Abstract:
The objective of this doctoral study was to identify waterbodies in New Zealand containing cyanobacterial blooms and mats, to assess the species composition and to establish types and concentrations of cyanotoxins in samples obtained.
A total of 271 water and cyanobacterial mat samples from 147 different waterbodies around New Zealand were collected or received between January 2001 and December 2004. Sixty seven percent were found to contain cyanobacteria and 4l% of the samples contained cyanobacteria in sufficiently high concentrations to be termed a bloom. A total of 54 different cyanobacteria species were recorded.
Prior to 1987, 33 lakes in New Zealand were recorded as having experienced cyanobacterial blooms. In the present study an additional 18 lakes were recorded as having experienced blooms. Eight bloom forming cyanobacteria species not previously identified in New Zealand (Anabaena planktonica, Cylindrospermopsis raciborskii, Microcystis botrys, M. panniformis, M. icthtyoblabe, M. wesenbergii, Planktothrix peronata f. attenuata and Sphaerocavum brasiliense) were found to be dominant or co-dominant in at least some cyanobacterial blooms. In addition to these species, three non-dominant species were identified that were also new records for New Zealand.
The water and cyanobacterial mat samples were analysed using ELISA's, LC/MS, HPLC and neuroblastoma assays for cyanotoxins and identified; microcystins/nodularins (102 samples from 54 different locations), anatoxin-a (3 samples from 3 different locations), cylindrospermopsins (l sample) and saxitoxins (48 santples from 4l different locations). Species from the genera Microcystis, Anabaena, Cylindrospermopsis, Nostoc, Planktothrix, Oscillatoria and Phormidium produce these cyanotoxins.
An in-depth study in Lakes Rotoehu and Rotoiti investigated the relationship between cyanobacteria species composition and levels of microcystins over a six month period and examined accumulation of microcystins in rainbow trout (Oncorhynchtts mykiss) and freshwater mussels (Hydridella menziesi).
Weekly water samples collected from both lakes showed that cyanobacteria species and levels of microcystins can vary over time during a bloom event. When phytoplankton samples were dominated by very high cell concentration of Microcystis spp. they were found to contain microcystins. Generally cell counts were found to be a poor indicator of levels of microcystins in the water samples, suggesting that cell counts alone are not a satisfactory way of identifying human health dangers in waterbodies containing cyanobacteria.
Microcystins were detected in rainbow trout liver and muscle tissue, and in freshwater mussels. The Total Daily Intake of microcystins recommended by the World Health Organisation for humans is 0.04 pg kg-1 tdoy-1. A 70kg human consuming 300g of muscle tissue would have exceeded this level in 50% (Lake Rotoiti) and 7l% (Lake Rotoehu) of the samples. Health problems could result if more than 300 g of trout muscle tissue was consumed on a regular basis over an extended period.
This study has demonstrated that the prevalence of freshwater cyanotoxin-producing cyanobacteria is widespread in New Zealand waterbodies and these cyanotoxins pose a potential health risk to both humans and animals either directly or indirectly.
