Bay, a hotspot of bloom formation. We also observed a seasonal shift in heterocyte and akinete abundance indicative of late-season nutrient limitation. Most striking was the seasonal turnover of D. lemmermannii strains, suggesting strain adaptation to specific environmental conditions. These results offer valuable and actionable insights for managers and provide a foundation for additional work to clarify drivers of bloom formation in Lake Superior.

microbiology↗

bioRxiv2020

Fluvial seeding of cyanobacterial blooms in oligotrophic Lake Superior

Lake Superior has recently begun experiencing cyanobacterial blooms comprised of Dolichospermum lemmermannii near the Apostle Islands and along the southern shore of the western arm. Little is known about the origin of these blooms. Experiments were conducted during the summers of 2017 and 2018 to identify sources of propagules and characteristics of sites that were potential sources. The 2017 experiments were conducting using a factorial design with three source zones (Harbor, River, and Lake), two nutrient conditions (high and low N:P), and three temperatures (15, 20, and 25 {degrees}C). At the end of the experiment, cyanobacteria were most abundant from the River and Harbor zones at low N:P and 20 and 25 {degrees}C, with D. lemmermannii most abundant at 20 {degrees}C. Subsequently in 2018 we evaluated 26 specific inland locations from three waterbody types (Coastal, Lake/Pond, and River) and explored similarities among those sites that produced cyanobacteria in high abundance when samples were incubated under optimal conditions (low N:P and 25 {degrees}C). Under these growing conditions, we found high cyanobacteria abundance developed in samples from river sites with low ambient temperatures and high conductivity. Field monitoring showed that Lake Superior nearshore temperatures were higher than rivers. These observations suggest that blooms of D. lemmermannii in Lake Superior are initiated by fluvial seeding of propagules and highlight the importance of warmer temperatures and favorable nutrient and light conditions for subsequent extensive cyanobacterial growth. We argue that the watershed is an important source of biological loading of D. lemmermannii to Lake Superior, and that when those cells reach the nearshore where there is warmer water temperatures and increased light, they can grow in abundance to produce blooms.

ecology↗