Benthic HAB Discussion: March 17, 2025

Presenters and Topics

Mike Thomas, M.S., California Waterboards

Implementation of a benthic cyanobacteria tiered monitoring program for public health protection in Northern California rivers

The North Coast Regional Water Quality Control Board conducted a series of studies to evaluate their tiered monitoring recommendations for benthic cyanobacteria in rivers, which include: deploying Solid Phase Adsorption Toxin Tracking (SPATT) passive samplers to monitor for increasing cyanotoxins; conducting visual assessments to determine cyanobacterial percent cover; and collecting benthic mat samples to confirm bloom toxicity. Study results demonstrated that SPATTs can provide early indications of increasing cyanobacterial percent cover and toxicity in river systems. The studies also confirmed that the tiered monitoring approach is an appropriate and cost-effective methodology to inform posting recommendations in northern California rivers.

Cathy Wazniak, M.S., Amy Hamilton, B.S., Maryland Department of Natural Resources

Hidden neurotoxins in cyanobacterial harmful algal mats in Maryland

Presence of cyanobacterial Harmful Algal Mats (cyanoHAMs) have been increasing in many regions around the U.S. and internationally. Detection of microcystin in benthic mats was first noted in Maryland in 2017 and 2019 associated with Oscillatoria mats. Additionally in 2019, anatoxin was detected in mixed mats in the Potomac and Patapsco Rivers and in Carter Creek and Clopper Lake in 2020 associated with mats containing Anabaena. This led to several special projects to evaluate toxin in benthic mats, starting in 2021.

Joanna Blaszczak, PhD, Jordan Zabrecky, PhD Candidate, University of Nevada, Reno, Blaszczak Lab

Macroinvertebrate communities in benthic anatoxin-producing cyanobacterial mats

The ecological effects of toxin-producing benthic cyanobacterial mats, such as anatoxin-producing Microcoleus mats, on benthic macroinvertebrate (BMI) communities in rivers are unclear. To examine differences in BMI communities within and surrounding Microcoleus mats, we collected 6 rocks in a paired design (3 Microcoleus-dominated & 3 green algae-dominated rocks within a 1 m radius) within three distributed riffles along a 1 km reach of the South Fork Eel River in northern California in 2022. While we observed no differences in taxa richness or abundance.