07 April 2014

Signs of mass fish deaths ahead?

Brown 'teh-o' coloured water reported near Pulau Ubin over the last few days. What does this mean? Please let me know if you notice coloured water on our Northern shores, or you spot many dead fishes. You can send it to me via facebook or email me hello@wildsingapore.com
Plus, an insightful article on harmful algal blooms (aka plankton bloom) in Malaysia, their impact on fish farming and human health.

Commenting on my facebook post about this photo, Prof Teh Tiong Sa says that "The teh-o water is probably peat water washed out from the swamps after heavy rain. Some rivers in Singapore also discharge peat water into the sea in the past."

Indeed, Noven Chew, shared on 6 Apr this photo of palm oil waste around her fish farm near Pulau Ubin, that turned the water there 'kopi-o' colour for the last one week.
Photo by Noven Chew
Noven Chew also shared an sms from AVA sent to fish farmers on 4 Apr warning that elevated levels of plankton were detected.
Photo by Noven Chew

Meanwhile, there was an insightful article about Harmful Algal Blooms in Malaysia: Toxic tides - Risks from harmful microalgae by Tan Cheng Li The Star 7 Apr 14. This fascinating article covered these issues with information from Dr Lim Po Teen, head of University Malaysia’s Bachok Marine Research Station in Kelantan.

What caused the mass fish deaths in Tanjung Kupang, Malaysia on 11 Feb, near Tuas in Singapore?

"A harmful algal bloom (HAB), or what is commonly referred to as red tide, a sudden population explosion of a toxin-producing microalgae. The offensive microalgae was identified as Karlodinium australe, which caught scientists by surprise. "This is the first time we are seeing a bloom of this species, which has never been reported as toxic," says Dr Leaw Chui Pin, a marine molecular biologist who has worked on harmful microalgae for 14 years."

What causes harmful algal blooms?

"The sudden proliferation of microalgae is triggered by enrichment of waters (what is called eutrophication). The increase in nutrients comes from land-based discharges such as fertiliser-laden runoffs from plantations and livestock farms, and sewage effluent. Harmful algal blooms are always related to increased activities in coastal areas."

Natural upwelling can also release long-buried organic matter which enriches the water. Seabed dredging can also have the same effect. Lim points out that the algal bloom in Sabah last year coincided with the laying of water pipes on the sea bed between Kota Kinabalu and Pulau Gaya. Similarly, there was land reclamation work near the fish farms in Tanjung Kupang during the HAB.

Another source of coastal water enrichment is caged fish culture, especially when trash fish is used as feed. “Any uneaten fish will quickly sink to the bottom and cause eutrophication. It is better to use feed that can stay suspended in the water column, instead of sinking very fast.”

Algae blooms tend to occur in sheltered places with restricted water movements, such as lagoons, ports and embayments.

“It all comes down to what we do on land,” says Dr Lim.

What are the worrying trends in harmful algal blooms in Malaysia?

Shipping can transport harmful microalgae to distant places. This happens when ballast water, which may contain non-native species, is indiscriminately released in a foreign port. Dr Lim says the species – Pyrodinium bahamense – that had caused paralytic shellfish poisoning in Sabah last year, has since been found at two sites in Peninsular Malaysia. This species is very toxic and has always posed a problem for Sabah.

Why has there been no red tide warnings in Peninsular Malaysia?

No red tide warnings have ever been issued in Peninsular Malaysia. Because monitoring is almost non-existent and there is low awareness on harmful algal blooms.

What is the harmful algal bloom situation like in the Johor Strait?

In a 2009 study on the Straits of Johor, researchers from Universiti Malaysia Sarawak and the Fisheries Research Institute found 11 microalgae species, with seven associated with blooms and harmful either as fish killers or toxin producers. The presence of these potentially harmful species should be considered in future expansion of aquaculture industry in the straits.

What is the impact of harmful algal blooms on fish?

Microalgae inflict harm when they produce toxins which cause fish kills or which accumulate in shellfish, causing paralytic shellfish poisoning when the contaminated seafood is consumed by humans or marine mammals. Fish kills happen when the microalgae produce toxins which attack fish gills. This stalls the transportation of oxygen through the gills, hence suffocating the fish. Some toxins irritate the gills, triggering secretion of mucous which also lead to suffocation.

Blooms of non-toxic microalgae can also lead to fish die-offs too as the decomposition of the large mass can deplete the water of oxygen, creating hypoxic or anoxic conditions.

How dangerous are harmful algal blooms to humans?

The immediate signs of paralytic shellfish poisoning T are numbness or tingling of the lips and tongue, which spreads to the fingers and toes. Other symptoms are a sensation of lightness, salivation, intense thirst and temporary blindness. These symptoms are followed by a loss of muscular coordination, terminating in paralysis as well as inability to breathe. There is no known antidote for paralytic shellfish poisoning, so treatment is supportive, such as artificial respiration.

Please let me know if you notice coloured water on our Northern shores, or you spot many dead fishes. You can send it to my via facebook or email me hello@wildsingapore.com


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