QE: Toxic cyanobacteria in Singapore’s reservoirs: effects of ecological variables on population growth and toxin production (Maxine Allayne Darlene Mowe, 28 June 2012: 10.00am)

Department of Biological Sciences, NUS
Qualifying Examination

Toxic cyanobacteria in Singapore’s reservoirs: effects of ecological variables on population growth and toxin production
Speaker:               Maxine Allayne Darlene Mowe (Graduate Student, Dept. of Biological Sciences, NUS)
Date:                    28 June 2012, Thursday
Time:                   10am
Venue:                 DBS Conference Room (S3 Level 5, #05-01)
Supervisor:         Assistant Prof. Darren Yeo (NUS)
Co-supervisors:   Assistant Prof. Peter Todd (NUS), Sr. Lecturer Simon Mitrovic (UTS), Assoc Prof. Richard Lim (UTS)


Singapore has 17 reservoirs, with a combined catchment amounting to two-thirds of the city state’s total land area. With more unprotected catchments in urban areas, the likelihood of anthropogenic nutrient input to the reservoirs has increased. Nutrient input is one of the many factors that leads to harmful algal blooms, which have been recorded over the past 20 years in various local reservoirs. Although the trophic status of some reservoirs has improved, others are encountering eutrophication problems (Yang & Chiam- Tai 1991).

There are a variety of causes behind harmful algal blooms, which are frequently dominated by cyanobacteria, in Singapore’s reservoirs; it is often not one causative factor that triggers a bloom, but the combination of several. Factors that play a role in increasing the occurrence and severity of cyanobacterial blooms include increased phosphorous, nitrogen and micronutrient loads from runoff (Downs et al. 2008). Ecological interactions between the cyanobacterial species and herbivorous zooplankton may also influence the ability of cyanobacterial species to dominate the phytoplankton community (Kirk & Gilbert 1992).

To understand the effects of this range of environmental factors on harmful cyanobacterial blooms in Singapore, water sampling will be carried out and individual strains of toxic cyanobacteria will be isolated in the laboratory. Once isolated, approximately 10 cyanobacterial species will be cultured ex situ under different environmental conditions. Toxin production and growth will be monitored with changing environmental parameters such as light, temperature, macronutrients (nitrogen and phosphorous). Extensive laboratory manipulations will then be carried out in order to ascertain the conditions for optimal toxin production of the isolated cyanobacterial species.

The study will be carried out over all reservoirs to pinpoint the level of possible harmful algal bloom formation for each species. Using the cultured strains, microcosm experiments with herbivorous zooplankton will be carried out, in order to ascertain if the presence of zooplankton causes an increase in toxin production of cyanobacteria. Hypotheses based on the findings from the manipulative laboratory experiments will be tested with in-situ exclusion experiments using limnocorrals to be placed in various reservoirs. The outcome of this study would help to inform raw water management practices for prevention or control of cyanobacterial blooms in Singapore reservoirs.

All are welcome


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