Toxic tides: Risks from harmful microalgae
BY TAN CHENG LI
Harmful algal bloom, or red tide, off Sabah.
|
|
There is a need to step up monitoring of our coastal waters for harmful algal blooms as they pose public safety concerns and economic risks.
ON the morning of Feb 11, fish farm operators in Tanjung Kupang, Johor, woke up to the ghastly sight of fish floating belly up in their pens in the Straits of Johor. In the days that followed, the fish kept dying.
The fish kill lasted two weeks, at the end of which commercially valuable stocks of snappers, estuary cods, seabass and threadfins in some nine farms were wiped out. One operator reported losses of RM150,000.
ADVERTISEMENT
The mass mortality has since been blamed on a harmful algal bloom (HAB), or what is commonly referred to as red tide, a sudden population explosion of a toxin-producing microalgae.
While HABs are not often reported in Peninsular Malaysia, Sabah is no stranger to the phenomenon. Its first HAB was reported in 1976 and this has been a fairly annual occurrence since. In January and February last year, shellfish poisoning claimed three lives and over 40 people fell ill in Sepanggar and Inanam, both near Kota Kinabalu, in the state’s worst case of HAB.
In fact, the Sabah Fisheries Department has not lifted its red tide alert which it had issued in October 2011. In January, following the sighting of reddish-brown waters off Kota Kinabalu, director Rayner Stuel Galid said the red tide warning was still in effect and the toxins which were detected for eight months of last year continued to be seen from Tuaran to Kuala Penyu.
These incidents of HABs may be signs of what’s to come. According to Universiti Malaya marine ecologist Dr Lim Po Teen, HABs are occurring more frequently and in more locations over the past decade, and involve previously unknown species.
Depending on the species, a sudden bloom of microalgae can turn sea water red, white, green, cloudy or foamy.
In the Tanjung Kupang case, 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.
She says researchers conducted water sampling 10 days after the fish die-offs first happened, yet they still found a high density of the organism, between one million to two million per litre. She notes that the bloom affected even big fishes. Samples will be sent to their Japanese collaborators to measure the amount of toxins in the dead fish.
Leaw says scientists have characterised 40 species of harmful and potentially harmful microalgae in Malaysia, and foresee there may be more in our waters.
Water sampling in the Straits of Johor confirmed a bloom of the microalgae Karlodinium australe during the fish kills in Tanjung Kupang, Johor.
Noxious effects
Until 1990, problems related to paralytic shellfish poisoning were confined to the west coast of Sabah. In early 1991, it was recorded for the first time in Peninsular Malaysia when three people became ill after eating farmed mussels from Sebatu, Malacca. It was only years later that Alexandrium tamiyanavichi was confirmed as the toxin producer. Since then, HABs have been reported in various parts of the peninsula.
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.
In 2001, six people in Tumpat, Kelantan, were hospitalised and one of them died, after consuming shellfish contaminated with toxin from Alexandrium minutum.
Scientists say the term “red tide” is misleading as HABs do not just paint the water red; some turn the water cloudy, brown or foamy. The discolouration in the water is most visible in the morning. As the day warms up, the mass of microalgae will sink down to avoid extreme heat.
Not all algae blooms are harmful – even if it is red in colour. In Lumut, Perak and Penang, there have been blooms of Ceratium furca, which does not produce toxins although it has the characteristic red tide effect.
However, blooms of non-toxic microalgae can lead to fish die-offs too as the decomposition of the large mass can deplete the water of oxygen, creating hypoxic or anoxic conditions.
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,” says Lim, head of UM’s Bachok Marine Research Station in Kelantan.
Fuelling the growth
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,” says Lim, who has researched on microalgae for 14 years.
Algae blooms tend to occur in sheltered places with restricted water movements, such as lagoons, ports and embayments. Sarawak does not have major problems with algae blooms due to strong tidal action which flushes the coastal waters.
Lim notes that 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. He 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.
No paralytic shellfish poisoning was reported from Port Dickson, but Kuantan had one incident in November, although there was no fatality.
This species is very toxic and has always posed a problem for Sabah.
Because of its long history of red tides, the Sabah Fisheries Department has put in place surveillance of HABs. It involves regular water sampling and testing of molluscs and fish. If tests show over 400 mouse unit of the toxin per 100g of tissue, the shellfish cannot be sold.
No red tide warnings have ever been issued in Peninsular Malaysia since monitoring is almost non-existent and awareness on HABs, low. To avert the harmful and economically damaging effects of HABs, Lim says monitoring of our coastal waters has to be stepped up.
Currently, there is insufficient HAB scrutiny in peninsular Malaysia, partly due to the lack of trained personnel. As such, the Science, Technology and Innovation Ministry and local scientists have organised training workshops on water sampling methods and identification of harmful microalgae (see note below).
Keep a lookout
Lim says more locations should be monitored, particularly sites with previously known HABs and those with fish and shellfish farms. One such place is Kuala Selangor, which has one of the largest cockle beds in the country.
He says the toxin-producing Gymnodinum catenatum has been detected there, although in low numbers.
This species can cause paralytic shellfish poisoning, but this has not been seen in Sabah, where it can also be found.
Our small and scattered seafood culture industry, however, is proving difficult to monitor. “The shellfish industry in New Zealand is big, so the producers there can afford to pay for regular testing. On the other hand, the value of mussels here is low, so how can the farmers pay for tests?” says Lim.
He asserts, though, that monitoring is crucial to ensure the safety of our seafood products for local consumption and export. In fact, Singapore has stopped imports of cockles from Kuala Selangor, citing a lack of proper monitoring of seafood safety. Fish farm operators should be aware of HABs in order to minimise risks. Lim says selection of mariculture sites based on previously known HABs cases and the ability to predict HABs will help them avoid unwanted losses. Sites with no record of potential harmful species and good water exchanges are preferable.
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.
If a bloom does happen, fish farm operators can use plastic sheet skirtings to prevent the fish from direct contact with the harmful microalgae. In Japan, the use of moveable pens has been helpful. In the long run, however, the problem of enrichment of coastal waters has to be looked at.
“It all comes down to what we do on land,” says Dr Lim. A well-informed public will help ensure public safety. Once a warning on HAB has been announced, the public should avoid shellfish in the affected area. Symptoms of poisoning are seen within 30 to 60 minutes of consuming contaminated seafood.
The immediate signs 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.
There will be a workshop on Systematic and Advanced Methodologies in Harmful Algae Monitoring on Aug 12-15 at the Bachok Marine Research Station in Bachok, Kelantan. The workshop is targeted at fisheries personnel and aquaculture farm operators. It will introduce new monitoring technology, techniques in field samplings, skills in qualitative and quantitive analyses, and options for future monitoring programmes.
The workshop is organised by the National Oceanography Directorate, the Science, Technology and Innovation Ministry, and Universiti Malaya. For more information, e-mail cpleaw@um.edu.my or ptlim@um.edu.my.
source from: http://www.thestar.com.my/News/Environment/2014/04/07/Toxic-tides-Risks-from-harmful-microalgae/
Posts
0 Comment :
Post a Comment
Thanks for your comment!