Spatial and temporal variability in Phormidium mats and associated anatoxin-a and homoanatoxin-a in two New Zealand rivers

Abstract

Toxic benthic cyanobacterial proliferations in freshwater are becoming increasingly prevalent, and associated animal poisonings are being reported with greater regularity. Despite this, few studies have investigated spatial and temporal variations in freshwater mat-forming Cyanobacteria and their associated toxin production. Some sections of the Hutt and Wainuiomata rivers (lower North Island, New Zealand) contain extensive Phormidium sp. proliferations that sometimes produce anatoxin-a (ATX) and homoanatoxin-a (HTX). The percentage coverage of Phormidium sp., ATX and/or HTX concentrations and a suite of physicochemical parameters were monitored at 8 sites for 12 mo. The percentage coverage of Phormidium mats was greater in the summer months and these correlated with warmer water temperatures and stable river flows. Flows in excess of 3 times the mean resulted in the removal of Phormidium mats. There was no correlation between the presence/absence of Phormidium mats and water-soluble nutrients. The presence and concentration of ATX and/or HTX and their degradation products, dihydroanatoxin-a and dihydrohomoanatoxin-a, was highly variable across all sites and over time. Anatoxin-a and HTX occurrence was restricted to periods of warm water temperatures (above 13.4°C) and below average river flows.

Successional Change in Microbial Communities of Benthic Phormidium-Dominated Biofilms

“…Many of the common bloom forming species produce toxins that can cause illness or death in humans and animals [1][2][3][4]. Despite numerous cases of toxicity caused by benthic species [5][6][7][8][9][10], these organisms have been poorly studied in comparison to their planktonic counterparts [11,12].…”

Spatial and Temporal Dynamics of Potentially Toxic Cyanobacteria in the Riverine Region of a Temperate Estuarine System Altered by Weirs

“…Phormidium sp. has a competitive advantage in that the species can thrive in the oligotrophic portions or riverine zones [15]. This species was more abundant at stations without weirs.…”

“…These structures can change riverine systems to lacustrine conditions [10,14]. When riverine waters become impounded, changes in water quality and biota are detected [15,16]. For example, the Murray River in Australia has been observed to be more favourable to cyanobacterial growth in areas where weirs were installed, as opposed to free-flowing areas [17].…”

Costs of harmful blooms of freshwater cyanobacteria

“…Benthic mat-forming species (e.g., Phormidium) are also becoming increasingly problematic in both standing and running waters (Heath, Wood, and Ryan, 2011;Wood et al, 2012). The economic costs of cyanoHABs are mainly associated with these genera and relate to both the precautionary measures taken to avoid more severe impacts (e.g., closure or restriction of recreational access to water bodies) and the direct effects of toxins (e.g., stock deaths).…”