Large scale fish deaths in Singapore attributed to plankton blooms

Plankton bloom
Source: Wikimedia Commons

Coastal farms around Changi and Lim Chu Kang Jetty lost thousands of fish, two weekends ago due to plankton blooms. Till now, about 600 tonnes of fishes have died and about 55 coastal farms are affected due to this plankton bloom. Algal blooms suck the oxygen from water, suffocating other marine life and can be deadly.

“Plankton blooms tend to occur whenever there is a dry spell or drought. This is likely to be a recurrent problem with global warming, with greater incidence of both droughts as well as heavy, intense storms, said Minister for the Environment and Water Resources Vivian Balakrishnan.

Plankton blooms have been occurring in Singapore since 2009 and is likely to happen every year. Last year a similar plankton bloom costed 53 farms and about 500 tonnes of fish.

Agri-Food and Veterinary Authority (AVA) has been investigating, if the causes of fish deaths in West Johor Strait off Lim Chu Kang (two weeks back) and the East Johor strait off Pasir Ris (three weeks back) are different and how to monitor the water for plankton blooms and develop a contingency plan in future.

Preliminary studies by AVA shows that the Karlodinium veneficum species of algae could be behind the East Johor Strait bloom. Some of the common reasons for fish death include low dissolved oxygen levels leading to suffocation, some algae produce neurotoxins that kill fish (like Dinoflagellates), farm pollution (the blue glow in Hong Kong seas, seen early this year).

“It is crucial to know what we are dealing with. If we cannot confirm what is the cause of fish kills, then we are not ready to manage it,” says Marine expert Lim Po Teen of the University of Malaya.

AVA does routine surveys of pH, dissolved oxygen levels, water temperature and salinity in these farming areas and gives early alerts to farmers in case of any unusual fish or water conditions.

Assoc Prof Lim suggests that Singapore could take cues from the monitoring programmes used by the aquaculture industries in New Zealand and Japan. Remote sensing to detect chlorophyll-a( a specific form of chlorophyll used in oxygenic photosynthesis) and other algal pigments in water could be adopted, said Dr Angela Capper of James Cook University’s College of Marine and Environmental Sciences.

“Molecular approaches are a progressive tool playing a key role in the identification of harmful algal bloom species. Satellite and predictive modelling based on a range of parameters including climatic conditions and sea-surface temperatures also assist with the implementation of mitigation strategies,” she said.

AVA has assured the public that the fish samples from the affected farms were free from biotoxins and are safe to consume.