Mat Forming Toxic Benthic Cyanobacteria in New Zealand: Species Diversity and Abundance, Cyanotoxin Production and Concentrations
Authors:   , Heath Mark W. 
Published: November 2021

<p>Recent research has shown that toxic cyanobacteria are more widespread in New Zealand water bodies than previously thought. However, that work has largely focused on planktonic species. Toxin production associated with benthic cyanobacteria is less widely understood despite benthic mat-forming cyanobacteria being prevalent throughout New Zealand rivers. Little is known on species responsible for toxin production, their distribution, frequency and factors triggering toxin production. This study is divided into two phases; (1) a phylogeographic study of benthic cyanobacteria from multiple rivers across New Zealand and (2) an in-depth study of spatial and temporal variability of toxic benthic cyanobacteria in two rivers. Benthic cyanobacterial mats were collected from 22 different waterbodies around New Zealand between January 2005 and December 2008 and their anatoxin content determined using liquid chromatography-mass spectrometry. Thirty seven isolates were obtained from these samples and a polyphasic approach was used to identify them. Liquid chromatography-mass spectrometry and targeted PCR were used to determine if the isolates were producing anatoxins and microcystins. Phormidium autumnale was the dominant cyanobacterium within the isolates, although molecular and morphological data indicated the existence of multiple strains within this species. Two isolates of Ph. autumnale produced anatoxin-a and formed their own clade based on partial 16S rRNA gene sequences. These data indicate that benthic Ph. autumnale mats are composed of multiple morphospecies and anatoxin production is dependant on the presence of anatoxin-producing genotypes. Microcystin production was confirmed in a potentially novel isolate, closely related to Planktothrix spp. This species was responsible for the death of a dog in the Waitaki river (South Island, New Zealand). Cyanobacterial abundance, diversity and toxin production were monitored fortnightly in an in-depth study of the Hutt and Wainuiomata rivers (Wellington, New Zealand), over a 12 month period. Environmental parameters were correlated with cyanobacterial abundance and anatoxin production at eight locations along the rivers to elucidate possible causal factors. Cyanobacterial proliferations and associated anatoxin production were spatially and temporally variable across eight different sampling sites. Both river flow and temperature had a significant effect on cyanobacterial abundance. Multiple physicochemical factors including nutrients and periphyton growth appear to be interacting to influence cyanobacterial abundance. The presence and concentration of anatoxin-a and homoanatoxin-a and their degradation products dihydro-anatoxin-a and dihydro-homoanatoxin-a were also highly variable across all sites and over time. Anatoxin concentration did not correlate with any physicochemical parameters. The results of this study have demonstrated that the prevalence of freshwater cyanotoxin-producing benthic cyanobacteria is widespread in New Zealand and that toxin concentration is variable and unpredictable. This research will assist water managers in addressing the complex management issues associated with benthic cyanobacterial proliferations.</p>