Abstract:The aim of this study was to investigate effects on health of exposure to cyanobacteria as a result of recreational water activities. Participants, who were aged six years and over, were interviewed at water recreation sites in South Australia, New South Wales and Victoria on selected Sundays during January and February 1995. Telephone follow-up was conducted two and seven days later to record any subsequent diarrhoea, vomiting, flu-like symptoms, skin rashes, mouth ulcers, fevers and eye or ear irritations. On the Sundays of interview, water samples from the sites were collected for cyanobacterial cell counts and toxin analysis. There were 852 participants, of whom 75 did not have water contact on the day of interview and were considered unexposed. The 777 who had water contact were considered exposed. No significant differences in overall symptoms were found between the unexposed and exposed after two days. At seven days, there was a significant trend to increasing symptom occurrence with duration of exposure ( P = 0.03). There was a significant trend to increasing symptom occurrence with increase in cell count ( P = 0.04). Participants exposed to more than 5000 cells per mL for more than one hour had a significantly higher symptom occurrence rate than the unexposed. Symptoms were not correlated with the presence of hepatotoxins. These results suggest symptom occurrence was associated with duration of contact with water containing cyanobacteria, and with cyanobacterial cell density. The findings suggest that the current safety threshold for exposure of 20 000 cells per mL may be too high. (Aust N
Cyst beds of Alexandrium catenella (a causative organism
of Paralytic Shellfish Poisoning) are widespread in New South Wales coastal
and estuarine waters (temperature range 13–25˚C). Cysts produced by
cultured isolates exhibited dormancy periods at 17˚C as short as
28–55 days. This contrasts with the usually longer dormancy requirements
of temperate populations of A. catenella from Japan (97
days at 23˚C) and of A. tamarense from Cape Cod or
British Columbia. With some Australian cysts, a 1-h temperature increase from
17˚ to 25˚C (equivalent to summer heating of shallow estuaries)
improved germination success (up to 100% germination achieved after 98
days), but cold–dark storage did not produce the lengthened dormancy
requirements that have been reported overseas for overwintering temperate cyst
populations. The significance of this finding is that different geographic
isolates of the same dinoflagellate taxon can have different cyst dormancy
requirements which play different ecological roles (overwintering strategy
v. rapid cycling between benthos and plankton).
A 24 h incubation study was conducted in situ in Manly Dam reservoir, Sydney, Australia. The study aimed to evaluate the relative effectiveness of grazing on phytoplankton by a resident macrozooplankton community, dominated by the cladoceran Ceriodaphnia and some copepods, in comparison with grazing by added, non-resident Daphnia carinata in the absence of the resident macrozooplankton community. Although there was some variability in the measured grazing rates among incubation bottles (volume: 1.28 L), D. carinata with a mean body size of 30.8 g dry weight were more efficient grazers than the reservoir macrozooplankton community with a mean body size of 2.5 g dry weight. The weight-specific clearance rate of D. carinata was 2-65 times higher than that of the resident reservoir community for five taxa of reservoir phytoplankton examined. In comparing the evidence from the literature on the limited ability of D. carinata to graze on cyanobacteria, a management strategy using D. carinata for the reduction of phytoplankton biomass may need to be considered separately from one designed to specifically control undesirable taxa, such as the cyanobacteria Microcystis and Anabaena.
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